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(0.000,0.000) Categories 
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(0.000,0.000) Permission 
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(0.000,0.000) PLDI’09, 
(0.000,0.000) June 
(0.000,0.000) 15–20, 
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(0.000,0.000) 978-1-60558-392-1/09/06. 
(0.000,0.000) . 
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(0.000,0.000) performance. 
(0.000,0.000) Compilers 
(0.000,0.000) for 
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(0.000,0.000) rely 
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(0.000,0.000) means 
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(0.000,0.000) compiler 
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(0.000,0.000) generate 
(0.000,0.000) opti- 
(0.000,0.000) mized 
(0.000,0.000) machine 
(0.000,0.000) code, 
(0.000,0.000) traditional 
(0.000,0.000) static 
(0.000,0.000) analysis 
(0.000,0.000) is 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) e 
(0.000,0.000) xpensi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) and 
(0.000,0.000) hence 
(0.000,0.000) not 
(0.000,0.000) well 
(0.000,0.000) s 
(0.000,0.000) uited 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) highly 
(0.000,0.000) interacti 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) en 
(0.000,0.000) vironment 
(0.000,0.000) of 
(0.000,0.000) a 
(0.000,0.000) web 
(0.000,0.000) bro 
(0.000,0.000) wser 
(0.000,0.000) . 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) present 
(0.000,0.000) a 
(0.000,0.000) trace-based 
(0.000,0.000) compilation 
(0.000,0.000) technique 
(0.000,0.000) for 
(0.000,0.000) dynamic 
(0.000,0.000) languages 
(0.000,0.000) that 
(0.000,0.000) reconciles 
(0.000,0.000) speed 
(0.000,0.000) of 
(0.000,0.000) compilation 
(0.000,0.000) with 
(0.000,0.000) e 
(0.000,0.000) xcellent 
(0.000,0.000) per 
(0.000,0.000) - 
(0.000,0.000) formance 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) generated 
(0.000,0.000) machine 
(0.000,0.000) code. 
(0.000,0.000) Our 
(0.000,0.000) system 
(0.000,0.000) uses 
(0.000,0.000) a 
(0.000,0.000) mix 
(0.000,0.000) ed- 
(0.000,0.000) mode 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution 
(0.000,0.000) approach: 
(0.000,0.000) the 
(0.000,0.000) system 
(0.000,0.000) starts 
(0.000,0.000) running 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) f 
(0.000,0.000) ast-starting 
(0.000,0.000) bytecode 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) As 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) runs 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) system 
(0.000,0.000) identifies 
(0.000,0.000) hot 
(0.000,0.000) (frequently 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecuted) 
(0.000,0.000) bytecode 
(0.000,0.000) sequences, 
(0.000,0.000) records 
(0.000,0.000) them, 
(0.000,0.000) and 
(0.000,0.000) compiles 
(0.000,0.000) them 
(0.000,0.000) to 
(0.000,0.000) f 
(0.000,0.000) ast 
(0.000,0.000) nati 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) code. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) c 
(0.000,0.000) all 
(0.000,0.000) such 
(0.000,0.000) a 
(0.000,0.000) se- 
(0.000,0.000) quence 
(0.000,0.000) of 
(0.000,0.000) instructions 
(0.000,0.000) a 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) . 
(0.000,0.000) Unlik 
(0.000,0.000) e 
(0.000,0.000) method-based 
(0.000,0.000) dynamic 
(0.000,0.000) compilers, 
(0.000,0.000) our 
(0.000,0.000) dynamic 
(0.000,0.000) com- 
(0.000,0.000) piler 
(0.000,0.000) operates 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) granularity 
(0.000,0.000) of 
(0.000,0.000) indi 
(0.000,0.000) vidual 
(0.000,0.000) loops. 
(0.000,0.000) This 
(0.000,0.000) design 
(0.000,0.000) choice 
(0.000,0.000) is 
(0.000,0.000) based 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xpectation 
(0.000,0.000) that 
(0.000,0.000) programs 
(0.000,0.000) spend 
(0.000,0.000) most 
(0.000,0.000) of 
(0.000,0.000) their 
(0.000,0.000) time 
(0.000,0.000) in 
(0.000,0.000) hot 
(0.000,0.000) loops. 
(0.000,0.000) Ev 
(0.000,0.000) en 
(0.000,0.000) in 
(0.000,0.000) dynamically 
(0.000,0.000) typed 
(0.000,0.000) languages, 
(0.000,0.000) we 
(0.000,0.000) e 
(0.000,0.000) xpect 
(0.000,0.000) hot 
(0.000,0.000) l 
(0.000,0.000) oops 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) mostly 
(0.000,0.000) type-stable 
(0.000,0.000) , 
(0.000,0.000) meaning 
(0.000,0.000) t 
(0.000,0.000) hat 
(0.000,0.000) the 
(0.000,0.000) types 
(0.000,0.000) of 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) are 
(0.000,0.000) in 
(0.000,0.000) v 
(0.000,0.000) ariant. 
(0.000,0.000) (12) 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) we 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) e 
(0.000,0.000) xpect 
(0.000,0.000) loop 
(0.000,0.000) coun- 
(0.000,0.000) ters 
(0.000,0.000) that 
(0.000,0.000) start 
(0.000,0.000) as 
(0.000,0.000) inte 
(0.000,0.000) gers 
(0.000,0.000) to 
(0.000,0.000) remain 
(0.000,0.000) inte 
(0.000,0.000) gers 
(0.000,0.000) for 
(0.000,0.000) all 
(0.000,0.000) iterations. 
(0.000,0.000) When 
(0.000,0.000) both 
(0.000,0.000) of 
(0.000,0.000) these 
(0.000,0.000) e 
(0.000,0.000) xpectations 
(0.000,0.000) hold, 
(0.000,0.000) a 
(0.000,0.000) trace-based 
(0.000,0.000) compiler 
(0.000,0.000) can 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution 
(0.000,0.000) with 
(0.000,0.000) a 
(0.000,0.000) small 
(0.000,0.000) number 
(0.000,0.000) of 
(0.000,0.000) type-specialized, 
(0.000,0.000) ef- 
(0.000,0.000) ficiently 
(0.000,0.000) compiled 
(0.000,0.000) traces. 
(0.000,0.000) Each 
(0.000,0.000) compiled 
(0.000,0.000) trace 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) ers 
(0.000,0.000) one 
(0.000,0.000) path 
(0.000,0.000) through 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) with 
(0.000,0.000) one 
(0.000,0.000) mapping 
(0.000,0.000) of 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) to 
(0.000,0.000) types. 
(0.000,0.000) When 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecutes 
(0.000,0.000) a 
(0.000,0.000) compiled 
(0.000,0.000) trace, 
(0.000,0.000) it 
(0.000,0.000) cannot 
(0.000,0.000) guarantee 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) path 
(0.000,0.000) will 
(0.000,0.000) be 
(0.000,0.000) follo 
(0.000,0.000) wed 
(0.000,0.000) or 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) types 
(0.000,0.000) will 
(0.000,0.000) occur 
(0.000,0.000) in 
(0.000,0.000) subsequent 
(0.000,0.000) loop 
(0.000,0.000) iterations. 
(0.000,0.000) Hence, 
(0.000,0.000) recording 
(0.000,0.000) and 
(0.000,0.000) compiling 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) speculates 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) path 
(0.000,0.000) and 
(0.000,0.000) typing 
(0.000,0.000) will 
(0.000,0.000) be 
(0.000,0.000) e 
(0.000,0.000) xac 
(0.000,0.000) tly 
(0.000,0.000) as 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) were 
(0.000,0.000) during 
(0.000,0.000) recording 
(0.000,0.000) for 
(0.000,0.000) subsequent 
(0.000,0.000) iterations 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) loop. 
(0.000,0.000) Ev 
(0.000,0.000) ery 
(0.000,0.000) compiled 
(0.000,0.000) trace 
(0.000,0.000) contains 
(0.000,0.000) all 
(0.000,0.000) the 
(0.000,0.000) guar 
(0.000,0.000) ds 
(0.000,0.000) (checks) 
(0.000,0.000) required 
(0.000,0.000) to 
(0.000,0.000) v 
(0.000,0.000) alidate 
(0.000,0.000) the 
(0.000,0.000) speculation. 
(0.000,0.000) If 
(0.000,0.000) one 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) guards 
(0.000,0.000) f 
(0.000,0.000) ails 
(0.000,0.000) (if 
(0.000,0.000) control 
(0.000,0.000) flo 
(0.000,0.000) w 
(0.000,0.000) is 
(0.000,0.000) dif 
(0.000,0.000) ferent, 
(0.000,0.000) or 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) of 
(0.000,0.000) a 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) type 
(0.000,0.000) is 
(0.000,0.000) generated), 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) e 
(0.000,0.000) xits. 
(0.000,0.000) If 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) becomes 
(0.000,0.000) hot, 
(0.000,0.000) the 
(0.000,0.000) V 
(0.000,0.000) M 
(0.000,0.000) can 
(0.000,0.000) record 
(0.000,0.000) a 
(0.000,0.000) br 
(0.000,0.000) anc 
(0.000,0.000) h 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) starting 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) to 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) ne 
(0.000,0.000) w 
(0.000,0.000) path. 
(0.000,0.000) In 
(0.000,0.000) this 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) records 
(0.000,0.000) a 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) tr 
(0.000,0.000) ee 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) ering 
(0.000,0.000) all 
(0.000,0.000) the 
(0.000,0.000) hot 
(0.000,0.000) paths 
(0.000,0.000) through 
(0.000,0.000) the 
(0.000,0.000) loop. 
(0.000,0.000) Nested 
(0.000,0.000) loops 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) dif 
(0.000,0.000) ficult 
(0.000,0.000) to 
(0.000,0.000) optimize 
(0.000,0.000) for 
(0.000,0.000) tracing 
(0.000,0.000) VMs. 
(0.000,0.000) In 
(0.000,0.000) a 
(0.000,0.000) na 
(0.000,0.000) ¨ 
(0.000,0.000) ıv 
(0.000,0.000) e 
(0.000,0.000) implementation, 
(0.000,0.000) inner 
(0.000,0.000) loops 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) become 
(0.000,0.000) hot 
(0.000,0.000) first, 
(0.000,0.000) and 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) start 
(0.000,0.000) tracing 
(0.000,0.000) there. 
(0.000,0.000) When 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) e 
(0.000,0.000) xits, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) detect 
(0.000,0.000) that 
(0.000,0.000) a 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) branch 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) tak 
(0.000,0.000) en. 
(0.000,0.000) The 
(0.000,0.000) VM 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) try 
(0.000,0.000) to 
(0.000,0.000) record 
(0.000,0.000) a 
(0.000,0.000) branch 
(0.000,0.000) trace, 
(0.000,0.000) and 
(0.000,0.000) find 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) reaches 
(0.000,0.000) not 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) , 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) . 
(0.000,0.000) At 
(0.000,0.000) this 
(0.000,0.000) point, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) could 
(0.000,0.000) continue 
(0.000,0.000) tracing 
(0.000,0.000) until 
(0.000,0.000) it 
(0.000,0.000) reaches 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) ag 
(0.000,0.000) ain, 
(0.000,0.000) thus 
(0.000,0.000) tracing 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) loop 
(0.000,0.000) inside 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) tree 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop. 
(0.000,0.000) But 
(0.000,0.000) this 
(0.000,0.000) requires 
(0.000,0.000) tracing 
(0.000,0.000) a 
(0.000,0.000) cop 
(0.000,0.000) y 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) loop 
(0.000,0.000) for 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) and 
(0.000,0.000) type 
(0.000,0.000) combination 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop. 
(0.000,0.000) In 
(0.000,0.000) essence, 
(0.000,0.000) t 
(0.000,0.000) his 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) form 
(0.000,0.000) of 
(0.000,0.000) unintended 
(0.000,0.000) tail 
(0.000,0.000) duplication, 
(0.000,0.000) which 
(0.000,0.000) can 
(0.000,0.000) easily 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) erflo 
(0.000,0.000) w 
(0.000,0.000) the 
(0.000,0.000) code 
(0.000,0.000) cache. 
(0.000,0.000) Alternati 
(0.000,0.000) v 
(0.000,0.000) ely 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) could 
(0.000,0.000) simply 
(0.000,0.000) stop 
(0.000,0.000) tracing, 
(0.000,0.000) and 
(0.000,0.000) gi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) up 
(0.000,0.000) on 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) tracing 
(0.000,0.000) outer 
(0.000,0.000) loops. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) solv 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) nested 
(0.000,0.000) loop 
(0.000,0.000) problem 
(0.000,0.000) by 
(0.000,0.000) recording 
(0.000,0.000) nested 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) tr 
(0.000,0.000) ees 
(0.000,0.000) . 
(0.000,0.000) Our 
(0.000,0.000) system 
(0.000,0.000) traces 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) e 
(0.000,0.000) xactly 
(0.000,0.000) as 
(0.000,0.000) the 
(0.000,0.000) na 
(0.000,0.000) ¨ 
(0.000,0.000) ıv 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ersion. 
(0.000,0.000) The 
(0.000,0.000) system 
(0.000,0.000) stops 
(0.000,0.000) e 
(0.000,0.000) xtending 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) tree 
(0.000,0.000) when 
(0.000,0.000) it 
(0.000,0.000) reaches 
(0.000,0.000) an 
(0.000,0.000) outer 
(0.000,0.000) loop, 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) then 
(0.000,0.000) it 
(0.000,0.000) starts 
(0.000,0.000) a 
(0.000,0.000) ne 
(0.000,0.000) w 
(0.000,0.000) trace 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) . 
(0.000,0.000) When 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) loop 
(0.000,0.000) reaches 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) system 
(0.000,0.000) tries 
(0.000,0.000) to 
(0.000,0.000) call 
(0.000,0.000) the 
(0.000,0.000) trac 
(0.000,0.000) e 
(0.000,0.000) tree 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop. 
(0.000,0.000) If 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) succeeds, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) records 
(0.000,0.000) the 
(0.000,0.000) cal 
(0.000,0.000) l 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) tree 
(0.000,0.000) as 
(0.000,0.000) part 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) trace 
(0.000,0.000) and 
(0.000,0.000) finishes 
(0.000,0.000) the 
(0.000,0.000) outer 
(0.000,0.000) trace 
(0.000,0.000) as 
(0.000,0.000) normal. 
(0.000,0.000) In 
(0.000,0.000) this 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) , 
(0.000,0.000) our 
(0.000,0.000) system 
(0.000,0.000) can 
(0.000,0.000) trace 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) number 
(0.000,0.000) of 
(0.000,0.000) loops 
(0.000,0.000) nested 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) depth 
(0.000,0.000) without 
(0.000,0.000) causing 
(0.000,0.000) e 
(0.000,0.000) xcessi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) tail 
(0.000,0.000) duplication. 
(0.000,0.000) These 
(0.000,0.000) techniques 
(0.000,0.000) allo 
(0.000,0.000) w 
(0.000,0.000) a 
(0.000,0.000) VM 
(0.000,0.000) to 
(0.000,0.000) dynamically 
(0.000,0.000) translate 
(0.000,0.000) a 
(0.000,0.000) pro- 
(0.000,0.000) gram 
(0.000,0.000) to 
(0.000,0.000) nested, 
(0.000,0.000) type-specialized 
(0.000,0.000) trace 
(0.000,0.000) trees. 
(0.000,0.000) Because 
(0.000,0.000) traces 
(0.000,0.000) can 
(0.000,0.000) cross 
(0.000,0.000) function 
(0.000,0.000) call 
(0.000,0.000) boundaries, 
(0.000,0.000) our 
(0.000,0.000) techniques 
(0.000,0.000) also 
(0.000,0.000) achie 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) ef- 
(0.000,0.000) fects 
(0.000,0.000) of 
(0.000,0.000) inlining. 
(0.000,0.000) Because 
(0.000,0.000) traces 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) no 
(0.000,0.000) internal 
(0.000,0.000) control-flo 
(0.000,0.000) w 
(0.000,0.000) joins, 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) optimized 
(0.000,0.000) in 
(0.000,0.000) linear 
(0.000,0.000) time 
(0.000,0.000) by 
(0.000,0.000) a 
(0.000,0.000) simple 
(0.000,0.000) compiler 
(0.000,0.000) (10). 
(0.000,0.000) Thus, 
(0.000,0.000) our 
(0.000,0.000) tracing 
(0.000,0.000) VM 
(0.000,0.000) ef 
(0.000,0.000) ficiently 
(0.000,0.000) performs 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) kind 
(0.000,0.000) of 
(0.000,0.000) op- 
(0.000,0.000) timizations 
(0.000,0.000) that 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) require 
(0.000,0.000) interprocedural 
(0.000,0.000) analysis 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) static 
(0.000,0.000) optimization 
(0.000,0.000) setting. 
(0.000,0.000) This 
(0.000,0.000) mak 
(0.000,0.000) es 
(0.000,0.000) tracing 
(0.000,0.000) an 
(0.000,0.000) attracti 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) and 
(0.000,0.000) ef 
(0.000,0.000) fecti 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) tool 
(0.000,0.000) to 
(0.000,0.000) type 
(0.000,0.000) specialize 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) en 
(0.000,0.000) comple 
(0.000,0.000) x 
(0.000,0.000) function 
(0.000,0.000) call-rich 
(0.000,0.000) code. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) implemented 
(0.000,0.000) these 
(0.000,0.000) techniques 
(0.000,0.000) for 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xisting 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) in- 
(0.000,0.000) terpreter 
(0.000,0.000) , 
(0.000,0.000) SpiderMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) . 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) call 
(0.000,0.000) the 
(0.000,0.000) resulting 
(0.000,0.000) tracing 
(0.000,0.000) VM 
(0.000,0.000) T 
(0.000,0.000) r 
(0.000,0.000) ace- 
(0.000,0.000) Monk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) . 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) supports 
(0.000,0.000) all 
(0.000,0.000) the 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) features 
(0.000,0.000) of 
(0.000,0.000) Spi- 
(0.000,0.000) derMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) , 
(0.000,0.000) with 
(0.000,0.000) a 
(0.000,0.000) 2x-20x 
(0.000,0.000) speedup 
(0.000,0.000) for 
(0.000,0.000) traceable 
(0.000,0.000) programs. 
(0.000,0.000) This 
(0.000,0.000) paper 
(0.000,0.000) mak 
(0.000,0.000) es 
(0.000,0.000) the 
(0.000,0.000) follo 
(0.000,0.000) wing 
(0.000,0.000) contrib 
(0.000,0.000) utions: 
(0.000,0.000) • 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) e 
(0.000,0.000) xplain 
(0.000,0.000) an 
(0.000,0.000) algorithm 
(0.000,0.000) for 
(0.000,0.000) dynam 
(0.000,0.000) ically 
(0.000,0.000) forming 
(0.000,0.000) trace 
(0.000,0.000) trees 
(0.000,0.000) to 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) a 
(0.000,0.000) program, 
(0.000,0.000) representing 
(0.000,0.000) nested 
(0.000,0.000) loops 
(0.000,0.000) as 
(0.000,0.000) nested 
(0.000,0.000) trace 
(0.000,0.000) trees. 
(0.000,0.000) • 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) e 
(0.000,0.000) xplain 
(0.000,0.000) ho 
(0.000,0.000) w 
(0.000,0.000) to 
(0.000,0.000) speculati 
(0.000,0.000) v 
(0.000,0.000) ely 
(0.000,0.000) generate 
(0.000,0.000) ef 
(0.000,0.000) ficient 
(0.000,0.000) type-specialized 
(0.000,0.000) code 
(0.000,0.000) for 
(0.000,0.000) traces 
(0.000,0.000) from 
(0.000,0.000) dynamic 
(0.000,0.000) language 
(0.000,0.000) programs. 
(0.000,0.000) • 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) alidate 
(0.000,0.000) our 
(0.000,0.000) tracing 
(0.000,0.000) techniques 
(0.000,0.000) in 
(0.000,0.000) an 
(0.000,0.000) implementation 
(0.000,0.000) based 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) SpiderMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) int 
(0.000,0.000) erpreter 
(0.000,0.000) , 
(0.000,0.000) achie 
(0.000,0.000) ving 
(0.000,0.000) 2x-20x 
(0.000,0.000) speedups 
(0.000,0.000) on 
(0.000,0.000) man 
(0.000,0.000) y 
(0.000,0.000) programs. 
(0.000,0.000) The 
(0.000,0.000) remainder 
(0.000,0.000) of 
(0.000,0.000) this 
(0.000,0.000) paper 
(0.000,0.000) is 
(0.000,0.000) or 
(0.000,0.000) g 
(0.000,0.000) anized 
(0.000,0.000) as 
(0.000,0.000) follo 
(0.000,0.000) ws. 
(0.000,0.000) Section 
(0.000,0.000) 3 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) general 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) ervie 
(0.000,0.000) w 
(0.000,0.000) of 
(0.000,0.000) trace 
(0.000,0.000) t 
(0.000,0.000) ree 
(0.000,0.000) based 
(0.000,0.000) compilation 
(0.000,0.000) we 
(0.000,0.000) use 
(0.000,0.000) to 
(0.000,0.000) cap- 
(0.000,0.000) ture 
(0.000,0.000) and 
(0.000,0.000) compile 
(0.000,0.000) frequently 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecuted 
(0.000,0.000) code 
(0.000,0.000) re 
(0.000,0.000) gions. 
(0.000,0.000) In 
(0.000,0.000) Section 
(0.000,0.000) 4 
(0.000,0.000) we 
(0.000,0.000) describe 
(0.000,0.000) our 
(0.000,0.000) approach 
(0.000,0.000) of 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) ering 
(0.000,0.000) nested 
(0.000,0.000) loops 
(0.000,0.000) using 
(0.000,0.000) a 
(0.000,0.000) num- 
(0.000,0.000) ber 
(0.000,0.000) of 
(0.000,0.000) indi 
(0.000,0.000) vidual 
(0.000,0.000) trace 
(0.000,0.000) trees. 
(0.000,0.000) In 
(0.000,0.000) Section 
(0.000,0.000) 5 
(0.000,0.000) we 
(0.000,0.000) describe 
(0.000,0.000) our 
(0.000,0.000) trace- 
(0.000,0.000) compilation 
(0.000,0.000) ba 
(0.000,0.000) sed 
(0.000,0.000) speculati 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) type 
(0.000,0.000) specialization 
(0.000,0.000) approach 
(0.000,0.000) we 
(0.000,0.000) use 
(0.000,0.000) to 
(0.000,0.000) generate 
(0.000,0.000) ef 
(0.000,0.000) ficient 
(0.000,0.000) machine 
(0.000,0.000) code 
(0.000,0.000) from 
(0.000,0.000) recorded 
(0.000,0.000) bytecode 
(0.000,0.000) traces. 
(0.000,0.000) Our 
(0.000,0.000) implementation 
(0.000,0.000) of 
(0.000,0.000) a 
(0.000,0.000) dynamic 
(0.000,0.000) type-specializing 
(0.000,0.000) compiler 
(0.000,0.000) for 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) is 
(0.000,0.000) described 
(0.000,0.000) in 
(0.000,0.000) Section 
(0.000,0.000) 6. 
(0.000,0.000) Related 
(0.000,0.000) w 
(0.000,0.000) ork 
(0.000,0.000) is 
(0.000,0.000) discussed 
(0.000,0.000) in 
(0.000,0.000) Section 
(0.000,0.000) 8. 
(0.000,0.000) In 
(0.000,0.000) Section 
(0.000,0.000) 7 
(0.000,0.000) we 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) aluate 
(0.000,0.000) our 
(0.000,0.000) dynamic 
(0.000,0.000) compiler 
(0.000,0.000) based 
(0.000,0.000) on 
(0.000,0.000) 1 
(0.000,0.000) for 
(0.000,0.000) (var 
(0.000,0.000) i 
(0.000,0.000) = 
(0.000,0.000) 2; 
(0.000,0.000) i 
(0.000,0.000) < 
(0.000,0.000) 100; 
(0.000,0.000) ++i) 
(0.000,0.000) { 
(0.000,0.000) 2 
(0.000,0.000) if 
(0.000,0.000) (!primes[i]) 
(0.000,0.000) 3 
(0.000,0.000) continue; 
(0.000,0.000) 4 
(0.000,0.000) for 
(0.000,0.000) (var 
(0.000,0.000) k 
(0.000,0.000) = 
(0.000,0.000) i 
(0.000,0.000) + 
(0.000,0.000) i; 
(0.000,0.000) i 
(0.000,0.000) < 
(0.000,0.000) 100; 
(0.000,0.000) k 
(0.000,0.000) += 
(0.000,0.000) i) 
(0.000,0.000) 5 
(0.000,0.000) primes[k] 
(0.000,0.000) = 
(0.000,0.000) false; 
(0.000,0.000) 6 
(0.000,0.000) } 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 1. 
(0.164,239.103) Sample 
(0.164,239.103) pr 
(0.164,239.103) ogram: 
(0.164,239.103) sie 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) of 
(0.164,239.103) Eratosthenes. 
(0.164,239.103) primes 
(0.164,239.103) is 
(0.164,239.103) initialized 
(0.164,239.103) to 
(0.164,239.103) an 
(0.164,239.103) array 
(0.164,239.103) of 
(0.164,239.103) 100 
(0.164,239.103) false 
(0.164,239.103) v 
(0.164,239.103) alues 
(0.164,239.103) on 
(0.164,239.103) entry 
(0.164,239.103) to 
(0.164,239.103) this 
(0.164,239.103) code 
(0.164,239.103) snippet. 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 2. 
(0.164,239.103) State 
(0.164,239.103) machine 
(0.164,239.103) describing 
(0.164,239.103) the 
(0.164,239.103) major 
(0.164,239.103) acti 
(0.164,239.103) vities 
(0.164,239.103) of 
(0.164,239.103) T 
(0.164,239.103) race- 
(0.164,239.103) Monk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) and 
(0.164,239.103) the 
(0.164,239.103) conditions 
(0.164,239.103) that 
(0.164,239.103) cause 
(0.164,239.103) transitions 
(0.164,239.103) to 
(0.164,239.103) a 
(0.164,239.103) ne 
(0.164,239.103) w 
(0.164,239.103) acti 
(0.164,239.103) v- 
(0.164,239.103) ity 
(0.164,239.103) . 
(0.164,239.103) In 
(0.164,239.103) the 
(0.164,239.103) dark 
(0.164,239.103) box, 
(0.164,239.103) TM 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecutes 
(0.164,239.103) JS 
(0.164,239.103) as 
(0.164,239.103) compiled 
(0.164,239.103) traces. 
(0.164,239.103) In 
(0.164,239.103) the 
(0.164,239.103) light 
(0.164,239.103) gray 
(0.164,239.103) box 
(0.164,239.103) es, 
(0.164,239.103) TM 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecutes 
(0.164,239.103) JS 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) standard 
(0.164,239.103) interpreter 
(0.164,239.103) . 
(0.164,239.103) White 
(0.164,239.103) box 
(0.164,239.103) es 
(0.164,239.103) are 
(0.164,239.103) o 
(0.164,239.103) v 
(0.164,239.103) erhead. 
(0.164,239.103) Thus, 
(0.164,239.103) to 
(0.164,239.103) maximize 
(0.164,239.103) performance, 
(0.164,239.103) we 
(0.164,239.103) need 
(0.164,239.103) to 
(0.164,239.103) maximize 
(0.164,239.103) time 
(0.164,239.103) spent 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) dark 
(0.164,239.103) est 
(0.164,239.103) box 
(0.164,239.103) and 
(0.164,239.103) minimize 
(0.164,239.103) time 
(0.164,239.103) spent 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) white 
(0.164,239.103) box 
(0.164,239.103) es. 
(0.164,239.103) The 
(0.164,239.103) best 
(0.164,239.103) case 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) loop 
(0.164,239.103) where 
(0.164,239.103) the 
(0.164,239.103) types 
(0.164,239.103) at 
(0.164,239.103) the 
(0.164,239.103) loop 
(0.164,239.103) edge 
(0.164,239.103) are 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) as 
(0.164,239.103) the 
(0.164,239.103) types 
(0.164,239.103) on 
(0.164,239.103) entry–then 
(0.164,239.103) TM 
(0.164,239.103) can 
(0.164,239.103) stay 
(0.164,239.103) in 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) until 
(0.164,239.103) the 
(0.164,239.103) loop 
(0.164,239.103) is 
(0.164,239.103) done. 
(0.164,239.103) a 
(0.164,239.103) set 
(0.164,239.103) of 
(0.164,239.103) industry 
(0.164,239.103) benchmarks. 
(0.164,239.103) The 
(0.164,239.103) paper 
(0.164,239.103) ends 
(0.164,239.103) with 
(0.164,239.103) conclusions 
(0.164,239.103) in 
(0.164,239.103) Section 
(0.164,239.103) 9 
(0.164,239.103) and 
(0.164,239.103) an 
(0.164,239.103) outlook 
(0.164,239.103) on 
(0.164,239.103) future 
(0.164,239.103) w 
(0.164,239.103) ork 
(0.164,239.103) is 
(0.164,239.103) presented 
(0.164,239.103) in 
(0.164,239.103) Section 
(0.164,239.103) 10. 
(0.164,239.103) 2. 
(0.164,239.103) Ov 
(0.164,239.103) er 
(0.164,239.103) view: 
(0.164,239.103) Example 
(0.164,239.103) T 
(0.164,239.103) racing 
(0.164,239.103) Run 
(0.164,239.103) This 
(0.164,239.103) section 
(0.164,239.103) pro 
(0.164,239.103) vides 
(0.164,239.103) an 
(0.164,239.103) o 
(0.164,239.103) v 
(0.164,239.103) ervie 
(0.164,239.103) w 
(0.164,239.103) of 
(0.164,239.103) our 
(0.164,239.103) system 
(0.164,239.103) by 
(0.164,239.103) describing 
(0.164,239.103) ho 
(0.164,239.103) w 
(0.164,239.103) T 
(0.164,239.103) raceMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecutes 
(0.164,239.103) an 
(0.164,239.103) e 
(0.164,239.103) xample 
(0.164,239.103) program. 
(0.164,239.103) The 
(0.164,239.103) e 
(0.164,239.103) xample 
(0.164,239.103) program, 
(0.164,239.103) sho 
(0.164,239.103) wn 
(0.164,239.103) in 
(0.164,239.103) Figure 
(0.164,239.103) 1, 
(0.164,239.103) computes 
(0.164,239.103) the 
(0.164,239.103) first 
(0.164,239.103) 100 
(0.164,239.103) prime 
(0.164,239.103) numbers 
(0.164,239.103) with 
(0.164,239.103) nested 
(0.164,239.103) loops. 
(0.164,239.103) The 
(0.164,239.103) narra 
(0.164,239.103) ti 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) should 
(0.164,239.103) be 
(0.164,239.103) read 
(0.164,239.103) along 
(0.164,239.103) with 
(0.164,239.103) Figure 
(0.164,239.103) 2, 
(0.164,239.103) which 
(0.164,239.103) describes 
(0.164,239.103) the 
(0.164,239.103) acti 
(0.164,239.103) vities 
(0.164,239.103) T 
(0.164,239.103) raceMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) performs 
(0.164,239.103) and 
(0.164,239.103) when 
(0.164,239.103) it 
(0.164,239.103) transitions 
(0.164,239.103) between 
(0.164,239.103) the 
(0.164,239.103) loops. 
(0.164,239.103) T 
(0.164,239.103) raceMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) al 
(0.164,239.103) w 
(0.164,239.103) ays 
(0.164,239.103) be 
(0.164,239.103) gins 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecuting 
(0.164,239.103) a 
(0.164,239.103) program 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) byte- 
(0.164,239.103) code 
(0.164,239.103) interpreter 
(0.164,239.103) . 
(0.164,239.103) Ev 
(0.164,239.103) ery 
(0.164,239.103) loop 
(0.164,239.103) back 
(0.164,239.103) edge 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) potential 
(0.164,239.103) tra 
(0.164,239.103) ce 
(0.164,239.103) point. 
(0.164,239.103) When 
(0.164,239.103) the 
(0.164,239.103) interpreter 
(0.164,239.103) crosses 
(0.164,239.103) a 
(0.164,239.103) loop 
(0.164,239.103) edge, 
(0.164,239.103) T 
(0.164,239.103) raceMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) in 
(0.164,239.103) v 
(0.164,239.103) ok 
(0.164,239.103) es 
(0.164,239.103) the 
(0.164,239.103) tr 
(0.164,239.103) ace 
(0.164,239.103) monitor 
(0.164,239.103) , 
(0.164,239.103) which 
(0.164,239.103) may 
(0.164,239.103) decide 
(0.164,239.103) to 
(0.164,239.103) record 
(0.164,239.103) or 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecute 
(0.164,239.103) a 
(0.164,239.103) nat 
(0.164,239.103) i 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) trace. 
(0.164,239.103) At 
(0.164,239.103) the 
(0.164,239.103) start 
(0.164,239.103) of 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecution, 
(0.164,239.103) there 
(0.164,239.103) are 
(0.164,239.103) no 
(0.164,239.103) compiled 
(0.164,239.103) traces 
(0.164,239.103) yet, 
(0.164,239.103) so 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) monitor 
(0.164,239.103) counts 
(0.164,239.103) the 
(0.164,239.103) number 
(0.164,239.103) of 
(0.164,239.103) times 
(0.164,239.103) each 
(0.164,239.103) loop 
(0.164,239.103) back 
(0.164,239.103) edge 
(0.164,239.103) is 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecuted 
(0.164,239.103) until 
(0.164,239.103) a 
(0.164,239.103) loop 
(0.164,239.103) becomes 
(0.164,239.103) hot 
(0.164,239.103) , 
(0.164,239.103) currently 
(0.164,239.103) after 
(0.164,239.103) 2 
(0.164,239.103) crossings. 
(0.164,239.103) Note 
(0.164,239.103) that 
(0.164,239.103) the 
(0.164,239.103) w 
(0.164,239.103) ay 
(0.164,239.103) our 
(0.164,239.103) loops 
(0.164,239.103) are 
(0.164,239.103) compiled, 
(0.164,239.103) the 
(0.164,239.103) loop 
(0.164,239.103) edge 
(0.164,239.103) is 
(0.164,239.103) crossed 
(0.164,239.103) before 
(0.164,239.103) entering 
(0.164,239.103) the 
(0.164,239.103) loop, 
(0.164,239.103) so 
(0.164,239.103) the 
(0.164,239.103) second 
(0.164,239.103) crossing 
(0.164,239.103) occurs 
(0.164,239.103) immediat 
(0.164,239.103) ely 
(0.164,239.103) after 
(0.164,239.103) the 
(0.164,239.103) first 
(0.164,239.103) iteration. 
(0.164,239.103) Here 
(0.164,239.103) is 
(0.164,239.103) the 
(0.164,239.103) sequence 
(0.164,239.103) of 
(0.164,239.103) e 
(0.164,239.103) v 
(0.164,239.103) ents 
(0.164,239.103) brok 
(0.164,239.103) en 
(0.164,239.103) do 
(0.164,239.103) wn 
(0.164,239.103) by 
(0.164,239.103) outer 
(0.164,239.103) loop 
(0.164,239.103) iteration: 
(0.000,0.000) v0 
(0.000,0.000) := 
(0.000,0.000) ld 
(0.000,0.000) state[748] 
(0.000,0.000) // 
(0.000,0.000) load 
(0.000,0.000) primes 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) activation 
(0.000,0.000) record 
(0.000,0.000) st 
(0.000,0.000) sp[0], 
(0.000,0.000) v0 
(0.000,0.000) // 
(0.000,0.000) store 
(0.000,0.000) primes 
(0.000,0.000) to 
(0.000,0.000) interpreter 
(0.000,0.000) stack 
(0.000,0.000) v1 
(0.000,0.000) := 
(0.000,0.000) ld 
(0.000,0.000) state[764] 
(0.000,0.000) // 
(0.000,0.000) load 
(0.000,0.000) k 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) activation 
(0.000,0.000) record 
(0.000,0.000) v2 
(0.000,0.000) := 
(0.000,0.000) i2f(v1) 
(0.000,0.000) // 
(0.000,0.000) convert 
(0.000,0.000) k 
(0.000,0.000) from 
(0.000,0.000) int 
(0.000,0.000) to 
(0.000,0.000) double 
(0.000,0.000) st 
(0.000,0.000) sp[8], 
(0.000,0.000) v1 
(0.000,0.000) // 
(0.000,0.000) store 
(0.000,0.000) k 
(0.000,0.000) to 
(0.000,0.000) interpreter 
(0.000,0.000) stack 
(0.000,0.000) st 
(0.000,0.000) sp[16], 
(0.000,0.000) 0 
(0.000,0.000) // 
(0.000,0.000) store 
(0.000,0.000) false 
(0.000,0.000) to 
(0.000,0.000) interpreter 
(0.000,0.000) stack 
(0.000,0.000) v3 
(0.000,0.000) := 
(0.000,0.000) ld 
(0.000,0.000) v0[4] 
(0.000,0.000) // 
(0.000,0.000) load 
(0.000,0.000) class 
(0.000,0.000) word 
(0.000,0.000) for 
(0.000,0.000) primes 
(0.000,0.000) v4 
(0.000,0.000) := 
(0.000,0.000) and 
(0.000,0.000) v3, 
(0.000,0.000) -4 
(0.000,0.000) // 
(0.000,0.000) mask 
(0.000,0.000) out 
(0.000,0.000) object 
(0.000,0.000) class 
(0.000,0.000) tag 
(0.000,0.000) for 
(0.000,0.000) primes 
(0.000,0.000) v5 
(0.000,0.000) := 
(0.000,0.000) eq 
(0.000,0.000) v4, 
(0.000,0.000) Array 
(0.000,0.000) // 
(0.000,0.000) test 
(0.000,0.000) whether 
(0.000,0.000) primes 
(0.000,0.000) is 
(0.000,0.000) an 
(0.000,0.000) array 
(0.000,0.000) xf 
(0.000,0.000) v5 
(0.000,0.000) // 
(0.000,0.000) side 
(0.000,0.000) exit 
(0.000,0.000) if 
(0.000,0.000) v5 
(0.000,0.000) is 
(0.000,0.000) false 
(0.000,0.000) v6 
(0.000,0.000) := 
(0.000,0.000) js_Array_set(v0, 
(0.000,0.000) v2, 
(0.000,0.000) false) 
(0.000,0.000) // 
(0.000,0.000) call 
(0.000,0.000) function 
(0.000,0.000) to 
(0.000,0.000) set 
(0.000,0.000) array 
(0.000,0.000) element 
(0.000,0.000) v7 
(0.000,0.000) := 
(0.000,0.000) eq 
(0.000,0.000) v6, 
(0.000,0.000) 0 
(0.000,0.000) // 
(0.000,0.000) test 
(0.000,0.000) return 
(0.000,0.000) value 
(0.000,0.000) from 
(0.000,0.000) call 
(0.000,0.000) xt 
(0.000,0.000) v7 
(0.000,0.000) // 
(0.000,0.000) side 
(0.000,0.000) exit 
(0.000,0.000) if 
(0.000,0.000) js_Array_set 
(0.000,0.000) returns 
(0.000,0.000) false. 
(0.164,502.117) Figur 
(0.164,502.117) e 
(0.164,502.117) 3. 
(0.164,502.117) LIR 
(0.164,502.117) snippet 
(0.164,502.117) f 
(0.164,502.117) or 
(0.164,502.117) sample 
(0.164,502.117) pr 
(0.164,502.117) ogram. 
(0.164,502.117) This 
(0.164,502.117) is 
(0.164,502.117) the 
(0.164,502.117) LIR 
(0.164,502.117) recorded 
(0.164,502.117) for 
(0.164,502.117) line 
(0.164,502.117) 5 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) sample 
(0.164,502.117) program 
(0.164,502.117) in 
(0.164,502.117) Figure 
(0.164,502.117) 1. 
(0.164,502.117) The 
(0.164,502.117) LIR 
(0.164,502.117) encodes 
(0.164,502.117) the 
(0.164,502.117) semantics 
(0.164,502.117) in 
(0.164,502.117) SSA 
(0.164,502.117) form 
(0.164,502.117) using 
(0.164,502.117) temporary 
(0.164,502.117) v 
(0.164,502.117) ariables. 
(0.164,502.117) The 
(0.164,502.117) LIR 
(0.164,502.117) also 
(0.164,502.117) encodes 
(0.164,502.117) all 
(0.164,502.117) the 
(0.164,502.117) stores 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) w 
(0.164,502.117) ould 
(0.164,502.117) do 
(0.164,502.117) to 
(0.164,502.117) its 
(0.164,502.117) data 
(0.164,502.117) stack. 
(0.164,502.117) Sometimes 
(0.164,502.117) these 
(0.164,502.117) stores 
(0.164,502.117) can 
(0.164,502.117) be 
(0.164,502.117) optimized 
(0.164,502.117) a 
(0.164,502.117) w 
(0.164,502.117) ay 
(0.164,502.117) as 
(0.164,502.117) the 
(0.164,502.117) stack 
(0.164,502.117) locations 
(0.164,502.117) are 
(0.164,502.117) li 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) only 
(0.164,502.117) on 
(0.164,502.117) e 
(0.164,502.117) xits 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) . 
(0.164,502.117) Finally 
(0.164,502.117) , 
(0.164,502.117) the 
(0.164,502.117) LIR 
(0.164,502.117) records 
(0.164,502.117) guards 
(0.164,502.117) and 
(0.164,502.117) side 
(0.164,502.117) e 
(0.164,502.117) xits 
(0.164,502.117) to 
(0.164,502.117) v 
(0.164,502.117) erify 
(0.164,502.117) the 
(0.164,502.117) assumptions 
(0.164,502.117) made 
(0.164,502.117) in 
(0.164,502.117) this 
(0.164,502.117) recording: 
(0.164,502.117) that 
(0.164,502.117) primes 
(0.164,502.117) is 
(0.164,502.117) an 
(0.164,502.117) array 
(0.164,502.117) and 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) call 
(0.164,502.117) to 
(0.164,502.117) set 
(0.164,502.117) its 
(0.164,502.117) element 
(0.164,502.117) succeeds. 
(0.164,502.117) mov 
(0.164,502.117) edx, 
(0.164,502.117) ebx(748) 
(0.164,502.117) // 
(0.164,502.117) load 
(0.164,502.117) primes 
(0.164,502.117) from 
(0.164,502.117) the 
(0.164,502.117) trace 
(0.164,502.117) activation 
(0.164,502.117) record 
(0.164,502.117) mov 
(0.164,502.117) edi(0), 
(0.164,502.117) edx 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) store 
(0.164,502.117) primes 
(0.164,502.117) to 
(0.164,502.117) interpreter 
(0.164,502.117) stack 
(0.164,502.117) mov 
(0.164,502.117) esi, 
(0.164,502.117) ebx(764) 
(0.164,502.117) // 
(0.164,502.117) load 
(0.164,502.117) k 
(0.164,502.117) from 
(0.164,502.117) the 
(0.164,502.117) trace 
(0.164,502.117) activation 
(0.164,502.117) record 
(0.164,502.117) mov 
(0.164,502.117) edi(8), 
(0.164,502.117) esi 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) store 
(0.164,502.117) k 
(0.164,502.117) to 
(0.164,502.117) interpreter 
(0.164,502.117) stack 
(0.164,502.117) mov 
(0.164,502.117) edi(16), 
(0.164,502.117) 0 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) store 
(0.164,502.117) false 
(0.164,502.117) to 
(0.164,502.117) interpreter 
(0.164,502.117) stack 
(0.164,502.117) mov 
(0.164,502.117) eax, 
(0.164,502.117) edx(4) 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) load 
(0.164,502.117) object 
(0.164,502.117) class 
(0.164,502.117) word 
(0.164,502.117) for 
(0.164,502.117) primes 
(0.164,502.117) and 
(0.164,502.117) eax, 
(0.164,502.117) -4 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) mask 
(0.164,502.117) out 
(0.164,502.117) object 
(0.164,502.117) class 
(0.164,502.117) tag 
(0.164,502.117) for 
(0.164,502.117) primes 
(0.164,502.117) cmp 
(0.164,502.117) eax, 
(0.164,502.117) Array 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) test 
(0.164,502.117) whether 
(0.164,502.117) primes 
(0.164,502.117) is 
(0.164,502.117) an 
(0.164,502.117) array 
(0.164,502.117) jne 
(0.164,502.117) side_exit_1 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) side 
(0.164,502.117) exit 
(0.164,502.117) if 
(0.164,502.117) primes 
(0.164,502.117) is 
(0.164,502.117) not 
(0.164,502.117) an 
(0.164,502.117) array 
(0.164,502.117) sub 
(0.164,502.117) esp, 
(0.164,502.117) 8 
(0.164,502.117) // 
(0.164,502.117) bump 
(0.164,502.117) stack 
(0.164,502.117) for 
(0.164,502.117) call 
(0.164,502.117) alignment 
(0.164,502.117) convention 
(0.164,502.117) push 
(0.164,502.117) false 
(0.164,502.117) // 
(0.164,502.117) push 
(0.164,502.117) last 
(0.164,502.117) argument 
(0.164,502.117) for 
(0.164,502.117) call 
(0.164,502.117) push 
(0.164,502.117) esi 
(0.164,502.117) // 
(0.164,502.117) push 
(0.164,502.117) first 
(0.164,502.117) argument 
(0.164,502.117) for 
(0.164,502.117) call 
(0.164,502.117) call 
(0.164,502.117) js_Array_set 
(0.164,502.117) // 
(0.164,502.117) call 
(0.164,502.117) function 
(0.164,502.117) to 
(0.164,502.117) set 
(0.164,502.117) array 
(0.164,502.117) element 
(0.164,502.117) add 
(0.164,502.117) esp, 
(0.164,502.117) 8 
(0.164,502.117) // 
(0.164,502.117) clean 
(0.164,502.117) up 
(0.164,502.117) extra 
(0.164,502.117) stack 
(0.164,502.117) space 
(0.164,502.117) mov 
(0.164,502.117) ecx, 
(0.164,502.117) ebx 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) created 
(0.164,502.117) by 
(0.164,502.117) register 
(0.164,502.117) allocator 
(0.164,502.117) test 
(0.164,502.117) eax, 
(0.164,502.117) eax 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) test 
(0.164,502.117) return 
(0.164,502.117) value 
(0.164,502.117) of 
(0.164,502.117) js_Array_set 
(0.164,502.117) je 
(0.164,502.117) side_exit_2 
(0.164,502.117) // 
(0.164,502.117) (*) 
(0.164,502.117) side 
(0.164,502.117) exit 
(0.164,502.117) if 
(0.164,502.117) call 
(0.164,502.117) failed 
(0.164,502.117) ... 
(0.164,502.117) side_exit_1: 
(0.164,502.117) mov 
(0.164,502.117) ecx, 
(0.164,502.117) ebp(-4) 
(0.164,502.117) // 
(0.164,502.117) restore 
(0.164,502.117) ecx 
(0.164,502.117) mov 
(0.164,502.117) esp, 
(0.164,502.117) ebp 
(0.164,502.117) // 
(0.164,502.117) restore 
(0.164,502.117) esp 
(0.164,502.117) jmp 
(0.164,502.117) epilog 
(0.164,502.117) // 
(0.164,502.117) jump 
(0.164,502.117) to 
(0.164,502.117) ret 
(0.164,502.117) statement 
(0.164,502.117) Figur 
(0.164,502.117) e 
(0.164,502.117) 4. 
(0.164,502.117) x86 
(0.164,502.117) snippet 
(0.164,502.117) f 
(0.164,502.117) or 
(0.164,502.117) sample 
(0.164,502.117) pr 
(0.164,502.117) ogram. 
(0.164,502.117) This 
(0.164,502.117) is 
(0.164,502.117) the 
(0.164,502.117) x86 
(0.164,502.117) code 
(0.164,502.117) compiled 
(0.164,502.117) from 
(0.164,502.117) the 
(0.164,502.117) LIR 
(0.164,502.117) snippet 
(0.164,502.117) in 
(0.164,502.117) Figure 
(0.164,502.117) 3. 
(0.164,502.117) Most 
(0.164,502.117) LIR 
(0.164,502.117) instructions 
(0.164,502.117) compile 
(0.164,502.117) to 
(0.164,502.117) a 
(0.164,502.117) single 
(0.164,502.117) x86 
(0.164,502.117) instruction. 
(0.164,502.117) Instructions 
(0.164,502.117) mark 
(0.164,502.117) ed 
(0.164,502.117) with 
(0.164,502.117) (*) 
(0.164,502.117) w 
(0.164,502.117) ould 
(0.164,502.117) be 
(0.164,502.117) omitted 
(0.164,502.117) by 
(0.164,502.117) an 
(0.164,502.117) idealized 
(0.164,502.117) compiler 
(0.164,502.117) that 
(0.164,502.117) kne 
(0.164,502.117) w 
(0.164,502.117) that 
(0.164,502.117) none 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) side 
(0.164,502.117) e 
(0.164,502.117) xits 
(0.164,502.117) w 
(0.164,502.117) ould 
(0.164,502.117) e 
(0.164,502.117) v 
(0.164,502.117) er 
(0.164,502.117) be 
(0.164,502.117) tak 
(0.164,502.117) en. 
(0.164,502.117) The 
(0.164,502.117) 17 
(0.164,502.117) instructions 
(0.164,502.117) generated 
(0.164,502.117) by 
(0.164,502.117) the 
(0.164,502.117) compiler 
(0.164,502.117) compare 
(0.164,502.117) f 
(0.164,502.117) a 
(0.164,502.117) v 
(0.164,502.117) orably 
(0.164,502.117) with 
(0.164,502.117) the 
(0.164,502.117) 100+ 
(0.164,502.117) instructions 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) w 
(0.164,502.117) ould 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecute 
(0.164,502.117) for 
(0.164,502.117) the 
(0.164,502.117) same 
(0.164,502.117) code 
(0.164,502.117) snippet, 
(0.164,502.117) including 
(0.164,502.117) 4 
(0.164,502.117) indirect 
(0.164,502.117) jumps. 
(0.164,502.117) i=2. 
(0.164,502.117) This 
(0.164,502.117) is 
(0.164,502.117) the 
(0.164,502.117) first 
(0.164,502.117) iteration 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) outer 
(0.164,502.117) loop. 
(0.164,502.117) The 
(0.164,502.117) loop 
(0.164,502.117) on 
(0.164,502.117) lines 
(0.164,502.117) 4-5 
(0.164,502.117) becomes 
(0.164,502.117) hot 
(0.164,502.117) on 
(0.164,502.117) its 
(0.164,502.117) second 
(0.164,502.117) iteration, 
(0.164,502.117) so 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) en- 
(0.164,502.117) ters 
(0.164,502.117) recording 
(0.164,502.117) mode 
(0.164,502.117) on 
(0.164,502.117) line 
(0.164,502.117) 4. 
(0.164,502.117) In 
(0.164,502.117) recording 
(0.164,502.117) m 
(0.164,502.117) ode, 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) records 
(0.164,502.117) the 
(0.164,502.117) code 
(0.164,502.117) along 
(0.164,502.117) the 
(0.164,502.117) trace 
(0.164,502.117) in 
(0.164,502.117) a 
(0.164,502.117) lo 
(0.164,502.117) w-le 
(0.164,502.117) v 
(0.164,502.117) el 
(0.164,502.117) compiler 
(0.164,502.117) intermedi- 
(0.164,502.117) ate 
(0.164,502.117) representation 
(0.164,502.117) we 
(0.164,502.117) call 
(0.164,502.117) LIR 
(0.164,502.117) . 
(0.164,502.117) The 
(0.164,502.117) LIR 
(0.164,502.117) trace 
(0.164,502.117) encodes 
(0.164,502.117) all 
(0.164,502.117) the 
(0.164,502.117) oper 
(0.164,502.117) - 
(0.164,502.117) ations 
(0.164,502.117) performed 
(0.164,502.117) and 
(0.164,502.117) the 
(0.164,502.117) types 
(0.164,502.117) of 
(0.164,502.117) all 
(0.164,502.117) operands. 
(0.164,502.117) The 
(0.164,502.117) LIR 
(0.164,502.117) trace 
(0.164,502.117) also 
(0.164,502.117) encodes 
(0.164,502.117) guar 
(0.164,502.117) ds 
(0.164,502.117) , 
(0.164,502.117) which 
(0.164,502.117) are 
(0.164,502.117) checks 
(0.164,502.117) that 
(0.164,502.117) v 
(0.164,502.117) erify 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) control 
(0.164,502.117) flo 
(0.164,502.117) w 
(0.164,502.117) and 
(0.164,502.117) types 
(0.164,502.117) are 
(0.164,502.117) identical 
(0.164,502.117) to 
(0.164,502.117) those 
(0.164,502.117) observ 
(0.164,502.117) ed 
(0.164,502.117) during 
(0.164,502.117) trace 
(0.164,502.117) recording. 
(0.164,502.117) Thus, 
(0.164,502.117) on 
(0.164,502.117) later 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecutions, 
(0.164,502.117) if 
(0.164,502.117) and 
(0.164,502.117) only 
(0.164,502.117) if 
(0.164,502.117) all 
(0.164,502.117) guards 
(0.164,502.117) are 
(0.164,502.117) passed, 
(0.164,502.117) the 
(0.164,502.117) trace 
(0.164,502.117) has 
(0.164,502.117) the 
(0.164,502.117) required 
(0.164,502.117) program 
(0.164,502.117) semantics. 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) stops 
(0.164,502.117) recording 
(0.164,502.117) when 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecution 
(0.164,502.117) returns 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) loop 
(0.164,502.117) header 
(0.164,502.117) or 
(0.164,502.117) e 
(0.164,502.117) xits 
(0.164,502.117) the 
(0.164,502.117) loop. 
(0.164,502.117) In 
(0.164,502.117) this 
(0.164,502.117) case, 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecution 
(0.164,502.117) returns 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) loop 
(0.164,502.117) header 
(0.164,502.117) on 
(0.164,502.117) line 
(0.164,502.117) 4. 
(0.164,502.117) After 
(0.164,502.117) recording 
(0.164,502.117) is 
(0.164,502.117) finished, 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) compiles 
(0.164,502.117) the 
(0.164,502.117) trace 
(0.164,502.117) to 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) using 
(0.164,502.117) the 
(0.164,502.117) recorded 
(0.164,502.117) type 
(0.164,502.117) information 
(0.164,502.117) for 
(0.164,502.117) optimization. 
(0.164,502.117) The 
(0.164,502.117) result 
(0.164,502.117) is 
(0.164,502.117) a 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) fragment 
(0.164,502.117) that 
(0.164,502.117) can 
(0.164,502.117) be 
(0.164,502.117) entered 
(0.164,502.117) if 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) PC 
(0.164,502.117) and 
(0.164,502.117) the 
(0.164,502.117) types 
(0.164,502.117) of 
(0.164,502.117) v 
(0.164,502.117) alues 
(0.164,502.117) match 
(0.164,502.117) those 
(0.164,502.117) observ 
(0.164,502.117) ed 
(0.164,502.117) when 
(0.164,502.117) trace 
(0.164,502.117) recording 
(0.164,502.117) w 
(0.164,502.117) as 
(0.164,502.117) started. 
(0.164,502.117) The 
(0.164,502.117) first 
(0.164,502.117) trace 
(0.164,502.117) in 
(0.164,502.117) our 
(0.164,502.117) e 
(0.164,502.117) xample, 
(0.164,502.117) T 
(0.164,502.117) 45 
(0.164,502.117) , 
(0.164,502.117) co 
(0.164,502.117) v 
(0.164,502.117) ers 
(0.164,502.117) lines 
(0.164,502.117) 4 
(0.164,502.117) and 
(0.164,502.117) 5. 
(0.164,502.117) This 
(0.164,502.117) trace 
(0.164,502.117) can 
(0.164,502.117) be 
(0.164,502.117) entered 
(0.164,502.117) if 
(0.164,502.117) the 
(0.164,502.117) PC 
(0.164,502.117) is 
(0.164,502.117) at 
(0.164,502.117) line 
(0.164,502.117) 4, 
(0.164,502.117) i 
(0.164,502.117) and 
(0.164,502.117) k 
(0.164,502.117) are 
(0.164,502.117) inte 
(0.164,502.117) gers, 
(0.164,502.117) and 
(0.164,502.117) primes 
(0.164,502.117) is 
(0.164,502.117) an 
(0.164,502.117) object. 
(0.164,502.117) After 
(0.164,502.117) compiling 
(0.164,502.117) T 
(0.164,502.117) 45 
(0.164,502.117) , 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) returns 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) and 
(0.164,502.117) loops 
(0.164,502.117) back 
(0.164,502.117) to 
(0.164,502.117) line 
(0.164,502.117) 1. 
(0.164,502.117) i=3. 
(0.164,502.117) No 
(0.164,502.117) w 
(0.164,502.117) the 
(0.164,502.117) loop 
(0.164,502.117) header 
(0.164,502.117) at 
(0.164,502.117) line 
(0.164,502.117) 1 
(0.164,502.117) has 
(0.164,502.117) become 
(0.164,502.117) hot, 
(0.164,502.117) so 
(0.164,502.117) T 
(0.164,502.117) race- 
(0.164,502.117) Monk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) starts 
(0.164,502.117) recording. 
(0.164,502.117) When 
(0.164,502.117) recording 
(0.164,502.117) reaches 
(0.164,502.117) line 
(0.164,502.117) 4, 
(0.164,502.117) T 
(0.164,502.117) race- 
(0.164,502.117) Monk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) observ 
(0.164,502.117) es 
(0.164,502.117) that 
(0.164,502.117) it 
(0.164,502.117) has 
(0.164,502.117) reached 
(0.164,502.117) an 
(0.164,502.117) inner 
(0.164,502.117) loop 
(0.164,502.117) header 
(0.164,502.117) that 
(0.164,502.117) al- 
(0.164,502.117) ready 
(0.164,502.117) has 
(0.164,502.117) a 
(0.164,502.117) compiled 
(0.164,502.117) trace, 
(0.164,502.117) so 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) attempts 
(0.164,502.117) to 
(0.164,502.117) nest 
(0.164,502.117) the 
(0.164,502.117) inner 
(0.164,502.117) loop 
(0.164,502.117) inside 
(0.164,502.117) the 
(0.164,502.117) current 
(0.164,502.117) trace. 
(0.164,502.117) The 
(0.164,502.117) first 
(0.164,502.117) step 
(0.164,502.117) is 
(0.164,502.117) to 
(0.164,502.117) ca 
(0.164,502.117) ll 
(0.164,502.117) the 
(0.164,502.117) inner 
(0.164,502.117) trace 
(0.164,502.117) as 
(0.164,502.117) a 
(0.164,502.117) subroutine. 
(0.164,502.117) This 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecutes 
(0.164,502.117) the 
(0.164,502.117) loop 
(0.164,502.117) on 
(0.164,502.117) line 
(0.164,502.117) 4 
(0.164,502.117) to 
(0.164,502.117) completion 
(0.164,502.117) and 
(0.164,502.117) then 
(0.164,502.117) returns 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) recorder 
(0.164,502.117) . 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) v 
(0.164,502.117) erifies 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) call 
(0.164,502.117) w 
(0.164,502.117) as 
(0.164,502.117) successful 
(0.164,502.117) and 
(0.164,502.117) then 
(0.164,502.117) records 
(0.164,502.117) the 
(0.164,502.117) call 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) inner 
(0.164,502.117) trace 
(0.164,502.117) as 
(0.164,502.117) part 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) current 
(0.164,502.117) trace. 
(0.164,502.117) Recor 
(0.164,502.117) ding 
(0.164,502.117) continues 
(0.164,502.117) until 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecution 
(0.164,502.117) reaches 
(0.164,502.117) line 
(0.164,502.117) 1, 
(0.164,502.117) and 
(0.164,502.117) at 
(0.164,502.117) which 
(0.164,502.117) point 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) finishes 
(0.164,502.117) and 
(0.164,502.117) compiles 
(0.164,502.117) a 
(0.164,502.117) trace 
(0.164,502.117) for 
(0.164,502.117) the 
(0.164,502.117) outer 
(0.164,502.117) loop, 
(0.164,502.117) T 
(0.164,502.117) 16 
(0.164,502.117) . 
(0.000,0.000) i=4. 
(0.000,0.000) On 
(0.000,0.000) this 
(0.000,0.000) iteration, 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) calls 
(0.000,0.000) T 
(0.000,0.000) 16 
(0.000,0.000) . 
(0.000,0.000) Because 
(0.000,0.000) i=4 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) if 
(0.000,0.000) statement 
(0.000,0.000) on 
(0.000,0.000) line 
(0.000,0.000) 2 
(0.000,0.000) is 
(0.000,0.000) tak 
(0.000,0.000) en. 
(0.000,0.000) This 
(0.000,0.000) branch 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) not 
(0.000,0.000) tak 
(0.000,0.000) en 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) original 
(0.000,0.000) trace, 
(0.000,0.000) so 
(0.000,0.000) this 
(0.000,0.000) causes 
(0.000,0.000) T 
(0.000,0.000) 16 
(0.000,0.000) to 
(0.000,0.000) f 
(0.000,0.000) ail 
(0.000,0.000) a 
(0.000,0.000) guard 
(0.000,0.000) and 
(0.000,0.000) tak 
(0.000,0.000) e 
(0.000,0.000) a 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit. 
(0.000,0.000) The 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) is 
(0.000,0.000) not 
(0.000,0.000) yet 
(0.000,0.000) hot, 
(0.000,0.000) so 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) returns 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) , 
(0.000,0.000) which 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecutes 
(0.000,0.000) the 
(0.000,0.000) continue 
(0.000,0.000) statement. 
(0.000,0.000) i=5. 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) calls 
(0.000,0.000) T 
(0.000,0.000) 16 
(0.000,0.000) , 
(0.000,0.000) which 
(0.000,0.000) in 
(0.000,0.000) turn 
(0.000,0.000) calls 
(0.000,0.000) the 
(0.000,0.000) nested 
(0.000,0.000) trace 
(0.000,0.000) T 
(0.000,0.000) 45 
(0.000,0.000) . 
(0.000,0.000) T 
(0.000,0.000) 16 
(0.000,0.000) loops 
(0.000,0.000) back 
(0.000,0.000) to 
(0.000,0.000) its 
(0.000,0.000) o 
(0.000,0.000) wn 
(0.000,0.000) header 
(0.000,0.000) , 
(0.000,0.000) starting 
(0.000,0.000) the 
(0.000,0.000) ne 
(0.000,0.000) xt 
(0.000,0.000) iteration 
(0.000,0.000) without 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) returning 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) monitor 
(0.000,0.000) . 
(0.000,0.000) i=6. 
(0.000,0.000) On 
(0.000,0.000) this 
(0.000,0.000) iteration, 
(0.000,0.000) the 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) on 
(0.000,0.000) line 
(0.000,0.000) 2 
(0.000,0.000) is 
(0.000,0.000) tak 
(0.000,0.000) en 
(0.000,0.000) ag 
(0.000,0.000) ain. 
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(0.000,0.000) time, 
(0.000,0.000) the 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) becomes 
(0.000,0.000) hot, 
(0.000,0.000) so 
(0.000,0.000) a 
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(0.000,0.000) T 
(0.000,0.000) 23 
(0.000,0.000) , 
(0.000,0.000) 1 
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(0.000,0.000) that 
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(0.000,0.000) v 
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(0.000,0.000) line 
(0.000,0.000) 3 
(0.000,0.000) and 
(0.000,0.000) returns 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) . 
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(0.000,0.000) the 
(0.000,0.000) end 
(0.000,0.000) of 
(0.000,0.000) T 
(0.000,0.000) 23 
(0.000,0.000) , 
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(0.000,0.000) directly 
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(0.000,0.000) start 
(0.000,0.000) of 
(0.000,0.000) T 
(0.000,0.000) 16 
(0.000,0.000) . 
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(0.000,0.000) side 
(0.000,0.000) e 
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(0.000,0.000) is 
(0.000,0.000) patched 
(0.000,0.000) so 
(0.000,0.000) that 
(0.000,0.000) on 
(0.000,0.000) future 
(0.000,0.000) iterations, 
(0.000,0.000) it 
(0.000,0.000) jumps 
(0.000,0.000) directly 
(0.000,0.000) to 
(0.000,0.000) T 
(0.000,0.000) 23 
(0.000,0.000) , 
(0.000,0.000) 1 
(0.000,0.000) . 
(0.000,0.000) At 
(0.000,0.000) this 
(0.000,0.000) point, 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) has 
(0.000,0.000) compiled 
(0.000,0.000) enough 
(0.000,0.000) traces 
(0.000,0.000) to 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) entire 
(0.000,0.000) nested 
(0.000,0.000) loop 
(0.000,0.000) st 
(0.000,0.000) ructure, 
(0.000,0.000) so 
(0.000,0.000) the 
(0.000,0.000) rest 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) runs 
(0.000,0.000) entirely 
(0.000,0.000) as 
(0.000,0.000) nati 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) code. 
(0.000,0.000) 3. 
(0.000,0.000) T 
(0.000,0.000) race 
(0.000,0.000) T 
(0.000,0.000) r 
(0.000,0.000) ees 
(0.000,0.000) In 
(0.000,0.000) this 
(0.000,0.000) section, 
(0.000,0.000) we 
(0.000,0.000) describe 
(0.000,0.000) traces, 
(0.000,0.000) trace 
(0.000,0.000) trees, 
(0.000,0.000) and 
(0.000,0.000) ho 
(0.000,0.000) w 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) are 
(0.000,0.000) formed 
(0.000,0.000) at 
(0.000,0.000) run 
(0.000,0.000) time. 
(0.000,0.000) Although 
(0.000,0.000) our 
(0.000,0.000) techniques 
(0.000,0.000) apply 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) dynamic 
(0.000,0.000) language 
(0.000,0.000) interpreter 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) will 
(0.000,0.000) describe 
(0.000,0.000) them 
(0.000,0.000) assuming 
(0.000,0.000) a 
(0.000,0.000) bytecode 
(0.000,0.000) interpreter 
(0.000,0.000) to 
(0.000,0.000) k 
(0.000,0.000) eep 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xposition 
(0.000,0.000) simple. 
(0.000,0.000) 3.1 
(0.000,0.000) T 
(0.000,0.000) races 
(0.000,0.000) A 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) is 
(0.000,0.000) sim 
(0.000,0.000) ply 
(0.000,0.000) a 
(0.000,0.000) program 
(0.000,0.000) path, 
(0.000,0.000) which 
(0.000,0.000) may 
(0.000,0.000) cross 
(0.000,0.000) function 
(0.000,0.000) call 
(0.000,0.000) boundaries. 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) focuses 
(0.000,0.000) on 
(0.000,0.000) loop 
(0.000,0.000) tr 
(0.000,0.000) aces 
(0.000,0.000) , 
(0.000,0.000) that 
(0.000,0.000) originate 
(0.000,0.000) at 
(0.000,0.000) a 
(0.000,0.000) loop 
(0.000,0.000) edge 
(0.000,0.000) and 
(0.000,0.000) represent 
(0.000,0.000) a 
(0.000,0.000) single 
(0.000,0.000) iteration 
(0.000,0.000) through 
(0.000,0.000) the 
(0.000,0.000) associated 
(0.000,0.000) loop. 
(0.000,0.000) Similar 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xtended 
(0.000,0.000) basic 
(0.000,0.000) block, 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) is 
(0.000,0.000) only 
(0.000,0.000) entered 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) top, 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) may 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) man 
(0.000,0.000) y 
(0.000,0.000) e 
(0.000,0.000) xits. 
(0.000,0.000) In 
(0.000,0.000) contrast 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xtended 
(0.000,0.000) basic 
(0.000,0.000) block, 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) can 
(0.000,0.000) contain 
(0.000,0.000) join 
(0.000,0.000) nodes. 
(0.000,0.000) Since 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) al 
(0.000,0.000) w 
(0.000,0.000) ays 
(0.000,0.000) only 
(0.000,0.000) follo 
(0.000,0.000) ws 
(0.000,0.000) one 
(0.000,0.000) single 
(0.000,0.000) path 
(0.000,0.000) through 
(0.000,0.000) the 
(0.000,0.000) original 
(0.000,0.000) program, 
(0.000,0.000) ho 
(0.000,0.000) we 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) , 
(0.000,0.000) join 
(0.000,0.000) nodes 
(0.000,0.000) are 
(0.000,0.000) not 
(0.000,0.000) recognizable 
(0.000,0.000) as 
(0.000,0.000) such 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) and 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) a 
(0.000,0.000) single 
(0.000,0.000) predecessor 
(0.000,0.000) node 
(0.000,0.000) lik 
(0.000,0.000) e 
(0.000,0.000) re 
(0.000,0.000) gular 
(0.000,0.000) nodes. 
(0.000,0.000) A 
(0.000,0.000) typed 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) annotated 
(0.000,0.000) with 
(0.000,0.000) a 
(0.000,0.000) type 
(0.000,0.000) for 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) v 
(0.000,0.000) ariable 
(0.000,0.000) (including 
(0.000,0.000) temporaries) 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) trace. 
(0.000,0.000) A 
(0.000,0.000) typed 
(0.000,0.000) trace 
(0.000,0.000) also 
(0.000,0.000) has 
(0.000,0.000) an 
(0.000,0.000) entry 
(0.000,0.000) type 
(0.000,0.000) map 
(0.000,0.000) gi 
(0.000,0.000) ving 
(0.000,0.000) the 
(0.000,0.000) required 
(0.000,0.000) types 
(0.000,0.000) for 
(0.000,0.000) v 
(0.000,0.000) ariables 
(0.000,0.000) used 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) before 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) are 
(0.000,0.000) defined. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) could 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) a 
(0.000,0.000) type 
(0.000,0.000) map 
(0.000,0.000) (x: 
(0.000,0.000) int, 
(0.000,0.000) b: 
(0.000,0.000) boolean) 
(0.000,0.000) , 
(0.000,0.000) meaning 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) may 
(0.000,0.000) be 
(0.000,0.000) entered 
(0.000,0.000) only 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) v 
(0.000,0.000) ariable 
(0.000,0.000) x 
(0.000,0.000) is 
(0.000,0.000) of 
(0.000,0.000) type 
(0.000,0.000) int 
(0.000,0.000) and 
(0.000,0.000) the 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) of 
(0.000,0.000) b 
(0.000,0.000) is 
(0.000,0.000) of 
(0.000,0.000) type 
(0.000,0.000) boolean 
(0.000,0.000) . 
(0.000,0.000) The 
(0.000,0.000) entry 
(0.000,0.000) type 
(0.000,0.000) map 
(0.000,0.000) is 
(0.000,0.000) much 
(0.000,0.000) lik 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) signature 
(0.000,0.000) of 
(0.000,0.000) a 
(0.000,0.000) function. 
(0.000,0.000) In 
(0.000,0.000) this 
(0.000,0.000) paper 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) only 
(0.000,0.000) discuss 
(0.000,0.000) typed 
(0.000,0.000) loop 
(0.000,0.000) traces, 
(0.000,0.000) and 
(0.000,0.000) we 
(0.000,0.000) will 
(0.000,0.000) refer 
(0.000,0.000) to 
(0.000,0.000) them 
(0.000,0.000) simply 
(0.000,0.000) as 
(0.000,0.000) “traces”. 
(0.000,0.000) The 
(0.000,0.000) k 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) property 
(0.000,0.000) of 
(0.000,0.000) typed 
(0.000,0.000) loop 
(0.000,0.000) traces 
(0.000,0.000) is 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) compiled 
(0.000,0.000) to 
(0.000,0.000) ef 
(0.000,0.000) ficient 
(0.000,0.000) machine 
(0.000,0.000) code 
(0.000,0.000) using 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) techniques 
(0.000,0.000) used 
(0.000,0.000) for 
(0.000,0.000) typed 
(0.000,0.000) languages. 
(0.000,0.000) In 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) , 
(0.000,0.000) traces 
(0.000,0.000) are 
(0.000,0.000) recorded 
(0.000,0.000) in 
(0.000,0.000) trace-fla 
(0.000,0.000) v 
(0.000,0.000) ored 
(0.000,0.000) SSA 
(0.000,0.000) LIR 
(0.000,0.000) (lo 
(0.000,0.000) w-le 
(0.000,0.000) v 
(0.000,0.000) el 
(0.000,0.000) intermediate 
(0.000,0.000) representation). 
(0.000,0.000) In 
(0.000,0.000) trace-fla 
(0.000,0.000) v 
(0.000,0.000) ored 
(0.000,0.000) SSA 
(0.000,0.000) (or 
(0.000,0.000) TSSA), 
(0.000,0.000) phi 
(0.000,0.000) nodes 
(0.000,0.000) appear 
(0.000,0.000) only 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) entry 
(0.000,0.000) point, 
(0.000,0.000) which 
(0.000,0.000) is 
(0.000,0.000) reached 
(0.000,0.000) both 
(0.000,0.000) on 
(0.000,0.000) entry 
(0.000,0.000) and 
(0.000,0.000) via 
(0.000,0.000) loop 
(0.000,0.000) edges. 
(0.000,0.000) The 
(0.000,0.000) im 
(0.000,0.000) portant 
(0.000,0.000) LIR 
(0.000,0.000) primiti 
(0.000,0.000) v 
(0.000,0.000) es 
(0.000,0.000) are 
(0.000,0.000) constant 
(0.000,0.000) v 
(0.000,0.000) alues, 
(0.000,0.000) memory 
(0.000,0.000) loads 
(0.000,0.000) and 
(0.000,0.000) stores 
(0.000,0.000) (by 
(0.000,0.000) address 
(0.000,0.000) and 
(0.000,0.000) of 
(0.000,0.000) fset), 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) operators, 
(0.000,0.000) floating-point 
(0.000,0.000) operators, 
(0.000,0.000) function 
(0.000,0.000) calls, 
(0.000,0.000) and 
(0.000,0.000) conditional 
(0.000,0.000) e 
(0.000,0.000) xits. 
(0.000,0.000) T 
(0.000,0.000) ype 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) ersions, 
(0.000,0.000) such 
(0.000,0.000) as 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) to 
(0.000,0.000) double, 
(0.000,0.000) are 
(0.000,0.000) represented 
(0.000,0.000) by 
(0.000,0.000) function 
(0.000,0.000) calls. 
(0.000,0.000) This 
(0.000,0.000) mak 
(0.000,0.000) es 
(0.000,0.000) the 
(0.000,0.000) LIR 
(0.000,0.000) used 
(0.000,0.000) by 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) independent 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) concrete 
(0.000,0.000) type 
(0.000,0.000) system 
(0.000,0.000) and 
(0.000,0.000) type 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) ersion 
(0.000,0.000) rules 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) source 
(0.000,0.000) language. 
(0.000,0.000) The 
(0.000,0.000) LIR 
(0.000,0.000) operations 
(0.000,0.000) are 
(0.000,0.000) generic 
(0.000,0.000) enough 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) back 
(0.000,0.000) end 
(0.000,0.000) compiler 
(0.000,0.000) is 
(0.000,0.000) language 
(0.000,0.000) independent. 
(0.000,0.000) Figure 
(0.000,0.000) 3 
(0.000,0.000) sho 
(0.000,0.000) ws 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xample 
(0.000,0.000) LIR 
(0.000,0.000) trace. 
(0.000,0.000) Bytecode 
(0.000,0.000) interpreters 
(0.000,0.000) typically 
(0.000,0.000) represent 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) arious 
(0.000,0.000) comple 
(0.000,0.000) x 
(0.000,0.000) data 
(0.000,0.000) structures 
(0.000,0.000) (e.g., 
(0.000,0.000) hash 
(0.000,0.000) tables) 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) box 
(0.000,0.000) ed 
(0.000,0.000) format 
(0.000,0.000) (i.e., 
(0.000,0.000) with 
(0.000,0.000) attached 
(0.000,0.000) type 
(0.000,0.000) tag 
(0.000,0.000) bits). 
(0.000,0.000) Since 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) i 
(0.000,0.000) s 
(0.000,0.000) intended 
(0.000,0.000) to 
(0.000,0.000) represent 
(0.000,0.000) ef 
(0.000,0.000) ficient 
(0.000,0.000) code 
(0.000,0.000) that 
(0.000,0.000) eliminates 
(0.000,0.000) all 
(0.000,0.000) that 
(0.000,0.000) comple 
(0.000,0.000) xity 
(0.000,0.000) , 
(0.000,0.000) our 
(0.000,0.000) traces 
(0.000,0.000) oper 
(0.000,0.000) - 
(0.000,0.000) ate 
(0.000,0.000) on 
(0.000,0.000) unbox 
(0.000,0.000) ed 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) in 
(0.000,0.000) simpl 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ariables 
(0.000,0.000) and 
(0.000,0.000) arrays 
(0.000,0.000) as 
(0.000,0.000) much 
(0.000,0.000) as 
(0.000,0.000) possible. 
(0.000,0.000) A 
(0.000,0.000) trace 
(0.000,0.000) records 
(0.000,0.000) a 
(0.000,0.000) ll 
(0.000,0.000) its 
(0.000,0.000) intermediate 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) small 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) record 
(0.000,0.000) area. 
(0.000,0.000) T 
(0.000,0.000) o 
(0.000,0.000) mak 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ariable 
(0.000,0.000) accesses 
(0.000,0.000) f 
(0.000,0.000) ast 
(0.000,0.000) on 
(0.000,0.000) trace, 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) also 
(0.000,0.000) imports 
(0.000,0.000) local 
(0.000,0.000) and 
(0.000,0.000) global 
(0.000,0.000) v 
(0.000,0.000) ariables 
(0.000,0.000) by 
(0.000,0.000) unboxing 
(0.000,0.000) them 
(0.000,0.000) and 
(0.000,0.000) cop 
(0.000,0.000) ying 
(0.000,0.000) them 
(0.000,0.000) to 
(0.000,0.000) its 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) record. 
(0.000,0.000) Thus, 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) can 
(0.000,0.000) read 
(0.000,0.000) and 
(0.000,0.000) write 
(0.000,0.000) these 
(0.000,0.000) v 
(0.000,0.000) ariables 
(0.000,0.000) wit 
(0.000,0.000) h 
(0.000,0.000) simple 
(0.000,0.000) loads 
(0.000,0.000) and 
(0.000,0.000) stores 
(0.000,0.000) from 
(0.000,0.000) a 
(0.000,0.000) nati 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) recording, 
(0.000,0.000) independently 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) boxing 
(0.000,0.000) mechanism 
(0.000,0.000) used 
(0.000,0.000) by 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) When 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) e 
(0.000,0.000) xits, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) box 
(0.000,0.000) es 
(0.000,0.000) the 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) from 
(0.000,0.000) this 
(0.000,0.000) nati 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) storage 
(0.000,0.000) location 
(0.000,0.000) and 
(0.000,0.000) copies 
(0.000,0.000) them 
(0.000,0.000) back 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) structures. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) control-flo 
(0.000,0.000) w 
(0.000,0.000) branch 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) source 
(0.000,0.000) program, 
(0.000,0.000) the 
(0.000,0.000) recorder 
(0.000,0.000) generates 
(0.000,0.000) conditional 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) LIR 
(0.000,0.000) inst 
(0.000,0.000) ructions. 
(0.000,0.000) These 
(0.000,0.000) instruc- 
(0.000,0.000) tions 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) if 
(0.000,0.000) required 
(0.000,0.000) control 
(0.000,0.000) flo 
(0.000,0.000) w 
(0.000,0.000) is 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) from 
(0.000,0.000) what 
(0.000,0.000) it 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) at 
(0.000,0.000) trac 
(0.000,0.000) e 
(0.000,0.000) recording, 
(0.000,0.000) ensuring 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) instructions 
(0.000,0.000) are 
(0.000,0.000) run 
(0.000,0.000) only 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) are 
(0.000,0.000) supposed 
(0.000,0.000) to. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) call 
(0.000,0.000) these 
(0.000,0.000) instructions 
(0.000,0.000) guar 
(0.000,0.000) d 
(0.000,0.000) instructions. 
(0.000,0.000) Most 
(0.000,0.000) of 
(0.000,0.000) our 
(0.000,0.000) traces 
(0.000,0.000) represent 
(0.000,0.000) loops 
(0.000,0.000) and 
(0.000,0.000) end 
(0.000,0.000) with 
(0.000,0.000) the 
(0.000,0.000) special 
(0.000,0.000) loop 
(0.000,0.000) LIR 
(0.000,0.000) instruction. 
(0.000,0.000) This 
(0.000,0.000) is 
(0.000,0.000) just 
(0.000,0.000) an 
(0.000,0.000) unconditional 
(0.000,0.000) branch 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) top 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) trace. 
(0.000,0.000) Such 
(0.000,0.000) traces 
(0.000,0.000) return 
(0.000,0.000) only 
(0.000,0.000) via 
(0.000,0.000) guards. 
(0.000,0.000) No 
(0.000,0.000) w 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) describe 
(0.000,0.000) the 
(0.000,0.000) k 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) optimizations 
(0.000,0.000) that 
(0.000,0.000) are 
(0.000,0.000) performed 
(0.000,0.000) as 
(0.000,0.000) part 
(0.000,0.000) of 
(0.000,0.000) recording 
(0.000,0.000) LIR. 
(0.000,0.000) All 
(0.000,0.000) of 
(0.000,0.000) thes 
(0.000,0.000) e 
(0.000,0.000) optimizations 
(0.000,0.000) reduce 
(0.000,0.000) comple 
(0.000,0.000) x 
(0.000,0.000) dynamic 
(0.000,0.000) language 
(0.000,0.000) constructs 
(0.000,0.000) to 
(0.000,0.000) simple 
(0.000,0.000) typed 
(0.000,0.000) constructs 
(0.000,0.000) by 
(0.000,0.000) spe- 
(0.000,0.000) cializing 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) current 
(0.000,0.000) trace. 
(0.000,0.000) Each 
(0.000,0.000) optimization 
(0.000,0.000) requires 
(0.000,0.000) guard 
(0.000,0.000) in- 
(0.000,0.000) structions 
(0.000,0.000) to 
(0.000,0.000) v 
(0.000,0.000) erify 
(0.000,0.000) their 
(0.000,0.000) assumptions 
(0.000,0.000) about 
(0.000,0.000) the 
(0.000,0.000) state 
(0.000,0.000) a 
(0.000,0.000) nd 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) if 
(0.000,0.000) necessary 
(0.000,0.000) . 
(0.000,0.000) T 
(0.000,0.000) ype 
(0.000,0.000) specialization. 
(0.000,0.000) All 
(0.000,0.000) LIR 
(0.000,0.000) primiti 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) s 
(0.000,0.000) apply 
(0.000,0.000) to 
(0.000,0.000) operands 
(0.000,0.000) of 
(0.000,0.000) specific 
(0.000,0.000) type 
(0.000,0.000) s. 
(0.000,0.000) Thus, 
(0.000,0.000) LIR 
(0.000,0.000) traces 
(0.000,0.000) are 
(0.000,0.000) necessarily 
(0.000,0.000) type-specialized, 
(0.000,0.000) and 
(0.000,0.000) a 
(0.000,0.000) compiler 
(0.000,0.000) can 
(0.000,0.000) easily 
(0.000,0.000) produc 
(0.000,0.000) e 
(0.000,0.000) a 
(0.000,0.000) translation 
(0.000,0.000) that 
(0.000,0.000) requires 
(0.000,0.000) no 
(0.000,0.000) type 
(0.000,0.000) dispatches. 
(0.000,0.000) A 
(0.000,0.000) typical 
(0.000,0.000) byt 
(0.000,0.000) ecode 
(0.000,0.000) interpreter 
(0.000,0.000) carri 
(0.000,0.000) es 
(0.000,0.000) tag 
(0.000,0.000) bits 
(0.000,0.000) along 
(0.000,0.000) with 
(0.000,0.000) each 
(0.000,0.000) v 
(0.000,0.000) alue, 
(0.000,0.000) and 
(0.000,0.000) to 
(0.000,0.000) perform 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) operation, 
(0.000,0.000) must 
(0.000,0.000) check 
(0.000,0.000) the 
(0.000,0.000) tag 
(0.000,0.000) bits, 
(0.000,0.000) dynamically 
(0.000,0.000) dispatch, 
(0.000,0.000) mask 
(0.000,0.000) out 
(0.000,0.000) the 
(0.000,0.000) tag 
(0.000,0.000) bits 
(0.000,0.000) to 
(0.000,0.000) reco 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) untagged 
(0.000,0.000) v 
(0.000,0.000) alue, 
(0.000,0.000) perform 
(0.000,0.000) the 
(0.000,0.000) operation, 
(0.000,0.000) and 
(0.000,0.000) then 
(0.000,0.000) reappl 
(0.000,0.000) y 
(0.000,0.000) tags. 
(0.000,0.000) LIR 
(0.000,0.000) omits 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) erything 
(0.000,0.000) e 
(0.000,0.000) xcept 
(0.000,0.000) the 
(0.000,0.000) operation 
(0.000,0.000) itself. 
(0.000,0.000) A 
(0.000,0.000) potential 
(0.000,0.000) problem 
(0.000,0.000) is 
(0.000,0.000) that 
(0.000,0.000) some 
(0.000,0.000) operations 
(0.000,0.000) can 
(0.000,0.000) produce 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) of 
(0.000,0.000) unpredictable 
(0.000,0.000) types. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) reading 
(0.000,0.000) a 
(0.000,0.000) property 
(0.000,0.000) from 
(0.000,0.000) an 
(0.000,0.000) object 
(0.000,0.000) could 
(0.000,0.000) yield 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) of 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) type, 
(0.000,0.000) not 
(0.000,0.000) ne 
(0.000,0.000) cessarily 
(0.000,0.000) the 
(0.000,0.000) type 
(0.000,0.000) observ 
(0.000,0.000) ed 
(0.000,0.000) during 
(0.000,0.000) rec 
(0.000,0.000) ording. 
(0.000,0.000) The 
(0.000,0.000) recorder 
(0.000,0.000) emits 
(0.000,0.000) guard 
(0.000,0.000) instructions 
(0.000,0.000) that 
(0.000,0.000) conditionally 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) operation 
(0.000,0.000) yields 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) of 
(0.000,0.000) a 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) type 
(0.000,0.000) from 
(0.000,0.000) that 
(0.000,0.000) seen 
(0.000,0.000) during 
(0.000,0.000) recording. 
(0.000,0.000) These 
(0.000,0.000) guard 
(0.000,0.000) instructions 
(0.000,0.000) guarantee 
(0.000,0.000) that 
(0.000,0.000) as 
(0.000,0.000) long 
(0.000,0.000) as 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution 
(0.000,0.000) is 
(0.000,0.000) on 
(0.000,0.000) trace, 
(0.000,0.000) the 
(0.000,0.000) types 
(0.000,0.000) of 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) match 
(0.000,0.000) those 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) typed 
(0.000,0.000) trace. 
(0.000,0.000) When 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) observ 
(0.000,0.000) es 
(0.000,0.000) a 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) along 
(0.000,0.000) such 
(0.000,0.000) a 
(0.000,0.000) type 
(0.000,0.000) guard, 
(0.000,0.000) a 
(0.000,0.000) ne 
(0.000,0.000) w 
(0.000,0.000) typed 
(0.000,0.000) trace 
(0.000,0.000) is 
(0.000,0.000) recorded 
(0.000,0.000) originating 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) location, 
(0.000,0.000) capturing 
(0.000,0.000) the 
(0.000,0.000) ne 
(0.000,0.000) w 
(0.000,0.000) type 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) operation 
(0.000,0.000) in 
(0.000,0.000) question. 
(0.000,0.000) Repr 
(0.000,0.000) esentation 
(0.000,0.000) specialization: 
(0.000,0.000) objects. 
(0.000,0.000) In 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aS 
(0.000,0.000) cript, 
(0.000,0.000) name 
(0.000,0.000) lookup 
(0.000,0.000) semantics 
(0.000,0.000) are 
(0.000,0.000) comple 
(0.000,0.000) x 
(0.000,0.000) and 
(0.000,0.000) potentially 
(0.000,0.000) e 
(0.000,0.000) xpensi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) because 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) include 
(0.000,0.000) features 
(0.000,0.000) lik 
(0.000,0.000) e 
(0.000,0.000) object 
(0.000,0.000) inheritance 
(0.000,0.000) and 
(0.000,0.000) eval 
(0.000,0.000) . 
(0.000,0.000) T 
(0.000,0.000) o 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) aluate 
(0.000,0.000) an 
(0.000,0.000) object 
(0.000,0.000) property 
(0.000,0.000) read 
(0.000,0.000) e 
(0.000,0.000) xpression 
(0.000,0.000) li 
(0.000,0.000) k 
(0.000,0.000) e 
(0.000,0.000) o.x 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) must 
(0.000,0.000) search 
(0.000,0.000) the 
(0.000,0.000) property 
(0.000,0.000) map 
(0.000,0.000) of 
(0.000,0.000) o 
(0.000,0.000) and 
(0.000,0.000) all 
(0.000,0.000) of 
(0.000,0.000) its 
(0.000,0.000) prototypes 
(0.000,0.000) and 
(0.000,0.000) parents. 
(0.000,0.000) Property 
(0.000,0.000) maps 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) implemented 
(0.000,0.000) with 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) data 
(0.000,0.000) structures 
(0.000,0.000) (e.g., 
(0.000,0.000) per 
(0.000,0.000) -object 
(0.000,0.000) hash 
(0.000,0.000) tables 
(0.000,0.000) or 
(0.000,0.000) shared 
(0.000,0.000) hash 
(0.000,0.000) tables), 
(0.000,0.000) so 
(0.000,0.000) the 
(0.000,0.000) search 
(0.000,0.000) process 
(0.000,0.000) also 
(0.000,0.000) must 
(0.000,0.000) dispatch 
(0.000,0.000) on 
(0.000,0.000) t 
(0.000,0.000) he 
(0.000,0.000) representation 
(0.000,0.000) of 
(0.000,0.000) each 
(0.000,0.000) object 
(0.000,0.000) found 
(0.000,0.000) during 
(0.000,0.000) search. 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) can 
(0.000,0.000) simply 
(0.000,0.000) observ 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) result 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) search 
(0.000,0.000) process 
(0.000,0.000) and 
(0.000,0.000) record 
(0.000,0.000) the 
(0.000,0.000) simplest 
(0.000,0.000) possible 
(0.000,0.000) LIR 
(0.000,0.000) to 
(0.000,0.000) access 
(0.000,0.000) the 
(0.000,0.000) property 
(0.000,0.000) v 
(0.000,0.000) alue. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) the 
(0.000,0.000) search 
(0.000,0.000) might 
(0.000,0.000) finds 
(0.000,0.000) the 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) of 
(0.000,0.000) o.x 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) prototype 
(0.000,0.000) of 
(0.000,0.000) o 
(0.000,0.000) , 
(0.000,0.000) which 
(0.000,0.000) uses 
(0.000,0.000) a 
(0.000,0.000) shared 
(0.000,0.000) hash-table 
(0.000,0.000) represen- 
(0.000,0.000) tation 
(0.000,0.000) that 
(0.000,0.000) places 
(0.000,0.000) x 
(0.000,0.000) in 
(0.000,0.000) sl 
(0.000,0.000) ot 
(0.000,0.000) 2 
(0.000,0.000) of 
(0.000,0.000) a 
(0.000,0.000) property 
(0.000,0.000) v 
(0.000,0.000) ector 
(0.000,0.000) . 
(0.000,0.000) Then 
(0.000,0.000) the 
(0.000,0.000) recorded 
(0.000,0.000) can 
(0.000,0.000) generate 
(0.000,0.000) LIR 
(0.000,0.000) that 
(0.000,0.000) reads 
(0.000,0.000) o.x 
(0.000,0.000) with 
(0.000,0.000) just 
(0.000,0.000) tw 
(0.000,0.000) o 
(0.000,0.000) or 
(0.000,0.000) three 
(0.000,0.000) loads: 
(0.000,0.000) one 
(0.000,0.000) to 
(0.000,0.000) get 
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(0.000,0.000) prototype, 
(0.000,0.000) possibly 
(0.000,0.000) one 
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(0.000,0.000) one 
(0.000,0.000) more 
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(0.000,0.000) slot 
(0.000,0.000) 2 
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(0.000,0.000) the 
(0.000,0.000) v 
(0.000,0.000) ector 
(0.000,0.000) . 
(0.000,0.000) This 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) ast 
(0.000,0.000) simplification 
(0.000,0.000) and 
(0.000,0.000) speedup 
(0.000,0.000) compared 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) original 
(0.000,0.000) interpreter 
(0.000,0.000) code. 
(0.000,0.000) Inheritance 
(0.000,0.000) relationships 
(0.000,0.000) and 
(0.000,0.000) object 
(0.000,0.000) representations 
(0.000,0.000) can 
(0.000,0.000) change 
(0.000,0.000) during 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecu- 
(0.000,0.000) tion, 
(0.000,0.000) so 
(0.000,0.000) the 
(0.000,0.000) simplified 
(0.000,0.000) code 
(0.000,0.000) require 
(0.000,0.000) s 
(0.000,0.000) guard 
(0.000,0.000) instructions 
(0.000,0.000) that 
(0.000,0.000) ensure 
(0.000,0.000) the 
(0.000,0.000) object 
(0.000,0.000) representation 
(0.000,0.000) is 
(0.000,0.000) the 
(0.000,0.000) same. 
(0.000,0.000) In 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) , 
(0.000,0.000) objects’ 
(0.000,0.000) rep- 
(0.000,0.000) resentations 
(0.000,0.000) are 
(0.000,0.000) assigned 
(0.000,0.000) an 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) k 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) called 
(0.000,0.000) the 
(0.000,0.000) object 
(0.000,0.000) shape 
(0.000,0.000) . 
(0.000,0.000) Thus, 
(0.000,0.000) the 
(0.000,0.000) guard 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) simple 
(0.000,0.000) equality 
(0.000,0.000) check 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) object 
(0.000,0.000) shape. 
(0.000,0.000) Repr 
(0.000,0.000) esentation 
(0.000,0.000) specialization: 
(0.000,0.000) numbers. 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) has 
(0.000,0.000) no 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) type, 
(0.000,0.000) only 
(0.000,0.000) a 
(0.000,0.000) Number 
(0.000,0.000) type 
(0.000,0.000) that 
(0.000,0.000) is 
(0.000,0.000) the 
(0.000,0.000) set 
(0.000,0.000) of 
(0.000,0.000) 64-bit 
(0.000,0.000) IEEE- 
(0.000,0.000) 754 
(0.000,0.000) floating-pointer 
(0.000,0.000) numbers 
(0.000,0.000) (“doubles”). 
(0.000,0.000) But 
(0.000,0.000) man 
(0.000,0.000) y 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) operators, 
(0.000,0.000) in 
(0.000,0.000) particular 
(0.000,0.000) array 
(0.000,0.000) accesses 
(0.000,0.000) and 
(0.000,0.000) bitwise 
(0.000,0.000) operators, 
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(0.000,0.000) on 
(0.000,0.000) inte 
(0.000,0.000) gers, 
(0.000,0.000) so 
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(0.000,0.000) y 
(0.000,0.000) first 
(0.000,0.000) con 
(0.000,0.000) v 
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(0.000,0.000) number 
(0.000,0.000) to 
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(0.000,0.000) , 
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(0.000,0.000) ert 
(0.000,0.000) an 
(0.000,0.000) y 
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(0.000,0.000) result 
(0.000,0.000) back 
(0.000,0.000) to 
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(0.000,0.000) double. 
(0.000,0.000) 1 
(0.000,0.000) Clearly 
(0.000,0.000) , 
(0.000,0.000) a 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) VM 
(0.000,0.000) that 
(0.000,0.000) w 
(0.000,0.000) ants 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) f 
(0.000,0.000) ast 
(0.000,0.000) must 
(0.000,0.000) find 
(0.000,0.000) a 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) to 
(0.000,0.000) operate 
(0.000,0.000) on 
(0.000,0.000) inte 
(0.000,0.000) gers 
(0.000,0.000) directly 
(0.000,0.000) and 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oid 
(0.000,0.000) these 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) ersions. 
(0.000,0.000) In 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) support 
(0.000,0.000) tw 
(0.000,0.000) o 
(0.000,0.000) representations 
(0.000,0.000) for 
(0.000,0.000) numbers: 
(0.000,0.000) inte 
(0.000,0.000) gers 
(0.000,0.000) and 
(0.000,0.000) doubles. 
(0.000,0.000) The 
(0.000,0.000) interpreter 
(0.000,0.000) uses 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) representations 
(0.000,0.000) as 
(0.000,0.000) much 
(0.000,0.000) as 
(0.000,0.000) it 
(0.000,0.000) can, 
(0.000,0.000) switching 
(0.000,0.000) for 
(0.000,0.000) results 
(0.000,0.000) that 
(0.000,0.000) can 
(0.000,0.000) only 
(0.000,0.000) be 
(0.000,0.000) represented 
(0.000,0.000) as 
(0.000,0.000) doubles. 
(0.000,0.000) When 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) is 
(0.000,0.000) started, 
(0.000,0.000) some 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) may 
(0.000,0.000) be 
(0.000,0.000) imported 
(0.000,0.000) and 
(0.000,0.000) represented 
(0.000,0.000) as 
(0.000,0.000) inte 
(0.000,0.000) gers. 
(0.000,0.000) Some 
(0.000,0.000) operations 
(0.000,0.000) on 
(0.000,0.000) inte 
(0.000,0.000) gers 
(0.000,0.000) require 
(0.000,0.000) guards. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) adding 
(0.000,0.000) tw 
(0.000,0.000) o 
(0.000,0.000) inte 
(0.000,0.000) gers 
(0.000,0.000) can 
(0.000,0.000) produce 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) too 
(0.000,0.000) lar 
(0.000,0.000) ge 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) representation. 
(0.000,0.000) Function 
(0.000,0.000) inlining 
(0.000,0.000) . 
(0.000,0.000) LIR 
(0.000,0.000) traces 
(0.000,0.000) can 
(0.000,0.000) cross 
(0.000,0.000) function 
(0.000,0.000) boundaries 
(0.000,0.000) in 
(0.000,0.000) either 
(0.000,0.000) direction, 
(0.000,0.000) achie 
(0.000,0.000) ving 
(0.000,0.000) function 
(0.000,0.000) inlining. 
(0.000,0.000) Mo 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) instructions 
(0.000,0.000) need 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) recorded 
(0.000,0.000) for 
(0.000,0.000) function 
(0.000,0.000) entry 
(0.000,0.000) and 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) to 
(0.000,0.000) cop 
(0.000,0.000) y 
(0.000,0.000) ar 
(0.000,0.000) guments 
(0.000,0.000) in 
(0.000,0.000) and 
(0.000,0.000) return 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) out 
(0.000,0.000) . 
(0.000,0.000) These 
(0.000,0.000) mo 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) statements 
(0.000,0.000) are 
(0.000,0.000) then 
(0.000,0.000) optimized 
(0.000,0.000) a 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) by 
(0.000,0.000) the 
(0.000,0.000) compiler 
(0.000,0.000) using 
(0.000,0.000) cop 
(0.000,0.000) y 
(0.000,0.000) propag 
(0.000,0.000) ation. 
(0.000,0.000) In 
(0.000,0.000) order 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) able 
(0.000,0.000) to 
(0.000,0.000) return 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) must 
(0.000,0.000) also 
(0.000,0.000) generate 
(0.000,0.000) LIR 
(0.000,0.000) to 
(0.000,0.000) record 
(0.000,0.000) that 
(0.000,0.000) a 
(0.000,0.000) call 
(0.000,0.000) frame 
(0.000,0.000) has 
(0.000,0.000) been 
(0.000,0.000) entered 
(0.000,0.000) and 
(0.000,0.000) e 
(0.000,0.000) xited. 
(0.000,0.000) The 
(0.000,0.000) frame 
(0.000,0.000) entry 
(0.000,0.000) and 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) LIR 
(0.000,0.000) sa 
(0.000,0.000) v 
(0.000,0.000) es 
(0.000,0.000) just 
(0.000,0.000) enough 
(0.000,0.000) information 
(0.000,0.000) to 
(0.000,0.000) allo 
(0.000,0.000) w 
(0.000,0.000) the 
(0.000,0.000) intepreter 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) restored 
(0.000,0.000) later 
(0.000,0.000) and 
(0.000,0.000) is 
(0.000,0.000) much 
(0.000,0.000) simpler 
(0.000,0.000) than 
(0.000,0.000) the 
(0.000,0.000) interpreter’ 
(0.000,0.000) s 
(0.000,0.000) standard 
(0.000,0.000) call 
(0.000,0.000) code. 
(0.000,0.000) If 
(0.000,0.000) the 
(0.000,0.000) function 
(0.000,0.000) being 
(0.000,0.000) entered 
(0.000,0.000) is 
(0.000,0.000) not 
(0.000,0.000) constant 
(0.000,0.000) (which 
(0.000,0.000) in 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) includes 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) call 
(0.000,0.000) by 
(0.000,0.000) function 
(0.000,0.000) name), 
(0.000,0.000) the 
(0.000,0.000) recorder 
(0.000,0.000) must 
(0.000,0.000) also 
(0.000,0.000) emit 
(0.000,0.000) LIR 
(0.000,0.000) to 
(0.000,0.000) guard 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) function 
(0.000,0.000) is 
(0.000,0.000) the 
(0.000,0.000) same. 
(0.000,0.000) Guards 
(0.000,0.000) and 
(0.000,0.000) side 
(0.000,0.000) exits. 
(0.000,0.000) Each 
(0.000,0.000) optimization 
(0.000,0.000) described 
(0.000,0.000) abo 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) requires 
(0.000,0.000) one 
(0.000,0.000) or 
(0.000,0.000) more 
(0.000,0.000) guards 
(0.000,0.000) to 
(0.000,0.000) v 
(0.000,0.000) erify 
(0.000,0.000) the 
(0.000,0.000) assumptions 
(0.000,0.000) made 
(0.000,0.000) in 
(0.000,0.000) doing 
(0.000,0.000) the 
(0.000,0.000) optimization. 
(0.000,0.000) A 
(0.000,0.000) guard 
(0.000,0.000) is 
(0.000,0.000) just 
(0.000,0.000) a 
(0.000,0.000) group 
(0.000,0.000) of 
(0.000,0.000) LIR 
(0.000,0.000) instructions 
(0.000,0.000) that 
(0.000,0.000) performs 
(0.000,0.000) a 
(0.000,0.000) test 
(0.000,0.000) and 
(0.000,0.000) conditional 
(0.000,0.000) e 
(0.000,0.000) xit. 
(0.000,0.000) The 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) branches 
(0.000,0.000) to 
(0.000,0.000) a 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) , 
(0.000,0.000) a 
(0.000,0.000) small 
(0.000,0.000) of 
(0.000,0.000) f-trace 
(0.000,0.000) piece 
(0.000,0.000) of 
(0.000,0.000) LIR 
(0.000,0.000) that 
(0.000,0.000) returns 
(0.000,0.000) a 
(0.000,0.000) pointer 
(0.000,0.000) to 
(0.000,0.000) a 
(0.000,0.000) structure 
(0.000,0.000) that 
(0.000,0.000) describes 
(0.000,0.000) the 
(0.000,0.000) reason 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) along 
(0.000,0.000) with 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) PC 
(0.000,0.000) at 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) point 
(0.000,0.000) and 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) other 
(0.000,0.000) dat 
(0.000,0.000) a 
(0.000,0.000) needed 
(0.000,0.000) to 
(0.000,0.000) restore 
(0.000,0.000) the 
(0.000,0.000) interpreter’ 
(0.000,0.000) s 
(0.000,0.000) state 
(0.000,0.000) structures. 
(0.000,0.000) Aborts. 
(0.000,0.000) Some 
(0.000,0.000) constructs 
(0.000,0.000) are 
(0.000,0.000) dif 
(0.000,0.000) ficult 
(0.000,0.000) to 
(0.000,0.000) record 
(0.000,0.000) in 
(0.000,0.000) LIR 
(0.000,0.000) traces. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) eval 
(0.000,0.000) or 
(0.000,0.000) calls 
(0.000,0.000) to 
(0.000,0.000) e 
(0.000,0.000) xternal 
(0.000,0.000) functions 
(0.000,0.000) can 
(0.000,0.000) change 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) state 
(0.000,0.000) in 
(0.000,0.000) unpredictable 
(0.000,0.000) w 
(0.000,0.000) ays, 
(0.000,0.000) making 
(0.000,0.000) it 
(0.000,0.000) dif 
(0.000,0.000) fic 
(0.000,0.000) ult 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) tracer 
(0.000,0.000) to 
(0.000,0.000) kno 
(0.000,0.000) w 
(0.000,0.000) the 
(0.000,0.000) current 
(0.000,0.000) type 
(0.000,0.000) map 
(0.000,0.000) in 
(0.000,0.000) order 
(0.000,0.000) to 
(0.000,0.000) continue 
(0.000,0.000) tracing. 
(0.000,0.000) A 
(0.000,0.000) tracing 
(0.000,0.000) implementation 
(0.000,0.000) can 
(0.000,0.000) also 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) number 
(0.000,0.000) of 
(0.000,0.000) other 
(0.000,0.000) limi- 
(0.000,0.000) tations, 
(0.000,0.000) e.g.,a 
(0.000,0.000) small-memory 
(0.000,0.000) de 
(0.000,0.000) vice 
(0.000,0.000) may 
(0.000,0.000) limit 
(0.000,0.000) the 
(0.000,0.000) length 
(0.000,0.000) of 
(0.000,0.000) traces. 
(0.000,0.000) When 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) situation 
(0.000,0.000) occurs 
(0.000,0.000) that 
(0.000,0.000) pre 
(0.000,0.000) v 
(0.000,0.000) ents 
(0.000,0.000) the 
(0.000,0.000) implementation 
(0.000,0.000) from 
(0.000,0.000) continuing 
(0.000,0.000) trace 
(0.000,0.000) recording, 
(0.000,0.000) the 
(0.000,0.000) implementation 
(0.000,0.000) aborts 
(0.000,0.000) trace 
(0.000,0.000) record- 
(0.000,0.000) ing 
(0.000,0.000) and 
(0.000,0.000) returns 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) monitor 
(0.000,0.000) . 
(0.000,0.000) 3.2 
(0.000,0.000) T 
(0.000,0.000) race 
(0.000,0.000) T 
(0.000,0.000) r 
(0.000,0.000) ees 
(0.000,0.000) Especially 
(0.000,0.000) simple 
(0.000,0.000) loops, 
(0.000,0.000) namely 
(0.000,0.000) those 
(0.000,0.000) where 
(0.000,0.000) control 
(0.000,0.000) flo 
(0.000,0.000) w 
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(0.000,0.000) a 
(0.000,0.000) single 
(0.000,0.000) trace. 
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(0.000,0.000) this 
(0.000,0.000) w 
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(0.000,0.000) w 
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(0.000,0.000) e 
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(0.000,0.000) The 
(0.000,0.000) goal 
(0.000,0.000) is 
(0.000,0.000) to 
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(0.000,0.000) trace 
(0.000,0.000) trees 
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(0.000,0.000) v 
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(0.000,0.000) paths 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) program. 
(0.164,119.552) 1 
(0.164,119.552) Arrays 
(0.164,119.552) are 
(0.164,119.552) actually 
(0.164,119.552) w 
(0.164,119.552) orse 
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(0.164,119.552) this: 
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(0.164,119.552) , 
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(0.164,119.552) array 
(0.164,119.552) implementation. 
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(0.164,119.552) a 
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(0.164,119.552) ee. 
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(0.164,119.552) headers, 
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(0.164,119.552) paths. 
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(0.164,119.552) raceMonk 
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(0.164,119.552) y 
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(0.164,119.552) headers 
(0.164,119.552) are 
(0.164,119.552) easy 
(0.164,119.552) to 
(0.164,119.552) detect–the 
(0.164,119.552) bytecode 
(0.164,119.552) compiler 
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(0.164,119.552) es 
(0.164,119.552) that 
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(0.164,119.552) loop 
(0.164,119.552) header 
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(0.164,119.552) it 
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(0.164,119.552) y 
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(0.164,119.552) certain 
(0.164,119.552) number 
(0.164,119.552) of 
(0.164,119.552) times 
(0.164,119.552) (2 
(0.164,119.552) in 
(0.164,119.552) the 
(0.164,119.552) current 
(0.164,119.552) implementation). 
(0.164,119.552) Starting 
(0.164,119.552) a 
(0.164,119.552) tree 
(0.164,119.552) just 
(0.164,119.552) means 
(0.164,119.552) starting 
(0.164,119.552) recordi 
(0.164,119.552) ng 
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(0.164,119.552) for 
(0.164,119.552) the 
(0.164,119.552) current 
(0.164,119.552) point 
(0.164,119.552) and 
(0.164,119.552) type 
(0.164,119.552) map 
(0.164,119.552) and 
(0.164,119.552) marking 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) as 
(0.164,119.552) the 
(0.164,119.552) root 
(0.164,119.552) of 
(0.164,119.552) a 
(0.164,119.552) tree. 
(0.164,119.552) Each 
(0.164,119.552) tree 
(0.164,119.552) is 
(0.164,119.552) associated 
(0.164,119.552) with 
(0.164,119.552) a 
(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) and 
(0.164,119.552) type 
(0.164,119.552) map, 
(0.164,119.552) so 
(0.164,119.552) there 
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(0.164,119.552) se 
(0.164,119.552) v 
(0.164,119.552) eral 
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(0.164,119.552) for 
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(0.164,119.552) v 
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(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) . 
(0.164,119.552) Closing 
(0.164,119.552) the 
(0.164,119.552) loop. 
(0.164,119.552) T 
(0.164,119.552) race 
(0.164,119.552) recording 
(0.164,119.552) can 
(0.164,119.552) end 
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(0.164,119.552) se 
(0.164,119.552) v 
(0.164,119.552) eral 
(0.164,119.552) w 
(0.164,119.552) ays. 
(0.164,119.552) Ideally 
(0.164,119.552) , 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) reaches 
(0.164,119.552) the 
(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) where 
(0.164,119.552) it 
(0.164,119.552) started 
(0.164,119.552) with 
(0.164,119.552) the 
(0.164,119.552) same 
(0.164,119.552) type 
(0.164,119.552) map 
(0.164,119.552) as 
(0.164,119.552) on 
(0.164,119.552) entry 
(0.164,119.552) . 
(0.164,119.552) This 
(0.164,119.552) is 
(0.164,119.552) called 
(0.164,119.552) a 
(0.164,119.552) type-stable 
(0.164,119.552) loop 
(0.164,119.552) iteration. 
(0.164,119.552) In 
(0.164,119.552) this 
(0.164,119.552) case, 
(0.164,119.552) the 
(0.164,119.552) end 
(0.164,119.552) of 
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(0.164,119.552) trace 
(0.164,119.552) can 
(0.164,119.552) jump 
(0.164,119.552) right 
(0.164,119.552) to 
(0.164,119.552) the 
(0.164,119.552) be 
(0.164,119.552) ginning, 
(0.164,119.552) as 
(0.164,119.552) all 
(0.164,119.552) the 
(0.164,119.552) v 
(0.164,119.552) alue 
(0.164,119.552) representations 
(0.164,119.552) are 
(0.164,119.552) e 
(0.164,119.552) xactly 
(0.164,119.552) as 
(0.164,119.552) needed 
(0.164,119.552) to 
(0.164,119.552) enter 
(0.164,119.552) the 
(0.164,119.552) trace. 
(0.164,119.552) The 
(0.164,119.552) jump 
(0.164,119.552) can 
(0.164,119.552) e 
(0.164,119.552) v 
(0.164,119.552) en 
(0.164,119.552) skip 
(0.164,119.552) the 
(0.164,119.552) usual 
(0.164,119.552) code 
(0.164,119.552) that 
(0.164,119.552) w 
(0.164,119.552) ould 
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(0.164,119.552) y 
(0.164,119.552) out 
(0.164,119.552) the 
(0.164,119.552) state 
(0.164,119.552) at 
(0.164,119.552) the 
(0.164,119.552) end 
(0.164,119.552) of 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) and 
(0.164,119.552) cop 
(0.164,119.552) y 
(0.164,119.552) it 
(0.164,119.552) back 
(0.164,119.552) in 
(0.164,119.552) to 
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(0.164,119.552) trace 
(0.164,119.552) acti 
(0.164,119.552) v 
(0.164,119.552) ation 
(0.164,119.552) record 
(0.164,119.552) to 
(0.164,119.552) enter 
(0.164,119.552) a 
(0.164,119.552) trace. 
(0.164,119.552) In 
(0.164,119.552) certain 
(0.164,119.552) cases 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) might 
(0.164,119.552) reach 
(0.164,119.552) the 
(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) with 
(0.164,119.552) a 
(0.164,119.552) dif 
(0.164,119.552) ferent 
(0.164,119.552) type 
(0.164,119.552) map. 
(0.164,119.552) This 
(0.164,119.552) scenario 
(0.164,119.552) is 
(0.164,119.552) sometime 
(0.164,119.552) observ 
(0.164,119.552) ed 
(0.164,119.552) for 
(0.164,119.552) the 
(0.164,119.552) first 
(0.164,119.552) iteration 
(0.164,119.552) of 
(0.164,119.552) a 
(0.164,119.552) loop. 
(0.164,119.552) Some 
(0.164,119.552) v 
(0.164,119.552) ariables 
(0.164,119.552) inside 
(0.164,119.552) the 
(0.164,119.552) loop 
(0.164,119.552) might 
(0.164,119.552) initially 
(0.164,119.552) be 
(0.164,119.552) undefined 
(0.164,119.552) , 
(0.164,119.552) before 
(0.164,119.552) the 
(0.164,119.552) y 
(0.164,119.552) are 
(0.164,119.552) set 
(0.164,119.552) to 
(0.164,119.552) a 
(0.164,119.552) concrete 
(0.164,119.552) type 
(0.164,119.552) during 
(0.164,119.552) the 
(0.164,119.552) first 
(0.164,119.552) loop 
(0.164,119.552) iteration. 
(0.164,119.552) When 
(0.164,119.552) recording 
(0.164,119.552) such 
(0.164,119.552) an 
(0.164,119.552) iteration, 
(0.164,119.552) t 
(0.164,119.552) he 
(0.164,119.552) recorder 
(0.164,119.552) cannot 
(0.164,119.552) link 
(0.164,119.552) the 
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(0.164,119.552) back 
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(0.164,119.552) o 
(0.164,119.552) wn 
(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) since 
(0.164,119.552) it 
(0.164,119.552) is 
(0.164,119.552) type-unstable 
(0.164,119.552) . 
(0.164,119.552) Instead, 
(0.164,119.552) the 
(0.164,119.552) iteration 
(0.164,119.552) is 
(0.164,119.552) terminated 
(0.164,119.552) with 
(0.164,119.552) a 
(0.164,119.552) side 
(0.164,119.552) e 
(0.164,119.552) xit 
(0.164,119.552) that 
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(0.164,119.552) w 
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(0.164,119.552) f 
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(0.164,119.552) and 
(0.164,119.552) return 
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(0.164,119.552) the 
(0.164,119.552) interpreter 
(0.164,119.552) . 
(0.164,119.552) At 
(0.164,119.552) the 
(0.164,119.552) same 
(0.164,119.552) time 
(0.164,119.552) a 
(0.164,119.552) ne 
(0.164,119.552) w 
(0.164,119.552) trace 
(0.164,119.552) is 
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(0.164,119.552) with 
(0.164,119.552) the 
(0.164,119.552) ne 
(0.164,119.552) w 
(0.164,119.552) type 
(0.164,119.552) map. 
(0.164,119.552) Ev 
(0.164,119.552) ery 
(0.164,119.552) time 
(0.164,119.552) an 
(0.164,119.552) additional 
(0.164,119.552) type- 
(0.164,119.552) unstable 
(0.164,119.552) trace 
(0.164,119.552) is 
(0.164,119.552) adde 
(0.164,119.552) d 
(0.164,119.552) to 
(0.164,119.552) a 
(0.164,119.552) re 
(0.164,119.552) gion, 
(0.164,119.552) its 
(0.164,119.552) e 
(0.164,119.552) xit 
(0.164,119.552) type 
(0.164,119.552) map 
(0.164,119.552) is 
(0.164,119.552) compared 
(0.164,119.552) to 
(0.164,119.552) the 
(0.164,119.552) entry 
(0.164,119.552) m 
(0.164,119.552) ap 
(0.164,119.552) of 
(0.164,119.552) all 
(0.164,119.552) e 
(0.164,119.552) xisting 
(0.164,119.552) traces 
(0.164,119.552) in 
(0.164,119.552) case 
(0.164,119.552) the 
(0.164,119.552) y 
(0.164,119.552) complement 
(0.164,119.552) each 
(0.164,119.552) other 
(0.164,119.552) . 
(0.164,119.552) W 
(0.164,119.552) ith 
(0.164,119.552) this 
(0.164,119.552) approach 
(0.164,119.552) we 
(0.164,119.552) are 
(0.164,119.552) able 
(0.164,119.552) to 
(0.164,119.552) co 
(0.164,119.552) v 
(0.164,119.552) er 
(0.164,119.552) type-unstable 
(0.164,119.552) loop 
(0.164,119.552) iterations 
(0.164,119.552) as 
(0.164,119.552) long 
(0.164,119.552) the 
(0.164,119.552) y 
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(0.164,119.552) v 
(0.164,119.552) entually 
(0.164,119.552) form 
(0.164,119.552) a 
(0.164,119.552) stable 
(0.164,119.552) equilibrium. 
(0.164,119.552) Finally 
(0.164,119.552) , 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) might 
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(0.164,119.552) loop 
(0.164,119.552) before 
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(0.164,119.552) the 
(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) , 
(0.164,119.552) for 
(0.164,119.552) e 
(0.164,119.552) xample 
(0.164,119.552) because 
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(0.164,119.552) x 
(0.164,119.552) ecution 
(0.164,119.552) reaches 
(0.164,119.552) a 
(0.164,119.552) break 
(0.164,119.552) or 
(0.164,119.552) return 
(0.164,119.552) statement. 
(0.164,119.552) In 
(0.164,119.552) this 
(0.164,119.552) case, 
(0.164,119.552) the 
(0.164,119.552) VM 
(0.164,119.552) simply 
(0.164,119.552) ends 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) with 
(0.164,119.552) an 
(0.164,119.552) e 
(0.164,119.552) xit 
(0.164,119.552) to 
(0.164,119.552) the 
(0.164,119.552) trace 
(0.164,119.552) monitor 
(0.164,119.552) . 
(0.164,119.552) As 
(0.164,119.552) mentioned 
(0.164,119.552) pre 
(0.164,119.552) viously 
(0.164,119.552) , 
(0.164,119.552) we 
(0.164,119.552) may 
(0.164,119.552) speculati 
(0.164,119.552) v 
(0.164,119.552) ely 
(0.164,119.552) chose 
(0.164,119.552) to 
(0.164,119.552) rep- 
(0.164,119.552) resent 
(0.164,119.552) certain 
(0.164,119.552) Number 
(0.164,119.552) -typed 
(0.164,119.552) v 
(0.164,119.552) alues 
(0.164,119.552) as 
(0.164,119.552) inte 
(0.164,119.552) gers 
(0.164,119.552) on 
(0.164,119.552) trace. 
(0.164,119.552) W 
(0.164,119.552) e 
(0.164,119.552) do 
(0.164,119.552) so 
(0.164,119.552) when 
(0.164,119.552) we 
(0.164,119.552) observ 
(0.164,119.552) e 
(0.164,119.552) that 
(0.164,119.552) Number 
(0.164,119.552) -typed 
(0.164,119.552) v 
(0.164,119.552) ariables 
(0.164,119.552) c 
(0.164,119.552) ontain 
(0.164,119.552) an 
(0.164,119.552) inte 
(0.164,119.552) ger 
(0.164,119.552) v 
(0.164,119.552) alue 
(0.164,119.552) at 
(0.164,119.552) trace 
(0.164,119.552) entry 
(0.164,119.552) . 
(0.164,119.552) If 
(0.164,119.552) during 
(0.164,119.552) trace 
(0.164,119.552) recording 
(0.164,119.552) the 
(0.164,119.552) v 
(0.164,119.552) ariable 
(0.164,119.552) is 
(0.164,119.552) une 
(0.164,119.552) x- 
(0.164,119.552) pectedly 
(0.164,119.552) assigned 
(0.164,119.552) a 
(0.164,119.552) non-inte 
(0.164,119.552) ger 
(0.164,119.552) v 
(0.164,119.552) alue, 
(0.164,119.552) we 
(0.164,119.552) ha 
(0.164,119.552) v 
(0.164,119.552) e 
(0.164,119.552) to 
(0.164,119.552) widen 
(0.164,119.552) the 
(0.164,119.552) type 
(0.164,119.552) of 
(0.164,119.552) the 
(0.164,119.552) v 
(0.164,119.552) ariable 
(0.164,119.552) to 
(0.164,119.552) a 
(0.164,119.552) double. 
(0.164,119.552) As 
(0.164,119.552) a 
(0.164,119.552) result, 
(0.164,119.552) the 
(0.164,119.552) recorded 
(0.164,119.552) trace 
(0.164,119.552) becomes 
(0.164,119.552) inherently 
(0.164,119.552) type-unstable 
(0.164,119.552) since 
(0.164,119.552) it 
(0.164,119.552) starts 
(0.164,119.552) with 
(0.164,119.552) an 
(0.164,119.552) i 
(0.164,119.552) nte 
(0.164,119.552) ger 
(0.164,119.552) v 
(0.164,119.552) alue 
(0.164,119.552) b 
(0.164,119.552) ut 
(0.164,119.552) ends 
(0.164,119.552) with 
(0.164,119.552) a 
(0.164,119.552) double 
(0.164,119.552) v 
(0.164,119.552) alue. 
(0.164,119.552) This 
(0.164,119.552) represents 
(0.164,119.552) a 
(0.164,119.552) mis-speculat 
(0.164,119.552) ion, 
(0.164,119.552) since 
(0.164,119.552) at 
(0.164,119.552) trace 
(0.164,119.552) entry 
(0.164,119.552) we 
(0.164,119.552) specialized 
(0.164,119.552) the 
(0.164,119.552) Number 
(0.164,119.552) -typed 
(0.164,119.552) v 
(0.164,119.552) alue 
(0.164,119.552) to 
(0.164,119.552) an 
(0.164,119.552) inte 
(0.164,119.552) ger 
(0.164,119.552) , 
(0.164,119.552) assuming 
(0.164,119.552) that 
(0.164,119.552) at 
(0.164,119.552) the 
(0.164,119.552) loop 
(0.164,119.552) edge 
(0.164,119.552) we 
(0.164,119.552) w 
(0.164,119.552) ould 
(0.164,119.552) ag 
(0.164,119.552) ain 
(0.164,119.552) find 
(0.164,119.552) an 
(0.164,119.552) inte 
(0.164,119.552) ger 
(0.164,119.552) v 
(0.164,119.552) alue 
(0.164,119.552) in 
(0.164,119.552) the 
(0.164,119.552) v 
(0.164,119.552) ariable, 
(0.164,119.552) allo 
(0.164,119.552) wing 
(0.164,119.552) us 
(0.164,119.552) to 
(0.164,119.552) close 
(0.164,119.552) the 
(0.164,119.552) loop. 
(0.164,119.552) T 
(0.164,119.552) o 
(0.164,119.552) a 
(0.164,119.552) v 
(0.164,119.552) oid 
(0.164,119.552) future 
(0.164,119.552) spec- 
(0.164,119.552) ulati 
(0.164,119.552) v 
(0.164,119.552) e 
(0.164,119.552) f 
(0.164,119.552) ai 
(0.164,119.552) lures 
(0.164,119.552) in 
(0.164,119.552) v 
(0.164,119.552) olving 
(0.164,119.552) this 
(0.164,119.552) v 
(0.164,119.552) ariable, 
(0.164,119.552) and 
(0.164,119.552) to 
(0.164,119.552) obtain 
(0.164,119.552) a 
(0.164,119.552) type-stable 
(0.164,119.552) trace 
(0.164,119.552) we 
(0.164,119.552) note 
(0.164,119.552) the 
(0.164,119.552) f 
(0.164,119.552) act 
(0.164,119.552) that 
(0.164,119.552) the 
(0.164,119.552) v 
(0.164,119.552) ariable 
(0.164,119.552) in 
(0.164,119.552) question 
(0.164,119.552) as 
(0.164,119.552) been 
(0.164,119.552) observ 
(0.164,119.552) ed 
(0.164,119.552) to 
(0.164,119.552) sometimes 
(0.164,119.552) hold 
(0.164,119.552) non-inte 
(0.164,119.552) ger 
(0.164,119.552) v 
(0.164,119.552) alues 
(0.164,119.552) in 
(0.164,119.552) an 
(0.164,119.552) advisory 
(0.164,119.552) data 
(0.164,119.552) structure 
(0.164,119.552) which 
(0.164,119.552) we 
(0.164,119.552) call 
(0.164,119.552) the 
(0.164,119.552) “oracle”. 
(0.164,119.552) When 
(0.164,119.552) compiling 
(0.164,119.552) loops, 
(0.164,119.552) we 
(0.164,119.552) consult 
(0.164,119.552) the 
(0.164,119.552) oracle 
(0.164,119.552) before 
(0.164,119.552) specializ- 
(0.164,119.552) ing 
(0.164,119.552) v 
(0.164,119.552) alues 
(0.164,119.552) to 
(0.164,119.552) inte 
(0.164,119.552) gers. 
(0.164,119.552) Speculation 
(0.164,119.552) to 
(0.164,119.552) w 
(0.164,119.552) ards 
(0.164,119.552) inte 
(0.164,119.552) gers 
(0.164,119.552) is 
(0.164,119.552) performed 
(0.164,119.552) only 
(0.164,119.552) if 
(0.164,119.552) no 
(0.164,119.552) adv 
(0.164,119.552) erse 
(0.164,119.552) information 
(0.164,119.552) is 
(0.164,119.552) kno 
(0.164,119.552) wn 
(0.164,119.552) to 
(0.164,119.552) the 
(0.164,119.552) oracle 
(0.164,119.552) about 
(0.164,119.552) that 
(0.164,119.552) particular 
(0.164,119.552) v 
(0.164,119.552) ariable. 
(0.164,119.552) Whene 
(0.164,119.552) v 
(0.164,119.552) er 
(0.164,119.552) we 
(0.164,119.552) accidentally 
(0.164,119.552) compile 
(0.164,119.552) a 
(0.164,119.552) loop 
(0.164,119.552) that 
(0.164,119.552) is 
(0.164,119.552) type-unstable 
(0.164,119.552) due 
(0.164,119.552) to 
(0.164,119.552) mis-speculation 
(0.164,119.552) of 
(0.164,119.552) a 
(0.164,119.552) Number 
(0.164,119.552) -typed 
(0.164,119.552) v 
(0.164,119.552) ari- 
(0.164,119.552) able, 
(0.164,119.552) we 
(0.164,119.552) immediately 
(0.164,119.552) trigger 
(0.164,119.552) the 
(0.164,119.552) recording 
(0.164,119.552) of 
(0.164,119.552) a 
(0.164,119.552) ne 
(0.164,119.552) w 
(0.164,119.552) trace, 
(0.164,119.552) which 
(0.164,119.552) based 
(0.164,119.552) on 
(0.164,119.552) the 
(0.164,119.552) no 
(0.164,119.552) w 
(0.164,119.552) updated 
(0.164,119.552) oracle 
(0.164,119.552) information 
(0.164,119.552) will 
(0.164,119.552) start 
(0.164,119.552) with 
(0.164,119.552) a 
(0.164,119.552) dou- 
(0.164,119.552) ble 
(0.164,119.552) v 
(0.164,119.552) alue 
(0.164,119.552) and 
(0.164,119.552) thus 
(0.164,119.552) become 
(0.164,119.552) type 
(0.164,119.552) stable. 
(0.164,119.552) Extending 
(0.164,119.552) a 
(0.164,119.552) tr 
(0.164,119.552) ee. 
(0.164,119.552) Side 
(0.164,119.552) e 
(0.164,119.552) xits 
(0.164,119.552) lead 
(0.164,119.552) to 
(0.164,119.552) di 
(0.164,119.552) f 
(0.164,119.552) ferent 
(0.164,119.552) paths 
(0.164,119.552) through 
(0.164,119.552) the 
(0.164,119.552) loop, 
(0.164,119.552) or 
(0.164,119.552) paths 
(0.164,119.552) with 
(0.164,119.552) dif 
(0.164,119.552) ferent 
(0.164,119.552) types 
(0.164,119.552) or 
(0.164,119.552) representations 
(0.164,119.552) . 
(0.164,119.552) Thus, 
(0.164,119.552) to 
(0.164,119.552) completely 
(0.164,119.552) co 
(0.164,119.552) v 
(0.164,119.552) er 
(0.164,119.552) the 
(0.164,119.552) loop, 
(0.164,119.552) the 
(0.164,119.552) VM 
(0.164,119.552) must 
(0.164,119.552) record 
(0.164,119.552) traces 
(0.164,119.552) starting 
(0.164,119.552) at 
(0.164,119.552) all 
(0.164,119.552) side 
(0.164,119.552) e 
(0.164,119.552) xits. 
(0.164,119.552) These 
(0.164,119.552) traces 
(0.164,119.552) are 
(0.164,119.552) recorded 
(0.164,119.552) much 
(0.164,119.552) lik 
(0.164,119.552) e 
(0.164,119.552) root 
(0.164,119.552) traces: 
(0.164,119.552) there 
(0.164,119.552) is 
(0.164,119.552) a 
(0.164,119.552) counter 
(0.164,119.552) for 
(0.164,119.552) each 
(0.164,119.552) side 
(0.164,119.552) e 
(0.164,119.552) xit, 
(0.164,119.552) and 
(0.164,119.552) when 
(0.164,119.552) the 
(0.164,119.552) counter 
(0.164,119.552) reaches 
(0.164,119.552) a 
(0.164,119.552) hotness 
(0.164,119.552) threshold, 
(0.164,119.552) recording 
(0.164,119.552) starts. 
(0.164,119.552) Recording 
(0.164,119.552) stops 
(0.164,119.552) e 
(0.164,119.552) xactly 
(0.164,119.552) as 
(0.164,119.552) for 
(0.164,119.552) the 
(0.164,119.552) root 
(0.164,119.552) trace, 
(0.164,119.552) using 
(0.164,119.552) the 
(0.164,119.552) loop 
(0.164,119.552) header 
(0.164,119.552) of 
(0.164,119.552) the 
(0.164,119.552) root 
(0.164,119.552) trace 
(0.164,119.552) as 
(0.164,119.552) the 
(0.164,119.552) tar 
(0.164,119.552) get 
(0.164,119.552) to 
(0.164,119.552) reach. 
(0.000,0.000) Our 
(0.000,0.000) implementation 
(0.000,0.000) does 
(0.000,0.000) not 
(0.000,0.000) e 
(0.000,0.000) xtend 
(0.000,0.000) at 
(0.000,0.000) all 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xits. 
(0.000,0.000) It 
(0.000,0.000) e 
(0.000,0.000) xtends 
(0.000,0.000) only 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) is 
(0.000,0.000) for 
(0.000,0.000) a 
(0.000,0.000) control-flo 
(0.000,0.000) w 
(0.000,0.000) branch, 
(0.000,0.000) and 
(0.000,0.000) only 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) does 
(0.000,0.000) not 
(0.000,0.000) lea 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) loop. 
(0.000,0.000) In 
(0.000,0.000) particular 
(0.000,0.000) we 
(0.000,0.000) do 
(0.000,0.000) not 
(0.000,0.000) w 
(0.000,0.000) ant 
(0.000,0.000) to 
(0.000,0.000) e 
(0.000,0.000) xtend 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) tree 
(0.000,0.000) along 
(0.000,0.000) a 
(0.000,0.000) path 
(0.000,0.000) that 
(0.000,0.000) leads 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) outer 
(0.000,0.000) loop, 
(0.000,0.000) because 
(0.000,0.000) we 
(0.000,0.000) w 
(0.000,0.000) ant 
(0.000,0.000) to 
(0.000,0.000) co 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) such 
(0.000,0.000) paths 
(0.000,0.000) in 
(0.000,0.000) an 
(0.000,0.000) outer 
(0.000,0.000) tree 
(0.000,0.000) through 
(0.000,0.000) tree 
(0.000,0.000) nesting 
(0.000,0.000) . 
(0.000,0.000) 3.3 
(0.000,0.000) Blacklisting 
(0.000,0.000) Sometimes, 
(0.000,0.000) a 
(0.000,0.000) program 
(0.000,0.000) follo 
(0.000,0.000) ws 
(0.000,0.000) a 
(0.000,0.000) path 
(0.000,0.000) that 
(0.000,0.000) cannot 
(0.000,0.000) be 
(0.000,0.000) compiled 
(0.000,0.000) into 
(0.000,0.000) a 
(0.000,0.000) trace, 
(0.000,0.000) usually 
(0.000,0.000) because 
(0.000,0.000) of 
(0.000,0.000) limitations 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) implementation. 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) does 
(0.000,0.000) not 
(0.000,0.000) currently 
(0.000,0.000) support 
(0.000,0.000) recording 
(0.000,0.000) thro 
(0.000,0.000) wing 
(0.000,0.000) and 
(0.000,0.000) catching 
(0.000,0.000) of 
(0.000,0.000) arbitrary 
(0.000,0.000) e 
(0.000,0.000) xceptions. 
(0.000,0.000) This 
(0.000,0.000) design 
(0.000,0.000) trade 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) chosen, 
(0.000,0.000) because 
(0.000,0.000) e 
(0.000,0.000) xceptions 
(0.000,0.000) are 
(0.000,0.000) usually 
(0.000,0.000) rare 
(0.000,0.000) in 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript. 
(0.000,0.000) Ho 
(0.000,0.000) we 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) , 
(0.000,0.000) if 
(0.000,0.000) a 
(0.000,0.000) program 
(0.000,0.000) opts 
(0.000,0.000) to 
(0.000,0.000) use 
(0.000,0.000) e 
(0.000,0.000) xceptions 
(0.000,0.000) intensi 
(0.000,0.000) v 
(0.000,0.000) ely 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) suddenly 
(0.000,0.000) incur 
(0.000,0.000) a 
(0.000,0.000) punishing 
(0.000,0.000) runt 
(0.000,0.000) ime 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) erhead 
(0.000,0.000) if 
(0.000,0.000) we 
(0.000,0.000) repeatedly 
(0.000,0.000) try 
(0.000,0.000) to 
(0.000,0.000) record 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) for 
(0.000,0.000) this 
(0.000,0.000) path 
(0.000,0.000) and 
(0.000,0.000) repeatedly 
(0.000,0.000) f 
(0.000,0.000) ail 
(0.000,0.000) to 
(0.000,0.000) do 
(0.000,0.000) so, 
(0.000,0.000) since 
(0.000,0.000) we 
(0.000,0.000) abort 
(0.000,0.000) tracing 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) time 
(0.000,0.000) we 
(0.000,0.000) observ 
(0.000,0.000) e 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xception 
(0.000,0.000) being 
(0.000,0.000) thro 
(0.000,0.000) wn. 
(0.000,0.000) As 
(0.000,0.000) a 
(0.000,0.000) result, 
(0.000,0.000) if 
(0.000,0.000) a 
(0.000,0.000) hot 
(0.000,0.000) loop 
(0.000,0.000) contains 
(0.000,0.000) traces 
(0.000,0.000) that 
(0.000,0.000) al 
(0.000,0.000) w 
(0.000,0.000) ays 
(0.000,0.000) f 
(0.000,0.000) ail, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) could 
(0.000,0.000) potentially 
(0.000,0.000) run 
(0.000,0.000) much 
(0.000,0.000) more 
(0.000,0.000) slo 
(0.000,0.000) wly 
(0.000,0.000) than 
(0.000,0.000) the 
(0.000,0.000) base 
(0.000,0.000) interpreter: 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) repeatedly 
(0.000,0.000) spends 
(0.000,0.000) t 
(0.000,0.000) ime 
(0.000,0.000) trying 
(0.000,0.000) to 
(0.000,0.000) record 
(0.000,0.000) traces, 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) is 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) able 
(0.000,0.000) to 
(0.000,0.000) run 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) . 
(0.000,0.000) T 
(0.000,0.000) o 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oid 
(0.000,0.000) this 
(0.000,0.000) problem, 
(0.000,0.000) whene 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) is 
(0.000,0.000) about 
(0.000,0.000) to 
(0.000,0.000) start 
(0.000,0.000) tracing, 
(0.000,0.000) it 
(0.000,0.000) must 
(0.000,0.000) try 
(0.000,0.000) to 
(0.000,0.000) predict 
(0.000,0.000) whether 
(0.000,0.000) it 
(0.000,0.000) will 
(0.000,0.000) finish 
(0.000,0.000) the 
(0.000,0.000) trace. 
(0.000,0.000) Our 
(0.000,0.000) prediction 
(0.000,0.000) algorithm 
(0.000,0.000) is 
(0.000,0.000) based 
(0.000,0.000) on 
(0.000,0.000) blac 
(0.000,0.000) klisting 
(0.000,0.000) traces 
(0.000,0.000) that 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) been 
(0.000,0.000) tried 
(0.000,0.000) and 
(0.000,0.000) f 
(0.000,0.000) ailed. 
(0.000,0.000) When 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) f 
(0.000,0.000) ails 
(0.000,0.000) to 
(0.000,0.000) finish 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) start- 
(0.000,0.000) ing 
(0.000,0.000) at 
(0.000,0.000) a 
(0.000,0.000) gi 
(0.000,0.000) v 
(0.000,0.000) en 
(0.000,0.000) point, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) records 
(0.000,0.000) that 
(0.000,0.000) a 
(0.000,0.000) f 
(0.000,0.000) ailure 
(0.000,0.000) has 
(0.000,0.000) occurred. 
(0.000,0.000) The 
(0.000,0.000) VM 
(0.000,0.000) also 
(0.000,0.000) sets 
(0.000,0.000) a 
(0.000,0.000) counter 
(0.000,0.000) so 
(0.000,0.000) that 
(0.000,0.000) it 
(0.000,0.000) will 
(0.000,0.000) not 
(0.000,0.000) try 
(0.000,0.000) to 
(0.000,0.000) record 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) starting 
(0.000,0.000) at 
(0.000,0.000) that 
(0.000,0.000) point 
(0.000,0.000) until 
(0.000,0.000) it 
(0.000,0.000) is 
(0.000,0.000) passed 
(0.000,0.000) a 
(0.000,0.000) fe 
(0.000,0.000) w 
(0.000,0.000) more 
(0.000,0.000) times 
(0.000,0.000) (32 
(0.000,0.000) in 
(0.000,0.000) our 
(0.000,0.000) imple- 
(0.000,0.000) mentation). 
(0.000,0.000) This 
(0.000,0.000) bac 
(0.000,0.000) k 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) counter 
(0.000,0.000) gi 
(0.000,0.000) v 
(0.000,0.000) es 
(0.000,0.000) t 
(0.000,0.000) emporary 
(0.000,0.000) conditions 
(0.000,0.000) that 
(0.000,0.000) pre 
(0.000,0.000) v 
(0.000,0.000) ent 
(0.000,0.000) tracing 
(0.000,0.000) a 
(0.000,0.000) chance 
(0.000,0.000) to 
(0.000,0.000) end. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) a 
(0.000,0.000) loop 
(0.000,0.000) may 
(0.000,0.000) beha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) dif 
(0.000,0.000) ferently 
(0.000,0.000) during 
(0.000,0.000) startup 
(0.000,0.000) than 
(0.000,0.000) during 
(0.000,0.000) its 
(0.000,0.000) steady-state 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution. 
(0.000,0.000) Af- 
(0.000,0.000) ter 
(0.000,0.000) a 
(0.000,0.000) gi 
(0.000,0.000) v 
(0.000,0.000) en 
(0.000,0.000) number 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) ailures 
(0.000,0.000) (2 
(0.000,0.000) in 
(0.000,0.000) our 
(0.000,0.000) implementation), 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) marks 
(0.000,0.000) the 
(0.000,0.000) fragment 
(0.000,0.000) as 
(0.000,0.000) blacklisted, 
(0.000,0.000) which 
(0.000,0.000) means 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) will 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) ag 
(0.000,0.000) ain 
(0.000,0.000) start 
(0.000,0.000) recording 
(0.000,0.000) at 
(0.000,0.000) that 
(0.000,0.000) point. 
(0.000,0.000) After 
(0.000,0.000) implem 
(0.000,0.000) enting 
(0.000,0.000) this 
(0.000,0.000) basic 
(0.000,0.000) strate 
(0.000,0.000) gy 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) observ 
(0.000,0.000) ed 
(0.000,0.000) that 
(0.000,0.000) for 
(0.000,0.000) small 
(0.000,0.000) loops 
(0.000,0.000) that 
(0.000,0.000) get 
(0.000,0.000) blacklisted, 
(0.000,0.000) the 
(0.000,0.000) system 
(0.000,0.000) can 
(0.000,0.000) spend 
(0.000,0.000) a 
(0.000,0.000) noticeable 
(0.000,0.000) amount 
(0.000,0.000) of 
(0.000,0.000) time 
(0.000,0.000) just 
(0.000,0.000) finding 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) fragment 
(0.000,0.000) and 
(0.000,0.000) determining 
(0.000,0.000) that 
(0.000,0.000) it 
(0.000,0.000) has 
(0.000,0.000) been 
(0.000,0.000) blacklisted. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) no 
(0.000,0.000) w 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oid 
(0.000,0.000) that 
(0.000,0.000) problem 
(0.000,0.000) by 
(0.000,0.000) patching 
(0.000,0.000) the 
(0.000,0.000) bytecode. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) define 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xtra 
(0.000,0.000) no-op 
(0.000,0.000) bytecode 
(0.000,0.000) that 
(0.000,0.000) indicates 
(0.000,0.000) a 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) . 
(0.000,0.000) The 
(0.000,0.000) VM 
(0.000,0.000) calls 
(0.000,0.000) into 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) monitor 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) time 
(0.000,0.000) the 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecutes 
(0.000,0.000) a 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) no-op. 
(0.000,0.000) T 
(0.000,0.000) o 
(0.000,0.000) blacklist 
(0.000,0.000) a 
(0.000,0.000) fragm 
(0.000,0.000) ent, 
(0.000,0.000) we 
(0.000,0.000) simply 
(0.000,0.000) replace 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) no-op 
(0.000,0.000) with 
(0.000,0.000) a 
(0.000,0.000) re 
(0.000,0.000) gular 
(0.000,0.000) no-op. 
(0.000,0.000) Thus, 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) will 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) ag 
(0.000,0.000) ain 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) en 
(0.000,0.000) call 
(0.000,0.000) into 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) monitor 
(0.000,0.000) . 
(0.000,0.000) There 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) related 
(0.000,0.000) problem 
(0.000,0.000) we 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) not 
(0.000,0.000) yet 
(0.000,0.000) solv 
(0.000,0.000) ed, 
(0.000,0.000) which 
(0.000,0.000) occurs 
(0.000,0.000) when 
(0.000,0.000) a 
(0.000,0.000) loop 
(0.000,0.000) meets 
(0.000,0.000) all 
(0.000,0.000) of 
(0.000,0.000) these 
(0.000,0.000) conditions: 
(0.000,0.000) • 
(0.000,0.000) The 
(0.000,0.000) VM 
(0.000,0.000) can 
(0.000,0.000) form 
(0.000,0.000) at 
(0.000,0.000) least 
(0.000,0.000) one 
(0.000,0.000) root 
(0.000,0.000) trace 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) loop. 
(0.000,0.000) • 
(0.000,0.000) There 
(0.000,0.000) is 
(0.000,0.000) at 
(0.000,0.000) least 
(0.000,0.000) one 
(0.000,0.000) hot 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) for 
(0.000,0.000) which 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) cannot 
(0.000,0.000) complete 
(0.000,0.000) a 
(0.000,0.000) trace. 
(0.000,0.000) • 
(0.000,0.000) The 
(0.000,0.000) loop 
(0.000,0.000) body 
(0.000,0.000) is 
(0.000,0.000) short. 
(0.000,0.000) In 
(0.000,0.000) this 
(0.000,0.000) case, 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) will 
(0.000,0.000) repeatedly 
(0.000,0.000) pass 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) header 
(0.000,0.000) , 
(0.000,0.000) search 
(0.000,0.000) for 
(0.000,0.000) a 
(0.000,0.000) trace, 
(0.000,0.000) find 
(0.000,0.000) it, 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecute 
(0.000,0.000) it, 
(0.000,0.000) and 
(0.000,0.000) f 
(0.000,0.000) all 
(0.000,0.000) back 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) W 
(0.000,0.000) ith 
(0.000,0.000) a 
(0.000,0.000) short 
(0.000,0.000) loop 
(0.000,0.000) body 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) erhead 
(0.000,0.000) of 
(0.000,0.000) finding 
(0.000,0.000) and 
(0.000,0.000) calling 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) is 
(0.000,0.000) high, 
(0.000,0.000) and 
(0.000,0.000) causes 
(0.000,0.000) performance 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) en 
(0.000,0.000) slo 
(0.000,0.000) wer 
(0.000,0.000) than 
(0.000,0.000) the 
(0.000,0.000) basic 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) So 
(0.000,0.000) f 
(0.000,0.000) ar 
(0.000,0.000) , 
(0.000,0.000) in 
(0.000,0.000) this 
(0.000,0.000) situation 
(0.000,0.000) we 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) impro 
(0.000,0.000) v 
(0.000,0.000) ed 
(0.000,0.000) the 
(0.000,0.000) implementation 
(0.000,0.000) so 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) can 
(0.000,0.000) complete 
(0.000,0.000) the 
(0.000,0.000) branch 
(0.000,0.000) trace. 
(0.000,0.000) But 
(0.000,0.000) it 
(0.000,0.000) is 
(0.000,0.000) hard 
(0.000,0.000) to 
(0.000,0.000) guarantee 
(0.000,0.000) that 
(0.000,0.000) this 
(0.000,0.000) situation 
(0.000,0.000) will 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) r 
(0.000,0.000) happen. 
(0.000,0.000) As 
(0.000,0.000) future 
(0.000,0.000) w 
(0.000,0.000) ork, 
(0.000,0.000) this 
(0.000,0.000) situation 
(0.000,0.000) could 
(0.000,0.000) be 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oided 
(0.000,0.000) by 
(0.000,0.000) detecting 
(0.000,0.000) and 
(0.000,0.000) blacklisting 
(0.000,0.000) loops 
(0.000,0.000) for 
(0.000,0.000) which 
(0.000,0.000) the 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) erage 
(0.000,0.000) trace 
(0.000,0.000) call 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecutes 
(0.000,0.000) fe 
(0.000,0.000) w 
(0.000,0.000) bytecodes 
(0.000,0.000) before 
(0.000,0.000) returning 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) 4. 
(0.000,0.000) Nested 
(0.000,0.000) T 
(0.000,0.000) race 
(0.000,0.000) T 
(0.000,0.000) r 
(0.000,0.000) ee 
(0.000,0.000) F 
(0.000,0.000) ormation 
(0.000,0.000) Figure 
(0.000,0.000) 7 
(0.000,0.000) sho 
(0.000,0.000) ws 
(0.000,0.000) basic 
(0.000,0.000) trace 
(0.000,0.000) tree 
(0.000,0.000) compilation 
(0.000,0.000) (11) 
(0.000,0.000) applied 
(0.000,0.000) to 
(0.000,0.000) a 
(0.000,0.000) nested 
(0.000,0.000) loop 
(0.000,0.000) where 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) contains 
(0.000,0.000) tw 
(0.000,0.000) o 
(0.000,0.000) paths. 
(0.000,0.000) Usually 
(0.000,0.000) , 
(0.000,0.000) the 
(0.000,0.000) inner 
(0.000,0.000) loop 
(0.000,0.000) (with 
(0.000,0.000) header 
(0.000,0.000) at 
(0.000,0.000) i 
(0.000,0.000) 2 
(0.000,0.000) ) 
(0.000,0.000) becomes 
(0.000,0.000) hot 
(0.000,0.000) first, 
(0.000,0.000) and 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) tree 
(0.000,0.000) is 
(0.000,0.000) rooted 
(0.000,0.000) at 
(0.000,0.000) that 
(0.000,0.000) point. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) the 
(0.000,0.000) first 
(0.000,0.000) recorded 
(0.000,0.000) trace 
(0.000,0.000) may 
(0.000,0.000) be 
(0.000,0.000) a 
(0.000,0.000) c 
(0.000,0.000) ycle 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 5. 
(0.164,239.103) A 
(0.164,239.103) tree 
(0.164,239.103) with 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) trac 
(0.164,239.103) es, 
(0.164,239.103) a 
(0.164,239.103) trunk 
(0.164,239.103) trace 
(0.164,239.103) and 
(0.164,239.103) one 
(0.164,239.103) branch 
(0.164,239.103) trace. 
(0.164,239.103) The 
(0.164,239.103) trunk 
(0.164,239.103) trace 
(0.164,239.103) contains 
(0.164,239.103) a 
(0.164,239.103) guard 
(0.164,239.103) to 
(0.164,239.103) which 
(0.164,239.103) a 
(0.164,239.103) branch 
(0.164,239.103) trace 
(0.164,239.103) w 
(0.164,239.103) as 
(0.164,239.103) attached. 
(0.164,239.103) The 
(0.164,239.103) branch 
(0.164,239.103) trace 
(0.164,239.103) contain 
(0.164,239.103) a 
(0.164,239.103) guard 
(0.164,239.103) that 
(0.164,239.103) may 
(0.164,239.103) f 
(0.164,239.103) ail 
(0.164,239.103) and 
(0.164,239.103) trigger 
(0.164,239.103) a 
(0.164,239.103) side 
(0.164,239.103) e 
(0.164,239.103) xit. 
(0.164,239.103) Both 
(0.164,239.103) the 
(0.164,239.103) trunk 
(0.164,239.103) and 
(0.164,239.103) the 
(0.164,239.103) branch 
(0.164,239.103) trace 
(0.164,239.103) loop 
(0.164,239.103) back 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) tree 
(0.164,239.103) anchor 
(0.164,239.103) , 
(0.164,239.103) which 
(0.164,239.103) is 
(0.164,239.103) the 
(0.164,239.103) be 
(0.164,239.103) ginning 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) tree. 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 6. 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) handle 
(0.164,239.103) type-unstable 
(0.164,239.103) loops 
(0.164,239.103) by 
(0.164,239.103) allo 
(0.164,239.103) wing 
(0.164,239.103) traces 
(0.164,239.103) to 
(0.164,239.103) compile 
(0.164,239.103) that 
(0.164,239.103) cannot 
(0.164,239.103) loop 
(0.164,239.103) back 
(0.164,239.103) to 
(0.164,239.103) themselv 
(0.164,239.103) es 
(0.164,239.103) due 
(0.164,239.103) to 
(0.164,239.103) a 
(0.164,239.103) type 
(0.164,239.103) mis- 
(0.164,239.103) match. 
(0.164,239.103) As 
(0.164,239.103) such 
(0.164,239.103) traces 
(0.164,239.103) accumulate, 
(0.164,239.103) we 
(0.164,239.103) attempt 
(0.164,239.103) to 
(0.164,239.103) connect 
(0.164,239.103) their 
(0.164,239.103) loop 
(0.164,239.103) edges 
(0.164,239.103) to 
(0.164,239.103) form 
(0.164,239.103) groups 
(0.164,239.103) of 
(0.164,239.103) trace 
(0.164,239.103) trees 
(0.164,239.103) that 
(0.164,239.103) can 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecute 
(0.164,239.103) without 
(0.164,239.103) ha 
(0.164,239.103) ving 
(0.164,239.103) to 
(0.164,239.103) side-e 
(0.164,239.103) xit 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) interpreter 
(0.164,239.103) to 
(0.164,239.103) co 
(0.164,239.103) v 
(0.164,239.103) er 
(0.164,239.103) odd 
(0.164,239.103) type 
(0.164,239.103) case 
(0.164,239.103) s. 
(0.164,239.103) This 
(0.164,239.103) is 
(0.164,239.103) par 
(0.164,239.103) - 
(0.164,239.103) ticularly 
(0.164,239.103) important 
(0.164,239.103) for 
(0.164,239.103) nested 
(0.164,239.103) trace 
(0.164,239.103) trees 
(0.164,239.103) where 
(0.164,239.103) an 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) tries 
(0.164,239.103) to 
(0.164,239.103) call 
(0.164,239.103) an 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) (or 
(0.164,239.103) in 
(0.164,239.103) this 
(0.164,239.103) case 
(0.164,239.103) a 
(0.164,239.103) forest 
(0.164,239.103) of 
(0.164,239.103) inner 
(0.164,239.103) trees), 
(0.164,239.103) since 
(0.164,239.103) inner 
(0.164,239.103) loops 
(0.164,239.103) frequently 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) initially 
(0.164,239.103) undefined 
(0.164,239.103) v 
(0.164,239.103) alues 
(0.164,239.103) which 
(0.164,239.103) change 
(0.164,239.103) type 
(0.164,239.103) to 
(0.164,239.103) a 
(0.164,239.103) concrete 
(0.164,239.103) v 
(0.164,239.103) alue 
(0.164,239.103) after 
(0.164,239.103) the 
(0.164,239.103) first 
(0.164,239.103) iteration. 
(0.164,239.103) through 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) l 
(0.164,239.103) oop, 
(0.164,239.103) { 
(0.164,239.103) i 
(0.164,239.103) 2 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 3 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 5 
(0.164,239.103) , 
(0.164,239.103) α 
(0.164,239.103) } 
(0.164,239.103) . 
(0.164,239.103) The 
(0.164,239.103) α 
(0.164,239.103) symbol 
(0.164,239.103) is 
(0.164,239.103) used 
(0.164,239.103) to 
(0.164,239.103) indicate 
(0.164,239.103) that 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) loops 
(0.164,239.103) back 
(0.164,239.103) the 
(0.164,239.103) tree 
(0.164,239.103) anchor 
(0.164,239.103) . 
(0.164,239.103) When 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecution 
(0.164,239.103) lea 
(0.164,239.103) v 
(0.164,239.103) es 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop, 
(0.164,239.103) the 
(0.164,239.103) basic 
(0.164,239.103) design 
(0.164,239.103) has 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) choices. 
(0.164,239.103) First, 
(0.164,239.103) the 
(0.164,239.103) system 
(0.164,239.103) can 
(0.164,239.103) stop 
(0.164,239.103) tracing 
(0.164,239.103) and 
(0.164,239.103) gi 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) up 
(0.164,239.103) on 
(0.164,239.103) compiling 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop, 
(0.164,239.103) clearly 
(0.164,239.103) an 
(0.164,239.103) undesirable 
(0.164,239.103) solution. 
(0.164,239.103) The 
(0.164,239.103) other 
(0.164,239.103) choice 
(0.164,239.103) is 
(0.164,239.103) to 
(0.164,239.103) continue 
(0.164,239.103) tracing, 
(0.164,239.103) compiling 
(0.164,239.103) traces 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop 
(0.164,239.103) inside 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop’ 
(0.164,239.103) s 
(0.164,239.103) trace 
(0.164,239.103) tree. 
(0.164,239.103) F 
(0.164,239.103) or 
(0.164,239.103) e 
(0.164,239.103) xample, 
(0.164,239.103) the 
(0.164,239.103) program 
(0.164,239.103) might 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) at 
(0.164,239.103) i 
(0.164,239.103) 5 
(0.164,239.103) and 
(0.164,239.103) record 
(0.164,239.103) a 
(0.164,239.103) branch 
(0.164,239.103) trace 
(0.164,239.103) that 
(0.164,239.103) incorporates 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop: 
(0.164,239.103) { 
(0.164,239.103) i 
(0.164,239.103) 5 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 7 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 1 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 6 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 7 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 1 
(0.164,239.103) , 
(0.164,239.103) α 
(0.164,239.103) } 
(0.164,239.103) . 
(0.164,239.103) Later 
(0.164,239.103) , 
(0.164,239.103) the 
(0.164,239.103) program 
(0.164,239.103) might 
(0.164,239.103) tak 
(0.164,239.103) e 
(0.164,239.103) the 
(0.164,239.103) other 
(0.164,239.103) branch 
(0.164,239.103) at 
(0.164,239.103) i 
(0.164,239.103) 2 
(0.164,239.103) and 
(0.164,239.103) then 
(0.164,239.103) e 
(0.164,239.103) xit, 
(0.164,239.103) recording 
(0.164,239.103) another 
(0.164,239.103) branch 
(0.164,239.103) trace 
(0.164,239.103) incorporating 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop: 
(0.164,239.103) { 
(0.164,239.103) i 
(0.164,239.103) 2 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 4 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 5 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 7 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 1 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 6 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 7 
(0.164,239.103) , 
(0.164,239.103) i 
(0.164,239.103) 1 
(0.164,239.103) , 
(0.164,239.103) α 
(0.164,239.103) } 
(0.164,239.103) . 
(0.164,239.103) Thus, 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop 
(0.164,239.103) is 
(0.164,239.103) recorded 
(0.164,239.103) and 
(0.164,239.103) compiled 
(0.164,239.103) twice, 
(0.164,239.103) and 
(0.164,239.103) both 
(0.164,239.103) copies 
(0.164,239.103) must 
(0.164,239.103) be 
(0.164,239.103) retained 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) cache. 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 7. 
(0.164,239.103) Control 
(0.164,239.103) flo 
(0.164,239.103) w 
(0.164,239.103) graph 
(0.164,239.103) of 
(0.164,239.103) a 
(0.164,239.103) nested 
(0.164,239.103) loop 
(0.164,239.103) with 
(0.164,239.103) an 
(0.164,239.103) if 
(0.164,239.103) statement 
(0.164,239.103) inside 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) most 
(0.164,239.103) loop 
(0.164,239.103) (a). 
(0.164,239.103) An 
(0.164,239.103) inner 
(0.164,239.103) tre 
(0.164,239.103) e 
(0.164,239.103) captures 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop, 
(0.164,239.103) and 
(0.164,239.103) is 
(0.164,239.103) nested 
(0.164,239.103) inside 
(0.164,239.103) an 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) which 
(0.164,239.103) “calls” 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree. 
(0.164,239.103) The 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) returns 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) once 
(0.164,239.103) it 
(0.164,239.103) e 
(0.164,239.103) xits 
(0.164,239.103) along 
(0.164,239.103) its 
(0.164,239.103) loop 
(0.164,239.103) condition 
(0.164,239.103) guard 
(0.164,239.103) (b). 
(0.164,239.103) In 
(0.164,239.103) general, 
(0.164,239.103) if 
(0.164,239.103) loops 
(0.164,239.103) are 
(0.164,239.103) nes 
(0.164,239.103) ted 
(0.164,239.103) to 
(0.164,239.103) depth 
(0.164,239.103) k 
(0.164,239.103) , 
(0.164,239.103) and 
(0.164,239.103) each 
(0.164,239.103) loop 
(0.164,239.103) has 
(0.164,239.103) n 
(0.164,239.103) paths 
(0.164,239.103) (on 
(0.164,239.103) geometric 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) erage), 
(0.164,239.103) this 
(0.164,239.103) na 
(0.164,239.103) ¨ 
(0.164,239.103) ıv 
(0.164,239.103) e 
(0.164,239.103) strate 
(0.164,239.103) gy 
(0.164,239.103) yields 
(0.164,239.103) O 
(0.164,239.103) ( 
(0.164,239.103) n 
(0.164,239.103) k 
(0.164,239.103) ) 
(0.164,239.103) traces, 
(0.164,239.103) which 
(0.164,239.103) can 
(0.164,239.103) easily 
(0.164,239.103) fill 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) cache. 
(0.164,239.103) In 
(0.164,239.103) order 
(0.164,239.103) to 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) e 
(0.164,239.103) cute 
(0.164,239.103) programs 
(0.164,239.103) with 
(0.164,239.103) nested 
(0.164,239.103) loops 
(0.164,239.103) ef 
(0.164,239.103) ficientl 
(0.164,239.103) y 
(0.164,239.103) , 
(0.164,239.103) a 
(0.164,239.103) tracing 
(0.164,239.103) system 
(0.164,239.103) needs 
(0.164,239.103) a 
(0.164,239.103) technique 
(0.164,239.103) for 
(0.164,239.103) co 
(0.164,239.103) v 
(0.164,239.103) ering 
(0.164,239.103) the 
(0.164,239.103) nested 
(0.164,239.103) loops 
(0.164,239.103) with 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) without 
(0.164,239.103) e 
(0.164,239.103) xponential 
(0.164,239.103) trace 
(0.164,239.103) duplication. 
(0.164,239.103) 4.1 
(0.164,239.103) Nesting 
(0.164,239.103) Algorithm 
(0.164,239.103) The 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) insight 
(0.164,239.103) is 
(0.164,239.103) that 
(0.164,239.103) if 
(0.164,239.103) each 
(0.164,239.103) loop 
(0.164,239.103) is 
(0.164,239.103) represented 
(0.164,239.103) by 
(0.164,239.103) its 
(0.164,239.103) o 
(0.164,239.103) wn 
(0.164,239.103) trace 
(0.164,239.103) tree, 
(0.164,239.103) the 
(0.164,239.103) code 
(0.164,239.103) for 
(0.164,239.103) each 
(0.164,239.103) loop 
(0.164,239.103) can 
(0.164,239.103) be 
(0.164,239.103) contained 
(0.164,239.103) only 
(0.164,239.103) in 
(0.164,239.103) its 
(0.164,239.103) o 
(0.164,239.103) wn 
(0.164,239.103) tree, 
(0.164,239.103) and 
(0.164,239.103) outer 
(0.164,239.103) loop 
(0.164,239.103) paths 
(0.164,239.103) will 
(0.164,239.103) not 
(0.164,239.103) be 
(0.164,239.103) duplicated. 
(0.164,239.103) Another 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) f 
(0.164,239.103) act 
(0.164,239.103) is 
(0.164,239.103) that 
(0.164,239.103) we 
(0.164,239.103) are 
(0.164,239.103) not 
(0.164,239.103) tracing 
(0.164,239.103) arbitrary 
(0.164,239.103) bytec 
(0.164,239.103) odes 
(0.164,239.103) that 
(0.164,239.103) might 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) irreduceable 
(0.164,239.103) control 
(0.164,239.103) flo 
(0.164,239.103) w 
(0.164,239.103) graphs, 
(0.164,239.103) b 
(0.164,239.103) ut 
(0.164,239.103) rather 
(0.164,239.103) byt 
(0.164,239.103) ecodes 
(0.164,239.103) produced 
(0.164,239.103) by 
(0.164,239.103) a 
(0.164,239.103) compiler 
(0.164,239.103) for 
(0.164,239.103) a 
(0.164,239.103) language 
(0.164,239.103) with 
(0.164,239.103) structured 
(0.164,239.103) control 
(0.164,239.103) flo 
(0.164,239.103) w 
(0.164,239.103) . 
(0.164,239.103) Thus, 
(0.164,239.103) gi 
(0.164,239.103) v 
(0.164,239.103) en 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) loop 
(0.164,239.103) edges, 
(0.164,239.103) the 
(0.164,239.103) system 
(0.164,239.103) can 
(0.164,239.103) easily 
(0.164,239.103) determine 
(0.164,239.103) whether 
(0.164,239.103) the 
(0.164,239.103) y 
(0.164,239.103) are 
(0.164,239.103) nested 
(0.164,239.103) and 
(0.164,239.103) which 
(0.164,239.103) is 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop. 
(0.164,239.103) Using 
(0.164,239.103) this 
(0.164,239.103) kno 
(0.164,239.103) wledge, 
(0.164,239.103) the 
(0.164,239.103) system 
(0.164,239.103) can 
(0.164,239.103) compile 
(0.164,239.103) inner 
(0.164,239.103) and 
(0.164,239.103) outer 
(0.164,239.103) loops 
(0.164,239.103) separately 
(0.164,239.103) , 
(0.164,239.103) and 
(0.164,239.103) mak 
(0.164,239.103) e 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop’ 
(0.164,239.103) s 
(0.164,239.103) traces 
(0.164,239.103) call 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop’ 
(0.164,239.103) s 
(0.164,239.103) trace 
(0.164,239.103) tree. 
(0.164,239.103) The 
(0.164,239.103) algorithm 
(0.164,239.103) for 
(0.164,239.103) b 
(0.164,239.103) uilding 
(0.164,239.103) nested 
(0.164,239.103) trace 
(0.164,239.103) trees 
(0.164,239.103) is 
(0.164,239.103) as 
(0.164,239.103) follo 
(0.164,239.103) ws. 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) start 
(0.164,239.103) tracing 
(0.164,239.103) at 
(0.164,239.103) loop 
(0.164,239.103) headers 
(0.164,239.103) e 
(0.164,239.103) xactly 
(0.164,239.103) as 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) basic 
(0.164,239.103) tracing 
(0.164,239.103) system. 
(0.164,239.103) When 
(0.164,239.103) we 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) a 
(0.164,239.103) loop 
(0.164,239.103) (detected 
(0.164,239.103) by 
(0.164,239.103) comparing 
(0.164,239.103) the 
(0.164,239.103) interpreter 
(0.164,239.103) PC 
(0.164,239.103) with 
(0.164,239.103) the 
(0.164,239.103) range 
(0.164,239.103) gi 
(0.164,239.103) v 
(0.164,239.103) en 
(0.164,239.103) by 
(0.164,239.103) the 
(0.164,239.103) loop 
(0.164,239.103) edge), 
(0.164,239.103) we 
(0.164,239.103) stop 
(0.164,239.103) the 
(0.164,239.103) trace. 
(0.164,239.103) The 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) step 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) algorithm 
(0.164,239.103) occurs 
(0.164,239.103) when 
(0.164,239.103) we 
(0.164,239.103) are 
(0.164,239.103) recording 
(0.164,239.103) a 
(0.164,239.103) trace 
(0.164,239.103) for 
(0.164,239.103) loop 
(0.164,239.103) L 
(0.164,239.103) R 
(0.164,239.103) ( 
(0.164,239.103) R 
(0.164,239.103) for 
(0.164,239.103) loop 
(0.164,239.103) being 
(0.164,239.103) recorded) 
(0.164,239.103) and 
(0.164,239.103) we 
(0.164,239.103) reach 
(0.164,239.103) the 
(0.164,239.103) header 
(0.164,239.103) of 
(0.164,239.103) a 
(0.164,239.103) dif 
(0.164,239.103) ferent 
(0.164,239.103) loop 
(0.164,239.103) L 
(0.164,239.103) O 
(0.164,239.103) ( 
(0.164,239.103) O 
(0.164,239.103) for 
(0.164,239.103) other 
(0.164,239.103) loop). 
(0.164,239.103) Note 
(0.164,239.103) that 
(0.164,239.103) L 
(0.164,239.103) O 
(0.164,239.103) must 
(0.164,239.103) be 
(0.164,239.103) an 
(0.164,239.103) inner 
(0.164,239.103) loop 
(0.164,239.103) of 
(0.164,239.103) L 
(0.164,239.103) R 
(0.164,239.103) because 
(0.164,239.103) we 
(0.164,239.103) stop 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) when 
(0.164,239.103) we 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) a 
(0.164,239.103) loop. 
(0.164,239.103) • 
(0.164,239.103) If 
(0.164,239.103) L 
(0.164,239.103) O 
(0.164,239.103) has 
(0.164,239.103) a 
(0.164,239.103) type- 
(0.164,239.103) matching 
(0.164,239.103) compiled 
(0.164,239.103) trace 
(0.164,239.103) tree, 
(0.164,239.103) we 
(0.164,239.103) call 
(0.164,239.103) L 
(0.164,239.103) O 
(0.164,239.103) as 
(0.164,239.103) a 
(0.164,239.103) nested 
(0.164,239.103) trace 
(0.164,239.103) tree. 
(0.164,239.103) If 
(0.164,239.103) the 
(0.164,239.103) call 
(0.164,239.103) succeeds, 
(0.164,239.103) then 
(0.164,239.103) we 
(0.164,239.103) record 
(0.164,239.103) the 
(0.164,239.103) call 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) for 
(0.164,239.103) L 
(0.164,239.103) R 
(0.164,239.103) . 
(0.164,239.103) On 
(0.164,239.103) future 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecutions, 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) for 
(0.164,239.103) L 
(0.164,239.103) R 
(0.164,239.103) will 
(0.164,239.103) call 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) trace 
(0.164,239.103) directly 
(0.164,239.103) . 
(0.164,239.103) • 
(0.164,239.103) If 
(0.164,239.103) L 
(0.164,239.103) O 
(0.164,239.103) does 
(0.164,239.103) not 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) a 
(0.164,239.103) type-matching 
(0.164,239.103) compiled 
(0.164,239.103) trace 
(0.164,239.103) tree 
(0.164,239.103) yet, 
(0.164,239.103) we 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) to 
(0.164,239.103) obtain 
(0.164,239.103) it 
(0.164,239.103) before 
(0.164,239.103) we 
(0.164,239.103) are 
(0.164,239.103) able 
(0.164,239.103) to 
(0.164,239.103) proceed. 
(0.164,239.103) In 
(0.164,239.103) order 
(0.164,239.103) to 
(0.164,239.103) do 
(0.164,239.103) this, 
(0.164,239.103) we 
(0.164,239.103) simply 
(0.164,239.103) abort 
(0.164,239.103) recording 
(0.164,239.103) the 
(0.164,239.103) first 
(0.164,239.103) trace. 
(0.164,239.103) The 
(0.164,239.103) trace 
(0.164,239.103) monitor 
(0.164,239.103) will 
(0.164,239.103) see 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop 
(0.164,239.103) header 
(0.164,239.103) , 
(0.164,239.103) and 
(0.164,239.103) wi 
(0.164,239.103) ll 
(0.164,239.103) immediately 
(0.164,239.103) start 
(0.164,239.103) recording 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) loop. 
(0.164,239.103) 2 
(0.164,239.103) If 
(0.164,239.103) all 
(0.164,239.103) the 
(0.164,239.103) loops 
(0.164,239.103) in 
(0.164,239.103) a 
(0.164,239.103) nest 
(0.164,239.103) are 
(0.164,239.103) type-stable, 
(0.164,239.103) then 
(0.164,239.103) loop 
(0.164,239.103) nesting 
(0.164,239.103) creates 
(0.164,239.103) no 
(0.164,239.103) duplication. 
(0.164,239.103) Otherwise, 
(0.164,239.103) if 
(0.164,239.103) loops 
(0.164,239.103) are 
(0.164,239.103) nested 
(0.164,239.103) to 
(0.164,239.103) a 
(0.164,239.103) depth 
(0.164,239.103) k 
(0.164,239.103) , 
(0.164,239.103) and 
(0.164,239.103) each 
(0.164,119.552) 2 
(0.164,119.552) Instead 
(0.164,119.552) of 
(0.164,119.552) aborting 
(0.164,119.552) the 
(0.164,119.552) outer 
(0.164,119.552) recording, 
(0.164,119.552) we 
(0.164,119.552) could 
(0.164,119.552) principally 
(0.164,119.552) merely 
(0.164,119.552) sus- 
(0.164,119.552) pend 
(0.164,119.552) the 
(0.164,119.552) recording, 
(0.164,119.552) b 
(0.164,119.552) ut 
(0.164,119.552) that 
(0.164,119.552) w 
(0.164,119.552) ould 
(0.164,119.552) require 
(0.164,119.552) the 
(0.164,119.552) implementation 
(0.164,119.552) to 
(0.164,119.552) be 
(0.164,119.552) able 
(0.164,119.552) to 
(0.164,119.552) record 
(0.164,119.552) se 
(0.164,119.552) v 
(0.164,119.552) eral 
(0.164,119.552) traces 
(0.164,119.552) simultaneously 
(0.164,119.552) , 
(0.164,119.552) complicating 
(0.164,119.552) the 
(0.164,119.552) implementation, 
(0.164,119.552) while 
(0.164,119.552) sa 
(0.164,119.552) ving 
(0.164,119.552) only 
(0.164,119.552) a 
(0.164,119.552) fe 
(0.164,119.552) w 
(0.164,119.552) iterations 
(0.164,119.552) in 
(0.164,119.552) the 
(0.164,119.552) interpreter 
(0.164,119.552) . 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 8. 
(0.164,239.103) Control 
(0.164,239.103) flo 
(0.164,239.103) w 
(0.164,239.103) graph 
(0.164,239.103) of 
(0.164,239.103) a 
(0.164,239.103) loop 
(0.164,239.103) with 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) nested 
(0.164,239.103) loops 
(0.164,239.103) (left) 
(0.164,239.103) and 
(0.164,239.103) its 
(0.164,239.103) nested 
(0.164,239.103) trace 
(0.164,239.103) tree 
(0.164,239.103) configuration 
(0.164,239.103) (right). 
(0.164,239.103) The 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) calls 
(0.164,239.103) the 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) inner 
(0.164,239.103) nested 
(0.164,239.103) trace 
(0.164,239.103) trees 
(0.164,239.103) and 
(0.164,239.103) places 
(0.164,239.103) guards 
(0.164,239.103) at 
(0.164,239.103) their 
(0.164,239.103) side 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) locations. 
(0.164,239.103) loop 
(0.164,239.103) is 
(0.164,239.103) entered 
(0.164,239.103) with 
(0.164,239.103) m 
(0.164,239.103) dif 
(0.164,239.103) ferent 
(0.164,239.103) t 
(0.164,239.103) ype 
(0.164,239.103) maps 
(0.164,239.103) (on 
(0.164,239.103) geometric 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) erage), 
(0.164,239.103) then 
(0.164,239.103) we 
(0.164,239.103) compile 
(0.164,239.103) O 
(0.164,239.103) ( 
(0.164,239.103) m 
(0.164,239.103) k 
(0.164,239.103) ) 
(0.164,239.103) copies 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) innermost 
(0.164,239.103) loop. 
(0.164,239.103) As 
(0.164,239.103) long 
(0.164,239.103) as 
(0.164,239.103) m 
(0.164,239.103) is 
(0.164,239.103) close 
(0.164,239.103) to 
(0.164,239.103) 1, 
(0.164,239.103) the 
(0.164,239.103) resulting 
(0.164,239.103) trace 
(0.164,239.103) trees 
(0.164,239.103) will 
(0.164,239.103) be 
(0.164,239.103) tractable. 
(0.164,239.103) An 
(0.164,239.103) important 
(0.164,239.103) detail 
(0.164,239.103) is 
(0.164,239.103) that 
(0.164,239.103) the 
(0.164,239.103) call 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) trace 
(0.164,239.103) tree 
(0.164,239.103) must 
(0.164,239.103) act 
(0.164,239.103) lik 
(0.164,239.103) e 
(0.164,239.103) a 
(0.164,239.103) function 
(0.164,239.103) call 
(0.164,239.103) site: 
(0.164,239.103) it 
(0.164,239.103) must 
(0.164,239.103) return 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) point 
(0.164,239.103) e 
(0.164,239.103) v 
(0.164,239.103) ery 
(0.164,239.103) time. 
(0.164,239.103) The 
(0.164,239.103) goal 
(0.164,239.103) of 
(0.164,239.103) nesting 
(0.164,239.103) is 
(0.164,239.103) to 
(0.164,239.103) mak 
(0.164,239.103) e 
(0.164,239.103) inner 
(0.164,239.103) and 
(0.164,239.103) outer 
(0.164,239.103) loops 
(0.164,239.103) independent; 
(0.164,239.103) thus 
(0.164,239.103) when 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) is 
(0.164,239.103) called, 
(0.164,239.103) it 
(0.164,239.103) must 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) point 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) e 
(0.164,239.103) v 
(0.164,239.103) ery 
(0.164,239.103) time 
(0.164,239.103) with 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) type 
(0.164,239.103) map. 
(0.164,239.103) Because 
(0.164,239.103) we 
(0.164,239.103) cannot 
(0.164,239.103) actually 
(0.164,239.103) guarantee 
(0.164,239.103) this 
(0.164,239.103) property 
(0.164,239.103) , 
(0.164,239.103) we 
(0.164,239.103) must 
(0.164,239.103) guard 
(0.164,239.103) on 
(0.164,239.103) it 
(0.164,239.103) after 
(0.164,239.103) the 
(0.164,239.103) call, 
(0.164,239.103) and 
(0.164,239.103) side 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) if 
(0.164,239.103) the 
(0.164,239.103) property 
(0.164,239.103) does 
(0.164,239.103) not 
(0.164,239.103) hold. 
(0.164,239.103) A 
(0.164,239.103) common 
(0.164,239.103) reason 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) not 
(0.164,239.103) to 
(0.164,239.103) return 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) point 
(0.164,239.103) w 
(0.164,239.103) ould 
(0.164,239.103) be 
(0.164,239.103) if 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) took 
(0.164,239.103) a 
(0.164,239.103) ne 
(0.164,239.103) w 
(0.164,239.103) side 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) for 
(0.164,239.103) which 
(0.164,239.103) it 
(0.164,239.103) had 
(0.164,239.103) ne 
(0.164,239.103) v 
(0.164,239.103) er 
(0.164,239.103) compiled 
(0.164,239.103) a 
(0.164,239.103) trace. 
(0.164,239.103) At 
(0.164,239.103) this 
(0.164,239.103) point, 
(0.164,239.103) the 
(0.164,239.103) interpreter 
(0.164,239.103) PC 
(0.164,239.103) is 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree, 
(0.164,239.103) so 
(0.164,239.103) we 
(0.164,239.103) cannot 
(0.164,239.103) continue 
(0.164,239.103) recording 
(0.164,239.103) or 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecuting 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree. 
(0.164,239.103) If 
(0.164,239.103) this 
(0.164,239.103) happens 
(0.164,239.103) during 
(0.164,239.103) recording, 
(0.164,239.103) we 
(0.164,239.103) abort 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) trace, 
(0.164,239.103) to 
(0.164,239.103) gi 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) a 
(0.164,239.103) chance 
(0.164,239.103) to 
(0.164,239.103) finish 
(0.164,239.103) gro 
(0.164,239.103) wing. 
(0.164,239.103) A 
(0.164,239.103) fut 
(0.164,239.103) ure 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecution 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) w 
(0.164,239.103) ould 
(0.164,239.103) then 
(0.164,239.103) be 
(0.164,239.103) able 
(0.164,239.103) to 
(0.164,239.103) properly 
(0.164,239.103) finish 
(0.164,239.103) and 
(0.164,239.103) rec 
(0.164,239.103) ord 
(0.164,239.103) a 
(0.164,239.103) call 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree. 
(0.164,239.103) If 
(0.164,239.103) an 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) side 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) happens 
(0.164,239.103) during 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecution 
(0.164,239.103) of 
(0.164,239.103) a 
(0.164,239.103) compiled 
(0.164,239.103) trace 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree, 
(0.164,239.103) we 
(0.164,239.103) simply 
(0.164,239.103) e 
(0.164,239.103) xit 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) trace 
(0.164,239.103) and 
(0.164,239.103) start 
(0.164,239.103) recording 
(0.164,239.103) a 
(0.164,239.103) ne 
(0.164,239.103) w 
(0.164,239.103) branch 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree. 
(0.164,239.103) 4.2 
(0.164,239.103) Blacklisting 
(0.164,239.103) with 
(0.164,239.103) Nesting 
(0.164,239.103) The 
(0.164,239.103) blacklisting 
(0.164,239.103) algorithm 
(0.164,239.103) needs 
(0.164,239.103) modification 
(0.164,239.103) to 
(0.164,239.103) w 
(0.164,239.103) ork 
(0.164,239.103) well 
(0.164,239.103) with 
(0.164,239.103) nesting. 
(0.164,239.103) The 
(0.164,239.103) problem 
(0.164,239.103) is 
(0.164,239.103) that 
(0.164,239.103) outer 
(0.164,239.103) loop 
(0.164,239.103) traces 
(0.164,239.103) often 
(0.164,239.103) abort 
(0.164,239.103) during 
(0.164,239.103) startup 
(0.164,239.103) (because 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) is 
(0.164,239.103) not 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) ailable 
(0.164,239.103) or 
(0.164,239.103) tak 
(0.164,239.103) es 
(0.164,239.103) a 
(0.164,239.103) side 
(0.164,239.103) e 
(0.164,239.103) xit), 
(0.164,239.103) which 
(0.164,239.103) w 
(0.164,239.103) ould 
(0.164,239.103) lead 
(0.164,239.103) to 
(0.164,239.103) t 
(0.164,239.103) heir 
(0.164,239.103) being 
(0.164,239.103) quickly 
(0.164,239.103) blacklisted 
(0.164,239.103) by 
(0.164,239.103) the 
(0.164,239.103) basic 
(0.164,239.103) algorithm. 
(0.164,239.103) The 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) observ 
(0.164,239.103) ation 
(0.164,239.103) is 
(0.164,239.103) that 
(0.164,239.103) when 
(0.164,239.103) an 
(0.164,239.103) outer 
(0.164,239.103) tr 
(0.164,239.103) ace 
(0.164,239.103) aborts 
(0.164,239.103) because 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) is 
(0.164,239.103) not 
(0.164,239.103) ready 
(0.164,239.103) , 
(0.164,239.103) this 
(0.164,239.103) is 
(0.164,239.103) probably 
(0.164,239.103) a 
(0.164,239.103) temporary 
(0.164,239.103) condition. 
(0.164,239.103) Thus, 
(0.164,239.103) we 
(0.164,239.103) should 
(0.164,239.103) not 
(0.164,239.103) count 
(0.164,239.103) such 
(0.164,239.103) aborts 
(0.164,239.103) to 
(0.164,239.103) w 
(0.164,239.103) ard 
(0.164,239.103) blacklisting 
(0.164,239.103) as 
(0.164,239.103) long 
(0.164,239.103) as 
(0.164,239.103) we 
(0.164,239.103) are 
(0.164,239.103) able 
(0.164,239.103) to 
(0.164,239.103) b 
(0.164,239.103) uild 
(0.164,239.103) up 
(0.164,239.103) more 
(0.164,239.103) traces 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree. 
(0.164,239.103) In 
(0.164,239.103) our 
(0.164,239.103) implementation, 
(0.164,239.103) when 
(0.164,239.103) an 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) aborts 
(0.164,239.103) on 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree, 
(0.164,239.103) we 
(0.164,239.103) increment 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree’ 
(0.164,239.103) s 
(0.164,239.103) blacklist 
(0.164,239.103) counter 
(0.164,239.103) as 
(0.164,239.103) usual 
(0.164,239.103) and 
(0.164,239.103) back 
(0.164,239.103) of 
(0.164,239.103) f 
(0.164,239.103) on 
(0.164,239.103) compiling 
(0.164,239.103) it. 
(0.164,239.103) When 
(0.164,239.103) the 
(0.164,239.103) inner 
(0.164,239.103) tree 
(0.164,239.103) finis 
(0.164,239.103) hes 
(0.164,239.103) a 
(0.164,239.103) trace, 
(0.164,239.103) we 
(0.164,239.103) decrement 
(0.164,239.103) the 
(0.164,239.103) blacklist 
(0.164,239.103) count 
(0.164,239.103) er 
(0.164,239.103) on 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop, 
(0.164,239.103) “for 
(0.164,239.103) gi 
(0.164,239.103) ving” 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) loop 
(0.164,239.103) for 
(0.164,239.103) aborting 
(0.164,239.103) pre 
(0.164,239.103) viously 
(0.164,239.103) . 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) also 
(0.164,239.103) undo 
(0.164,239.103) the 
(0.164,239.103) back 
(0.164,239.103) of 
(0.164,239.103) f 
(0.164,239.103) so 
(0.164,239.103) that 
(0.164,239.103) the 
(0.164,239.103) outer 
(0.164,239.103) tree 
(0.164,239.103) can 
(0.164,239.103) start 
(0.164,239.103) immediately 
(0.164,239.103) trying 
(0.164,239.103) to 
(0.164,239.103) compile 
(0.164,239.103) the 
(0.164,239.103) ne 
(0.164,239.103) xt 
(0.164,239.103) time 
(0.164,239.103) we 
(0.164,239.103) reach 
(0.164,239.103) it. 
(0.164,239.103) 5. 
(0.164,239.103) T 
(0.164,239.103) race 
(0.164,239.103) T 
(0.164,239.103) r 
(0.164,239.103) ee 
(0.164,239.103) Optimization 
(0.164,239.103) This 
(0.164,239.103) section 
(0.164,239.103) e 
(0.164,239.103) xplains 
(0.164,239.103) ho 
(0.164,239.103) w 
(0.164,239.103) a 
(0.164,239.103) recorded 
(0.164,239.103) trace 
(0.164,239.103) is 
(0.164,239.103) translated 
(0.164,239.103) to 
(0.164,239.103) an 
(0.164,239.103) optimized 
(0.164,239.103) machine 
(0.164,239.103) code 
(0.164,239.103) trace. 
(0.164,239.103) The 
(0.164,239.103) trace 
(0.164,239.103) compilation 
(0.164,239.103) subsystem, 
(0.164,239.103) N 
(0.164,239.103) A 
(0.164,239.103) N 
(0.164,239.103) O 
(0.164,239.103) J 
(0.164,239.103) I 
(0.164,239.103) T 
(0.164,239.103) , 
(0.164,239.103) is 
(0.164,239.103) separate 
(0.164,239.103) from 
(0.164,239.103) the 
(0.164,239.103) VM 
(0.164,239.103) and 
(0.164,239.103) can 
(0.164,239.103) be 
(0.164,239.103) used 
(0.164,239.103) for 
(0.164,239.103) other 
(0.164,239.103) applications. 
(0.000,0.000) 5.1 
(0.000,0.000) Optimizations 
(0.000,0.000) Because 
(0.000,0.000) traces 
(0.000,0.000) are 
(0.000,0.000) in 
(0.000,0.000) SSA 
(0.000,0.000) form 
(0.000,0.000) and 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) no 
(0.000,0.000) join 
(0.000,0.000) points 
(0.000,0.000) or 
(0.000,0.000) φ 
(0.000,0.000) - 
(0.000,0.000) nodes, 
(0.000,0.000) certa 
(0.000,0.000) in 
(0.000,0.000) optimizations 
(0.000,0.000) a 
(0.000,0.000) re 
(0.000,0.000) easy 
(0.000,0.000) to 
(0.000,0.000) implement. 
(0.000,0.000) In 
(0.000,0.000) order 
(0.000,0.000) to 
(0.000,0.000) get 
(0.000,0.000) good 
(0.000,0.000) startup 
(0.000,0.000) performance, 
(0.000,0.000) the 
(0.000,0.000) optimizations 
(0.000,0.000) must 
(0.000,0.000) run 
(0.000,0.000) quickly 
(0.000,0.000) , 
(0.000,0.000) so 
(0.000,0.000) we 
(0.000,0.000) chose 
(0.000,0.000) a 
(0.000,0.000) small 
(0.000,0.000) set 
(0.000,0.000) of 
(0.000,0.000) optimizations. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) implemented 
(0.000,0.000) the 
(0.000,0.000) optimizations 
(0.000,0.000) as 
(0.000,0.000) pipelined 
(0.000,0.000) filters 
(0.000,0.000) so 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) turned 
(0.000,0.000) on 
(0.000,0.000) and 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) independently 
(0.000,0.000) , 
(0.000,0.000) and 
(0.000,0.000) yet 
(0.000,0.000) all 
(0.000,0.000) run 
(0.000,0.000) in 
(0.000,0.000) just 
(0.000,0.000) tw 
(0.000,0.000) o 
(0.000,0.000) l 
(0.000,0.000) oop 
(0.000,0.000) passes 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) trace: 
(0.000,0.000) one 
(0.000,0.000) forw 
(0.000,0.000) ard 
(0.000,0.000) and 
(0.000,0.000) one 
(0.000,0.000) backw 
(0.000,0.000) ard. 
(0.000,0.000) Ev 
(0.000,0.000) ery 
(0.000,0.000) time 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) recorder 
(0.000,0.000) emits 
(0.000,0.000) a 
(0.000,0.000) LIR 
(0.000,0.000) instruction, 
(0.000,0.000) the 
(0.000,0.000) in- 
(0.000,0.000) struction 
(0.000,0.000) is 
(0.000,0.000) immediately 
(0.000,0.000) passed 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) first 
(0.000,0.000) filter 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) forw 
(0.000,0.000) ard 
(0.000,0.000) pipeline. 
(0.000,0.000) Thus, 
(0.000,0.000) forw 
(0.000,0.000) ard 
(0.000,0.000) filte 
(0.000,0.000) r 
(0.000,0.000) optimizations 
(0.000,0.000) are 
(0.000,0.000) performed 
(0.000,0.000) as 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) is 
(0.000,0.000) recorded. 
(0.000,0.000) Each 
(0.000,0.000) filter 
(0.000,0.000) may 
(0.000,0.000) pass 
(0.000,0.000) each 
(0.000,0.000) instruction 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) ne 
(0.000,0.000) xt 
(0.000,0.000) filter 
(0.000,0.000) unchanged, 
(0.000,0.000) write 
(0.000,0.000) a 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) instruction 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) ne 
(0.000,0.000) xt 
(0.000,0.000) filter 
(0.000,0.000) , 
(0.000,0.000) or 
(0.000,0.000) write 
(0.000,0.000) no 
(0.000,0.000) instruction 
(0.000,0.000) at 
(0.000,0.000) all. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) the 
(0.000,0.000) constant 
(0.000,0.000) folding 
(0.000,0.000) filter 
(0.000,0.000) can 
(0.000,0.000) replace 
(0.000,0.000) a 
(0.000,0.000) multiply 
(0.000,0.000) instruction 
(0.000,0.000) lik 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) 13 
(0.000,0.000) := 
(0.000,0.000) mu 
(0.000,0.000) l 
(0.000,0.000) 3 
(0.000,0.000) , 
(0.000,0.000) 1000 
(0.000,0.000) with 
(0.000,0.000) a 
(0.000,0.000) constant 
(0.000,0.000) instruction 
(0.000,0.000) v 
(0.000,0.000) 13 
(0.000,0.000) = 
(0.000,0.000) 3000 
(0.000,0.000) . 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) currently 
(0.000,0.000) apply 
(0.000,0.000) four 
(0.000,0.000) forw 
(0.000,0.000) ard 
(0.000,0.000) filters: 
(0.000,0.000) • 
(0.000,0.000) On 
(0.000,0.000) ISAs 
(0.000,0.000) without 
(0.000,0.000) floating-point 
(0.000,0.000) instructions, 
(0.000,0.000) a 
(0.000,0.000) soft-float 
(0.000,0.000) filter 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) erts 
(0.000,0.000) floating-point 
(0.000,0.000) LIR 
(0.000,0.000) instructions 
(0.000,0.000) to 
(0.000,0.000) sequences 
(0.000,0.000) of 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) instructions. 
(0.000,0.000) • 
(0.000,0.000) CSE 
(0.000,0.000) (constant 
(0.000,0.000) sube 
(0.000,0.000) xpression 
(0.000,0.000) elimination), 
(0.000,0.000) • 
(0.000,0.000) e 
(0.000,0.000) xpression 
(0.000,0.000) simplification, 
(0.000,0.000) including 
(0.000,0.000) constant 
(0.000,0.000) folding 
(0.000,0.000) and 
(0.000,0.000) a 
(0.000,0.000) fe 
(0.000,0.000) w 
(0.000,0.000) algebraic 
(0.000,0.000) identities 
(0.000,0.000) (e.g., 
(0.000,0.000) a 
(0.000,0.000) − 
(0.000,0.000) a 
(0.000,0.000) = 
(0.000,0.000) 0 
(0.000,0.000) ), 
(0.000,0.000) and 
(0.000,0.000) • 
(0.000,0.000) source 
(0.000,0.000) language 
(0.000,0.000) semantic-specific 
(0.000,0.000) e 
(0.000,0.000) xpression 
(0.000,0.000) simplification, 
(0.000,0.000) primarily 
(0.000,0.000) algebraic 
(0.000,0.000) identit 
(0.000,0.000) ies 
(0.000,0.000) that 
(0.000,0.000) allo 
(0.000,0.000) w 
(0.000,0.000) D 
(0.000,0.000) O 
(0.000,0.000) U 
(0.000,0.000) B 
(0.000,0.000) L 
(0.000,0.000) E 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) replaced 
(0.000,0.000) with 
(0.000,0.000) I 
(0.000,0.000) N 
(0.000,0.000) T 
(0.000,0.000) . 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xample, 
(0.000,0.000) LIR 
(0.000,0.000) that 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) erts 
(0.000,0.000) an 
(0.000,0.000) I 
(0.000,0.000) N 
(0.000,0.000) T 
(0.000,0.000) to 
(0.000,0.000) a 
(0.000,0.000) D 
(0.000,0.000) O 
(0.000,0.000) U 
(0.000,0.000) B 
(0.000,0.000) L 
(0.000,0.000) E 
(0.000,0.000) and 
(0.000,0.000) then 
(0.000,0.000) back 
(0.000,0.000) ag 
(0.000,0.000) ain 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) be 
(0.000,0.000) remo 
(0.000,0.000) v 
(0.000,0.000) ed 
(0.000,0.000) by 
(0.000,0.000) this 
(0.000,0.000) filter 
(0.000,0.000) . 
(0.000,0.000) When 
(0.000,0.000) trace 
(0.000,0.000) recording 
(0.000,0.000) is 
(0.000,0.000) completed, 
(0.000,0.000) nanojit 
(0.000,0.000) runs 
(0.000,0.000) the 
(0.000,0.000) backw 
(0.000,0.000) ard 
(0.000,0.000) optimization 
(0.000,0.000) filters. 
(0.000,0.000) These 
(0.000,0.000) are 
(0.000,0.000) used 
(0.000,0.000) for 
(0.000,0.000) optimizations 
(0.000,0.000) that 
(0.000,0.000) require 
(0.000,0.000) backw 
(0.000,0.000) ard 
(0.000,0.000) program 
(0.000,0.000) analysis. 
(0.000,0.000) When 
(0.000,0.000) running 
(0.000,0.000) the 
(0.000,0.000) backw 
(0.000,0.000) ard 
(0.000,0.000) filters, 
(0.000,0.000) nanojit 
(0.000,0.000) reads 
(0.000,0.000) one 
(0.000,0.000) LIR 
(0.000,0.000) instruction 
(0.000,0.000) at 
(0.000,0.000) a 
(0.000,0.000) time, 
(0.000,0.000) and 
(0.000,0.000) t 
(0.000,0.000) he 
(0.000,0.000) reads 
(0.000,0.000) are 
(0.000,0.000) passed 
(0.000,0.000) through 
(0.000,0.000) the 
(0.000,0.000) pipeline. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) currently 
(0.000,0.000) apply 
(0.000,0.000) three 
(0.000,0.000) backw 
(0.000,0.000) ard 
(0.000,0.000) filters: 
(0.000,0.000) • 
(0.000,0.000) Dead 
(0.000,0.000) data-stack 
(0.000,0.000) store 
(0.000,0.000) elimination. 
(0.000,0.000) The 
(0.000,0.000) LIR 
(0.000,0.000) trace 
(0.000,0.000) encodes 
(0.000,0.000) man 
(0.000,0.000) y 
(0.000,0.000) stores 
(0.000,0.000) to 
(0.000,0.000) locations 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) stack. 
(0.000,0.000) But 
(0.000,0.000) these 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) are 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) read 
(0.000,0.000) back 
(0.000,0.000) before 
(0.000,0.000) e 
(0.000,0.000) xiting 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) (by 
(0.000,0.000) the 
(0.000,0.000) interpret 
(0.000,0.000) er 
(0.000,0.000) or 
(0.000,0.000) another 
(0.000,0.000) trace). 
(0.000,0.000) Thus, 
(0.000,0.000) stores 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) s 
(0.000,0.000) tack 
(0.000,0.000) that 
(0.000,0.000) are 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) erwritten 
(0.000,0.000) before 
(0.000,0.000) the 
(0.000,0.000) ne 
(0.000,0.000) xt 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) are 
(0.000,0.000) dead. 
(0.000,0.000) Store 
(0.000,0.000) s 
(0.000,0.000) to 
(0.000,0.000) locations 
(0.000,0.000) that 
(0.000,0.000) are 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) the 
(0.000,0.000) top 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) stack 
(0.000,0.000) at 
(0.000,0.000) future 
(0.000,0.000) e 
(0.000,0.000) xits 
(0.000,0.000) are 
(0.000,0.000) also 
(0.000,0.000) dead. 
(0.000,0.000) • 
(0.000,0.000) Dead 
(0.000,0.000) call-stack 
(0.000,0.000) store 
(0.000,0.000) elimination. 
(0.000,0.000) This 
(0.000,0.000) is 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) optimization 
(0.000,0.000) as 
(0.000,0.000) abo 
(0.000,0.000) v 
(0.000,0.000) e, 
(0.000,0.000) e 
(0.000,0.000) xcept 
(0.000,0.000) applied 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) interpreter’ 
(0.000,0.000) s 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) used 
(0.000,0.000) for 
(0.000,0.000) function 
(0.000,0.000) call 
(0.000,0.000) inlining. 
(0.000,0.000) • 
(0.000,0.000) Dead 
(0.000,0.000) code 
(0.000,0.000) elimination. 
(0.000,0.000) This 
(0.000,0.000) eliminates 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) operation 
(0.000,0.000) that 
(0.000,0.000) stores 
(0.000,0.000) to 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) that 
(0.000,0.000) is 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) used. 
(0.000,0.000) After 
(0.000,0.000) a 
(0.000,0.000) LIR 
(0.000,0.000) instruction 
(0.000,0.000) is 
(0.000,0.000) successfully 
(0.000,0.000) read 
(0.000,0.000) (“pulled”) 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) backw 
(0.000,0.000) ard 
(0.000,0.000) filter 
(0.000,0.000) pipeli 
(0.000,0.000) ne, 
(0.000,0.000) nanojit’ 
(0.000,0.000) s 
(0.000,0.000) code 
(0.000,0.000) generator 
(0.000,0.000) emits 
(0.000,0.000) nati 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) machine 
(0.000,0.000) instruction(s) 
(0.000,0.000) for 
(0.000,0.000) it. 
(0.000,0.000) 5.2 
(0.000,0.000) Register 
(0.000,0.000) Allocation 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) use 
(0.000,0.000) a 
(0.000,0.000) simple 
(0.000,0.000) greedy 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) allocator 
(0.000,0.000) that 
(0.000,0.000) mak 
(0.000,0.000) es 
(0.000,0.000) a 
(0.000,0.000) single 
(0.000,0.000) backw 
(0.000,0.000) ard 
(0.000,0.000) pass 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) (it 
(0.000,0.000) is 
(0.000,0.000) inte 
(0.000,0.000) grated 
(0.000,0.000) with 
(0.000,0.000) the 
(0.000,0.000) c 
(0.000,0.000) ode 
(0.000,0.000) gen- 
(0.000,0.000) erator). 
(0.000,0.000) By 
(0.000,0.000) the 
(0.000,0.000) time 
(0.000,0.000) the 
(0.000,0.000) allocator 
(0.000,0.000) has 
(0.000,0.000) reached 
(0.000,0.000) an 
(0.000,0.000) instruction 
(0.000,0.000) lik 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) 3 
(0.000,0.000) = 
(0.000,0.000) add 
(0.000,0.000) v 
(0.000,0.000) 1 
(0.000,0.000) , 
(0.000,0.000) v 
(0.000,0.000) 2 
(0.000,0.000) , 
(0.000,0.000) it 
(0.000,0.000) has 
(0.000,0.000) already 
(0.000,0.000) assigned 
(0.000,0.000) a 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) to 
(0.000,0.000) v 
(0.000,0.000) 3 
(0.000,0.000) . 
(0.000,0.000) If 
(0.000,0.000) v 
(0.000,0.000) 1 
(0.000,0.000) and 
(0.000,0.000) v 
(0.000,0.000) 2 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) not 
(0.000,0.000) yet 
(0.000,0.000) been 
(0.000,0.000) assigned 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) s, 
(0.000,0.000) the 
(0.000,0.000) all 
(0.000,0.000) ocator 
(0.000,0.000) assigns 
(0.000,0.000) a 
(0.000,0.000) free 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) to 
(0.000,0.000) each. 
(0.000,0.000) If 
(0.000,0.000) there 
(0.000,0.000) are 
(0.000,0.000) no 
(0.000,0.000) free 
(0.000,0.000) re 
(0.000,0.000) gisters, 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) is 
(0.000,0.000) selected 
(0.000,0.000) for 
(0.000,0.000) spilling. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) use 
(0.000,0.000) a 
(0.000,0.000) class 
(0.000,0.000) heuristic 
(0.000,0.000) that 
(0.000,0.000) sel 
(0.000,0.000) ects 
(0.000,0.000) the 
(0.000,0.000) “oldest” 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) - 
(0.000,0.000) carried 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) (6). 
(0.000,0.000) The 
(0.000,0.000) heuristic 
(0.000,0.000) considers 
(0.000,0.000) the 
(0.000,0.000) set 
(0.000,0.000) R 
(0.000,0.000) of 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) v 
(0.000,0.000) in 
(0.000,0.000) re 
(0.000,0.000) gisters 
(0.000,0.000) imme- 
(0.000,0.000) diately 
(0.000,0.000) after 
(0.000,0.000) the 
(0.000,0.000) current 
(0.000,0.000) instruction 
(0.000,0.000) for 
(0.000,0.000) spilling. 
(0.000,0.000) Let 
(0.000,0.000) v 
(0.000,0.000) m 
(0.000,0.000) be 
(0.000,0.000) the 
(0.000,0.000) last 
(0.000,0.000) instruction 
(0.000,0.000) before 
(0.000,0.000) the 
(0.000,0.000) current 
(0.000,0.000) where 
(0.000,0.000) each 
(0.000,0.000) v 
(0.000,0.000) is 
(0.000,0.000) referred 
(0.000,0.000) to. 
(0.000,0.000) Then 
(0.000,0.000) the 
(0.000,0.000) T 
(0.000,0.000) ag 
(9.963,0.199) JS 
(9.963,0.199) T 
(9.963,0.199) ype 
(9.963,0.199) Description 
(0.199,237.984) xx1 
(9.963,0.199) number 
(9.963,0.199) 31-bit 
(9.963,0.199) inte 
(9.963,0.199) ger 
(9.963,0.199) representation 
(9.963,0.199) 000 
(9.963,0.199) object 
(9.963,0.199) pointer 
(9.963,0.199) to 
(9.963,0.199) JSObject 
(9.963,0.199) handle 
(9.963,0.199) 010 
(9.963,0.199) number 
(9.963,0.199) pointer 
(9.963,0.199) to 
(9.963,0.199) double 
(9.963,0.199) handle 
(9.963,0.199) 100 
(9.963,0.199) string 
(9.963,0.199) pointer 
(9.963,0.199) to 
(9.963,0.199) JSString 
(9.963,0.199) handle 
(9.963,0.199) 110 
(9.963,0.199) boolean 
(9.963,0.199) enumeration 
(9.963,0.199) for 
(9.963,0.199) null, 
(9.963,0.199) undefined, 
(9.963,0.199) true, 
(9.963,0.199) f 
(9.963,0.199) alse 
(9.963,0.199) null, 
(9.963,0.199) or 
(9.963,0.199) undefined 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 9. 
(0.164,239.103) T 
(0.164,239.103) agged 
(0.164,239.103) v 
(0.164,239.103) alues 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) SpiderMonk 
(0.164,239.103) ey 
(0.164,239.103) JS 
(0.164,239.103) inter 
(0.164,239.103) pr 
(0.164,239.103) eter 
(0.164,239.103) . 
(0.164,239.103) T 
(0.164,239.103) esting 
(0.164,239.103) tags, 
(0.164,239.103) unboxing 
(0.164,239.103) (e 
(0.164,239.103) xtracting 
(0.164,239.103) the 
(0.164,239.103) untagged 
(0.164,239.103) v 
(0.164,239.103) alue) 
(0.164,239.103) and 
(0.164,239.103) boxing 
(0.164,239.103) (creating 
(0.164,239.103) tagged 
(0.164,239.103) v 
(0.164,239.103) alues) 
(0.164,239.103) are 
(0.164,239.103) significant 
(0.164,239.103) costs. 
(0.164,239.103) A 
(0.164,239.103) v 
(0.164,239.103) oiding 
(0.164,239.103) these 
(0.164,239.103) costs 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) benefit 
(0.164,239.103) of 
(0.164,239.103) tracing. 
(0.164,239.103) heuristic 
(0.164,239.103) selects 
(0.164,239.103) v 
(0.164,239.103) with 
(0.164,239.103) minimum 
(0.164,239.103) v 
(0.164,239.103) m 
(0.164,239.103) . 
(0.164,239.103) The 
(0.164,239.103) moti 
(0.164,239.103) v 
(0.164,239.103) ation 
(0.164,239.103) is 
(0.164,239.103) that 
(0.164,239.103) this 
(0.164,239.103) frees 
(0.164,239.103) up 
(0.164,239.103) a 
(0.164,239.103) re 
(0.164,239.103) gister 
(0.164,239.103) for 
(0.164,239.103) as 
(0.164,239.103) long 
(0.164,239.103) as 
(0.164,239.103) possible 
(0.164,239.103) gi 
(0.164,239.103) v 
(0.164,239.103) en 
(0.164,239.103) a 
(0.164,239.103) single 
(0.164,239.103) spill. 
(0.164,239.103) If 
(0.164,239.103) we 
(0.164,239.103) need 
(0.164,239.103) to 
(0.164,239.103) spill 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) alue 
(0.164,239.103) v 
(0.164,239.103) s 
(0.164,239.103) at 
(0.164,239.103) this 
(0.164,239.103) point, 
(0.164,239.103) we 
(0.164,239.103) ge 
(0.164,239.103) nerate 
(0.164,239.103) the 
(0.164,239.103) restore 
(0.164,239.103) code 
(0.164,239.103) just 
(0.164,239.103) after 
(0.164,239.103) the 
(0.164,239.103) code 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) current 
(0.164,239.103) instruction. 
(0.164,239.103) The 
(0.164,239.103) corresponding 
(0.164,239.103) spill 
(0.164,239.103) code 
(0.164,239.103) is 
(0.164,239.103) generated 
(0.164,239.103) just 
(0.164,239.103) after 
(0.164,239.103) the 
(0.164,239.103) last 
(0.164,239.103) point 
(0.164,239.103) where 
(0.164,239.103) v 
(0.164,239.103) s 
(0.164,239.103) w 
(0.164,239.103) as 
(0.164,239.103) used. 
(0.164,239.103) The 
(0.164,239.103) re 
(0.164,239.103) gister 
(0.164,239.103) that 
(0.164,239.103) w 
(0.164,239.103) as 
(0.164,239.103) assigned 
(0.164,239.103) to 
(0.164,239.103) v 
(0.164,239.103) s 
(0.164,239.103) is 
(0.164,239.103) mark 
(0.164,239.103) ed 
(0.164,239.103) free 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) preceding 
(0.164,239.103) code, 
(0.164,239.103) because 
(0.164,239.103) that 
(0.164,239.103) re 
(0.164,239.103) gister 
(0.164,239.103) can 
(0.164,239.103) no 
(0.164,239.103) w 
(0.164,239.103) be 
(0.164,239.103) used 
(0.164,239.103) freely 
(0.164,239.103) without 
(0.164,239.103) af 
(0.164,239.103) fecting 
(0.164,239.103) the 
(0.164,239.103) follo 
(0.164,239.103) wing 
(0.164,239.103) code 
(0.164,239.103) 6. 
(0.164,239.103) Implementation 
(0.164,239.103) T 
(0.164,239.103) o 
(0.164,239.103) demonstrate 
(0.164,239.103) the 
(0.164,239.103) ef 
(0.164,239.103) fecti 
(0.164,239.103) v 
(0.164,239.103) eness 
(0.164,239.103) of 
(0.164,239.103) our 
(0.164,239.103) approach, 
(0.164,239.103) we 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) im- 
(0.164,239.103) plemented 
(0.164,239.103) a 
(0.164,239.103) trace-based 
(0.164,239.103) dynamic 
(0.164,239.103) compiler 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) SpiderMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) V 
(0.164,239.103) irtual 
(0.164,239.103) Machine 
(0.164,239.103) (4). 
(0.164,239.103) SpiderM 
(0.164,239.103) onk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) is 
(0.164,239.103) the 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) VM 
(0.164,239.103) embedded 
(0.164,239.103) in 
(0.164,239.103) Mozilla’ 
(0.164,239.103) s 
(0.164,239.103) Firefox 
(0.164,239.103) open-source 
(0.164,239.103) web 
(0.164,239.103) bro 
(0.164,239.103) wser 
(0.164,239.103) (2), 
(0.164,239.103) which 
(0.164,239.103) is 
(0.164,239.103) used 
(0.164,239.103) by 
(0.164,239.103) more 
(0.164,239.103) than 
(0.164,239.103) 200 
(0.164,239.103) million 
(0.164,239.103) users 
(0.164,239.103) w 
(0.164,239.103) orld-wide. 
(0.164,239.103) The 
(0.164,239.103) core 
(0.164,239.103) of 
(0.164,239.103) SpiderMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) bytecode 
(0.164,239.103) interpreter 
(0.164,239.103) implemented 
(0.164,239.103) in 
(0.164,239.103) C++. 
(0.164,239.103) In 
(0.164,239.103) SpiderMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) , 
(0.164,239.103) all 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) v 
(0.164,239.103) alues 
(0.164,239.103) are 
(0.164,239.103) represented 
(0.164,239.103) by 
(0.164,239.103) the 
(0.164,239.103) type 
(0.164,239.103) jsval 
(0.164,239.103) . 
(0.164,239.103) A 
(0.164,239.103) jsval 
(0.164,239.103) is 
(0.164,239.103) machine 
(0.164,239.103) w 
(0.164,239.103) ord 
(0.164,239.103) in 
(0.164,239.103) which 
(0.164,239.103) up 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) 3 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) least 
(0.164,239.103) significant 
(0.164,239.103) bits 
(0.164,239.103) are 
(0.164,239.103) a 
(0.164,239.103) type 
(0.164,239.103) tag, 
(0.164,239.103) and 
(0.164,239.103) the 
(0.164,239.103) remaining 
(0.164,239.103) bits 
(0.164,239.103) are 
(0.164,239.103) data. 
(0.164,239.103) See 
(0.164,239.103) Figure 
(0.164,239.103) 6 
(0.164,239.103) for 
(0.164,239.103) details. 
(0.164,239.103) All 
(0.164,239.103) pointers 
(0.164,239.103) contai 
(0.164,239.103) ned 
(0.164,239.103) in 
(0.164,239.103) jsvals 
(0.164,239.103) point 
(0.164,239.103) to 
(0.164,239.103) GC-controlled 
(0.164,239.103) blocks 
(0.164,239.103) aligned 
(0.164,239.103) on 
(0.164,239.103) 8-byte 
(0.164,239.103) boundaries. 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) object 
(0.164,239.103) v 
(0.164,239.103) alues 
(0.164,239.103) are 
(0.164,239.103) mappings 
(0.164,239.103) of 
(0.164,239.103) string-v 
(0.164,239.103) alued 
(0.164,239.103) property 
(0.164,239.103) names 
(0.164,239.103) to 
(0.164,239.103) arbitrary 
(0.164,239.103) v 
(0.164,239.103) alues. 
(0.164,239.103) The 
(0.164,239.103) y 
(0.164,239.103) are 
(0.164,239.103) represented 
(0.164,239.103) in 
(0.164,239.103) one 
(0.164,239.103) of 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) w 
(0.164,239.103) ays 
(0.164,239.103) in 
(0.164,239.103) SpiderMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) . 
(0.164,239.103) Most 
(0.164,239.103) objects 
(0.164,239.103) are 
(0.164,239.103) represented 
(0.164,239.103) by 
(0.164,239.103) a 
(0.164,239.103) shared 
(0.164,239.103) struc- 
(0.164,239.103) tural 
(0.164,239.103) desc 
(0.164,239.103) ription, 
(0.164,239.103) called 
(0.164,239.103) the 
(0.164,239.103) object 
(0.164,239.103) shape 
(0.164,239.103) , 
(0.164,239.103) that 
(0.164,239.103) maps 
(0.164,239.103) property 
(0.164,239.103) names 
(0.164,239.103) to 
(0.164,239.103) array 
(0.164,239.103) inde 
(0.164,239.103) x 
(0.164,239.103) es 
(0.164,239.103) using 
(0.164,239.103) a 
(0.164,239.103) hash 
(0.164,239.103) table. 
(0.164,239.103) The 
(0.164,239.103) object 
(0.164,239.103) store 
(0.164,239.103) s 
(0.164,239.103) a 
(0.164,239.103) pointer 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) shape 
(0.164,239.103) and 
(0.164,239.103) the 
(0.164,239.103) array 
(0.164,239.103) of 
(0.164,239.103) its 
(0.164,239.103) o 
(0.164,239.103) wn 
(0.164,239.103) property 
(0.164,239.103) v 
(0.164,239.103) alues. 
(0.164,239.103) Objects 
(0.164,239.103) with 
(0.164,239.103) lar 
(0.164,239.103) ge, 
(0.164,239.103) unique 
(0.164,239.103) sets 
(0.164,239.103) of 
(0.164,239.103) property 
(0.164,239.103) names 
(0.164,239.103) store 
(0.164,239.103) their 
(0.164,239.103) properties 
(0.164,239.103) directly 
(0.164,239.103) in 
(0.164,239.103) a 
(0.164,239.103) hash 
(0.164,239.103) table. 
(0.164,239.103) The 
(0.164,239.103) g 
(0.164,239.103) arbage 
(0.164,239.103) collector 
(0.164,239.103) is 
(0.164,239.103) an 
(0.164,239.103) e 
(0.164,239.103) xact, 
(0.164,239.103) non-gene 
(0.164,239.103) rational, 
(0.164,239.103) stop-the- 
(0.164,239.103) w 
(0.164,239.103) orld 
(0.164,239.103) mark-and-sweep 
(0.164,239.103) collector 
(0.164,239.103) . 
(0.164,239.103) In 
(0.164,239.103) the 
(0.164,239.103) rest 
(0.164,239.103) of 
(0.164,239.103) this 
(0.164,239.103) section 
(0.164,239.103) we 
(0.164,239.103) discuss 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) areas 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) T 
(0.164,239.103) raceMon- 
(0.164,239.103) k 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) implementation. 
(0.164,239.103) 6.1 
(0.164,239.103) Calling 
(0.164,239.103) Compiled 
(0.164,239.103) T 
(0.164,239.103) races 
(0.164,239.103) Compiled 
(0.164,239.103) traces 
(0.164,239.103) are 
(0.164,239.103) stored 
(0.164,239.103) in 
(0.164,239.103) a 
(0.164,239.103) tr 
(0.164,239.103) ace 
(0.164,239.103) cac 
(0.164,239.103) he 
(0.164,239.103) , 
(0.164,239.103) inde 
(0.164,239.103) x 
(0.164,239.103) ed 
(0.164,239.103) by 
(0.164,239.103) intepreter 
(0.164,239.103) PC 
(0.164,239.103) and 
(0.164,239.103) type 
(0.164,239.103) map. 
(0.164,239.103) T 
(0.164,239.103) races 
(0.164,239.103) are 
(0.164,239.103) compiled 
(0.164,239.103) so 
(0.164,239.103) that 
(0.164,239.103) the 
(0.164,239.103) y 
(0.164,239.103) may 
(0.164,239.103) be 
(0.164,239.103) called 
(0.164,239.103) as 
(0.164,239.103) functions 
(0.164,239.103) using 
(0.164,239.103) standard 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) calling 
(0.164,239.103) con 
(0.164,239.103) v 
(0.164,239.103) entions 
(0.164,239.103) (e.g., 
(0.164,239.103) FASTCALL 
(0.164,239.103) on 
(0.164,239.103) x86). 
(0.164,239.103) The 
(0.164,239.103) interpreter 
(0.164,239.103) must 
(0.164,239.103) hit 
(0.164,239.103) a 
(0.164,239.103) loop 
(0.164,239.103) edge 
(0.164,239.103) and 
(0.164,239.103) enter 
(0.164,239.103) the 
(0.164,239.103) m 
(0.164,239.103) onitor 
(0.164,239.103) in 
(0.164,239.103) order 
(0.164,239.103) to 
(0.164,239.103) call 
(0.164,239.103) a 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) trace 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) first 
(0.164,239.103) time. 
(0.164,239.103) The 
(0.164,239.103) monitor 
(0.164,239.103) computes 
(0.164,239.103) the 
(0.164,239.103) current 
(0.164,239.103) type 
(0.164,239.103) map, 
(0.164,239.103) checks 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) cache 
(0.164,239.103) for 
(0.164,239.103) a 
(0.164,239.103) trace 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) current 
(0.164,239.103) PC 
(0.164,239.103) and 
(0.164,239.103) type 
(0.164,239.103) map, 
(0.164,239.103) and 
(0.164,239.103) if 
(0.164,239.103) it 
(0.164,239.103) finds 
(0.164,239.103) one, 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecutes 
(0.164,239.103) the 
(0.164,239.103) trace. 
(0.164,239.103) T 
(0.164,239.103) o 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecute 
(0.164,239.103) a 
(0.164,239.103) trace, 
(0.164,239.103) the 
(0.164,239.103) monitor 
(0.164,239.103) must 
(0.164,239.103) b 
(0.164,239.103) uild 
(0.164,239.103) a 
(0.164,239.103) trace 
(0.164,239.103) acti 
(0.164,239.103) v 
(0.164,239.103) ation 
(0.164,239.103) record 
(0.164,239.103) containi 
(0.164,239.103) ng 
(0.164,239.103) imported 
(0.164,239.103) local 
(0.164,239.103) and 
(0.164,239.103) global 
(0.164,239.103) v 
(0.164,239.103) ariables, 
(0.164,239.103) temporary 
(0.164,239.103) stack 
(0.164,239.103) s 
(0.164,239.103) pace, 
(0.164,239.103) and 
(0.164,239.103) space 
(0.164,239.103) for 
(0.164,239.103) ar 
(0.164,239.103) guments 
(0.164,239.103) to 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) calls. 
(0.164,239.103) The 
(0.164,239.103) local 
(0.164,239.103) and 
(0.164,239.103) global 
(0.164,239.103) v 
(0.164,239.103) alue 
(0.164,239.103) s 
(0.164,239.103) are 
(0.164,239.103) then 
(0.164,239.103) copied 
(0.164,239.103) from 
(0.164,239.103) the 
(0.164,239.103) interpreter 
(0.164,239.103) state 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) acti 
(0.164,239.103) v 
(0.164,239.103) ation 
(0.164,239.103) record. 
(0.164,239.103) Then, 
(0.164,239.103) the 
(0.164,239.103) trace 
(0.164,239.103) is 
(0.164,239.103) called 
(0.164,239.103) lik 
(0.164,239.103) e 
(0.164,239.103) a 
(0.164,239.103) normal 
(0.164,239.103) C 
(0.164,239.103) function 
(0.164,239.103) pointer 
(0.164,239.103) . 
(0.000,0.000) When 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) call 
(0.000,0.000) returns, 
(0.000,0.000) the 
(0.000,0.000) monitor 
(0.000,0.000) restores 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) state. 
(0.000,0.000) First, 
(0.000,0.000) the 
(0.000,0.000) monitor 
(0.000,0.000) checks 
(0.000,0.000) the 
(0.000,0.000) reason 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) and 
(0.000,0.000) applies 
(0.000,0.000) blacklisting 
(0.000,0.000) if 
(0.000,0.000) needed. 
(0.000,0.000) Then, 
(0.000,0.000) it 
(0.000,0.000) pops 
(0.000,0.000) or 
(0.000,0.000) synthesizes 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) frames 
(0.000,0.000) as 
(0.000,0.000) needed. 
(0.000,0.000) Finally 
(0.000,0.000) , 
(0.000,0.000) it 
(0.000,0.000) copies 
(0.000,0.000) the 
(0.000,0.000) imported 
(0.000,0.000) v 
(0.000,0.000) ariables 
(0.000,0.000) back 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) record 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) in- 
(0.000,0.000) terpreter 
(0.000,0.000) state. 
(0.000,0.000) At 
(0.000,0.000) least 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) current 
(0.000,0.000) implementation, 
(0.000,0.000) these 
(0.000,0.000) steps 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) a 
(0.000,0.000) non- 
(0.000,0.000) ne 
(0.000,0.000) gligible 
(0.000,0.000) runtime 
(0.000,0.000) cost, 
(0.000,0.000) so 
(0.000,0.000) minimizing 
(0.000,0.000) the 
(0.000,0.000) numbe 
(0.000,0.000) r 
(0.000,0.000) of 
(0.000,0.000) interpreter 
(0.000,0.000) - 
(0.000,0.000) to-trace 
(0.000,0.000) and 
(0.000,0.000) trac 
(0.000,0.000) e-to-interpreter 
(0.000,0.000) transitions 
(0.000,0.000) is 
(0.000,0.000) essential 
(0.000,0.000) for 
(0.000,0.000) perfor 
(0.000,0.000) - 
(0.000,0.000) mance. 
(0.000,0.000) (see 
(0.000,0.000) also 
(0.000,0.000) Section 
(0.000,0.000) 3.3). 
(0.000,0.000) Our 
(0.000,0.000) e 
(0.000,0.000) xperiments 
(0.000,0.000) (see 
(0.000,0.000) Figure 
(0.000,0.000) 12) 
(0.000,0.000) sho 
(0.000,0.000) w 
(0.000,0.000) that 
(0.000,0.000) for 
(0.000,0.000) programs 
(0.000,0.000) we 
(0.000,0.000) can 
(0.000,0.000) trace 
(0.000,0.000) well 
(0.000,0.000) such 
(0.000,0.000) transiti 
(0.000,0.000) ons 
(0.000,0.000) hap- 
(0.000,0.000) pen 
(0.000,0.000) infrequently 
(0.000,0.000) and 
(0.000,0.000) hence 
(0.000,0.000) do 
(0.000,0.000) not 
(0.000,0.000) contrib 
(0.000,0.000) ute 
(0.000,0.000) significantly 
(0.000,0.000) to 
(0.000,0.000) total 
(0.000,0.000) runtime. 
(0.000,0.000) In 
(0.000,0.000) a 
(0.000,0.000) fe 
(0.000,0.000) w 
(0.000,0.000) programs, 
(0.000,0.000) where 
(0.000,0.000) the 
(0.000,0.000) s 
(0.000,0.000) ystem 
(0.000,0.000) is 
(0.000,0.000) pre 
(0.000,0.000) v 
(0.000,0.000) ented 
(0.000,0.000) from 
(0.000,0.000) recording 
(0.000,0.000) branch 
(0.000,0.000) traces 
(0.000,0.000) for 
(0.000,0.000) hot 
(0.000,0.000) s 
(0.000,0.000) ide 
(0.000,0.000) e 
(0.000,0.000) xits 
(0.000,0.000) by 
(0.000,0.000) aborts, 
(0.000,0.000) this 
(0.000,0.000) cost 
(0.000,0.000) can 
(0.000,0.000) rise 
(0.000,0.000) to 
(0.000,0.000) up 
(0.000,0.000) to 
(0.000,0.000) 10% 
(0.000,0.000) of 
(0.000,0.000) total 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution 
(0.000,0.000) time. 
(0.000,0.000) 6.2 
(0.000,0.000) T 
(0.000,0.000) race 
(0.000,0.000) Stitching 
(0.000,0.000) T 
(0.000,0.000) ransitions 
(0.000,0.000) from 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) to 
(0.000,0.000) a 
(0.000,0.000) branch 
(0.000,0.000) trace 
(0.000,0.000) at 
(0.000,0.000) a 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oid 
(0.000,0.000) the 
(0.000,0.000) costs 
(0.000,0.000) of 
(0.000,0.000) calling 
(0.000,0.000) traces 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) monitor 
(0.000,0.000) , 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) feature 
(0.000,0.000) called 
(0.000,0.000) tr 
(0.000,0.000) ace 
(0.000,0.000) stitc 
(0.000,0.000) hing 
(0.000,0.000) . 
(0.000,0.000) At 
(0.000,0.000) a 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit, 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xiting 
(0.000,0.000) trace 
(0.000,0.000) only 
(0.000,0.000) needs 
(0.000,0.000) to 
(0.000,0.000) write 
(0.000,0.000) li 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) -carried 
(0.000,0.000) v 
(0.000,0.000) alues 
(0.000,0.000) back 
(0.000,0.000) to 
(0.000,0.000) its 
(0.000,0.000) trace 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) record. 
(0.000,0.000) In 
(0.000,0.000) our 
(0.000,0.000) im- 
(0.000,0.000) plementation, 
(0.000,0.000) identical 
(0.000,0.000) type 
(0.000,0.000) maps 
(0.000,0.000) yield 
(0.000,0.000) identical 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) record 
(0.000,0.000) layouts, 
(0.000,0.000) so 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ati 
(0.000,0.000) on 
(0.000,0.000) record 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) reused 
(0.000,0.000) immediately 
(0.000,0.000) by 
(0.000,0.000) the 
(0.000,0.000) branch 
(0.000,0.000) trace. 
(0.000,0.000) In 
(0.000,0.000) programs 
(0.000,0.000) with 
(0.000,0.000) branch 
(0.000,0.000) y 
(0.000,0.000) trace 
(0.000,0.000) trees 
(0.000,0.000) with 
(0.000,0.000) small 
(0.000,0.000) traces, 
(0.000,0.000) trace 
(0.000,0.000) stitching 
(0.000,0.000) has 
(0.000,0.000) a 
(0.000,0.000) noticeable 
(0.000,0.000) cost. 
(0.000,0.000) Although 
(0.000,0.000) writing 
(0.000,0.000) to 
(0.000,0.000) memory 
(0.000,0.000) and 
(0.000,0.000) then 
(0.000,0.000) soon 
(0.000,0.000) reading 
(0.000,0.000) back 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) be 
(0.000,0.000) e 
(0.000,0.000) xpected 
(0.000,0.000) to 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) a 
(0.000,0.000) high 
(0.000,0.000) L1 
(0.000,0.000) cache 
(0.000,0.000) hit 
(0.000,0.000) rate, 
(0.000,0.000) for 
(0.000,0.000) small 
(0.000,0.000) traces 
(0.000,0.000) the 
(0.000,0.000) increased 
(0.000,0.000) instruction 
(0.000,0.000) count 
(0.000,0.000) has 
(0.000,0.000) a 
(0.000,0.000) noticeable 
(0.000,0.000) cost. 
(0.000,0.000) Also, 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) writes 
(0.000,0.000) and 
(0.000,0.000) reads 
(0.000,0.000) are 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) close 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) dynam 
(0.000,0.000) ic 
(0.000,0.000) instruction 
(0.000,0.000) stream, 
(0.000,0.000) we 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) found 
(0.000,0.000) that 
(0.000,0.000) current 
(0.000,0.000) x86 
(0.000,0.000) processors 
(0.000,0.000) often 
(0.000,0.000) incur 
(0.000,0.000) penalties 
(0.000,0.000) of 
(0.000,0.000) 6 
(0.000,0.000) c 
(0.000,0.000) ycles 
(0.000,0.000) or 
(0.000,0.000) more 
(0.000,0.000) (e.g., 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) instructions 
(0.000,0.000) use 
(0.000,0.000) dif 
(0.000,0.000) ferent 
(0.000,0.000) base 
(0.000,0.000) re 
(0.000,0.000) gisters 
(0.000,0.000) with 
(0.000,0.000) equal 
(0.000,0.000) v 
(0.000,0.000) alues, 
(0.000,0.000) the 
(0.000,0.000) processor 
(0.000,0.000) may 
(0.000,0.000) not 
(0.000,0.000) be 
(0.000,0.000) able 
(0.000,0.000) to 
(0.000,0.000) detect 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) addresses 
(0.000,0.000) are 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) right 
(0.000,0.000) a 
(0.000,0.000) w 
(0.000,0.000) ay). 
(0.000,0.000) The 
(0.000,0.000) alternate 
(0.000,0.000) solution 
(0.000,0.000) is 
(0.000,0.000) to 
(0.000,0.000) recompile 
(0.000,0.000) an 
(0.000,0.000) entire 
(0.000,0.000) trace 
(0.000,0.000) tre 
(0.000,0.000) e, 
(0.000,0.000) thus 
(0.000,0.000) achie 
(0.000,0.000) ving 
(0.000,0.000) inter 
(0.000,0.000) -trace 
(0.000,0.000) re 
(0.000,0.000) gister 
(0.000,0.000) allocation 
(0.000,0.000) (10). 
(0.000,0.000) The 
(0.000,0.000) disadv 
(0.000,0.000) antage 
(0.000,0.000) is 
(0.000,0.000) that 
(0.000,0.000) tree 
(0.000,0.000) recompilation 
(0.000,0.000) tak 
(0.000,0.000) es 
(0.000,0.000) time 
(0.000,0.000) quadratic 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) number 
(0.000,0.000) of 
(0.000,0.000) traces. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) belie 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) cost 
(0.000,0.000) of 
(0.000,0.000) recompiling 
(0.000,0.000) a 
(0.000,0.000) trace 
(0.000,0.000) tree 
(0.000,0.000) e 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) time 
(0.000,0.000) a 
(0.000,0.000) branch 
(0.000,0.000) is 
(0.000,0.000) added 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) be 
(0.000,0.000) prohibiti 
(0.000,0.000) v 
(0.000,0.000) e. 
(0.000,0.000) That 
(0.000,0.000) problem 
(0.000,0.000) might 
(0.000,0.000) be 
(0.000,0.000) mitig 
(0.000,0.000) ated 
(0.000,0.000) by 
(0.000,0.000) recompiling 
(0.000,0.000) only 
(0.000,0.000) at 
(0.000,0.000) certain 
(0.000,0.000) points, 
(0.000,0.000) or 
(0.000,0.000) onl 
(0.000,0.000) y 
(0.000,0.000) for 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) hot, 
(0.000,0.000) stable 
(0.000,0.000) trees. 
(0.000,0.000) In 
(0.000,0.000) the 
(0.000,0.000) future, 
(0.000,0.000) multicore 
(0.000,0.000) hardw 
(0.000,0.000) are 
(0.000,0.000) is 
(0.000,0.000) e 
(0.000,0.000) xpected 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) common, 
(0.000,0.000) making 
(0.000,0.000) background 
(0.000,0.000) tree 
(0.000,0.000) recompilation 
(0.000,0.000) attracti 
(0.000,0.000) v 
(0.000,0.000) e. 
(0.000,0.000) In 
(0.000,0.000) a 
(0.000,0.000) closely 
(0.000,0.000) re- 
(0.000,0.000) lated 
(0.000,0.000) project 
(0.000,0.000) (13) 
(0.000,0.000) background 
(0.000,0.000) recompilation 
(0.000,0.000) yielded 
(0.000,0.000) speedups 
(0.000,0.000) of 
(0.000,0.000) up 
(0.000,0.000) to 
(0.000,0.000) 1.25x 
(0.000,0.000) on 
(0.000,0.000) benchmarks 
(0.000,0.000) with 
(0.000,0.000) man 
(0.000,0.000) y 
(0.000,0.000) branch 
(0.000,0.000) traces. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) plan 
(0.000,0.000) to 
(0.000,0.000) apply 
(0.000,0.000) this 
(0.000,0.000) technique 
(0.000,0.000) to 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) as 
(0.000,0.000) future 
(0.000,0.000) w 
(0.000,0.000) ork. 
(0.000,0.000) 6.3 
(0.000,0.000) T 
(0.000,0.000) race 
(0.000,0.000) Recording 
(0.000,0.000) The 
(0.000,0.000) job 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) recorder 
(0.000,0.000) is 
(0.000,0.000) to 
(0.000,0.000) emit 
(0.000,0.000) LIR 
(0.000,0.000) with 
(0.000,0.000) identical 
(0.000,0.000) semantics 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) currently 
(0.000,0.000) running 
(0.000,0.000) interpreter 
(0.000,0.000) bytecode 
(0.000,0.000) trace. 
(0.000,0.000) A 
(0.000,0.000) good 
(0.000,0.000) imple- 
(0.000,0.000) mentation 
(0.000,0.000) should 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) lo 
(0.000,0.000) w 
(0.000,0.000) impact 
(0.000,0.000) on 
(0.000,0.000) non-tracing 
(0.000,0.000) interpreter 
(0.000,0.000) per 
(0.000,0.000) - 
(0.000,0.000) formance 
(0.000,0.000) and 
(0.000,0.000) a 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) enient 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) for 
(0.000,0.000) implementers 
(0.000,0.000) to 
(0.000,0.000) maintain 
(0.000,0.000) se- 
(0.000,0.000) mantic 
(0.000,0.000) equi 
(0.000,0.000) v 
(0.000,0.000) alence. 
(0.000,0.000) In 
(0.000,0.000) our 
(0.000,0.000) implementation, 
(0.000,0.000) the 
(0.000,0.000) only 
(0.000,0.000) direct 
(0.000,0.000) modification 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) call 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) m 
(0.000,0.000) onitor 
(0.000,0.000) at 
(0.000,0.000) loop 
(0.000,0.000) edges. 
(0.000,0.000) In 
(0.000,0.000) our 
(0.000,0.000) benchmark 
(0.000,0.000) results 
(0.000,0.000) (see 
(0.000,0.000) Figure 
(0.000,0.000) 12) 
(0.000,0.000) the 
(0.000,0.000) total 
(0.000,0.000) time 
(0.000,0.000) spent 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) monitor 
(0.000,0.000) (for 
(0.000,0.000) all 
(0.000,0.000) acti 
(0.000,0.000) vities) 
(0.000,0.000) is 
(0.000,0.000) usually 
(0.000,0.000) less 
(0.000,0.000) than 
(0.000,0.000) 5%, 
(0.000,0.000) so 
(0.000,0.000) we 
(0.000,0.000) consider 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) impact 
(0.000,0.000) re 
(0.000,0.000) quirement 
(0.000,0.000) met. 
(0.000,0.000) Increm 
(0.000,0.000) enting 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) hit 
(0.000,0.000) counter 
(0.000,0.000) is 
(0.000,0.000) e 
(0.000,0.000) x- 
(0.000,0.000) pensi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) because 
(0.000,0.000) it 
(0.000,0.000) requires 
(0.000,0.000) us 
(0.000,0.000) to 
(0.000,0.000) look 
(0.000,0.000) up 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) cache, 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) we 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) tuned 
(0.000,0.000) our 
(0.000,0.000) loops 
(0.000,0.000) to 
(0.000,0.000) become 
(0.000,0.000) hot 
(0.000,0.000) and 
(0.000,0.000) trace 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) quickly 
(0.000,0.000) (on 
(0.000,0.000) the 
(0.000,0.000) second 
(0.000,0.000) iteration). 
(0.000,0.000) The 
(0.000,0.000) hit 
(0.000,0.000) counter 
(0.000,0.000) implementation 
(0.000,0.000) could 
(0.000,0.000) be 
(0.000,0.000) impro 
(0.000,0.000) v 
(0.000,0.000) ed, 
(0.000,0.000) which 
(0.000,0.000) might 
(0.000,0.000) gi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) us 
(0.000,0.000) a 
(0.000,0.000) small 
(0.000,0.000) increase 
(0.000,0.000) in 
(0.000,0.000) o 
(0.000,0.000) v 
(0.000,0.000) erall 
(0.000,0.000) perfor 
(0.000,0.000) - 
(0.000,0.000) mance, 
(0.000,0.000) as 
(0.000,0.000) well 
(0.000,0.000) as 
(0.000,0.000) more 
(0.000,0.000) fle 
(0.000,0.000) xibility 
(0.000,0.000) with 
(0.000,0.000) tuning 
(0.000,0.000) hotness 
(0.000,0.000) thresholds. 
(0.000,0.000) Once 
(0.000,0.000) a 
(0.000,0.000) loop 
(0.000,0.000) is 
(0.000,0.000) blacklisted 
(0.000,0.000) we 
(0.000,0.000) ne 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) call 
(0.000,0.000) into 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) monitor 
(0.000,0.000) for 
(0.000,0.000) that 
(0.000,0.000) loop 
(0.000,0.000) (see 
(0.000,0.000) Section 
(0.000,0.000) 3.3). 
(0.000,0.000) Recording 
(0.000,0.000) is 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ated 
(0.000,0.000) by 
(0.000,0.000) a 
(0.000,0.000) pointer 
(0.000,0.000) sw 
(0.000,0.000) ap 
(0.000,0.000) that 
(0.000,0.000) sets 
(0.000,0.000) the 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter’ 
(0.000,0.000) s 
(0.000,0.000) dispatch 
(0.000,0.000) ta 
(0.000,0.000) ble 
(0.000,0.000) to 
(0.000,0.000) call 
(0.000,0.000) a 
(0.000,0.000) single 
(0.000,0.000) “interrupt” 
(0.000,0.000) routine 
(0.000,0.000) for 
(0.000,0.000) e 
(0.000,0.000) v- 
(0.000,0.000) ery 
(0.000,0.000) bytecode. 
(0.000,0.000) The 
(0.000,0.000) interrupt 
(0.000,0.000) routine 
(0.000,0.000) first 
(0.000,0.000) calls 
(0.000,0.000) a 
(0.000,0.000) bytecode-specific 
(0.000,0.000) recording 
(0.000,0.000) routine. 
(0.000,0.000) Then, 
(0.000,0.000) it 
(0.000,0.000) turns 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) recording 
(0.000,0.000) if 
(0.000,0.000) necessary 
(0.000,0.000) (e.g., 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) ended). 
(0.000,0.000) Finally 
(0.000,0.000) , 
(0.000,0.000) it 
(0.000,0.000) jumps 
(0.000,0.000) to 
(0.000,0.000) the 
(0.000,0.000) standard 
(0.000,0.000) interpreter 
(0.000,0.000) byte- 
(0.000,0.000) code 
(0.000,0.000) implementation. 
(0.000,0.000) Some 
(0.000,0.000) bytecodes 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) ef 
(0.000,0.000) fects 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) type 
(0.000,0.000) map 
(0.000,0.000) that 
(0.000,0.000) cannot 
(0.000,0.000) be 
(0.000,0.000) predicted 
(0.000,0.000) before 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecuting 
(0.000,0.000) the 
(0.000,0.000) bytecode 
(0.000,0.000) (e.g., 
(0.000,0.000) call- 
(0.000,0.000) ing 
(0.000,0.000) String.charCodeAt 
(0.000,0.000) , 
(0.000,0.000) which 
(0.000,0.000) returns 
(0.000,0.000) an 
(0.000,0.000) inte 
(0.000,0.000) ger 
(0.000,0.000) or 
(0.000,0.000) NaN 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) inde 
(0.000,0.000) x 
(0.000,0.000) ar 
(0.000,0.000) gument 
(0.000,0.000) is 
(0.000,0.000) out 
(0.000,0.000) of 
(0.000,0.000) range). 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) these, 
(0.000,0.000) we 
(0.000,0.000) arrange 
(0.000,0.000) for 
(0.000,0.000) the 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter 
(0.000,0.000) to 
(0.000,0.000) call 
(0.000,0.000) into 
(0.000,0.000) the 
(0.000,0.000) recorder 
(0.000,0.000) ag 
(0.000,0.000) ain 
(0.000,0.000) after 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecuting 
(0.000,0.000) the 
(0.000,0.000) bytecode. 
(0.000,0.000) Since 
(0.000,0.000) such 
(0.000,0.000) hooks 
(0.000,0.000) are 
(0.000,0.000) relati 
(0.000,0.000) v 
(0.000,0.000) ely 
(0.000,0.000) rare, 
(0.000,0.000) we 
(0.000,0.000) embed 
(0.000,0.000) them 
(0.000,0.000) directly 
(0.000,0.000) into 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) , 
(0.000,0.000) with 
(0.000,0.000) an 
(0.000,0.000) additional 
(0.000,0.000) runtime 
(0.000,0.000) check 
(0.000,0.000) to 
(0.000,0.000) see 
(0.000,0.000) whether 
(0.000,0.000) a 
(0.000,0.000) recorder 
(0.000,0.000) is 
(0.000,0.000) currently 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) e. 
(0.000,0.000) While 
(0.000,0.000) separating 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) recorder 
(0.000,0.000) reduces 
(0.000,0.000) indi- 
(0.000,0.000) vidual 
(0.000,0.000) code 
(0.000,0.000) comple 
(0.000,0.000) xity 
(0.000,0.000) , 
(0.000,0.000) it 
(0.000,0.000) also 
(0.000,0.000) requires 
(0.000,0.000) careful 
(0.000,0.000) implementation 
(0.000,0.000) and 
(0.000,0.000) e 
(0.000,0.000) xtensi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) testing 
(0.000,0.000) to 
(0.000,0.000) achie 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) semantic 
(0.000,0.000) equi 
(0.000,0.000) v 
(0.000,0.000) alence. 
(0.000,0.000) In 
(0.000,0.000) some 
(0.000,0.000) cases 
(0.000,0.000) achie 
(0.000,0.000) ving 
(0.000,0.000) this 
(0.000,0.000) equi 
(0.000,0.000) v 
(0.000,0.000) alence 
(0.000,0.000) is 
(0.000,0.000) dif 
(0.000,0.000) ficult 
(0.000,0.000) since 
(0.000,0.000) Spi- 
(0.000,0.000) derMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) follo 
(0.000,0.000) ws 
(0.000,0.000) a 
(0.000,0.000) fat-bytecode 
(0.000,0.000) design, 
(0.000,0.000) which 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) found 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) beneficial 
(0.000,0.000) to 
(0.000,0.000) pure 
(0.000,0.000) interpreter 
(0.000,0.000) performance. 
(0.000,0.000) In 
(0.000,0.000) f 
(0.000,0.000) at-bytecode 
(0.000,0.000) designs, 
(0.000,0.000) indi 
(0.000,0.000) vidual 
(0.000,0.000) bytecodes 
(0.000,0.000) can 
(0.000,0.000) implement 
(0.000,0.000) comple 
(0.000,0.000) x 
(0.000,0.000) processing 
(0.000,0.000) (e.g., 
(0.000,0.000) the 
(0.000,0.000) getprop 
(0.000,0.000) bytecode, 
(0.000,0.000) which 
(0.000,0.000) imple- 
(0.000,0.000) ments 
(0.000,0.000) full 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) property 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) access, 
(0.000,0.000) including 
(0.000,0.000) s 
(0.000,0.000) pecial 
(0.000,0.000) cases 
(0.000,0.000) for 
(0.000,0.000) cached 
(0.000,0.000) and 
(0.000,0.000) dense 
(0.000,0.000) array 
(0.000,0.000) access). 
(0.000,0.000) F 
(0.000,0.000) at 
(0.000,0.000) bytecodes 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) tw 
(0.000,0.000) o 
(0.000,0.000) adv 
(0.000,0.000) antages: 
(0.000,0.000) fe 
(0.000,0.000) wer 
(0.000,0.000) bytecodes 
(0.000,0.000) means 
(0.000,0.000) lo 
(0.000,0.000) wer 
(0.000,0.000) dispatch 
(0.000,0.000) cost, 
(0.000,0.000) and 
(0.000,0.000) bigger 
(0.000,0.000) bytecode 
(0.000,0.000) impleme 
(0.000,0.000) ntations 
(0.000,0.000) gi 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) compiler 
(0.000,0.000) more 
(0.000,0.000) opportunities 
(0.000,0.000) to 
(0.000,0.000) optimize 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) F 
(0.000,0.000) at 
(0.000,0.000) bytecodes 
(0.000,0.000) are 
(0.000,0.000) a 
(0.000,0.000) problem 
(0.000,0.000) for 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) because 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) require 
(0.000,0.000) the 
(0.000,0.000) recorder 
(0.000,0.000) to 
(0.000,0.000) reimplement 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) special 
(0.000,0.000) c 
(0.000,0.000) ase 
(0.000,0.000) logic 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) . 
(0.000,0.000) Also, 
(0.000,0.000) the 
(0.000,0.000) adv 
(0.000,0.000) antages 
(0.000,0.000) are 
(0.000,0.000) reduced 
(0.000,0.000) because 
(0.000,0.000) (a) 
(0.000,0.000) dispatch 
(0.000,0.000) costs 
(0.000,0.000) are 
(0.000,0.000) eliminated 
(0.000,0.000) entirely 
(0.000,0.000) in 
(0.000,0.000) compiled 
(0.000,0.000) traces, 
(0.000,0.000) (b) 
(0.000,0.000) the 
(0.000,0.000) traces 
(0.000,0.000) contain 
(0.000,0.000) only 
(0.000,0.000) one 
(0.000,0.000) special 
(0.000,0.000) case, 
(0.000,0.000) not 
(0.000,0.000) the 
(0.000,0.000) interpreter’ 
(0.000,0.000) s 
(0.000,0.000) lar 
(0.000,0.000) ge 
(0.000,0.000) chunk 
(0.000,0.000) of 
(0.000,0.000) code, 
(0.000,0.000) and 
(0.000,0.000) (c) 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) spends 
(0.000,0.000) less 
(0.000,0.000) time 
(0.000,0.000) running 
(0.000,0.000) the 
(0.000,0.000) base 
(0.000,0.000) interpreter 
(0.000,0.000) . 
(0.000,0.000) One 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) we 
(0.000,0.000) ha 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) mitig 
(0.000,0.000) ated 
(0.000,0.000) these 
(0.000,0.000) problems 
(0.000,0.000) is 
(0.000,0.000) by 
(0.000,0.000) implementing 
(0.000,0.000) certain 
(0.000,0.000) comple 
(0.000,0.000) x 
(0.000,0.000) bytecodes 
(0.000,0.000) in 
(0.000,0.000) the 
(0.000,0.000) recorder 
(0.000,0.000) as 
(0.000,0.000) sequences 
(0.000,0.000) of 
(0.000,0.000) simple 
(0.000,0.000) bytecodes. 
(0.000,0.000) Expressing 
(0.000,0.000) the 
(0.000,0.000) original 
(0.000,0.000) semantics 
(0.000,0.000) this 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) is 
(0.000,0.000) not 
(0.000,0.000) too 
(0.000,0.000) dif- 
(0.000,0.000) ficult, 
(0.000,0.000) and 
(0.000,0.000) recording 
(0.000,0.000) simple 
(0.000,0.000) bytecodes 
(0.000,0.000) is 
(0.000,0.000) much 
(0.000,0.000) easier 
(0.000,0.000) . 
(0.000,0.000) This 
(0.000,0.000) enables 
(0.000,0.000) us 
(0.000,0.000) to 
(0.000,0.000) retain 
(0.000,0.000) the 
(0.000,0.000) adv 
(0.000,0.000) antages 
(0.000,0.000) of 
(0.000,0.000) f 
(0.000,0.000) at 
(0.000,0.000) bytecodes 
(0.000,0.000) while 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oiding 
(0.000,0.000) some 
(0.000,0.000) of 
(0.000,0.000) their 
(0.000,0.000) problems 
(0.000,0.000) for 
(0.000,0.000) trace 
(0.000,0.000) recording. 
(0.000,0.000) This 
(0.000,0.000) is 
(0.000,0.000) particularly 
(0.000,0.000) ef 
(0.000,0.000) fecti 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) for 
(0.000,0.000) f 
(0.000,0.000) at 
(0.000,0.000) bytecodes 
(0.000,0.000) that 
(0.000,0.000) recurse 
(0.000,0.000) back 
(0.000,0.000) into 
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(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) object, 
(0.000,0.000) since 
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(0.000,0.000) us 
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(0.000,0.000) function 
(0.000,0.000) call. 
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(0.000,0.000) is 
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(0.000,0.000) f 
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(0.000,0.000) codes 
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(0.000,0.000) purely 
(0.000,0.000) interpretati 
(0.000,0.000) v 
(0.000,0.000) ely 
(0.000,0.000) (i.e. 
(0.000,0.000) code 
(0.000,0.000) that 
(0.000,0.000) has 
(0.000,0.000) been 
(0.000,0.000) blacklisted), 
(0.000,0.000) the 
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(0.000,0.000) direct 
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(0.000,0.000) and 
(0.000,0.000) ef- 
(0.000,0.000) ficiently 
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(0.000,0.000) x 
(0.000,0.000) ecutes 
(0.000,0.000) the 
(0.000,0.000) f 
(0.000,0.000) at 
(0.000,0.000) opcodes. 
(0.000,0.000) 6.4 
(0.000,0.000) Pr 
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(0.000,0.000) SpiderMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) , 
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(0.000,0.000) y 
(0.000,0.000) VMs, 
(0.000,0.000) needs 
(0.000,0.000) to 
(0.000,0.000) preempt 
(0.000,0.000) the 
(0.000,0.000) user 
(0.000,0.000) program 
(0.000,0.000) periodically 
(0.000,0.000) . 
(0.000,0.000) The 
(0.000,0.000) main 
(0.000,0.000) reasons 
(0.000,0.000) are 
(0.000,0.000) to 
(0.000,0.000) pre 
(0.000,0.000) v 
(0.000,0.000) ent 
(0.000,0.000) infinitely 
(0.000,0.000) looping 
(0.000,0.000) scripts 
(0.000,0.000) from 
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(0.000,0.000) up 
(0.000,0.000) the 
(0.000,0.000) host 
(0.000,0.000) system 
(0.000,0.000) and 
(0.000,0.000) to 
(0.000,0.000) schedule 
(0.000,0.000) GC. 
(0.000,0.000) In 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) , 
(0.000,0.000) this 
(0.000,0.000) had 
(0.000,0.000) been 
(0.000,0.000) implemented 
(0.000,0.000) by 
(0.000,0.000) setting 
(0.000,0.000) a 
(0.000,0.000) “pre- 
(0.000,0.000) empt 
(0.000,0.000) no 
(0.000,0.000) w” 
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(0.000,0.000) w 
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(0.000,0.000) o 
(0.000,0.000) v 
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(0.000,0.000) y: 
(0.000,0.000) the 
(0.000,0.000) VM 
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(0.000,0.000) a 
(0.000,0.000) guard 
(0.000,0.000) on 
(0.000,0.000) the 
(0.000,0.000) preemption 
(0.000,0.000) flag 
(0.000,0.000) at 
(0.000,0.000) e 
(0.000,0.000) v 
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(0.000,0.000) loop 
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(0.000,0.000) W 
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(0.000,0.000) measured 
(0.000,0.000) less 
(0.000,0.000) than 
(0.000,0.000) a 
(0.000,0.000) 1% 
(0.000,0.000) increase 
(0.000,0.000) in 
(0.000,0.000) runtime 
(0.000,0.000) on 
(0.000,0.000) most 
(0.000,0.000) benchmarks 
(0.000,0.000) for 
(0.000,0.000) this 
(0.000,0.000) e 
(0.000,0.000) xtra 
(0.000,0.000) guard. 
(0.000,0.000) In 
(0.000,0.000) practice, 
(0.000,0.000) the 
(0.000,0.000) cost 
(0.000,0.000) is 
(0.000,0.000) detectable 
(0.000,0.000) only 
(0.000,0.000) for 
(0.000,0.000) programs 
(0.000,0.000) with 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) short 
(0.000,0.000) loops. 
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(0.000,0.000) tested 
(0.000,0.000) and 
(0.000,0.000) rejected 
(0.000,0.000) a 
(0.000,0.000) solution 
(0.000,0.000) that 
(0.000,0.000) a 
(0.000,0.000) v 
(0.000,0.000) oided 
(0.000,0.000) the 
(0.000,0.000) guards 
(0.000,0.000) by 
(0.000,0.000) compiling 
(0.000,0.000) the 
(0.000,0.000) loop 
(0.000,0.000) edge 
(0.000,0.000) as 
(0.000,0.000) a 
(0.000,0.000) n 
(0.000,0.000) unconditional 
(0.000,0.000) jump, 
(0.000,0.000) and 
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(0.000,0.000) the 
(0.000,0.000) jump 
(0.000,0.000) tar 
(0.000,0.000) get 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) routine 
(0.000,0.000) when 
(0.000,0.000) preemption 
(0.000,0.000) is 
(0.000,0.000) required. 
(0.000,0.000) This 
(0.000,0.000) solution 
(0.000,0.000) can 
(0.000,0.000) mak 
(0.000,0.000) e 
(0.000,0.000) the 
(0.000,0.000) normal 
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(0.000,0.000) f 
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(0.000,0.000) , 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) then 
(0.000,0.000) preemption 
(0.000,0.000) becomes 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) slo 
(0.000,0.000) w 
(0.000,0.000) . 
(0.000,0.000) The 
(0.000,0.000) implementation 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) also 
(0.000,0.000) v 
(0.000,0.000) ery 
(0.000,0.000) comple 
(0.000,0.000) x, 
(0.000,0.000) especially 
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(0.000,0.000) to 
(0.000,0.000) restart 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution 
(0.000,0.000) after 
(0.000,0.000) the 
(0.000,0.000) preemption. 
(0.000,0.000) 6.5 
(0.000,0.000) Calling 
(0.000,0.000) Exter 
(0.000,0.000) nal 
(0.000,0.000) Functions 
(0.000,0.000) Lik 
(0.000,0.000) e 
(0.000,0.000) most 
(0.000,0.000) interpreters, 
(0.000,0.000) SpiderMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) has 
(0.000,0.000) a 
(0.000,0.000) foreign 
(0.000,0.000) function 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) f 
(0.000,0.000) ace 
(0.000,0.000) (FFI) 
(0.000,0.000) that 
(0.000,0.000) allo 
(0.000,0.000) ws 
(0.000,0.000) it 
(0.000,0.000) to 
(0.000,0.000) call 
(0.000,0.000) C 
(0.000,0.000) b 
(0.000,0.000) uiltins 
(0.000,0.000) and 
(0.000,0.000) host 
(0.000,0.000) system 
(0.000,0.000) functions 
(0.000,0.000) (e.g., 
(0.000,0.000) web 
(0.000,0.000) bro 
(0.000,0.000) wser 
(0.000,0.000) control 
(0.000,0.000) and 
(0.000,0.000) DOM 
(0.000,0.000) access). 
(0.000,0.000) The 
(0.000,0.000) FFI 
(0.000,0.000) has 
(0.000,0.000) a 
(0.000,0.000) stan- 
(0.000,0.000) dard 
(0.000,0.000) signat 
(0.000,0.000) ure 
(0.000,0.000) for 
(0.000,0.000) JS-callable 
(0.000,0.000) functions, 
(0.000,0.000) the 
(0.000,0.000) k 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) ar 
(0.000,0.000) gument 
(0.000,0.000) of 
(0.000,0.000) which 
(0.000,0.000) is 
(0.000,0.000) an 
(0.000,0.000) array 
(0.000,0.000) of 
(0.000,0.000) box 
(0.000,0.000) ed 
(0.000,0.000) v 
(0.000,0.000) alues. 
(0.000,0.000) External 
(0.000,0.000) functions 
(0.000,0.000) called 
(0.000,0.000) through 
(0.000,0.000) the 
(0.000,0.000) FFI 
(0.000,0.000) interact 
(0.000,0.000) with 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) state 
(0.000,0.000) through 
(0.000,0.000) an 
(0.000,0.000) interpreter 
(0.000,0.000) API 
(0.000,0.000) (e.g., 
(0.000,0.000) to 
(0.000,0.000) read 
(0.000,0.000) a 
(0.000,0.000) property 
(0.000,0.000) from 
(0.000,0.000) an 
(0.000,0.000) ar 
(0.000,0.000) gument). 
(0.000,0.000) There 
(0.000,0.000) are 
(0.000,0.000) also 
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(0.000,0.000) b 
(0.000,0.000) uiltins 
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(0.000,0.000) do 
(0.000,0.000) not 
(0.000,0.000) use 
(0.000,0.000) the 
(0.000,0.000) FFI, 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) interact 
(0.000,0.000) with 
(0.000,0.000) the 
(0.000,0.000) program 
(0.000,0.000) state 
(0.000,0.000) i 
(0.000,0.000) n 
(0.000,0.000) the 
(0.000,0.000) same 
(0.000,0.000) w 
(0.000,0.000) ay 
(0.000,0.000) , 
(0.000,0.000) such 
(0.000,0.000) as 
(0.000,0.000) the 
(0.000,0.000) CallIteratorNext 
(0.000,0.000) function 
(0.000,0.000) used 
(0.000,0.000) with 
(0.000,0.000) it 
(0.000,0.000) erator 
(0.000,0.000) objects. 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) must 
(0.000,0.000) support 
(0.000,0.000) this 
(0.000,0.000) FFI 
(0.000,0.000) in 
(0.000,0.000) order 
(0.000,0.000) to 
(0.000,0.000) speed 
(0.000,0.000) up 
(0.000,0.000) code 
(0.000,0.000) that 
(0.000,0.000) interacts 
(0.000,0.000) with 
(0.000,0.000) the 
(0.000,0.000) host 
(0.000,0.000) system 
(0.000,0.000) inside 
(0.000,0.000) hot 
(0.000,0.000) loops. 
(0.000,0.000) Calling 
(0.000,0.000) e 
(0.000,0.000) xternal 
(0.000,0.000) functions 
(0.000,0.000) from 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
(0.000,0.000) y 
(0.000,0.000) is 
(0.000,0.000) potentially 
(0.000,0.000) dif- 
(0.000,0.000) ficult 
(0.000,0.000) because 
(0.000,0.000) trac 
(0.000,0.000) es 
(0.000,0.000) do 
(0.000,0.000) not 
(0.000,0.000) update 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) state 
(0.000,0.000) until 
(0.000,0.000) e 
(0.000,0.000) xit- 
(0.000,0.000) ing. 
(0.000,0.000) In 
(0.000,0.000) particular 
(0.000,0.000) , 
(0.000,0.000) e 
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(0.000,0.000) functions 
(0.000,0.000) may 
(0.000,0.000) need 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) or 
(0.000,0.000) the 
(0.000,0.000) global 
(0.000,0.000) v 
(0.000,0.000) ariables, 
(0.000,0.000) b 
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(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) may 
(0.000,0.000) be 
(0.000,0.000) out 
(0.000,0.000) of 
(0.000,0.000) date. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) the 
(0.000,0.000) out-of-date 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) problem, 
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(0.000,0.000) re 
(0.000,0.000) f 
(0.000,0.000) actored 
(0.000,0.000) some 
(0.000,0.000) of 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) API 
(0.000,0.000) implementation 
(0.000,0.000) functions 
(0.000,0.000) to 
(0.000,0.000) re-materialize 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) on 
(0.000,0.000) demand. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) de 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) loped 
(0.000,0.000) a 
(0.000,0.000) C++ 
(0.000,0.000) static 
(0.000,0.000) analysis 
(0.000,0.000) and 
(0.000,0.000) annotated 
(0.000,0.000) some 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter 
(0.000,0.000) funct 
(0.000,0.000) ions 
(0.000,0.000) in 
(0.000,0.000) order 
(0.000,0.000) to 
(0.000,0.000) v 
(0.000,0.000) erify 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) is 
(0.000,0.000) refreshed 
(0.000,0.000) at 
(0.000,0.000) an 
(0.000,0.000) y 
(0.000,0.000) point 
(0.000,0.000) it 
(0.000,0.000) needs 
(0.000,0.000) to 
(0.000,0.000) be 
(0.000,0.000) used. 
(0.000,0.000) In 
(0.000,0.000) order 
(0.000,0.000) to 
(0.000,0.000) access 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack, 
(0.000,0.000) a 
(0.000,0.000) function 
(0.000,0.000) must 
(0.000,0.000) be 
(0.000,0.000) annotated 
(0.000,0.000) as 
(0.000,0.000) either 
(0.000,0.000) F 
(0.000,0.000) O 
(0.000,0.000) R 
(0.000,0.000) C 
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(0.000,0.000) S 
(0.000,0.000) S 
(0.000,0.000) T 
(0.000,0.000) A 
(0.000,0.000) C 
(0.000,0.000) K 
(0.000,0.000) or 
(0.000,0.000) R 
(0.000,0.000) E 
(0.000,0.000) - 
(0.000,0.000) Q 
(0.000,0.000) U 
(0.000,0.000) I 
(0.000,0.000) R 
(0.000,0.000) E 
(0.000,0.000) S 
(0.000,0.000) S 
(0.000,0.000) T 
(0.000,0.000) A 
(0.000,0.000) C 
(0.000,0.000) K 
(0.000,0.000) . 
(0.000,0.000) These 
(0.000,0.000) annotations 
(0.000,0.000) are 
(0.000,0.000) also 
(0.000,0.000) required 
(0.000,0.000) i 
(0.000,0.000) n 
(0.000,0.000) order 
(0.000,0.000) to 
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(0.000,0.000) R 
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(0.000,0.000) T 
(0.000,0.000) A 
(0.000,0.000) C 
(0.000,0.000) K 
(0.000,0.000) functions, 
(0.000,0.000) which 
(0.000,0.000) are 
(0.000,0.000) presumed 
(0.000,0.000) to 
(0.000,0.000) access 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) transi 
(0.000,0.000) ti 
(0.000,0.000) v 
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(0.000,0.000) S 
(0.000,0.000) S 
(0.000,0.000) T 
(0.000,0.000) A 
(0.000,0.000) C 
(0.000,0.000) K 
(0.000,0.000) is 
(0.000,0.000) a 
(0.000,0.000) trusted 
(0.000,0.000) annotation, 
(0.000,0.000) applied 
(0.000,0.000) to 
(0.000,0.000) only 
(0.000,0.000) 5 
(0.000,0.000) functions, 
(0.000,0.000) that 
(0.000,0.000) means 
(0.000,0.000) the 
(0.000,0.000) function 
(0.000,0.000) refreshes 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack. 
(0.000,0.000) R 
(0.000,0.000) E 
(0.000,0.000) Q 
(0.000,0.000) U 
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(0.000,0.000) T 
(0.000,0.000) A 
(0.000,0.000) C 
(0.000,0.000) K 
(0.000,0.000) is 
(0.000,0.000) an 
(0.000,0.000) untrusted 
(0.000,0.000) annotation 
(0.000,0.000) that 
(0.000,0.000) means 
(0.000,0.000) the 
(0.000,0.000) func- 
(0.000,0.000) tion 
(0.000,0.000) may 
(0.000,0.000) only 
(0.000,0.000) be 
(0.000,0.000) called 
(0.000,0.000) if 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) has 
(0.000,0.000) already 
(0.000,0.000) been 
(0.000,0.000) refreshed. 
(0.000,0.000) Similarly 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) detect 
(0.000,0.000) when 
(0.000,0.000) host 
(0.000,0.000) functions 
(0.000,0.000) attem 
(0.000,0.000) pt 
(0.000,0.000) to 
(0.000,0.000) directly 
(0.000,0.000) read 
(0.000,0.000) or 
(0.000,0.000) write 
(0.000,0.000) global 
(0.000,0.000) v 
(0.000,0.000) ariables, 
(0.000,0.000) and 
(0.000,0.000) force 
(0.000,0.000) the 
(0.000,0.000) currently 
(0.000,0.000) running 
(0.000,0.000) trace 
(0.000,0.000) to 
(0.000,0.000) side 
(0.000,0.000) e 
(0.000,0.000) xit. 
(0.000,0.000) This 
(0.000,0.000) is 
(0.000,0.000) necessary 
(0.000,0.000) since 
(0.000,0.000) we 
(0.000,0.000) cache 
(0.000,0.000) and 
(0.000,0.000) unbox 
(0.000,0.000) global 
(0.000,0.000) v 
(0.000,0.000) ariables 
(0.000,0.000) into 
(0.000,0.000) the 
(0.000,0.000) acti 
(0.000,0.000) v 
(0.000,0.000) ation 
(0.000,0.000) record 
(0.000,0.000) during 
(0.000,0.000) trace 
(0.000,0.000) e 
(0.000,0.000) x 
(0.000,0.000) ecution. 
(0.000,0.000) Since 
(0.000,0.000) both 
(0.000,0.000) call-stack 
(0.000,0.000) access 
(0.000,0.000) and 
(0.000,0.000) global 
(0.000,0.000) v 
(0.000,0.000) ariable 
(0.000,0.000) access 
(0.000,0.000) are 
(0.000,0.000) rarely 
(0.000,0.000) performed 
(0.000,0.000) by 
(0.000,0.000) host 
(0.000,0.000) functions, 
(0.000,0.000) performance 
(0.000,0.000) is 
(0.000,0.000) not 
(0.000,0.000) significantly 
(0.000,0.000) af 
(0.000,0.000) fected 
(0.000,0.000) by 
(0.000,0.000) these 
(0.000,0.000) safety 
(0.000,0.000) mechanisms. 
(0.000,0.000) Another 
(0.000,0.000) problem 
(0.000,0.000) is 
(0.000,0.000) that 
(0.000,0.000) e 
(0.000,0.000) xternal 
(0.000,0.000) functions 
(0.000,0.000) can 
(0.000,0.000) ree 
(0.000,0.000) nter 
(0.000,0.000) the 
(0.000,0.000) inter 
(0.000,0.000) - 
(0.000,0.000) preter 
(0.000,0.000) by 
(0.000,0.000) calling 
(0.000,0.000) scripts, 
(0.000,0.000) which 
(0.000,0.000) in 
(0.000,0.000) turn 
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(0.000,0.000) ain 
(0.000,0.000) m 
(0.000,0.000) ight 
(0.000,0.000) w 
(0.000,0.000) ant 
(0.000,0.000) to 
(0.000,0.000) access 
(0.000,0.000) the 
(0.000,0.000) call 
(0.000,0.000) stack 
(0.000,0.000) or 
(0.000,0.000) global 
(0.000,0.000) v 
(0.000,0.000) ariables. 
(0.000,0.000) T 
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(0.000,0.000) address 
(0.000,0.000) this 
(0.000,0.000) problem, 
(0.000,0.000) we 
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(0.000,0.000) the 
(0.000,0.000) VM 
(0.000,0.000) set 
(0.000,0.000) a 
(0.000,0.000) flag 
(0.000,0.000) whene 
(0.000,0.000) v 
(0.000,0.000) er 
(0.000,0.000) the 
(0.000,0.000) interpreter 
(0.000,0.000) is 
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(0.000,0.000) while 
(0.000,0.000) a 
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(0.000,0.000) piled 
(0.000,0.000) trace 
(0.000,0.000) is 
(0.000,0.000) running. 
(0.000,0.000) Ev 
(0.000,0.000) ery 
(0.000,0.000) call 
(0.000,0.000) to 
(0.000,0.000) an 
(0.000,0.000) e 
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(0.000,0.000) function 
(0.000,0.000) then 
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(0.000,0.000) this 
(0.000,0.000) flag 
(0.000,0.000) and 
(0.000,0.000) e 
(0.000,0.000) xits 
(0.000,0.000) the 
(0.000,0.000) trace 
(0.000,0.000) immediately 
(0.000,0.000) after 
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(0.000,0.000) from 
(0.000,0.000) the 
(0.000,0.000) e 
(0.000,0.000) xternal 
(0.000,0.000) function 
(0.000,0.000) call 
(0.000,0.000) if 
(0.000,0.000) it 
(0.000,0.000) is 
(0.000,0.000) set. 
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(0.000,0.000) are 
(0.000,0.000) man 
(0.000,0.000) y 
(0.000,0.000) e 
(0.000,0.000) xternal 
(0.000,0.000) functions 
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(0.000,0.000) hat 
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(0.000,0.000) or 
(0.000,0.000) ne 
(0.000,0.000) v 
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(0.000,0.000) , 
(0.000,0.000) and 
(0.000,0.000) the 
(0.000,0.000) y 
(0.000,0.000) can 
(0.000,0.000) be 
(0.000,0.000) called 
(0.000,0.000) without 
(0.000,0.000) problem, 
(0.000,0.000) and 
(0.000,0.000) will 
(0.000,0.000) cause 
(0.000,0.000) trace 
(0.000,0.000) e 
(0.000,0.000) xit 
(0.000,0.000) only 
(0.000,0.000) if 
(0.000,0.000) necessary 
(0.000,0.000) . 
(0.000,0.000) The 
(0.000,0.000) FFI’ 
(0.000,0.000) s 
(0.000,0.000) box 
(0.000,0.000) ed 
(0.000,0.000) v 
(0.000,0.000) alue 
(0.000,0.000) array 
(0.000,0.000) requirement 
(0.000,0.000) has 
(0.000,0.000) a 
(0.000,0.000) performance 
(0.000,0.000) cost, 
(0.000,0.000) so 
(0.000,0.000) we 
(0.000,0.000) defined 
(0.000,0.000) a 
(0.000,0.000) ne 
(0.000,0.000) w 
(0.000,0.000) FFI 
(0.000,0.000) that 
(0.000,0.000) allo 
(0.000,0.000) w 
(0.000,0.000) s 
(0.000,0.000) C 
(0.000,0.000) functions 
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(0.000,0.000) notated 
(0.000,0.000) with 
(0.000,0.000) their 
(0.000,0.000) ar 
(0.000,0.000) gument 
(0.000,0.000) types 
(0.000,0.000) so 
(0.000,0.000) that 
(0.000,0.000) the 
(0.000,0.000) tracer 
(0.000,0.000) can 
(0.000,0.000) call 
(0.000,0.000) them 
(0.000,0.000) directly 
(0.000,0.000) , 
(0.000,0.000) without 
(0.000,0.000) unnecessary 
(0.000,0.000) ar 
(0.000,0.000) gument 
(0.000,0.000) con 
(0.000,0.000) v 
(0.000,0.000) ersions. 
(0.000,0.000) Currently 
(0.000,0.000) , 
(0.000,0.000) we 
(0.000,0.000) do 
(0.000,0.000) not 
(0.000,0.000) support 
(0.000,0.000) calling 
(0.000,0.000) nati 
(0.000,0.000) v 
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(0.000,0.000) o 
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(0.000,0.000) functions 
(0.000,0.000) or 
(0.000,0.000) DOM 
(0.000,0.000) functions 
(0.000,0.000) directly 
(0.000,0.000) from 
(0.000,0.000) trace. 
(0.000,0.000) Support 
(0.000,0.000) is 
(0.000,0.000) planned 
(0.000,0.000) future 
(0.000,0.000) w 
(0.000,0.000) ork. 
(0.000,0.000) 6.6 
(0.000,0.000) Corr 
(0.000,0.000) ectness 
(0.000,0.000) During 
(0.000,0.000) de 
(0.000,0.000) v 
(0.000,0.000) elopment, 
(0.000,0.000) we 
(0.000,0.000) had 
(0.000,0.000) access 
(0.000,0.000) to 
(0.000,0.000) e 
(0.000,0.000) xisting 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) test 
(0.000,0.000) suites, 
(0.000,0.000) b 
(0.000,0.000) ut 
(0.000,0.000) most 
(0.000,0.000) of 
(0.000,0.000) them 
(0.000,0.000) were 
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(0.000,0.000) tracing 
(0.000,0.000) VMs 
(0.000,0.000) in 
(0.000,0.000) mind 
(0.000,0.000) and 
(0.000,0.000) contained 
(0.000,0.000) fe 
(0.000,0.000) w 
(0.000,0.000) loops. 
(0.000,0.000) One 
(0.000,0.000) tool 
(0.000,0.000) that 
(0.000,0.000) helped 
(0.000,0.000) us 
(0.000,0.000) greatly 
(0.000,0.000) w 
(0.000,0.000) as 
(0.000,0.000) Mozilla’ 
(0.000,0.000) s 
(0.000,0.000) Ja 
(0.000,0.000) v 
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(0.000,0.000) Z 
(0.000,0.000) Z 
(0.000,0.000) , 
(0.000,0.000) which 
(0.000,0.000) generates 
(0.000,0.000) random 
(0.000,0.000) Ja 
(0.000,0.000) v 
(0.000,0.000) aScript 
(0.000,0.000) programs 
(0.000,0.000) by 
(0.000,0.000) nesting 
(0.000,0.000) random 
(0.000,0.000) language 
(0.000,0.000) elements. 
(0.000,0.000) W 
(0.000,0.000) e 
(0.000,0.000) modified 
(0.000,0.000) J 
(0.000,0.000) S 
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(0.000,0.000) Z 
(0.000,0.000) Z 
(0.000,0.000) to 
(0.000,0.000) generate 
(0.000,0.000) loops, 
(0.000,0.000) and 
(0.000,0.000) also 
(0.000,0.000) to 
(0.000,0.000) test 
(0.000,0.000) more 
(0.000,0.000) hea 
(0.000,0.000) vily 
(0.000,0.000) certain 
(0.000,0.000) constructs 
(0.000,0.000) we 
(0.000,0.000) suspected 
(0.000,0.000) w 
(0.000,0.000) ould 
(0.000,0.000) re 
(0.000,0.000) v 
(0.000,0.000) eal 
(0.000,0.000) fla 
(0.000,0.000) ws 
(0.000,0.000) in 
(0.000,0.000) our 
(0.000,0.000) implementation. 
(0.000,0.000) F 
(0.000,0.000) or 
(0.000,0.000) e 
(0.000,0.000) xam- 
(0.000,0.000) ple, 
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(0.000,0.000) suspected 
(0.000,0.000) b 
(0.000,0.000) ugs 
(0.000,0.000) in 
(0.000,0.000) T 
(0.000,0.000) raceMonk 
(0.000,0.000) e 
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(0.000,0.000) s 
(0.000,0.000) handling 
(0.000,0.000) of 
(0.000,0.000) type-unstable 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 11. 
(0.164,239.103) Fraction 
(0.164,239.103) of 
(0.164,239.103) dynamic 
(0.164,239.103) bytecodes 
(0.164,239.103) executed 
(0.164,239.103) by 
(0.164,239.103) inter 
(0.164,239.103) - 
(0.164,239.103) pr 
(0.164,239.103) eter 
(0.164,239.103) and 
(0.164,239.103) on 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) traces. 
(0.164,239.103) The 
(0.164,239.103) speedup 
(0.164,239.103) vs. 
(0.164,239.103) interpreter 
(0.164,239.103) is 
(0.164,239.103) sho 
(0.164,239.103) wn 
(0.164,239.103) in 
(0.164,239.103) parentheses 
(0.164,239.103) ne 
(0.164,239.103) xt 
(0.164,239.103) to 
(0.164,239.103) each 
(0.164,239.103) test. 
(0.164,239.103) The 
(0.164,239.103) fraction 
(0.164,239.103) of 
(0.164,239.103) bytecodes 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) e- 
(0.164,239.103) cuted 
(0.164,239.103) whil 
(0.164,239.103) e 
(0.164,239.103) recording 
(0.164,239.103) is 
(0.164,239.103) too 
(0.164,239.103) small 
(0.164,239.103) to 
(0.164,239.103) see 
(0.164,239.103) in 
(0.164,239.103) this 
(0.164,239.103) figure, 
(0.164,239.103) e 
(0.164,239.103) xcept 
(0.164,239.103) for 
(0.164,239.103) crypto-md5 
(0.164,239.103) , 
(0.164,239.103) where 
(0.164,239.103) fully 
(0.164,239.103) 3% 
(0.164,239.103) of 
(0.164,239.103) bytecodes 
(0.164,239.103) are 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecuted 
(0.164,239.103) while 
(0.164,239.103) recording. 
(0.164,239.103) In 
(0.164,239.103) most 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) test 
(0.164,239.103) s, 
(0.164,239.103) almost 
(0.164,239.103) all 
(0.164,239.103) the 
(0.164,239.103) bytecodes 
(0.164,239.103) are 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) e- 
(0.164,239.103) cuted 
(0.164,239.103) by 
(0.164,239.103) compiled 
(0.164,239.103) traces. 
(0.164,239.103) Three 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) benchmarks 
(0.164,239.103) are 
(0.164,239.103) not 
(0.164,239.103) traced 
(0.164,239.103) at 
(0.164,239.103) all 
(0.164,239.103) and 
(0.164,239.103) run 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) interpreter 
(0.164,239.103) . 
(0.164,239.103) loops 
(0.164,239.103) and 
(0.164,239.103) hea 
(0.164,239.103) vily 
(0.164,239.103) branching 
(0.164,239.103) code, 
(0.164,239.103) and 
(0.164,239.103) a 
(0.164,239.103) specialized 
(0.164,239.103) fuzz 
(0.164,239.103) tester 
(0.164,239.103) in- 
(0.164,239.103) deed 
(0.164,239.103) re 
(0.164,239.103) v 
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(0.164,239.103) se 
(0.164,239.103) v 
(0.164,239.103) eral 
(0.164,239.103) re 
(0.164,239.103) gressions 
(0.164,239.103) which 
(0.164,239.103) we 
(0.164,239.103) subsequently 
(0.164,239.103) corrected. 
(0.164,239.103) 7. 
(0.164,239.103) Ev 
(0.164,239.103) aluation 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) e 
(0.164,239.103) v 
(0.164,239.103) aluated 
(0.164,239.103) our 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) tracing 
(0.164,239.103) implementation 
(0.164,239.103) using 
(0.164,239.103) Sun- 
(0.164,239.103) Spider 
(0.164,239.103) , 
(0.164,239.103) the 
(0.164,239.103) indus 
(0.164,239.103) try 
(0.164,239.103) standard 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) benchmark 
(0.164,239.103) suite. 
(0.164,239.103) SunSpi- 
(0.164,239.103) der 
(0.164,239.103) consists 
(0.164,239.103) of 
(0.164,239.103) 26 
(0.164,239.103) short-running 
(0.164,239.103) (less 
(0.164,239.103) than 
(0.164,239.103) 250ms, 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) era 
(0.164,239.103) ge 
(0.164,239.103) 26ms) 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) programs. 
(0.164,239.103) This 
(0.164,239.103) is 
(0.164,239.103) in 
(0.164,239.103) stark 
(0.164,239.103) contrast 
(0.164,239.103) to 
(0.164,239.103) benchmark 
(0.164,239.103) suites 
(0.164,239.103) such 
(0.164,239.103) as 
(0.164,239.103) SpecJVM98 
(0.164,239.103) (3) 
(0.164,239.103) used 
(0.164,239.103) to 
(0.164,239.103) e 
(0.164,239.103) v 
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(0.164,239.103) desktop 
(0.164,239.103) and 
(0.164,239.103) serv 
(0.164,239.103) er 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) a 
(0.164,239.103) VMs. 
(0.164,239.103) Man 
(0.164,239.103) y 
(0.164,239.103) programs 
(0.164,239.103) in 
(0.164,239.103) those 
(0.164,239.103) benchmarks 
(0.164,239.103) use 
(0.164,239.103) lar 
(0.164,239.103) ge 
(0.164,239.103) data 
(0.164,239.103) sets 
(0.164,239.103) and 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecute 
(0.164,239.103) for 
(0.164,239.103) minutes. 
(0.164,239.103) The 
(0.164,239.103) SunSpider 
(0.164,239.103) programs 
(0.164,239.103) carry 
(0.164,239.103) out 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) ariety 
(0.164,239.103) of 
(0.164,239.103) tasks, 
(0.164,239.103) primarily 
(0.164,239.103) 3d 
(0.164,239.103) rendering, 
(0.164,239.103) bit-bashing, 
(0.164,239.103) cryptographic 
(0.164,239.103) encoding, 
(0.164,239.103) math 
(0.164,239.103) k 
(0.164,239.103) ernels, 
(0.164,239.103) and 
(0.164,239.103) string 
(0.164,239.103) processing. 
(0.164,239.103) All 
(0.164,239.103) e 
(0.164,239.103) xperiments 
(0.164,239.103) were 
(0.164,239.103) performed 
(0.164,239.103) on 
(0.164,239.103) a 
(0.164,239.103) MacBook 
(0.164,239.103) Pro 
(0.164,239.103) with 
(0.164,239.103) 2.2 
(0.164,239.103) GHz 
(0.164,239.103) Core 
(0.164,239.103) 2 
(0.164,239.103) processor 
(0.164,239.103) and 
(0.164,239.103) 2 
(0.164,239.103) GB 
(0.164,239.103) RAM 
(0.164,239.103) running 
(0.164,239.103) MacOS 
(0.164,239.103) 10.5. 
(0.164,239.103) Benchmark 
(0.164,239.103) r 
(0.164,239.103) esults. 
(0.164,239.103) The 
(0.164,239.103) main 
(0.164,239.103) question 
(0.164,239.103) is 
(0.164,239.103) whether 
(0.164,239.103) programs 
(0.164,239.103) run 
(0.164,239.103) f 
(0.164,239.103) aster 
(0.164,239.103) with 
(0.164,239.103) tracing. 
(0.164,239.103) F 
(0.164,239.103) or 
(0.164,239.103) this, 
(0.164,239.103) we 
(0.164,239.103) ran 
(0.164,239.103) the 
(0.164,239.103) standard 
(0.164,239.103) SunSpider 
(0.164,239.103) test 
(0.164,239.103) dri 
(0.164,239.103) v 
(0.164,239.103) er 
(0.164,239.103) , 
(0.164,239.103) which 
(0.164,239.103) starts 
(0.164,239.103) a 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) interpreter 
(0.164,239.103) , 
(0.164,239.103) loads 
(0.164,239.103) and 
(0.164,239.103) runs 
(0.164,239.103) each 
(0.164,239.103) program 
(0.164,239.103) once 
(0.164,239.103) for 
(0.164,239.103) w 
(0.164,239.103) armup, 
(0.164,239.103) then 
(0.164,239.103) loads 
(0.164,239.103) and 
(0.164,239.103) runs 
(0.164,239.103) each 
(0.164,239.103) program 
(0.164,239.103) 10 
(0.164,239.103) times 
(0.164,239.103) and 
(0.164,239.103) reports 
(0.164,239.103) the 
(0.164,239.103) a 
(0.164,239.103) v 
(0.164,239.103) erage 
(0.164,239.103) time 
(0.164,239.103) tak 
(0.164,239.103) en 
(0.164,239.103) by 
(0.164,239.103) each. 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) ran 
(0.164,239.103) 4 
(0.164,239.103) dif 
(0.164,239.103) fer 
(0.164,239.103) - 
(0.164,239.103) ent 
(0.164,239.103) configurations 
(0.164,239.103) for 
(0.164,239.103) comparison: 
(0.164,239.103) (a) 
(0.164,239.103) SpiderMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) , 
(0.164,239.103) the 
(0.164,239.103) baseline 
(0.164,239.103) interpreter 
(0.164,239.103) , 
(0.164,239.103) (b) 
(0.164,239.103) T 
(0.164,239.103) raceMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) , 
(0.164,239.103) (d) 
(0.164,239.103) SquirrelFish 
(0.164,239.103) Extreme 
(0.164,239.103) (SFX), 
(0.164,239.103) the 
(0.164,239.103) call-threaded 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) interpreter 
(0.164,239.103) used 
(0.164,239.103) in 
(0.164,239.103) Apple’ 
(0.164,239.103) s 
(0.164,239.103) W 
(0.164,239.103) ebKit, 
(0.164,239.103) and 
(0.164,239.103) (e) 
(0.164,239.103) V8, 
(0.164,239.103) the 
(0.164,239.103) method-compiling 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) VM 
(0.164,239.103) from 
(0.164,239.103) Google. 
(0.164,239.103) Figure 
(0.164,239.103) 10 
(0.164,239.103) sho 
(0.164,239.103) ws 
(0.164,239.103) the 
(0.164,239.103) relati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) speedups 
(0.164,239.103) achie 
(0.164,239.103) v 
(0.164,239.103) ed 
(0.164,239.103) by 
(0.164,239.103) tracing, 
(0.164,239.103) SFX, 
(0.164,239.103) and 
(0.164,239.103) V8 
(0.164,239.103) ag 
(0.164,239.103) ainst 
(0.164,239.103) the 
(0.164,239.103) baseline 
(0.164,239.103) (SpiderMonk 
(0.164,239.103) e 
(0.164,239.103) y). 
(0.164,239.103) T 
(0.164,239.103) racing 
(0.164,239.103) achie 
(0.164,239.103) v 
(0.164,239.103) es 
(0.164,239.103) the 
(0.164,239.103) best 
(0.164,239.103) speedups 
(0.164,239.103) in 
(0.164,239.103) inte 
(0.164,239.103) ger 
(0.164,239.103) -hea 
(0.164,239.103) vy 
(0.164,239.103) be 
(0.164,239.103) nchmarks, 
(0.164,239.103) up 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) 25x 
(0.164,239.103) speedup 
(0.164,239.103) on 
(0.164,239.103) bitops-bitwise-and 
(0.164,239.103) . 
(0.164,239.103) T 
(0.164,239.103) raceMonk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) is 
(0.164,239.103) the 
(0.164,239.103) f 
(0.164,239.103) astest 
(0.164,239.103) VM 
(0.164,239.103) on 
(0.164,239.103) 9 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) 26 
(0.164,239.103) benchmarks 
(0.164,239.103) ( 
(0.164,239.103) 3d-morph 
(0.164,239.103) , 
(0.164,239.103) bitops-3bit-bits-in-byte 
(0.164,239.103) , 
(0.164,239.103) bitops-bitwise- 
(0.164,239.103) and 
(0.164,239.103) , 
(0.164,239.103) crypto-sha1 
(0.164,239.103) , 
(0.164,239.103) math-cordic 
(0.164,239.103) , 
(0.164,239.103) math-partial-sums 
(0.164,239.103) , 
(0.164,239.103) math- 
(0.164,239.103) spectral-norm 
(0.164,239.103) , 
(0.164,239.103) string-base64 
(0.164,239.103) , 
(0.164,239.103) string-validate-input 
(0.164,239.103) ). 
(0.164,502.117) Figur 
(0.164,502.117) e 
(0.164,502.117) 10. 
(0.164,502.117) Speedup 
(0.164,502.117) vs. 
(0.164,502.117) a 
(0.164,502.117) baseline 
(0.164,502.117) Ja 
(0.164,502.117) v 
(0.164,502.117) aScript 
(0.164,502.117) interpreter 
(0.164,502.117) (SpiderMonk 
(0.164,502.117) e 
(0.164,502.117) y) 
(0.164,502.117) for 
(0.164,502.117) our 
(0.164,502.117) trace-based 
(0.164,502.117) JIT 
(0.164,502.117) compiler 
(0.164,502.117) , 
(0.164,502.117) Apple’ 
(0.164,502.117) s 
(0.164,502.117) SquirrelFish 
(0.164,502.117) Extreme 
(0.164,502.117) inline 
(0.164,502.117) threading 
(0.164,502.117) interpreter 
(0.164,502.117) and 
(0.164,502.117) Google’ 
(0.164,502.117) s 
(0.164,502.117) V8 
(0.164,502.117) JS 
(0.164,502.117) compiler 
(0.164,502.117) . 
(0.164,502.117) Our 
(0.164,502.117) system 
(0.164,502.117) generates 
(0.164,502.117) particularly 
(0.164,502.117) ef 
(0.164,502.117) ficient 
(0.164,502.117) code 
(0.164,502.117) for 
(0.164,502.117) programs 
(0.164,502.117) that 
(0.164,502.117) benefit 
(0.164,502.117) most 
(0.164,502.117) from 
(0.164,502.117) type 
(0.164,502.117) specialization, 
(0.164,502.117) which 
(0.164,502.117) includes 
(0.164,502.117) SunSpider 
(0.164,502.117) Benchmark 
(0.164,502.117) programs 
(0.164,502.117) that 
(0.164,502.117) perform 
(0.164,502.117) bit 
(0.164,502.117) manipulation. 
(0.164,502.117) W 
(0.164,502.117) e 
(0.164,502.117) type-s 
(0.164,502.117) pecialize 
(0.164,502.117) the 
(0.164,502.117) code 
(0.164,502.117) in 
(0.164,502.117) question 
(0.164,502.117) to 
(0.164,502.117) use 
(0.164,502.117) inte 
(0.164,502.117) ger 
(0.164,502.117) arithmet 
(0.164,502.117) ic, 
(0.164,502.117) which 
(0.164,502.117) substantially 
(0.164,502.117) impro 
(0.164,502.117) v 
(0.164,502.117) es 
(0.164,502.117) performance. 
(0.164,502.117) F 
(0.164,502.117) or 
(0.164,502.117) one 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) benchmark 
(0.164,502.117) programs 
(0.164,502.117) we 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecute 
(0.164,502.117) 25 
(0.164,502.117) times 
(0.164,502.117) f 
(0.164,502.117) aster 
(0.164,502.117) than 
(0.164,502.117) the 
(0.164,502.117) SpiderMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) interpre 
(0.164,502.117) ter 
(0.164,502.117) , 
(0.164,502.117) and 
(0.164,502.117) almost 
(0.164,502.117) 5 
(0.164,502.117) times 
(0.164,502.117) f 
(0.164,502.117) aster 
(0.164,502.117) than 
(0.164,502.117) V8 
(0.164,502.117) and 
(0.164,502.117) SFX. 
(0.164,502.117) F 
(0.164,502.117) or 
(0.164,502.117) a 
(0.164,502.117) lar 
(0.164,502.117) ge 
(0.164,502.117) number 
(0.164,502.117) of 
(0.164,502.117) benchmarks 
(0.164,502.117) all 
(0.164,502.117) three 
(0.164,502.117) VMs 
(0.164,502.117) produce 
(0.164,502.117) similar 
(0.164,502.117) results. 
(0.164,502.117) W 
(0.164,502.117) e 
(0.164,502.117) perform 
(0.164,502.117) w 
(0.164,502.117) orst 
(0.164,502.117) on 
(0.164,502.117) benchmark 
(0.164,502.117) programs 
(0.164,502.117) that 
(0.164,502.117) we 
(0.164,502.117) do 
(0.164,502.117) not 
(0.164,502.117) trace 
(0.164,502.117) and 
(0.164,502.117) instead 
(0.164,502.117) f 
(0.164,502.117) a 
(0.164,502.117) ll 
(0.164,502.117) back 
(0.164,502.117) onto 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) . 
(0.164,502.117) This 
(0.164,502.117) includes 
(0.164,502.117) the 
(0.164,502.117) recursi 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) benchmarks 
(0.164,502.117) access-binary-trees 
(0.164,502.117) and 
(0.164,502.117) control-flow-recursive 
(0.164,502.117) , 
(0.164,502.117) for 
(0.164,502.117) which 
(0.164,502.117) we 
(0.164,502.117) currently 
(0.164,502.117) don’ 
(0.164,502.117) t 
(0.164,502.117) generate 
(0.164,502.117) an 
(0.164,502.117) y 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code. 
(0.164,502.117) In 
(0.164,502.117) particular 
(0.164,502.117) , 
(0.164,502.117) the 
(0.164,502.117) bitops 
(0.164,502.117) benchmarks 
(0.164,502.117) are 
(0.164,502.117) short 
(0.164,502.117) programs 
(0.164,502.117) that 
(0.164,502.117) per 
(0.164,502.117) - 
(0.164,502.117) form 
(0.164,502.117) man 
(0.164,502.117) y 
(0.164,502.117) bitwise 
(0.164,502.117) operations, 
(0.164,502.117) so 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) can 
(0.164,502.117) co 
(0.164,502.117) v 
(0.164,502.117) er 
(0.164,502.117) the 
(0.164,502.117) en- 
(0.164,502.117) tire 
(0.164,502.117) program 
(0.164,502.117) with 
(0.164,502.117) 1 
(0.164,502.117) or 
(0.164,502.117) 2 
(0.164,502.117) traces 
(0.164,502.117) that 
(0.164,502.117) opera 
(0.164,502.117) te 
(0.164,502.117) on 
(0.164,502.117) inte 
(0.164,502.117) gers. 
(0.164,502.117) T 
(0.164,502.117) raceMon- 
(0.164,502.117) k 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) runs 
(0.164,502.117) all 
(0.164,502.117) the 
(0.164,502.117) other 
(0.164,502.117) progr 
(0.164,502.117) ams 
(0.164,502.117) in 
(0.164,502.117) this 
(0.164,502.117) set 
(0.164,502.117) almost 
(0.164,502.117) entirely 
(0.164,502.117) as 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code. 
(0.164,502.117) regexp-dna 
(0.164,502.117) is 
(0.164,502.117) dominated 
(0.164,502.117) by 
(0.164,502.117) re 
(0.164,502.117) gular 
(0.164,502.117) e 
(0.164,502.117) xpression 
(0.164,502.117) ma 
(0.164,502.117) tching, 
(0.164,502.117) which 
(0.164,502.117) is 
(0.164,502.117) implemented 
(0.164,502.117) in 
(0.164,502.117) all 
(0.164,502.117) 3 
(0.164,502.117) VMs 
(0.164,502.117) by 
(0.164,502.117) a 
(0.164,502.117) special 
(0.164,502.117) re 
(0.164,502.117) gular 
(0.164,502.117) e 
(0.164,502.117) xpression 
(0.164,502.117) compiler 
(0.164,502.117) . 
(0.164,502.117) Thus, 
(0.164,502.117) performance 
(0.164,502.117) on 
(0.164,502.117) this 
(0.164,502.117) benchmark 
(0.164,502.117) has 
(0.164,502.117) little 
(0.164,502.117) relation 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) trace 
(0.164,502.117) compilation 
(0.164,502.117) approach 
(0.164,502.117) discussed 
(0.164,502.117) in 
(0.164,502.117) this 
(0.164,502.117) paper 
(0.164,502.117) . 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y’ 
(0.164,502.117) s 
(0.164,502.117) smaller 
(0.164,502.117) speedups 
(0.164,502.117) on 
(0.164,502.117) the 
(0.164,502.117) other 
(0.164,502.117) benchmarks 
(0.164,502.117) can 
(0.164,502.117) be 
(0.164,502.117) attrib 
(0.164,502.117) uted 
(0.164,502.117) to 
(0.164,502.117) a 
(0.164,502.117) fe 
(0.164,502.117) w 
(0.164,502.117) specific 
(0.164,502.117) causes: 
(0.164,502.117) • 
(0.164,502.117) The 
(0.164,502.117) implementation 
(0.164,502.117) does 
(0.164,502.117) not 
(0.164,502.117) currently 
(0.164,502.117) trace 
(0.164,502.117) recursion, 
(0.164,502.117) so 
(0.164,502.117) T 
(0.164,502.117) raceMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) achie 
(0.164,502.117) v 
(0.164,502.117) es 
(0.164,502.117) a 
(0.164,502.117) small 
(0.164,502.117) speedup 
(0.164,502.117) or 
(0.164,502.117) no 
(0.164,502.117) speedup 
(0.164,502.117) on 
(0.164,502.117) benchmarks 
(0.164,502.117) that 
(0.164,502.117) use 
(0.164,502.117) recursion 
(0.164,502.117) e 
(0.164,502.117) xtensi 
(0.164,502.117) v 
(0.164,502.117) ely: 
(0.164,502.117) 3d-cube 
(0.164,502.117) , 
(0.164,502.117) 3d- 
(0.164,502.117) raytrace 
(0.164,502.117) , 
(0.164,502.117) access-binary-trees 
(0.164,502.117) , 
(0.164,502.117) string-tagcloud 
(0.164,502.117) , 
(0.164,502.117) and 
(0.164,502.117) controlflow-recursive 
(0.164,502.117) . 
(0.164,502.117) • 
(0.164,502.117) The 
(0.164,502.117) implementation 
(0.164,502.117) does 
(0.164,502.117) not 
(0.164,502.117) currently 
(0.164,502.117) trace 
(0.164,502.117) eval 
(0.164,502.117) and 
(0.164,502.117) some 
(0.164,502.117) other 
(0.164,502.117) functions 
(0.164,502.117) implemented 
(0.164,502.117) in 
(0.164,502.117) C. 
(0.164,502.117) Because 
(0.164,502.117) date-format- 
(0.164,502.117) tofte 
(0.164,502.117) and 
(0.164,502.117) date-format-xparb 
(0.164,502.117) use 
(0.164,502.117) such 
(0.164,502.117) functions 
(0.164,502.117) in 
(0.164,502.117) their 
(0.164,502.117) main 
(0.164,502.117) loops, 
(0.164,502.117) we 
(0.164,502.117) do 
(0.164,502.117) not 
(0.164,502.117) trace 
(0.164,502.117) them. 
(0.164,502.117) • 
(0.164,502.117) The 
(0.164,502.117) implementation 
(0.164,502.117) does 
(0.164,502.117) not 
(0.164,502.117) currently 
(0.164,502.117) trace 
(0.164,502.117) through 
(0.164,502.117) re 
(0.164,502.117) gular 
(0.164,502.117) e 
(0.164,502.117) xpression 
(0.164,502.117) replace 
(0.164,502.117) operations. 
(0.164,502.117) The 
(0.164,502.117) replace 
(0.164,502.117) function 
(0.164,502.117) can 
(0.164,502.117) be 
(0.164,502.117) passed 
(0.164,502.117) a 
(0.164,502.117) function 
(0.164,502.117) object 
(0.164,502.117) used 
(0.164,502.117) to 
(0.164,502.117) compute 
(0.164,502.117) the 
(0.164,502.117) replacement 
(0.164,502.117) te 
(0.164,502.117) xt. 
(0.164,502.117) Our 
(0.164,502.117) implementation 
(0.164,502.117) currently 
(0.164,502.117) does 
(0.164,502.117) not 
(0.164,502.117) trace 
(0.164,502.117) functions 
(0.164,502.117) called 
(0.164,502.117) as 
(0.164,502.117) replace 
(0.164,502.117) functions. 
(0.164,502.117) The 
(0.164,502.117) run 
(0.164,502.117) time 
(0.164,502.117) of 
(0.164,502.117) string-unpack-code 
(0.164,502.117) is 
(0.164,502.117) dominated 
(0.164,502.117) by 
(0.164,502.117) such 
(0.164,502.117) a 
(0.164,502.117) replace 
(0.164,502.117) call. 
(0.164,502.117) • 
(0.164,502.117) T 
(0.164,502.117) w 
(0.164,502.117) o 
(0.164,502.117) programs 
(0.164,502.117) trace 
(0.164,502.117) well, 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) ha 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) a 
(0.164,502.117) long 
(0.164,502.117) compilation 
(0.164,502.117) time. 
(0.164,502.117) access-nbody 
(0.164,502.117) forms 
(0.164,502.117) a 
(0.164,502.117) lar 
(0.164,502.117) ge 
(0.164,502.117) number 
(0.164,502.117) of 
(0.164,502.117) traces 
(0.164,502.117) (81). 
(0.164,502.117) crypto-md5 
(0.164,502.117) forms 
(0.164,502.117) one 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) ry 
(0.164,502.117) long 
(0.164,502.117) trace. 
(0.164,502.117) W 
(0.164,502.117) e 
(0.164,502.117) e 
(0.164,502.117) xpec 
(0.164,502.117) t 
(0.164,502.117) to 
(0.164,502.117) impro 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) performance 
(0.164,502.117) on 
(0.164,502.117) this 
(0.164,502.117) programs 
(0.164,502.117) by 
(0.164,502.117) impro 
(0.164,502.117) ving 
(0.164,502.117) the 
(0.164,502.117) compilation 
(0.164,502.117) speed 
(0.164,502.117) of 
(0.164,502.117) nano- 
(0.164,502.117) jit. 
(0.164,502.117) • 
(0.164,502.117) Some 
(0.164,502.117) programs 
(0.164,502.117) trace 
(0.164,502.117) v 
(0.164,502.117) ery 
(0.164,502.117) well, 
(0.164,502.117) and 
(0.164,502.117) speed 
(0.164,502.117) up 
(0.164,502.117) compared 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) , 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) are 
(0.164,502.117) not 
(0.164,502.117) as 
(0.164,502.117) f 
(0.164,502.117) ast 
(0.164,502.117) as 
(0.164,502.117) SFX 
(0.164,502.117) and/or 
(0.164,502.117) V8, 
(0.164,502.117) namely 
(0.164,502.117) bitops-bits-in-byte 
(0.164,502.117) , 
(0.164,502.117) bitops-nsieve-bits 
(0.164,502.117) , 
(0.164,502.117) access- 
(0.164,502.117) fannkuch 
(0.164,502.117) , 
(0.164,502.117) access-nsieve 
(0.164,502.117) , 
(0.164,502.117) and 
(0.164,502.117) crypto-aes 
(0.164,502.117) . 
(0.164,502.117) The 
(0.164,502.117) reason 
(0.164,502.117) is 
(0.164,502.117) not 
(0.164,502.117) clear 
(0.164,502.117) , 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) all 
(0.164,502.117) of 
(0.164,502.117) these 
(0.164,502.117) programs 
(0.164,502.117) ha 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) nested 
(0.164,502.117) loops 
(0.164,502.117) with 
(0.164,502.117) small 
(0.164,502.117) bodies, 
(0.164,502.117) so 
(0.164,502.117) we 
(0.164,502.117) suspec 
(0.164,502.117) t 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) implementation 
(0.164,502.117) has 
(0.164,502.117) a 
(0.164,502.117) rela- 
(0.164,502.117) ti 
(0.164,502.117) v 
(0.164,502.117) ely 
(0.164,502.117) high 
(0.164,502.117) cost 
(0.164,502.117) for 
(0.164,502.117) calling 
(0.164,502.117) nested 
(0.164,502.117) traces. 
(0.164,502.117) string-fasta 
(0.164,502.117) traces 
(0.164,502.117) well, 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) its 
(0.164,502.117) run 
(0.164,502.117) time 
(0.164,502.117) is 
(0.164,502.117) dominated 
(0.164,502.117) by 
(0.164,502.117) string 
(0.164,502.117) processing 
(0.164,502.117) b 
(0.164,502.117) uiltins, 
(0.164,502.117) which 
(0.164,502.117) are 
(0.164,502.117) unaf 
(0.164,502.117) fected 
(0.164,502.117) by 
(0.164,502.117) tracing 
(0.164,502.117) and 
(0.164,502.117) seem 
(0.164,502.117) to 
(0.164,502.117) be 
(0.164,502.117) less 
(0.164,502.117) ef 
(0.164,502.117) ficient 
(0.164,502.117) in 
(0.164,502.117) SpiderMonk 
(0.164,502.117) e 
(0.164,502.117) y 
(0.164,502.117) than 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) tw 
(0.164,502.117) o 
(0.164,502.117) other 
(0.164,502.117) VMs. 
(0.164,502.117) Detailed 
(0.164,502.117) perf 
(0.164,502.117) ormance 
(0.164,502.117) metrics. 
(0.164,502.117) In 
(0.164,502.117) Figure 
(0.164,502.117) 11 
(0.164,502.117) we 
(0.164,502.117) sho 
(0.164,502.117) w 
(0.164,502.117) the 
(0.164,502.117) frac- 
(0.164,502.117) tion 
(0.164,502.117) of 
(0.164,502.117) instructions 
(0.164,502.117) interprete 
(0.164,502.117) d 
(0.164,502.117) and 
(0.164,502.117) the 
(0.164,502.117) fraction 
(0.164,502.117) of 
(0.164,502.117) instructions 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) e- 
(0.164,502.117) cuted 
(0.164,502.117) as 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code. 
(0.164,502.117) This 
(0.164,502.117) figure 
(0.164,502.117) sho 
(0.164,502.117) ws 
(0.164,502.117) that 
(0.164,502.117) for 
(0.164,502.117) man 
(0.164,502.117) y 
(0.164,502.117) programs, 
(0.164,502.117) we 
(0.164,502.117) are 
(0.164,502.117) able 
(0.164,502.117) to 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecute 
(0.164,502.117) almost 
(0.164,502.117) all 
(0.164,502.117) the 
(0.164,502.117) code 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) ely 
(0.164,502.117) . 
(0.164,502.117) Figure 
(0.164,502.117) 12 
(0.164,502.117) breaks 
(0.164,502.117) do 
(0.164,502.117) wn 
(0.164,502.117) the 
(0.164,502.117) total 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecution 
(0.164,502.117) time 
(0.164,502.117) into 
(0.164,502.117) four 
(0.164,502.117) acti 
(0.164,502.117) v- 
(0.164,502.117) ities: 
(0.164,502.117) interpreting 
(0.164,502.117) bytecodes 
(0.164,502.117) while 
(0.164,502.117) not 
(0.164,502.117) recording, 
(0.164,502.117) recording 
(0.164,502.117) traces 
(0.164,502.117) (including 
(0.164,502.117) time 
(0.164,502.117) tak 
(0.164,502.117) en 
(0.164,502.117) to 
(0.164,502.117) interpret 
(0.164,502.117) the 
(0.164,502.117) recorded 
(0.164,502.117) trace), 
(0.164,502.117) compiling 
(0.164,502.117) traces 
(0.164,502.117) to 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code, 
(0.164,502.117) and 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecuting 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) traces. 
(0.164,502.117) These 
(0.164,502.117) detailed 
(0.164,502.117) metrics 
(0.164,502.117) allo 
(0.164,502.117) w 
(0.164,502.117) us 
(0.164,502.117) to 
(0.164,502.117) estimate 
(0.164,502.117) parameters 
(0.164,502.117) for 
(0.164,502.117) a 
(0.164,502.117) simple 
(0.164,502.117) model 
(0.164,502.117) of 
(0.164,502.117) tracing 
(0.164,502.117) performance. 
(0.164,502.117) These 
(0.164,502.117) estimates 
(0.164,502.117) should 
(0.164,502.117) be 
(0.164,502.117) considered 
(0.164,502.117) v 
(0.164,502.117) ery 
(0.164,502.117) rough, 
(0.164,502.117) as 
(0.164,502.117) the 
(0.164,502.117) v 
(0.164,502.117) alues 
(0.164,502.117) observ 
(0.164,502.117) ed 
(0.164,502.117) on 
(0.164,502.117) the 
(0.164,502.117) indi 
(0.164,502.117) vidual 
(0.164,502.117) benchmarks 
(0.164,502.117) ha 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) lar 
(0.164,502.117) ge 
(0.164,502.117) standard 
(0.164,502.117) de 
(0.164,502.117) viations 
(0.164,502.117) (on 
(0.164,502.117) the 
(0.164,502.117) order 
(0.164,502.117) of 
(0.164,502.117) the 
(0.000,0.000) Loops 
(0.000,0.000) T 
(0.000,0.000) rees 
(0.000,0.000) T 
(0.000,0.000) races 
(0.000,0.000) Aborts 
(0.000,0.000) Flushes 
(0.000,0.000) T 
(0.000,0.000) re 
(0.000,0.000) es/Loop 
(0.000,0.000) T 
(0.000,0.000) races/T 
(0.000,0.000) ree 
(0.000,0.000) T 
(0.000,0.000) races/Loop 
(0.000,0.000) Speedup 
(0.199,479.234) 3d-cube 
(0.199,479.234) 25 
(0.199,479.234) 27 
(0.199,479.234) 29 
(0.199,479.234) 3 
(0.199,479.234) 0 
(0.199,479.234) 1.1 
(0.199,479.234) 1.1 
(0.199,479.234) 1.2 
(0.199,479.234) 2.20x 
(0.199,479.234) 3d-morph 
(0.199,479.234) 5 
(0.199,479.234) 8 
(0.199,479.234) 8 
(0.199,479.234) 2 
(0.199,479.234) 0 
(0.199,479.234) 1.6 
(0.199,479.234) 1.0 
(0.199,479.234) 1.6 
(0.199,479.234) 2.86x 
(0.199,479.234) 3d-raytrace 
(0.199,479.234) 10 
(0.199,479.234) 25 
(0.199,479.234) 100 
(0.199,479.234) 10 
(0.199,479.234) 1 
(0.199,479.234) 2.5 
(0.199,479.234) 4.0 
(0.199,479.234) 10.0 
(0.199,479.234) 1.18x 
(0.199,479.234) access-binary-trees 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 5 
(0.199,479.234) 0 
(0.199,479.234) - 
(0.199,479.234) - 
(0.199,479.234) - 
(0.199,479.234) 0.93x 
(0.199,479.234) access-f 
(0.199,479.234) annkuch 
(0.199,479.234) 10 
(0.199,479.234) 34 
(0.199,479.234) 57 
(0.199,479.234) 24 
(0.199,479.234) 0 
(0.199,479.234) 3.4 
(0.199,479.234) 1.7 
(0.199,479.234) 5.7 
(0.199,479.234) 2.20x 
(0.199,479.234) access-nbody 
(0.199,479.234) 8 
(0.199,479.234) 16 
(0.199,479.234) 18 
(0.199,479.234) 5 
(0.199,479.234) 0 
(0.199,479.234) 2.0 
(0.199,479.234) 1.1 
(0.199,479.234) 2.3 
(0.199,479.234) 4.19x 
(0.199,479.234) access-nsie 
(0.199,479.234) v 
(0.199,479.234) e 
(0.199,479.234) 3 
(0.199,479.234) 6 
(0.199,479.234) 8 
(0.199,479.234) 3 
(0.199,479.234) 0 
(0.199,479.234) 2.0 
(0.199,479.234) 1.3 
(0.199,479.234) 2.7 
(0.199,479.234) 3.05x 
(0.199,479.234) bitops-3bit-bits-in-byte 
(0.199,479.234) 2 
(0.199,479.234) 2 
(0.199,479.234) 2 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.0 
(0.199,479.234) 25.47x 
(0.199,479.234) bitops-bits-in-byte 
(0.199,479.234) 3 
(0.199,479.234) 3 
(0.199,479.234) 4 
(0.199,479.234) 1 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.3 
(0.199,479.234) 1.3 
(0.199,479.234) 8.67x 
(0.199,479.234) bitops-bitwise-and 
(0.199,479.234) 1 
(0.199,479.234) 1 
(0.199,479.234) 1 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.0 
(0.199,479.234) 25.20x 
(0.199,479.234) bitops-nsie 
(0.199,479.234) v 
(0.199,479.234) e-bits 
(0.199,479.234) 3 
(0.199,479.234) 3 
(0.199,479.234) 5 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.7 
(0.199,479.234) 1.7 
(0.199,479.234) 2.75x 
(0.199,479.234) controlflo 
(0.199,479.234) w-recursi 
(0.199,479.234) v 
(0.199,479.234) e 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1 
(0.199,479.234) 0 
(0.199,479.234) - 
(0.199,479.234) - 
(0.199,479.234) - 
(0.199,479.234) 0.98x 
(0.199,479.234) crypto-aes 
(0.199,479.234) 50 
(0.199,479.234) 72 
(0.199,479.234) 78 
(0.199,479.234) 19 
(0.199,479.234) 0 
(0.199,479.234) 1.4 
(0.199,479.234) 1.1 
(0.199,479.234) 1.6 
(0.199,479.234) 1.64x 
(0.199,479.234) crypto-md5 
(0.199,479.234) 4 
(0.199,479.234) 4 
(0.199,479.234) 5 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.3 
(0.199,479.234) 1.3 
(0.199,479.234) 2.30x 
(0.199,479.234) crypto-sha1 
(0.199,479.234) 5 
(0.199,479.234) 5 
(0.199,479.234) 10 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 2.0 
(0.199,479.234) 2.0 
(0.199,479.234) 5.95x 
(0.199,479.234) date-format-tofte 
(0.199,479.234) 3 
(0.199,479.234) 3 
(0.199,479.234) 4 
(0.199,479.234) 7 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.3 
(0.199,479.234) 1.3 
(0.199,479.234) 1.07x 
(0.199,479.234) date-format-xparb 
(0.199,479.234) 3 
(0.199,479.234) 3 
(0.199,479.234) 11 
(0.199,479.234) 3 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 3.7 
(0.199,479.234) 3.7 
(0.199,479.234) 0.98x 
(0.199,479.234) math-cordic 
(0.199,479.234) 2 
(0.199,479.234) 4 
(0.199,479.234) 5 
(0.199,479.234) 1 
(0.199,479.234) 0 
(0.199,479.234) 2.0 
(0.199,479.234) 1.3 
(0.199,479.234) 2.5 
(0.199,479.234) 4.92x 
(0.199,479.234) math-partial-sums 
(0.199,479.234) 2 
(0.199,479.234) 4 
(0.199,479.234) 4 
(0.199,479.234) 1 
(0.199,479.234) 0 
(0.199,479.234) 2.0 
(0.199,479.234) 1.0 
(0.199,479.234) 2.0 
(0.199,479.234) 5.90x 
(0.199,479.234) math-spectral-norm 
(0.199,479.234) 15 
(0.199,479.234) 20 
(0.199,479.234) 20 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.3 
(0.199,479.234) 1.0 
(0.199,479.234) 1.3 
(0.199,479.234) 7.12x 
(0.199,479.234) re 
(0.199,479.234) ge 
(0.199,479.234) xp-dna 
(0.199,479.234) 2 
(0.199,479.234) 2 
(0.199,479.234) 2 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.0 
(0.199,479.234) 1.0 
(0.199,479.234) 4.21x 
(0.199,479.234) string-base64 
(0.199,479.234) 3 
(0.199,479.234) 5 
(0.199,479.234) 7 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.7 
(0.199,479.234) 1.4 
(0.199,479.234) 2.3 
(0.199,479.234) 2.53x 
(0.199,479.234) string-f 
(0.199,479.234) asta 
(0.199,479.234) 5 
(0.199,479.234) 11 
(0.199,479.234) 15 
(0.199,479.234) 6 
(0.199,479.234) 0 
(0.199,479.234) 2.2 
(0.199,479.234) 1.4 
(0.199,479.234) 3.0 
(0.199,479.234) 1.49x 
(0.199,479.234) string-tagcloud 
(0.199,479.234) 3 
(0.199,479.234) 6 
(0.199,479.234) 6 
(0.199,479.234) 5 
(0.199,479.234) 0 
(0.199,479.234) 2.0 
(0.199,479.234) 1.0 
(0.199,479.234) 2.0 
(0.199,479.234) 1.09x 
(0.199,479.234) string-unpack-code 
(0.199,479.234) 4 
(0.199,479.234) 4 
(0.199,479.234) 37 
(0.199,479.234) 0 
(0.199,479.234) 0 
(0.199,479.234) 1.0 
(0.199,479.234) 9.3 
(0.199,479.234) 9.3 
(0.199,479.234) 1.20x 
(0.199,479.234) string-v 
(0.199,479.234) alidate-input 
(0.199,479.234) 6 
(0.199,479.234) 10 
(0.199,479.234) 13 
(0.199,479.234) 1 
(0.199,479.234) 0 
(0.199,479.234) 1.7 
(0.199,479.234) 1.3 
(0.199,479.234) 2.2 
(0.199,479.234) 1.86x 
(0.164,502.117) Figur 
(0.164,502.117) e 
(0.164,502.117) 13. 
(0.164,502.117) Detailed 
(0.164,502.117) trace 
(0.164,502.117) recording 
(0.164,502.117) statistics 
(0.164,502.117) for 
(0.164,502.117) the 
(0.164,502.117) SunSpider 
(0.164,502.117) benchmark 
(0.164,502.117) set. 
(0.164,502.117) mean). 
(0.164,502.117) W 
(0.164,502.117) e 
(0.164,502.117) e 
(0.164,502.117) xclude 
(0.164,502.117) regexp-dna 
(0.164,502.117) from 
(0.164,502.117) the 
(0.164,502.117) follo 
(0.164,502.117) wing 
(0.164,502.117) calculations, 
(0.164,502.117) because 
(0.164,502.117) most 
(0.164,502.117) of 
(0.164,502.117) its 
(0.164,502.117) time 
(0.164,502.117) is 
(0.164,502.117) spent 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) r 
(0.164,502.117) e 
(0.164,502.117) gular 
(0.164,502.117) e 
(0.164,502.117) xpression 
(0.164,502.117) matcher 
(0.164,502.117) , 
(0.164,502.117) which 
(0.164,502.117) has 
(0.164,502.117) much 
(0.164,502.117) dif 
(0.164,502.117) ferent 
(0.164,502.117) performance 
(0.164,502.117) characteristics 
(0.164,502.117) from 
(0.164,502.117) the 
(0.164,502.117) other 
(0.164,502.117) programs. 
(0.164,502.117) (Note 
(0.164,502.117) that 
(0.164,502.117) this 
(0.164,502.117) only 
(0.164,502.117) mak 
(0.164,502.117) es 
(0.164,502.117) a 
(0.164,502.117) dif 
(0.164,502.117) ference 
(0.164,502.117) of 
(0.164,502.117) about 
(0.164,502.117) 10% 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) results.) 
(0.164,502.117) Di 
(0.164,502.117) viding 
(0.164,502.117) the 
(0.164,502.117) total 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecution 
(0.164,502.117) time 
(0.164,502.117) in 
(0.164,502.117) processor 
(0.164,502.117) clock 
(0.164,502.117) c 
(0.164,502.117) ycles 
(0.164,502.117) by 
(0.164,502.117) the 
(0.164,502.117) number 
(0.164,502.117) of 
(0.164,502.117) bytecodes 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecuted 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) base 
(0.164,502.117) interpreter 
(0.164,502.117) sho 
(0.164,502.117) ws 
(0.164,502.117) that 
(0.164,502.117) on 
(0.164,502.117) a 
(0.164,502.117) v 
(0.164,502.117) erage, 
(0.164,502.117) a 
(0.164,502.117) bytecode 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecute 
(0.164,502.117) s 
(0.164,502.117) in 
(0.164,502.117) about 
(0.164,502.117) 35 
(0.164,502.117) c 
(0.164,502.117) ycles. 
(0.164,502.117) Nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) traces 
(0.164,502.117) tak 
(0.164,502.117) e 
(0.164,502.117) about 
(0.164,502.117) 9 
(0.164,502.117) c 
(0.164,502.117) ycle 
(0.164,502.117) s 
(0.164,502.117) per 
(0.164,502.117) bytecode, 
(0.164,502.117) a 
(0.164,502.117) 3.9x 
(0.164,502.117) speedup 
(0.164,502.117) o 
(0.164,502.117) v 
(0.164,502.117) er 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) . 
(0.164,502.117) Using 
(0.164,502.117) similar 
(0.164,502.117) computations, 
(0.164,502.117) we 
(0.164,502.117) find 
(0.164,502.117) that 
(0.164,502.117) trace 
(0.164,502.117) recording 
(0.164,502.117) tak 
(0.164,502.117) es 
(0.164,502.117) about 
(0.164,502.117) 3800 
(0.164,502.117) c 
(0.164,502.117) ycles 
(0.164,502.117) per 
(0.164,502.117) bytecode, 
(0.164,502.117) and 
(0.164,502.117) compilation 
(0.164,502.117) 3150 
(0.164,502.117) c 
(0.164,502.117) ycles 
(0.164,502.117) per 
(0.164,502.117) bytecode. 
(0.164,502.117) Hence, 
(0.164,502.117) during 
(0.164,502.117) recording 
(0.164,502.117) and 
(0.164,502.117) compiling 
(0.164,502.117) the 
(0.164,502.117) VM 
(0.164,502.117) runs 
(0.164,502.117) at 
(0.164,502.117) 1/200 
(0.164,502.117) the 
(0.164,502.117) s 
(0.164,502.117) peed 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) . 
(0.164,502.117) Because 
(0.164,502.117) it 
(0.164,502.117) costs 
(0.164,502.117) 6950 
(0.164,502.117) c 
(0.164,502.117) ycles 
(0.164,502.117) to 
(0.164,502.117) compile 
(0.164,502.117) a 
(0.164,502.117) bytecode, 
(0.164,502.117) and 
(0.164,502.117) we 
(0.164,502.117) sa 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) 26 
(0.164,502.117) c 
(0.164,502.117) ycles 
(0.164,502.117) each 
(0.164,502.117) time 
(0.164,502.117) that 
(0.164,502.117) code 
(0.164,502.117) is 
(0.164,502.117) run 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) ely 
(0.164,502.117) , 
(0.164,502.117) we 
(0.164,502.117) break 
(0.164,502.117) e 
(0.164,502.117) v 
(0.164,502.117) en 
(0.164,502.117) after 
(0.164,502.117) running 
(0.164,502.117) a 
(0.164,502.117) trace 
(0.164,502.117) 270 
(0.164,502.117) times. 
(0.164,502.117) The 
(0.164,502.117) other 
(0.164,502.117) VMs 
(0.164,502.117) we 
(0.164,502.117) compared 
(0.164,502.117) with 
(0.164,502.117) achie 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) an 
(0.164,502.117) o 
(0.164,502.117) v 
(0.164,502.117) erall 
(0.164,502.117) speedup 
(0.164,502.117) of 
(0.164,502.117) 3.0x 
(0.164,502.117) relati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) to 
(0.164,502.117) our 
(0.164,502.117) baseline 
(0.164,502.117) interpreter 
(0.164,502.117) . 
(0.164,502.117) Our 
(0.164,502.117) estimated 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) speedup 
(0.164,502.117) of 
(0.164,502.117) 3.9x 
(0.164,502.117) is 
(0.164,502.117) significantly 
(0.164,502.117) better 
(0.164,502.117) . 
(0.164,502.117) This 
(0.164,502.117) suggests 
(0.164,502.117) that 
(0.164,502.117) our 
(0.164,502.117) compilation 
(0.164,502.117) techniques 
(0.164,502.117) can 
(0.164,502.117) generate 
(0.164,502.117) more 
(0.164,502.117) ef 
(0.164,502.117) fi 
(0.164,502.117) cient 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) than 
(0.164,502.117) an 
(0.164,502.117) y 
(0.164,502.117) other 
(0.164,502.117) current 
(0.164,502.117) Ja 
(0.164,502.117) v 
(0.164,502.117) aScript 
(0.164,502.117) VM. 
(0.164,502.117) These 
(0.164,502.117) estimates 
(0.164,502.117) also 
(0.164,502.117) indicate 
(0.164,502.117) that 
(0.164,502.117) our 
(0.164,502.117) startup 
(0.164,502.117) performance 
(0.164,502.117) could 
(0.164,502.117) be 
(0.164,502.117) substantially 
(0.164,502.117) better 
(0.164,502.117) if 
(0.164,502.117) we 
(0.164,502.117) impro 
(0.164,502.117) v 
(0.164,502.117) ed 
(0.164,502.117) the 
(0.164,502.117) speed 
(0.164,502.117) of 
(0.164,502.117) trace 
(0.164,502.117) recording 
(0.164,502.117) and 
(0.164,502.117) compilation. 
(0.164,502.117) The 
(0.164,502.117) estimated 
(0.164,502.117) 200x 
(0.164,502.117) slo 
(0.164,502.117) wdo 
(0.164,502.117) wn 
(0.164,502.117) for 
(0.164,502.117) recording 
(0.164,502.117) and 
(0.164,502.117) compilation 
(0.164,502.117) is 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) ry 
(0.164,502.117) rough, 
(0.164,502.117) and 
(0.164,502.117) may 
(0.164,502.117) be 
(0.164,502.117) influenced 
(0.164,502.117) by 
(0.164,502.117) startup 
(0.164,502.117) f 
(0.164,502.117) actors 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) interpreter 
(0.164,502.117) (e.g., 
(0.164,502.117) caches 
(0.164,502.117) that 
(0.164,502.117) ha 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) not 
(0.164,502.117) w 
(0.164,502.117) armed 
(0.164,502.117) up 
(0.164,502.117) yet 
(0.164,502.117) during 
(0.164,502.117) recording). 
(0.164,502.117) One 
(0.164,502.117) observ 
(0.164,502.117) ation 
(0.164,502.117) supporting 
(0.164,502.117) this 
(0.164,502.117) conjecture 
(0.164,502.117) is 
(0.164,502.117) that 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) tracer 
(0.164,502.117) , 
(0.164,502.117) interpreted 
(0.164,502.117) bytecodes 
(0.164,502.117) tak 
(0.164,502.117) e 
(0.164,502.117) about 
(0.164,502.117) 180 
(0.164,502.117) c 
(0.164,502.117) ycles 
(0.164,502.117) to 
(0.164,502.117) run. 
(0.164,502.117) Still, 
(0.164,502.117) recording 
(0.164,502.117) and 
(0.164,502.117) compilation 
(0.164,502.117) are 
(0.164,502.117) clearly 
(0.164,502.117) both 
(0.164,502.117) e 
(0.164,502.117) xpensi 
(0.164,502.117) v 
(0.164,502.117) e, 
(0.164,502.117) and 
(0.164,502.117) a 
(0.164,502.117) better 
(0.164,502.117) implementation, 
(0.164,502.117) possibly 
(0.164,502.117) including 
(0.164,502.117) redesign 
(0.164,502.117) of 
(0.164,502.117) the 
(0.164,502.117) LIR 
(0.164,502.117) abstract 
(0.164,502.117) syntax 
(0.164,502.117) or 
(0.164,502.117) encoding, 
(0.164,502.117) w 
(0.164,502.117) ould 
(0.164,502.117) impro 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) startup 
(0.164,502.117) performance. 
(0.164,502.117) Our 
(0.164,502.117) performance 
(0.164,502.117) results 
(0.164,502.117) confirm 
(0.164,502.117) that 
(0.164,502.117) type 
(0.164,502.117) specialization 
(0.164,502.117) using 
(0.164,502.117) trace 
(0.164,502.117) trees 
(0.164,502.117) substantially 
(0.164,502.117) impro 
(0.164,502.117) v 
(0.164,502.117) es 
(0.164,502.117) performance. 
(0.164,502.117) W 
(0.164,502.117) e 
(0.164,502.117) are 
(0.164,502.117) able 
(0.164,502.117) to 
(0.164,502.117) outperform 
(0.164,502.117) the 
(0.164,502.117) f 
(0.164,502.117) astest 
(0.164,502.117) a 
(0.164,502.117) v 
(0.164,502.117) ailable 
(0.164,502.117) Ja 
(0.164,502.117) v 
(0.164,502.117) aScript 
(0.164,502.117) com 
(0.164,502.117) piler 
(0.164,502.117) (V8) 
(0.164,502.117) and 
(0.164,502.117) the 
(0.164,502.117) f 
(0.164,502.117) astest 
(0.164,502.117) a 
(0.164,502.117) v 
(0.164,502.117) ailable 
(0.164,502.117) Ja 
(0.164,502.117) v 
(0.164,502.117) aScript 
(0.164,502.117) inline 
(0.164,502.117) threaded 
(0.164,502.117) interpret 
(0.164,502.117) er 
(0.164,502.117) (SFX) 
(0.164,502.117) on 
(0.164,502.117) 9 
(0.164,502.117) of 
(0.164,502.117) 26 
(0.164,502.117) benchmarks. 
(0.164,502.117) 8. 
(0.164,502.117) Related 
(0.164,502.117) W 
(0.164,502.117) ork 
(0.164,502.117) T 
(0.164,502.117) race 
(0.164,502.117) optimization 
(0.164,502.117) f 
(0.164,502.117) or 
(0.164,502.117) dynamic 
(0.164,502.117) languages. 
(0.164,502.117) The 
(0.164,502.117) closest 
(0.164,502.117) area 
(0.164,502.117) of 
(0.164,502.117) related 
(0.164,502.117) w 
(0.164,502.117) ork 
(0.164,502.117) is 
(0.164,502.117) on 
(0.164,502.117) applying 
(0.164,502.117) trace 
(0.164,502.117) optimization 
(0.164,502.117) to 
(0.164,502.117) type-specialize 
(0.164,502.117) dynamic 
(0.164,502.117) languages. 
(0.164,502.117) Existing 
(0.164,502.117) w 
(0.164,502.117) ork 
(0.164,502.117) shares 
(0.164,502.117) the 
(0.164,502.117) idea 
(0.164,502.117) of 
(0.164,502.117) generating 
(0.164,502.117) type-specialized 
(0.164,502.117) code 
(0.164,502.117) speculat 
(0.164,502.117) i 
(0.164,502.117) v 
(0.164,502.117) ely 
(0.164,502.117) with 
(0.164,502.117) guards 
(0.164,502.117) along 
(0.164,502.117) interpreter 
(0.164,502.117) traces. 
(0.164,502.117) T 
(0.164,502.117) o 
(0.164,502.117) our 
(0.164,502.117) kno 
(0.164,502.117) wledge, 
(0.164,502.117) Rigo’ 
(0.164,502.117) s 
(0.164,502.117) Psyco 
(0.164,502.117) (16) 
(0.164,502.117) is 
(0.164,502.117) the 
(0.164,502.117) only 
(0.164,502.117) published 
(0.164,502.117) type-specializing 
(0.164,502.117) trace 
(0.164,502.117) compiler 
(0.164,502.117) for 
(0.164,502.117) a 
(0.164,502.117) dynamic 
(0.164,502.117) language 
(0.164,502.117) (Python). 
(0.164,502.117) Psyco 
(0.164,502.117) does 
(0.164,502.117) not 
(0.164,502.117) attempt 
(0.164,502.117) to 
(0.164,502.117) identify 
(0.164,502.117) hot 
(0.164,502.117) loops 
(0.164,502.117) or 
(0.164,502.117) inl 
(0.164,502.117) ine 
(0.164,502.117) function 
(0.164,502.117) calls. 
(0.164,502.117) Instead, 
(0.164,502.117) Psyco 
(0.164,502.117) transforms 
(0.164,502.117) loops 
(0.164,502.117) to 
(0.164,502.117) mutual 
(0.164,502.117) recursion 
(0.164,502.117) before 
(0.164,502.117) running 
(0.164,502.117) and 
(0.164,502.117) traces 
(0.164,502.117) all 
(0.164,502.117) operations. 
(0.164,502.117) P 
(0.164,502.117) all’ 
(0.164,502.117) s 
(0.164,502.117) LuaJIT 
(0.164,502.117) is 
(0.164,502.117) a 
(0.164,502.117) Lua 
(0.164,502.117) VM 
(0.164,502.117) in 
(0.164,502.117) de 
(0.164,502.117) v 
(0.164,502.117) elopment 
(0.164,502.117) that 
(0.164,502.117) uses 
(0.164,502.117) tra 
(0.164,502.117) ce 
(0.164,502.117) com- 
(0.164,502.117) pilation 
(0.164,502.117) ideas. 
(0.164,502.117) (1). 
(0.164,502.117) There 
(0.164,502.117) are 
(0.164,502.117) no 
(0.164,502.117) publications 
(0.164,502.117) on 
(0.164,502.117) LuaJIT 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) the 
(0.164,502.117) cre- 
(0.164,502.117) ator 
(0.164,502.117) has 
(0.164,502.117) told 
(0.164,502.117) us 
(0.164,502.117) that 
(0.164,502.117) LuaJIT 
(0.164,502.117) has 
(0.164,502.117) a 
(0.164,502.117) similar 
(0.164,502.117) design 
(0.164,502.117) to 
(0.164,502.117) our 
(0.164,502.117) system, 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) will 
(0.164,502.117) use 
(0.164,502.117) a 
(0.164,502.117) less 
(0.164,502.117) aggressi 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) type 
(0.164,502.117) speculation 
(0.164,502.117) (e.g., 
(0.164,502.117) using 
(0.164,502.117) a 
(0.164,502.117) floating- 
(0.164,502.117) point 
(0.164,502.117) representation 
(0.164,502.117) for 
(0.164,502.117) all 
(0.164,502.117) number 
(0.164,502.117) v 
(0.164,502.117) alues) 
(0.164,502.117) and 
(0.164,502.117) does 
(0.164,502.117) not 
(0.164,502.117) generate 
(0.164,502.117) nested 
(0.164,502.117) traces 
(0.164,502.117) for 
(0.164,502.117) nested 
(0.164,502.117) loops. 
(0.164,502.117) General 
(0.164,502.117) trace 
(0.164,502.117) optimization. 
(0.164,502.117) General 
(0.164,502.117) trace 
(0.164,502.117) optimization 
(0.164,502.117) has 
(0.164,502.117) a 
(0.164,502.117) longer 
(0.164,502.117) history 
(0.164,502.117) that 
(0.164,502.117) has 
(0.164,502.117) treated 
(0.164,502.117) mostly 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) and 
(0.164,502.117) typed 
(0.164,502.117) languages 
(0.164,502.117) lik 
(0.164,502.117) e 
(0.164,502.117) Ja 
(0.164,502.117) v 
(0.164,502.117) a. 
(0.164,502.117) Thus, 
(0.164,502.117) these 
(0.164,502.117) systems 
(0.164,502.117) ha 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) focused 
(0.164,502.117) less 
(0.164,502.117) on 
(0.164,502.117) type 
(0.164,502.117) specialization 
(0.164,502.117) and 
(0.164,502.117) more 
(0.164,502.117) on 
(0.164,502.117) other 
(0.164,502.117) optimizations. 
(0.164,502.117) Dynamo 
(0.164,502.117) (7) 
(0.164,502.117) by 
(0.164,502.117) Bala 
(0.164,502.117) et 
(0.164,502.117) al, 
(0.164,502.117) introduced 
(0.164,502.117) nati 
(0.164,502.117) v 
(0.164,502.117) e 
(0.164,502.117) code 
(0.164,502.117) tracing 
(0.164,502.117) as 
(0.164,502.117) a 
(0.164,502.117) replacement 
(0.164,502.117) for 
(0.164,502.117) profile-guided 
(0.164,502.117) optimization 
(0.164,502.117) (PGO). 
(0.164,502.117) A 
(0.164,502.117) major 
(0.164,502.117) goal 
(0.164,502.117) w 
(0.164,502.117) as 
(0.164,502.117) to 
(0.164,502.117) perform 
(0.164,502.117) PGO 
(0.164,502.117) online 
(0.164,502.117) so 
(0.164,502.117) that 
(0.164,502.117) the 
(0.164,502.117) profile 
(0.164,502.117) w 
(0.164,502.117) as 
(0.164,502.117) specific 
(0.164,502.117) to 
(0.164,502.117) the 
(0.164,502.117) current 
(0.164,502.117) e 
(0.164,502.117) x 
(0.164,502.117) ecution. 
(0.164,502.117) Dynamo 
(0.164,502.117) used 
(0.164,502.117) loop 
(0.164,502.117) headers 
(0.164,502.117) as 
(0.164,502.117) candidate 
(0.164,502.117) hot 
(0.164,502.117) traces, 
(0.164,502.117) b 
(0.164,502.117) ut 
(0.164,502.117) did 
(0.164,502.117) not 
(0.164,502.117) try 
(0.164,502.117) to 
(0.164,502.117) create 
(0.164,502.117) loop 
(0.164,502.117) traces 
(0.164,502.117) specifically 
(0.164,502.117) . 
(0.164,502.117) T 
(0.164,502.117) race 
(0.164,502.117) trees 
(0.164,502.117) were 
(0.164,502.117) originally 
(0.164,502.117) proposed 
(0.164,502.117) by 
(0.164,502.117) Gal 
(0.164,502.117) et 
(0.164,502.117) al. 
(0.164,502.117) (11) 
(0.164,502.117) in 
(0.164,502.117) the 
(0.164,502.117) conte 
(0.164,502.117) xt 
(0.164,502.117) of 
(0.164,502.117) Ja 
(0.164,502.117) v 
(0.164,502.117) a, 
(0.164,502.117) a 
(0.164,502.117) statically 
(0.164,502.117) typed 
(0.164,502.117) language. 
(0.164,502.117) Their 
(0.164,502.117) trace 
(0.164,502.117) trees 
(0.164,502.117) ac- 
(0.164,502.117) tually 
(0.164,502.117) inlined 
(0.164,502.117) parts 
(0.164,502.117) of 
(0.164,502.117) outer 
(0.164,502.117) loops 
(0.164,502.117) within 
(0.164,502.117) the 
(0.164,502.117) inner 
(0.164,502.117) loops 
(0.164,502.117) (because 
(0.164,239.103) Figur 
(0.164,239.103) e 
(0.164,239.103) 12. 
(0.164,239.103) Fraction 
(0.164,239.103) of 
(0.164,239.103) time 
(0.164,239.103) spent 
(0.164,239.103) on 
(0.164,239.103) major 
(0.164,239.103) VM 
(0.164,239.103) acti 
(0.164,239.103) vities. 
(0.164,239.103) The 
(0.164,239.103) speedup 
(0.164,239.103) vs. 
(0.164,239.103) interpreter 
(0.164,239.103) is 
(0.164,239.103) sho 
(0.164,239.103) wn 
(0.164,239.103) in 
(0.164,239.103) parentheses 
(0.164,239.103) ne 
(0.164,239.103) xt 
(0.164,239.103) to 
(0.164,239.103) each 
(0.164,239.103) test. 
(0.164,239.103) Most 
(0.164,239.103) programs 
(0.164,239.103) where 
(0.164,239.103) the 
(0.164,239.103) VM 
(0.164,239.103) spends 
(0.164,239.103) the 
(0.164,239.103) majority 
(0.164,239.103) of 
(0.164,239.103) its 
(0.164,239.103) time 
(0.164,239.103) run- 
(0.164,239.103) ning 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) a 
(0.164,239.103) good 
(0.164,239.103) speedup. 
(0.164,239.103) Recording 
(0.164,239.103) and 
(0.164,239.103) compilation 
(0.164,239.103) costs 
(0.164,239.103) can 
(0.164,239.103) be 
(0.164,239.103) substantial; 
(0.164,239.103) speeding 
(0.164,239.103) up 
(0.164,239.103) those 
(0.164,239.103) parts 
(0.164,239.103) of 
(0.164,239.103) the 
(0.164,239.103) implemen- 
(0.164,239.103) tation 
(0.164,239.103) w 
(0.164,239.103) ould 
(0.164,239.103) impro 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) SunSpider 
(0.164,239.103) performance. 
(0.164,239.103) inner 
(0.164,239.103) loops 
(0.164,239.103) become 
(0.164,239.103) hot 
(0.164,239.103) first), 
(0.164,239.103) leading 
(0.164,239.103) to 
(0.164,239.103) much 
(0.164,239.103) greater 
(0.164,239.103) tail 
(0.164,239.103) duplica- 
(0.164,239.103) tion. 
(0.164,239.103) YETI, 
(0.164,239.103) from 
(0.164,239.103) Zaleski 
(0.164,239.103) et 
(0.164,239.103) al. 
(0.164,239.103) (19) 
(0.164,239.103) applied 
(0.164,239.103) Dynamo-style 
(0.164,239.103) tracing 
(0.164,239.103) to 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) a 
(0.164,239.103) in 
(0.164,239.103) order 
(0.164,239.103) to 
(0.164,239.103) achie 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) inli 
(0.164,239.103) ning, 
(0.164,239.103) indirect 
(0.164,239.103) jump 
(0.164,239.103) elimination, 
(0.164,239.103) and 
(0.164,239.103) other 
(0.164,239.103) optimizations. 
(0.164,239.103) Their 
(0.164,239.103) primary 
(0.164,239.103) focus 
(0.164,239.103) w 
(0.164,239.103) as 
(0.164,239.103) on 
(0.164,239.103) designing 
(0.164,239.103) an 
(0.164,239.103) interpreter 
(0.164,239.103) that 
(0.164,239.103) could 
(0.164,239.103) easily 
(0.164,239.103) be 
(0.164,239.103) gradually 
(0.164,239.103) re-engineered 
(0.164,239.103) as 
(0.164,239.103) a 
(0.164,239.103) tracing 
(0.164,239.103) VM. 
(0.164,239.103) Sug 
(0.164,239.103) anuma 
(0.164,239.103) et 
(0.164,239.103) al. 
(0.164,239.103) (18) 
(0.164,239.103) described 
(0.164,239.103) re 
(0.164,239.103) gion-based 
(0.164,239.103) compilation 
(0.164,239.103) (RBC), 
(0.164,239.103) a 
(0.164,239.103) relati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) of 
(0.164,239.103) tracing. 
(0.164,239.103) A 
(0.164,239.103) re 
(0.164,239.103) gion 
(0.164,239.103) is 
(0.164,239.103) an 
(0.164,239.103) subprogram 
(0.164,239.103) w 
(0.164,239.103) orth 
(0.164,239.103) optimizing 
(0.164,239.103) that 
(0.164,239.103) can 
(0.164,239.103) include 
(0.164,239.103) subsets 
(0.164,239.103) of 
(0.164,239.103) an 
(0.164,239.103) y 
(0.164,239.103) number 
(0.164,239.103) of 
(0.164,239.103) methods. 
(0.164,239.103) Thus, 
(0.164,239.103) the 
(0.164,239.103) com- 
(0.164,239.103) piler 
(0.164,239.103) has 
(0.164,239.103) more 
(0.164,239.103) fle 
(0.164,239.103) xibility 
(0.164,239.103) and 
(0.164,239.103) can 
(0.164,239.103) potentially 
(0.164,239.103) generate 
(0.164,239.103) better 
(0.164,239.103) code, 
(0.164,239.103) b 
(0.164,239.103) ut 
(0.164,239.103) the 
(0.164,239.103) profiling 
(0.164,239.103) and 
(0.164,239.103) compilation 
(0.164,239.103) systems 
(0.164,239.103) are 
(0.164,239.103) correspondingly 
(0.164,239.103) more 
(0.164,239.103) comple 
(0.164,239.103) x. 
(0.164,239.103) T 
(0.164,239.103) ype 
(0.164,239.103) specialization 
(0.164,239.103) f 
(0.164,239.103) or 
(0.164,239.103) dynamic 
(0.164,239.103) languages. 
(0.164,239.103) Dynamic 
(0.164,239.103) lan- 
(0.164,239.103) guage 
(0.164,239.103) implementors 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) long 
(0.164,239.103) recognized 
(0.164,239.103) the 
(0.164,239.103) im 
(0.164,239.103) portance 
(0.164,239.103) of 
(0.164,239.103) type 
(0.164,239.103) specialization 
(0.164,239.103) for 
(0.164,239.103) performance. 
(0.164,239.103) Most 
(0.164,239.103) pre 
(0.164,239.103) vious 
(0.164,239.103) w 
(0.164,239.103) ork 
(0.164,239.103) has 
(0.164,239.103) focused 
(0.164,239.103) on 
(0.164,239.103) methods 
(0.164,239.103) instead 
(0.164,239.103) of 
(0.164,239.103) traces. 
(0.164,239.103) Chambers 
(0.164,239.103) et. 
(0.164,239.103) al 
(0.164,239.103) (9) 
(0.164,239.103) pioneered 
(0.164,239.103) the 
(0.164,239.103) idea 
(0.164,239.103) of 
(0.164,239.103) compiling 
(0.164,239.103) multiple 
(0.164,239.103) v 
(0.164,239.103) ersions 
(0.164,239.103) of 
(0.164,239.103) a 
(0.164,239.103) procedure 
(0.164,239.103) specialized 
(0.164,239.103) for 
(0.164,239.103) the 
(0.164,239.103) input 
(0.164,239.103) types 
(0.164,239.103) in 
(0.164,239.103) the 
(0.164,239.103) lan- 
(0.164,239.103) guage 
(0.164,239.103) Self. 
(0.164,239.103) In 
(0.164,239.103) one 
(0.164,239.103) implementation, 
(0.164,239.103) the 
(0.164,239.103) y 
(0.164,239.103) generated 
(0.164,239.103) a 
(0.164,239.103) specialized 
(0.164,239.103) method 
(0.164,239.103) online 
(0.164,239.103) each 
(0.164,239.103) time 
(0.164,239.103) a 
(0.164,239.103) method 
(0.164,239.103) w 
(0.164,239.103) as 
(0.164,239.103) called 
(0.164,239.103) with 
(0.164,239.103) ne 
(0.164,239.103) w 
(0.164,239.103) input 
(0.164,239.103) types. 
(0.164,239.103) In 
(0.164,239.103) another 
(0.164,239.103) , 
(0.164,239.103) the 
(0.164,239.103) y 
(0.164,239.103) used 
(0.164,239.103) an 
(0.164,239.103) of 
(0.164,239.103) fline 
(0.164,239.103) whole-program 
(0.164,239.103) static 
(0.164,239.103) analysis 
(0.164,239.103) to 
(0.164,239.103) infer 
(0.164,239.103) input 
(0.164,239.103) types 
(0.164,239.103) and 
(0.164,239.103) constant 
(0.164,239.103) recei 
(0.164,239.103) v 
(0.164,239.103) er 
(0.164,239.103) types 
(0.164,239.103) at 
(0.164,239.103) call 
(0.164,239.103) sites. 
(0.164,239.103) Interest- 
(0.164,239.103) ingly 
(0.164,239.103) , 
(0.164,239.103) the 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) techniques 
(0.164,239.103) produced 
(0.164,239.103) nearly 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) performance. 
(0.164,239.103) Salib 
(0.164,239.103) (17) 
(0.164,239.103) designed 
(0.164,239.103) a 
(0.164,239.103) type 
(0.164,239.103) inference 
(0.164,239.103) algorithm 
(0.164,239.103) for 
(0.164,239.103) Python 
(0.164,239.103) based 
(0.164,239.103) on 
(0.164,239.103) the 
(0.164,239.103) Cartesian 
(0.164,239.103) Produc 
(0.164,239.103) t 
(0.164,239.103) Algorithm 
(0.164,239.103) and 
(0.164,239.103) used 
(0.164,239.103) the 
(0.164,239.103) results 
(0.164,239.103) to 
(0.164,239.103) special- 
(0.164,239.103) ize 
(0.164,239.103) on 
(0.164,239.103) types 
(0.164,239.103) and 
(0.164,239.103) translate 
(0.164,239.103) the 
(0.164,239.103) program 
(0.164,239.103) to 
(0.164,239.103) C++. 
(0.164,239.103) McClosk 
(0.164,239.103) e 
(0.164,239.103) y 
(0.164,239.103) (14) 
(0.164,239.103) has 
(0.164,239.103) w 
(0.164,239.103) ork 
(0.164,239.103) in 
(0.164,239.103) progress 
(0.164,239.103) based 
(0.164,239.103) on 
(0.164,239.103) a 
(0.164,239.103) language- 
(0.164,239.103) independent 
(0.164,239.103) t 
(0.164,239.103) ype 
(0.164,239.103) inference 
(0.164,239.103) that 
(0.164,239.103) is 
(0.164,239.103) used 
(0.164,239.103) to 
(0.164,239.103) generate 
(0.164,239.103) ef 
(0.164,239.103) ficient 
(0.164,239.103) C 
(0.164,239.103) implementations 
(0.164,239.103) of 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) and 
(0.164,239.103) Python 
(0.164,239.103) programs. 
(0.164,239.103) Nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) generation 
(0.164,239.103) by 
(0.164,239.103) inter 
(0.164,239.103) pr 
(0.164,239.103) eters. 
(0.164,239.103) The 
(0.164,239.103) traditional 
(0.164,239.103) inter 
(0.164,239.103) - 
(0.164,239.103) preter 
(0.164,239.103) design 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) virtual 
(0.164,239.103) machine 
(0.164,239.103) that 
(0.164,239.103) directly 
(0.164,239.103) e 
(0.164,239.103) x 
(0.164,239.103) ecutes 
(0.164,239.103) ASTs 
(0.164,239.103) or 
(0.164,239.103) machine-code-lik 
(0.164,239.103) e 
(0.164,239.103) bytecodes. 
(0.164,239.103) Researchers 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) sho 
(0.164,239.103) wn 
(0.164,239.103) ho 
(0.164,239.103) w 
(0.164,239.103) to 
(0.164,239.103) gen- 
(0.164,239.103) erate 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) with 
(0.164,239.103) nearly 
(0.164,239.103) the 
(0.164,239.103) same 
(0.164,239.103) structure 
(0.164,239.103) b 
(0.164,239.103) ut 
(0.164,239.103) better 
(0.164,239.103) perfor 
(0.164,239.103) - 
(0.164,239.103) mance. 
(0.164,239.103) Call 
(0.164,239.103) threading, 
(0.164,239.103) also 
(0.164,239.103) kno 
(0.164,239.103) wn 
(0.164,239.103) as 
(0.164,239.103) conte 
(0.164,239.103) xt 
(0.164,239.103) threading 
(0.164,239.103) (8), 
(0.164,239.103) compiles 
(0.164,239.103) methods 
(0.164,239.103) by 
(0.164,239.103) generating 
(0.164,239.103) a 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) call 
(0.164,239.103) instruction 
(0.164,239.103) to 
(0.164,239.103) an 
(0.164,239.103) interpreter 
(0.164,239.103) method 
(0.164,239.103) for 
(0.164,239.103) each 
(0.164,239.103) interpreter 
(0.164,239.103) bytecode. 
(0.164,239.103) A 
(0.164,239.103) call-return 
(0.164,239.103) pair 
(0.164,239.103) has 
(0.164,239.103) been 
(0.164,239.103) sho 
(0.164,239.103) wn 
(0.164,239.103) to 
(0.164,239.103) be 
(0.164,239.103) a 
(0.164,239.103) potentially 
(0.164,239.103) much 
(0.164,239.103) more 
(0.164,239.103) e 
(0.164,239.103) f 
(0.164,239.103) ficient 
(0.164,239.103) dispatch 
(0.164,239.103) mechanism 
(0.164,239.103) than 
(0.164,239.103) the 
(0.164,239.103) indirect 
(0.164,239.103) jumps 
(0.164,239.103) used 
(0.164,239.103) in 
(0.164,239.103) standard 
(0.164,239.103) bytecode 
(0.164,239.103) interpreters. 
(0.164,239.103) Inline 
(0.164,239.103) threading 
(0.164,239.103) (15) 
(0.164,239.103) copies 
(0.164,239.103) chunks 
(0.164,239.103) of 
(0.164,239.103) interpre 
(0.164,239.103) ter 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) which 
(0.164,239.103) implement 
(0.164,239.103) the 
(0.164,239.103) required 
(0.164,239.103) bytecodes 
(0.164,239.103) into 
(0.164,239.103) a 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) cache, 
(0.164,239.103) thus 
(0.164,239.103) acting 
(0.164,239.103) as 
(0.164,239.103) a 
(0.164,239.103) simple 
(0.164,239.103) per 
(0.164,239.103) -method 
(0.164,239.103) JIT 
(0.164,239.103) compi 
(0.164,239.103) ler 
(0.164,239.103) that 
(0.164,239.103) eliminates 
(0.164,239.103) the 
(0.164,239.103) dispatch 
(0.164,239.103) o 
(0.164,239.103) v 
(0.164,239.103) erhead. 
(0.164,239.103) Neither 
(0.164,239.103) call 
(0.164,239.103) threading 
(0.164,239.103) nor 
(0.164,239.103) inline 
(0.164,239.103) threading 
(0.164,239.103) perform 
(0.164,239.103) type 
(0.164,239.103) special- 
(0.164,239.103) ization. 
(0.164,239.103) Apple’ 
(0.164,239.103) s 
(0.164,239.103) SquirrelFish 
(0.164,239.103) Extreme 
(0.164,239.103) (5) 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) implementa- 
(0.164,239.103) tion 
(0.164,239.103) based 
(0.164,239.103) on 
(0.164,239.103) call 
(0.164,239.103) threading 
(0.164,239.103) with 
(0.164,239.103) selecti 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) inline 
(0.164,239.103) threading. 
(0.164,239.103) Com- 
(0.164,239.103) bined 
(0.164,239.103) with 
(0.164,239.103) ef 
(0.164,239.103) ficient 
(0.164,239.103) interpreter 
(0.164,239.103) engineering, 
(0.164,239.103) these 
(0.164,239.103) threading 
(0.164,239.103) tech- 
(0.164,239.103) niques 
(0.164,239.103) ha 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) gi 
(0.164,239.103) v 
(0.164,239.103) en 
(0.164,239.103) SFX 
(0.164,239.103) e 
(0.164,239.103) xcellent 
(0.164,239.103) performance 
(0.164,239.103) on 
(0.164,239.103) the 
(0.164,239.103) standard 
(0.164,239.103) Sun- 
(0.164,239.103) Spider 
(0.164,239.103) benchmarks. 
(0.164,239.103) Google’ 
(0.164,239.103) s 
(0.164,239.103) V8 
(0.164,239.103) is 
(0.164,239.103) a 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
(0.164,239.103) implementation 
(0.164,239.103) primarily 
(0.164,239.103) based 
(0.164,239.103) on 
(0.164,239.103) inline 
(0.164,239.103) threading, 
(0.164,239.103) with 
(0.164,239.103) call 
(0.164,239.103) threading 
(0.164,239.103) only 
(0.164,239.103) for 
(0.164,239.103) v 
(0.164,239.103) ery 
(0.164,239.103) comple 
(0.164,239.103) x 
(0.164,239.103) operations. 
(0.164,239.103) 9. 
(0.164,239.103) Conclusions 
(0.164,239.103) This 
(0.164,239.103) paper 
(0.164,239.103) described 
(0.164,239.103) ho 
(0.164,239.103) w 
(0.164,239.103) to 
(0.164,239.103) run 
(0.164,239.103) dynamic 
(0.164,239.103) languages 
(0.164,239.103) ef 
(0.164,239.103) ficiently 
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(0.164,239.103) recording 
(0.164,239.103) hot 
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(0.164,239.103) and 
(0.164,239.103) generating 
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(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code. 
(0.164,239.103) Our 
(0.164,239.103) technique 
(0.164,239.103) focuses 
(0.164,239.103) on 
(0.164,239.103) aggressi 
(0.164,239.103) v 
(0.164,239.103) ely 
(0.164,239.103) inlined 
(0.164,239.103) loops, 
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(0.164,239.103) for 
(0.164,239.103) each 
(0.164,239.103) loop, 
(0.164,239.103) it 
(0.164,239.103) generates 
(0.164,239.103) a 
(0.164,239.103) tree 
(0.164,239.103) of 
(0.164,239.103) nati 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) traces 
(0.164,239.103) represe 
(0.164,239.103) nting 
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(0.164,239.103) and 
(0.164,239.103) v 
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(0.164,239.103) types 
(0.164,239.103) through 
(0.164,239.103) the 
(0.164,239.103) loop 
(0.164,239.103) observ 
(0.164,239.103) ed 
(0.164,239.103) at 
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(0.164,239.103) time. 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) e 
(0.164,239.103) xplained 
(0.164,239.103) ho 
(0.164,239.103) w 
(0.164,239.103) to 
(0.164,239.103) identify 
(0.164,239.103) loop 
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(0.164,239.103) and 
(0.164,239.103) generate 
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(0.164,239.103) traces 
(0.164,239.103) in 
(0.164,239.103) order 
(0.164,239.103) to 
(0.164,239.103) a 
(0.164,239.103) v 
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(0.164,239.103) e 
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(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) code 
(0.164,239.103) duplication 
(0.164,239.103) due 
(0.164,239.103) to 
(0.164,239.103) the 
(0.164,239.103) man 
(0.164,239.103) y 
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(0.164,239.103) a 
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(0.164,239.103) nest. 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) described 
(0.164,239.103) our 
(0.164,239.103) type 
(0.164,239.103) specialization 
(0.164,239.103) algorithm. 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) also 
(0.164,239.103) des 
(0.164,239.103) cribed 
(0.164,239.103) our 
(0.164,239.103) trace 
(0.164,239.103) compiler 
(0.164,239.103) , 
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(0.164,239.103) from 
(0.164,239.103) an 
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(0.164,239.103) optimized 
(0.164,239.103) nati 
(0.164,239.103) v 
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(0.164,239.103) code 
(0.164,239.103) in 
(0.164,239.103) tw 
(0.164,239.103) o 
(0.164,239.103) linear 
(0.164,239.103) passes. 
(0.164,239.103) Our 
(0.164,239.103) e 
(0.164,239.103) xperimental 
(0.164,239.103) results 
(0.164,239.103) sho 
(0.164,239.103) w 
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(0.164,239.103) in 
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(0.164,239.103) loops 
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(0.164,239.103) only 
(0.164,239.103) a 
(0.164,239.103) fe 
(0.164,239.103) w 
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(0.164,239.103) ferent 
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(0.164,239.103) of 
(0.164,239.103) v 
(0.164,239.103) alue 
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(0.164,239.103) of 
(0.164,239.103) v 
(0.164,239.103) ariables. 
(0.164,239.103) Thus, 
(0.164,239.103) a 
(0.164,239.103) small 
(0.164,239.103) number 
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(0.164,239.103) is 
(0.164,239.103) suf 
(0.164,239.103) ficient 
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(0.164,239.103) run 
(0.164,239.103) a 
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(0.164,239.103) ef 
(0.164,239.103) fi 
(0.164,239.103) ciently 
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(0.164,239.103) also 
(0.164,239.103) sho 
(0.164,239.103) w 
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(0.164,239.103) amenable 
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(0.164,239.103) tracing, 
(0.164,239.103) we 
(0.164,239.103) achie 
(0.164,239.103) v 
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(0.164,239.103) speedups 
(0.164,239.103) of 
(0.164,239.103) 2x 
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(0.164,239.103) e 
(0.164,239.103) W 
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(0.164,239.103) in 
(0.164,239.103) a 
(0.164,239.103) number 
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(0.164,239.103) to 
(0.164,239.103) further 
(0.164,239.103) impro 
(0.164,239.103) v 
(0.164,239.103) e 
(0.164,239.103) the 
(0.164,239.103) performance 
(0.164,239.103) of 
(0.164,239.103) our 
(0.164,239.103) trace-based 
(0.164,239.103) Ja 
(0.164,239.103) v 
(0.164,239.103) aScript 
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(0.164,239.103) . 
(0.164,239.103) W 
(0.164,239.103) e 
(0.164,239.103) currently 
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(0.164,239.103) trace 
(0.164,239.103) across 
(0.164,239.103) recursi 
(0.164,239.103) v 
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(0.164,239.103) function 
(0.164,239.103) call 
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(0.164,239.103) b 
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(0.164,239.103) add 
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(0.164,239.103) support 
(0.164,239.103) for 
(0.164,239.103) this 
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(0.164,239.103) y 
(0.164,239.103) in 
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(0.164,239.103) dynamic 
(0.164,239.103) compiler 
(0.164,239.103) in 
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(0.164,239.103) to 
(0.164,239.103) minimize 
(0.164,239.103) JIT 
(0.164,239.103) pause 
(0.164,239.103) times 
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(0.164,239.103) the 
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(0.164,239.103) as 
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(0.164,239.103) code 
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(0.164,239.103) W 
(0.164,239.103) e 
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(0.164,239.103) on 
(0.164,239.103) adding 
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(0.164,239.103) for 
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(0.164,239.103) across 
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(0.164,239.103) gular 
(0.164,239.103) e 
(0.164,239.103) x- 
(0.164,239.103) pression 
(0.164,239.103) substitutions 
(0.164,239.103) using 
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(0.164,239.103) e 
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(0.164,239.103) ecuted 
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(0.164,239.103) v 
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(0.164,239.103) the 
(0.164,239.103) National 
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(0.164,239.103) F 
(0.164,239.103) oundation 
(0.164,239.103) under 
(0.164,239.103) grants 
(0.164,239.103) CNS-0615443 
(0.164,239.103) and 
(0.164,239.103) CNS-0627747, 
(0.164,239.103) as 
(0.164,239.103) well 
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(0.164,239.103) The 
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(0.164,239.103) Go 
(0.164,239.103) v 
(0.164,239.103) ernment 
(0.164,239.103) is 
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(0.164,239.103) ute 
(0.164,239.103) reprints 
(0.164,239.103) for 
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(0.164,239.103) purposes 
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(0.164,239.103) y 
(0.164,239.103) opinions, 
(0.164,239.103) findings, 
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(0.164,239.103) the 
(0.164,239.103) author 
(0.164,239.103) and 
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(0.000,0.000) ws, 
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(0.000,0.000) foundation 
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(0.000,0.000) roadmap 
(0.000,0.000) 2008 
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(0.000,0.000) http://lua-users.or 
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(0.000,0.000) [2] 
(0.000,0.000) Mozilla 
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(0.000,0.000) email 
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(0.000,0.000) - 
(0.000,0.000) http://www 
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(0.000,0.000) [3] 
(0.000,0.000) SPECJVM98 
(0.000,0.000) - 
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(0.000,0.000) Compilers: 
(0.000,0.000) Principles, 
(0.000,0.000) techniques, 
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(0.000,0.000) V 
(0.000,0.000) irtual 
(0.000,0.000) Machine 
(0.000,0.000) In- 
(0.000,0.000) terpreters. 
(0.000,0.000) In 
(0.000,0.000) Code 
(0.000,0.000) Gener 
(0.000,0.000) ation 
(0.000,0.000) and 
(0.000,0.000) Optimization, 
(0.000,0.000) 2005. 
(0.000,0.000) CGO 
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(0.000,0.000) Customization: 
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(0.000,0.000) Compiler 
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(0.000,0.000) echnology 
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(0.000,0.000) , 
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(0.000,0.000) O 
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(0.000,0.000) Pro- 
(0.000,0.000) gramming 
(0.000,0.000) Language. 
(0.000,0.000) In 
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(0.000,0.000) Gal. 
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(0.000,0.000) Bytecode 
(0.000,0.000) V 
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(0.000,0.000) and 
(0.000,0.000) Compilation 
(0.000,0.000) in 
(0.000,0.000) a 
(0.000,0.000) V 
(0.000,0.000) irtual 
(0.000,0.000) Mac 
(0.000,0.000) hine 
(0.000,0.000) Dissertation 
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(0.000,0.000) PhD 
(0.000,0.000) thesis, 
(0.000,0.000) Uni 
(0.000,0.000) v 
(0.000,0.000) ersity 
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(0.000,0.000) Franz. 
(0.000,0.000) HotpathVM: 
(0.000,0.000) An 
(0.000,0.000) ef 
(0.000,0.000) fecti 
(0.000,0.000) v 
(0.000,0.000) e 
(0.000,0.000) JIT 
(0.000,0.000) compiler 
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(0.000,0.000) resource-constrained 
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(0.000,0.000) Execution 
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(0.000,0.000) , 
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(0.000,0.000) Chambers. 
(0.000,0.000) Measurement 
(0.000,0.000) and 
(0.000,0.000) Application 
(0.000,0.000) of 
(0.000,0.000) Dynamic 
(0.000,0.000) Recei 
(0.000,0.000) v 
(0.000,0.000) er 
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(0.000,0.000) Distrib 
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(0.000,0.000) A 
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(0.000,0.000) just-in-time 
(0.000,0.000) compiler 
(0.000,0.000) for 
(0.000,0.000) ja 
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(0.000,0.000) Dept.of 
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(0.000,0.000) at 
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(0.000,0.000) Piumarta 
(0.000,0.000) and 
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(0.000,0.000) Optimizing 
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(0.000,0.000) code 
(0.000,0.000) by 
(0.000,0.000) selec- 
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(0.000,0.000) Specialization 
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(0.000,0.000) ype 
(0.000,0.000) Inferencer 
(0.000,0.000) and 
(0.000,0.000) C 
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(0.000,0.000) Master’ 
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(0.000,0.000) Thesis 
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(0.000,0.000) tion 
(0.000,0.000) T 
(0.000,0.000) echnique 
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(0.000,0.000) Dynamic 
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(0.000,0.000) and 
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(0.000,0.000) YETI: 
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(0.000,0.000) In 
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