BT
/F41 8.9664 Tf 54 712.0299 Td[(6.5)-1000(Calling)-250(Exter)15(nal)-250(Functions)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(Lik)10(e)-254(most)-254(interpreters,)-254(SpiderMonk)10(e)15(y)-254(has)-254(a)-254(foreign)-254(function)-254(inter)20(-)]TJ 0 -9.9626 Td[(f)10(ace)-231(\050FFI\051)-232(that)-231(allo)25(ws)-232(it)-231(to)-232(call)-231(C)-232(b)20(uiltins)-231(and)-232(host)-231(system)-232(functions)]TJ 0 -9.9627 Td[(\050e.g.,)-301(web)-301(bro)25(wser)-301(control)-301(and)-300(DOM)-301(access\051.)-301(The)-301(FFI)-301(has)-301(a)-301(stan-)]TJ 0 -9.9626 Td[(dard)-225(signat)1(ure)-225(for)-225(JS-callable)-224(functions,)-225(the)-224(k)10(e)15(y)-225(ar)18(gument)-224(of)-225(which)]TJ 0 -9.9627 Td[(is)-313(an)-313(array)-313(of)-313(box)15(ed)-312(v)25(alues.)-313(External)-313(functions)-313(called)-313(through)-313(the)]TJ 0 -9.9626 Td[(FFI)-214(interact)-215(with)-214(the)-214(program)-215(state)-214(through)-215(an)-214(interpreter)-214(API)-215(\050e.g.,)]TJ 0 -9.9626 Td[(to)-280(read)-279(a)-280(property)-279(from)-280(an)-279(ar)18(gument\051.)-280(There)-279(are)-280(also)-279(certain)-280(inter)20(-)]TJ 0 -9.9627 Td[(preter)-223(b)20(uiltins)-224(that)-223(do)-224(not)-223(use)-223(the)-224(FFI,)-223(b)20(ut)-224(interact)-223(with)-223(the)-224(program)]TJ 0 -9.9626 Td[(state)-369(i)1(n)-369(the)-369(same)-368(w)10(ay)65(,)-369(such)-368(as)-369(the)]TJ/F33 8.9664 Tf 130.5975 0 Td[(CallIteratorNext)]TJ/F42 8.9664 Tf 78.6212 0 Td[(function)]TJ -209.2187 -9.9627 Td[(used)-325(with)-325(it)1(erator)-325(objects.)-325(T)35(raceMonk)10(e)15(y)-325(must)-324(support)-325(this)-325(FFI)-325(in)]TJ 0 -9.9626 Td[(order)-218(to)-218(speed)-217(up)-218(code)-218(that)-218(interacts)-218(with)-217(the)-218(host)-218(system)-218(inside)-218(hot)]TJ 0 -9.9626 Td[(loops.)]TJ 11.9552 -9.9627 Td[(Calling)-225(e)15(xternal)-226(functions)-225(from)-226(T)35(raceMonk)10(e)15(y)-225(is)-226(potentially)-225(dif-)]TJ -11.9552 -9.9626 Td[(\002cult)-330(because)-330(trac)1(es)-330(do)-330(not)-330(update)-330(the)-329(interpreter)-330(state)-330(until)-330(e)15(xit-)]TJ 0 -9.9627 Td[(ing.)-268(In)-268(particular)40(,)-268(e)15(xternal)-269(functions)-268(may)-268(need)-268(the)-268(call)-268(stack)-269(or)-268(the)]TJ 0 -9.9626 Td[(global)-250(v)25(ariables,)-250(b)20(ut)-250(the)15(y)-250(may)-250(be)-250(out)-250(of)-250(date.)]TJ 11.9552 -9.9626 Td[(F)15(or)-340(the)-340(out-of-date)-340(call)-340(stack)-340(problem,)-340(we)-340(re)1(f)10(actored)-340(some)-340(of)]TJ -11.9552 -9.9627 Td[(the)-302(interpreter)-303(API)-302(implementation)-302(functions)-302(to)-302(re-materialize)-303(the)]TJ 0 -9.9626 Td[(interpreter)-250(call)-250(stack)-250(on)-250(demand.)]TJ 11.9552 -9.9627 Td[(W)80(e)-311(de)26(v)14(e)1(loped)-311(a)-310(C++)-311(static)-310(analysis)-311(and)-310(annotated)-311(some)-310(inter)20(-)]TJ -11.9552 -9.9626 Td[(preter)-361(funct)1(ions)-361(in)-361(order)-360(to)-361(v)15(erify)-360(that)-361(the)-360(call)-361(stack)-360(is)-361(refreshed)]TJ 0 -9.9626 Td[(at)-327(an)15(y)-327(point)-327(it)-326(needs)-327(to)-327(be)-327(used.)-327(In)-327(order)-326(to)-327(access)-327(the)-327(call)-327(stack,)]TJ 0 -9.9627 Td[(a)-470(function)-469(must)-470(be)-469(annotated)-470(as)-469(either)-495(F)]TJ/F42 7.1731 Tf 157.6439 0 Td[(O)-62(R)-61(C)-62(E)-62(S)]TJ/F42 8.9664 Tf 25.3297 0 Td[(S)]TJ/F42 7.1731 Tf 5.4335 0 Td[(T)31(A)-22(C)-61(K)]TJ/F42 8.9664 Tf 24.3304 0 Td[(or)-495(R)]TJ/F42 7.1731 Tf 18.3321 0 Td[(E)]TJ/F42 8.9664 Tf 4.8238 0 Td[(-)]TJ/F42 7.1731 Tf -235.6693 -9.9626 Td[(Q)-52(U)-61(I)-62(R)-62(E)-62(S)]TJ/F42 8.9664 Tf 28.4857 0 Td[(S)]TJ/F42 7.1731 Tf 5.4336 0 Td[(T)31(A)-22(C)-61(K)]TJ/F42 8.9664 Tf 20.1202 0 Td[(.)-232(These)-233(annotations)-232(are)-233(also)-232(required)-233(i)1(n)-233(order)-232(to)-233(call)]TJ -54.0395 -9.9627 Td[(R)]TJ/F42 7.1731 Tf 6.4288 0 Td[(E)-61(Q)-52(U)-62(I)-62(R)-62(E)-61(S)]TJ/F42 8.9664 Tf 33.3095 0 Td[(S)]TJ/F42 7.1731 Tf 5.4336 0 Td[(T)31(A)-22(C)-61(K)]TJ/F42 8.9664 Tf 22.1792 0 Td[(functions,)-230(which)-229(are)-230(presumed)-229(to)-230(access)-230(the)-229(call)]TJ -67.5752 -9.9626 Td[(stack)-345(transi)1(ti)25(v)15(ely)65(.)-370(F)]TJ/F42 7.1731 Tf 71.9106 0 Td[(O)-62(R)-61(C)-62(E)-62(S)]TJ/F42 8.9664 Tf 25.3297 0 Td[(S)]TJ/F42 7.1731 Tf 5.4336 0 Td[(T)31(A)-22(C)-61(K)]TJ/F42 8.9664 Tf 23.2098 0 Td[(is)-345(a)-344(trusted)-345(annotation,)-344(applied)]TJ -125.8837 -9.9626 Td[(to)-223(only)-222(5)-223(functions,)-222(that)-223(means)-223(the)-222(function)-223(refreshes)-222(the)-223(call)-223(stack.)]TJ 0.2241 -9.9627 Td[(R)]TJ/F42 7.1731 Tf 6.4288 0 Td[(E)-61(Q)-52(U)-62(I)-62(R)-62(E)-61(S)]TJ/F42 8.9664 Tf 33.3096 0 Td[(S)]TJ/F42 7.1731 Tf 5.4335 0 Td[(T)31(A)-22(C)-61(K)]TJ/F42 8.9664 Tf 22.8303 0 Td[(is)-302(an)-302(untrusted)-303(annotation)-302(that)-302(means)-302(the)-303(func-)]TJ -68.2263 -9.9626 Td[(tion)-234(may)-235(only)-234(be)-235(called)-234(if)-234(the)-235(call)-234(stack)-235(has)-234(already)-234(been)-235(refreshed.)]TJ 11.9551 -9.9627 Td[(Similarly)65(,)-435(we)-436(detect)-435(when)-436(host)-435(functions)-436(attem)1(pt)-436(to)-435(directly)]TJ -11.9551 -9.9626 Td[(read)-234(or)-234(write)-234(global)-233(v)25(ariables,)-234(and)-234(force)-234(the)-234(currently)-234(running)-234(trace)]TJ 0 -9.9626 Td[(to)-388(side)-388(e)15(xit.)-388(This)-389(is)-388(necessary)-388(since)-388(we)-388(cache)-388(and)-389(unbox)-388(global)]TJ 0 -9.9627 Td[(v)25(ariables)-250(into)-250(the)-250(acti)25(v)25(ation)-250(record)-250(during)-250(trace)-250(e)15(x)15(ecution.)]TJ 11.9551 -9.9626 Td[(Since)-504(both)-504(call-stack)-504(access)-504(and)-504(global)-504(v)25(ariable)-504(access)-504(are)]TJ -11.9551 -9.9627 Td[(rarely)-198(performed)-199(by)-198(host)-199(functions,)-198(performance)-199(is)-198(not)-199(signi\002cantly)]TJ 0 -9.9626 Td[(af)25(fected)-250(by)-250(these)-250(safety)-250(mechanisms.)]TJ 11.9551 -9.9626 Td[(Another)-233(problem)-233(is)-233(that)-233(e)15(xternal)-233(functions)-233(can)-233(ree)1(nter)-233(the)-233(inter)20(-)]TJ -11.9551 -9.9627 Td[(preter)-287(by)-287(calling)-287(scripts,)-287(which)-287(in)-287(turn)-287(ag)5(ain)-288(m)1(ight)-288(w)10(ant)-287(to)-287(access)]TJ 0 -9.9626 Td[(the)-217(call)-217(stack)-217(or)-217(global)-217(v)25(ariables.)-217(T)80(o)-217(address)-217(this)-218(problem,)-217(we)-217(made)]TJ 0 -9.9627 Td[(the)-203(VM)-203(set)-203(a)-203(\003ag)-203(whene)25(v)15(er)-203(the)-203(interpreter)-203(is)-204(r)1(eentered)-204(while)-203(a)-203(com-)]TJ 0 -9.9626 Td[(piled)-250(trace)-250(is)-250(running.)]TJ 11.9551 -9.9626 Td[(Ev)15(ery)-232(call)-232(to)-231(an)-232(e)15(xternal)-232(function)-232(then)-231(checks)-232(this)-232(\003ag)-232(and)-231(e)15(xits)]TJ -11.9551 -9.9627 Td[(the)-206(trace)-206(immediately)-206(after)-206(returning)-206(from)-206(the)-207(e)15(xternal)-206(function)-206(call)]TJ 0 -9.9626 Td[(if)-282(it)-281(is)-282(set.)-282(There)-282(are)-281(man)15(y)-282(e)15(xternal)-282(functions)-282(t)1(hat)-282(seldom)-282(or)-282(ne)25(v)15(er)]TJ 0 -9.9627 Td[(reenter)40(,)-395(and)-395(the)15(y)-395(can)-395(be)-395(called)-395(without)-395(problem,)-395(and)-395(will)-395(cause)]TJ 0 -9.9626 Td[(trace)-250(e)15(xit)-250(only)-250(if)-250(necessary)65(.)]TJ 11.9551 -9.9626 Td[(The)-423(FFI')55(s)-422(box)15(ed)-423(v)25(alue)-422(array)-423(requirement)-422(has)-423(a)-422(performance)]TJ -11.9551 -9.9627 Td[(cost,)-369(so)-370(we)-369(de\002ned)-370(a)-369(ne)25(w)-370(FFI)-369(that)-370(allo)25(w)1(s)-370(C)-369(functions)-370(to)-369(be)-370(an-)]TJ 0 -9.9626 Td[(notated)-320(with)-320(their)-321(ar)18(gument)-320(types)-320(so)-320(that)-321(the)-320(tracer)-320(can)-320(call)-321(them)]TJ 0 -9.9627 Td[(directly)65(,)-250(without)-250(unnecessary)-250(ar)18(gument)-250(con)40(v)15(ersions.)]TJ 11.9551 -9.9626 Td[(Currently)65(,)-258(we)-258(do)-258(not)-258(support)-258(calling)-258(nati)25(v)15(e)-258(property)-258(get)-258(and)-258(set)]TJ -11.9551 -9.9626 Td[(o)15(v)15(erride)-299(functions)-300(or)-299(DOM)-300(functions)-299(directly)-300(from)-299(trace.)-300(Support)]TJ 0 -9.9627 Td[(is)-250(planned)-250(future)-250(w)10(ork.)]TJ/F41 8.9664 Tf 0 -17.9327 Td[(6.6)-1000(Corr)18(ectness)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(During)-482(de)25(v)15(elopment,)-481(we)-482(had)-482(access)-482(to)-481(e)15(xisting)-482(Ja)20(v)25(aScript)-482(test)]TJ 0 -9.9627 Td[(suites,)-363(b)20(ut)-363(most)-363(of)-363(them)-363(were)-363(not)-363(designed)-363(with)-364(tracing)-363(VMs)-363(in)]TJ 0 -9.9626 Td[(mind)-250(and)-250(contained)-250(fe)25(w)-250(loops.)]TJ 11.9551 -9.9626 Td[(One)-346(tool)-346(that)-346(helped)-346(us)-346(greatly)-346(w)10(as)-346(Mozilla')55(s)-346(Ja)20(v)25(aScript)-346(fuzz)]TJ -11.9551 -9.9627 Td[(tester)40(,)]TJ/F42 7.1731 Tf 24.6182 0 Td[(J)-62(S)-62(F)-61(U)-62(N)-62(F)-61(U)-62(Z)-61(Z)]TJ/F42 8.9664 Tf 42.8138 0 Td[(,)-345(which)-344(generates)-345(random)-345(Ja)20(v)25(aScript)-344(programs)]TJ -67.432 -9.9626 Td[(by)-378(nesting)-377(random)-378(language)-378(elements.)-377(W)80(e)-378(modi\002ed)]TJ/F42 7.1731 Tf 196.2896 0 Td[(J)-62(S)-62(F)-61(U)-62(N)-62(F)-61(U)-62(Z)-61(Z)]TJ/F42 8.9664 Tf -196.2896 -9.9627 Td[(to)-311(generate)-311(loops,)-310(and)-311(also)-311(to)-311(test)-310(more)-311(hea)20(vily)-311(certain)-311(constructs)]TJ 0 -9.9626 Td[(we)-236(suspected)-237(w)10(ould)-236(re)25(v)15(eal)-236(\003a)15(ws)-236(in)-237(our)-236(implementation.)-236(F)15(or)-237(e)15(xam-)]TJ 0 -9.9626 Td[(ple,)-195(we)-194(suspected)-195(b)20(ugs)-194(in)-195(T)35(raceMonk)10(e)15(y')55(s)-195(handling)-194(of)-195(type-unstable)]TJ
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Td[(cuted)-304(by)-303(compiled)-304(traces.)-303(Three)-304(of)-303(the)-304(benchmarks)-304(are)-303(not)-304(traced)]TJ 0 -9.9627 Td[(at)-250(all)-250(and)-250(run)-250(in)-250(the)-250(interpreter)55(.)]TJ 0 -29.4951 Td[(loops)-267(and)-266(hea)20(vily)-267(branching)-266(code,)-267(and)-266(a)-267(specialized)-267(fuzz)-266(tester)-267(in-)]TJ 0 -9.9627 Td[(deed)-193(re)25(v)15(ealed)-194(se)25(v)15(eral)-193(re)15(gressions)-194(which)-193(we)-193(subsequently)-194(corrected.)]TJ/F41 10.9589 Tf 0 -24.1524 Td[(7.)-1000(Ev)10(aluation)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(W)80(e)-430(e)25(v)25(aluated)-430(our)-431(Ja)20(v)25(aScript)-430(tracing)-430(implementation)-430(using)-431(Sun-)]TJ 0 -9.9626 Td[(Spider)40(,)-290(the)-291(indus)1(try)-291(standard)-290(Ja)20(v)25(aScript)-290(benchmark)-290(suite.)-291(SunSpi-)]TJ 0 -9.9627 Td[(der)-322(consists)-322(of)-323(26)-322(short-running)-322(\050less)-322(than)-322(250ms,)-323(a)20(v)15(era)1(ge)-323(26ms\051)]TJ 0 -9.9626 Td[(Ja)20(v)25(aScript)-298(programs.)-299(This)-299(is)-298(in)-299(stark)-298(contrast)-299(to)-298(benchmark)-299(suites)]TJ 0 -9.9627 Td[(such)-328(as)-329(SpecJVM98)-328(\0503\051)-328(used)-328(to)-329(e)25(v)25(aluate)-328(desktop)-328(and)-328(serv)15(er)-329(Ja)20(v)25(a)]TJ 0 -9.9626 Td[(VMs.)-268(Man)15(y)-267(programs)-268(in)-268(those)-267(benchmarks)-268(use)-268(lar)18(ge)-267(data)-268(sets)-268(and)]TJ 0 -9.9626 Td[(e)15(x)15(ecute)-220(for)-220(minutes.)-220(The)-220(SunSpider)-220(programs)-220(carry)-220(out)-220(a)-220(v)25(ariety)-220(of)]TJ 0 -9.9627 Td[(tasks,)-232(primarily)-232(3d)-232(rendering,)-232(bit-bashing,)-233(cryptographic)-232(encoding,)]TJ 0 -9.9626 Td[(math)-250(k)10(ernels,)-250(and)-250(string)-250(processing.)]TJ 11.9552 -9.9627 Td[(All)-363(e)15(xperiments)-363(were)-364(performed)-363(on)-363(a)-364(MacBook)-363(Pro)-363(with)-363(2.2)]TJ -11.9552 -9.9626 Td[(GHz)-250(Core)-250(2)-250(processor)-250(and)-250(2)-250(GB)-250(RAM)-250(running)-250(MacOS)-250(10.5.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Benchmark)-380(r)18(esults.)]TJ/F42 8.9664 Tf 79.1263 0 Td[(The)-380(main)-380(question)-380(is)-380(whether)-380(programs)]TJ -91.0815 -9.9627 Td[(run)-240(f)10(aster)-240(with)-240(tracing.)-240(F)15(or)-240(this,)-240(we)-240(ran)-240(the)-240(standard)-240(SunSpider)-240(test)]TJ 0 -9.9626 Td[(dri)25(v)15(er)40(,)-389(which)-390(starts)-389(a)-390(Ja)20(v)25(aScript)-389(interpreter)40(,)-389(loads)-390(and)-389(runs)-390(each)]TJ 0 -9.9627 Td[(program)-349(once)-349(for)-349(w)10(armup,)-348(then)-349(loads)-349(and)-349(runs)-349(each)-349(program)-349(10)]TJ 0 -9.9626 Td[(times)-281(and)-281(reports)-281(the)-281(a)20(v)15(erage)-281(time)-281(tak)10(en)-281(by)-281(each.)-281(W)80(e)-282(ran)-281(4)-281(dif)25(fer)20(-)]TJ 0 -9.9626 Td[(ent)-271(con\002gurations)-272(for)-271(comparison:)-272(\050a\051)-271(SpiderMonk)10(e)15(y)65(,)-271(the)-272(baseline)]TJ 0 -9.9627 Td[(interpreter)40(,)-274(\050b\051)-275(T)35(raceMonk)10(e)15(y)65(,)-274(\050d\051)-275(SquirrelFish)-274(Extreme)-274(\050SFX\051,)-275(the)]TJ 0 -9.9626 Td[(call-threaded)-380(Ja)20(v)25(aScript)-380(interpreter)-379(used)-380(in)-380(Apple')55(s)-380(W)80(ebKit,)-380(and)]TJ 0 -9.9627 Td[(\050e\051)-250(V8,)-250(the)-250(method-compiling)-250(Ja)20(v)25(aScript)-250(VM)-250(from)-250(Google.)]TJ 11.9552 -9.9626 Td[(Figure)-197(10)-198(sho)25(ws)-197(the)-197(relati)25(v)15(e)-197(speedups)-198(achie)25(v)15(ed)-197(by)-197(tracing,)-197(SFX,)]TJ -11.9552 -9.9626 Td[(and)-267(V8)-268(ag)5(ainst)-267(the)-267(baseline)-268(\050SpiderMonk)10(e)15(y\051.)-267(T)35(racing)-267(achie)25(v)15(es)-268(the)]TJ 0 -9.9627 Td[(best)-257(speedups)-256(in)-257(inte)15(ger)20(-hea)20(vy)-257(be)1(nchmarks,)-257(up)-257(to)-256(the)-257(25x)-257(speedup)]TJ 0 -9.9626 Td[(on)]TJ/F33 8.9664 Tf 11.208 0 Td[(bitops-bitwise-and)]TJ/F42 8.9664 Tf 84.7313 0 Td[(.)]TJ -83.9841 -9.9627 Td[(T)35(raceMonk)10(e)15(y)-435(is)-435(the)-436(f)10(astest)-435(VM)-435(on)-435(9)-436(of)-435(the)-435(26)-435(benchmarks)]TJ -11.9552 -9.9626 Td[(\050)]TJ/F33 8.9664 Tf 2.9858 0 Td[(3d-morph)]TJ/F42 8.9664 Tf 37.6583 0 Td[(,)]TJ/F33 8.9664 Tf 7.4374 0 Td[(bitops-3bit-bits-in-byte)]TJ/F42 8.9664 Tf 112.9751 0 Td[(,)]TJ/F33 8.9664 Tf 7.4374 0 Td[(bitops-bitwise-)]TJ -168.494 -9.9626 Td[(and)]TJ/F42 8.9664 Tf 14.1219 0 Td[(,)]TJ/F33 8.9664 Tf 4.4651 0 Td[(crypto-sha1)]TJ/F42 8.9664 Tf 51.7802 0 Td[(,)]TJ/F33 8.9664 Tf 4.4652 0 Td[(math-cordic)]TJ/F42 8.9664 Tf 51.7802 0 Td[(,)]TJ/F33 8.9664 Tf 4.4652 0 Td[(math-partial-sums)]TJ/F42 8.9664 Tf 80.0239 0 Td[(,)]TJ/F33 8.9664 Tf 4.4652 0 Td[(math-)]TJ -215.5669 -9.9627 Td[(spectral-norm)]TJ/F42 8.9664 Tf 61.1948 0 Td[(,)]TJ/F33 8.9664 Tf 6.3166 0 Td[(string-base64)]TJ/F42 8.9664 Tf 61.1948 0 Td[(,)]TJ/F33 8.9664 Tf 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/F41 8.9664 Tf 54 431.3179 Td[(Figur)18(e)-311(10.)]TJ/F42 8.9664 Tf 43.7208 0 Td[(Speedup)-311(vs.)-311(a)-311(baseline)-311(Ja)20(v)25(aScript)-311(interpreter)-311(\050SpiderMonk)10(e)15(y\051)-311(for)-312(our)-311(trace-based)-311(JIT)-311(compiler)40(,)-311(Apple')55(s)-311(SquirrelFish)-311(Extreme)]TJ -43.7208 -9.9627 Td[(inline)-205(threading)-205(interpreter)-205(and)-205(Google')55(s)-205(V8)-205(JS)-205(compiler)55(.)-205(Our)-205(system)-205(generates)-205(particularly)-205(ef)25(\002cient)-205(code)-205(for)-205(programs)-205(that)-205(bene\002t)-205(most)-205(from)]TJ 0 -9.9626 Td[(type)-269(specialization,)-270(which)-269(includes)-269(SunSpider)-270(Benchmark)-269(programs)-270(that)-269(perform)-269(bit)-270(manipulation.)-269(W)80(e)-270(type-s)1(pecialize)-270(the)-269(code)-270(in)-269(question)]TJ 0 -9.9626 Td[(to)-313(use)-313(inte)15(ger)-313(arithmet)1(ic,)-313(which)-313(substantially)-313(impro)15(v)15(es)-313(performance.)-313(F)15(or)-313(one)-312(of)-313(the)-313(benchmark)-313(programs)-313(we)-313(e)15(x)15(ecute)-312(25)-313(times)-313(f)10(aster)-313(than)]TJ 0 -9.9627 Td[(the)-250(SpiderMonk)10(e)15(y)-251(interpre)1(ter)40(,)-251(and)-250(almost)-250(5)-251(times)-250(f)10(aster)-250(than)-250(V8)-251(and)-250(SFX.)-250(F)15(or)-251(a)-250(lar)18(ge)-250(number)-250(of)-251(benchmarks)-250(all)-250(three)-250(VMs)-251(produce)-250(similar)]TJ 0 -9.9626 Td[(results.)-249(W)80(e)-250(perform)-249(w)10(orst)-249(on)-250(benchmark)-249(programs)-249(that)-250(we)-249(do)-249(not)-250(trace)-249(and)-249(instead)-250(f)10(a)1(ll)-250(back)-249(onto)-249(the)-250(interpreter)55(.)-249(This)-249(includes)-250(the)-249(recursi)25(v)15(e)]TJ 0 -9.9627 Td[(benchmarks)]TJ/F33 8.9664 Tf 45.5667 0 Td[(access-binary-trees)]TJ/F42 8.9664 Tf 91.6802 0 Td[(and)]TJ/F33 8.9664 Tf 15.189 0 Td[(control-flow-recursive)]TJ/F42 8.9664 Tf 103.5604 0 Td[(,)-250(for)-250(which)-250(we)-250(currently)-250(don')18(t)-250(generate)-250(an)15(y)-250(nati)25(v)15(e)-250(code.)]TJ -255.9963 -29.8879 Td[(In)-278(particular)40(,)-277(the)]TJ/F33 8.9664 Tf 62.1391 0 Td[(bitops)]TJ/F42 8.9664 Tf 30.7344 0 Td[(benchmarks)-278(are)-277(short)-278(programs)-278(that)-278(per)20(-)]TJ -92.8735 -9.9626 Td[(form)-299(man)15(y)-300(bitwise)-299(operations,)-300(so)-299(T)35(raceMonk)10(e)15(y)-299(can)-300(co)15(v)15(er)-299(the)-300(en-)]TJ 0 -9.9627 Td[(tire)-245(program)-245(with)-245(1)-245(or)-245(2)-245(traces)-245(that)-246(opera)1(te)-246(on)-245(inte)15(gers.)-245(T)35(raceMon-)]TJ 0 -9.9626 Td[(k)10(e)15(y)-265(runs)-265(all)-265(the)-265(other)-265(progr)1(ams)-265(in)-265(this)-265(set)-265(almost)-265(entirely)-265(as)-265(nati)25(v)15(e)]TJ 0 -9.9627 Td[(code.)]TJ/F33 8.9664 Tf 11.9552 -9.9626 Td[(regexp-dna)]TJ/F42 8.9664 Tf 51.7706 0 Td[(is)-524(dominated)-524(by)-524(re)15(gular)-524(e)15(xpression)-524(ma)1(tching,)]TJ -63.7258 -9.9626 Td[(which)-251(is)-250(implemented)-251(in)-250(all)-251(3)-250(VMs)-251(by)-250(a)-251(special)-250(re)15(gular)-251(e)15(xpression)]TJ 0 -9.9627 Td[(compiler)55(.)-313(Thus,)-313(performance)-313(on)-313(this)-313(benchmark)-313(has)-313(little)-313(relation)]TJ 0 -9.9626 Td[(to)-250(the)-250(trace)-250(compilation)-250(approach)-250(discussed)-250(in)-250(this)-250(paper)55(.)]TJ 11.9552 -9.9627 Td[(T)35(raceMonk)10(e)15(y')55(s)-287(smaller)-287(speedups)-288(on)-287(the)-287(other)-287(benchmarks)-287(can)]TJ -11.9552 -9.9626 Td[(be)-250(attrib)20(uted)-250(to)-250(a)-250(fe)25(w)-250(speci\002c)-250(causes:)]TJ/F26 7.9701 Tf 5.2303 -25.2391 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(The)-552(implementation)-552(does)-553(not)-552(currently)-552(trace)-552(recursion,)-552(so)]TJ 0 -9.9626 Td[(T)35(raceMonk)10(e)15(y)-534(achie)25(v)15(es)-534(a)-534(small)-534(speedup)-534(or)-534(no)-534(speedup)-534(on)]TJ 0 -9.9627 Td[(benchmarks)-593(that)-593(use)-593(recursion)-593(e)15(xtensi)25(v)15(ely:)]TJ/F33 8.9664 Tf 171.5197 0 Td[(3d-cube)]TJ/F42 8.9664 Tf 32.951 0 Td[(,)]TJ/F33 8.9664 Tf 7.5594 0 Td[(3d-)]TJ -212.0301 -9.9626 Td[(raytrace)]TJ/F42 8.9664 Tf 37.6584 0 Td[(,)]TJ/F33 8.9664 Tf 5.1661 0 Td[(access-binary-trees)]TJ/F42 8.9664 Tf 89.4385 0 Td[(,)]TJ/F33 8.9664 Tf 5.1661 0 Td[(string-tagcloud)]TJ/F42 8.9664 Tf 70.6094 0 Td[(,)-326(and)]TJ/F33 8.9664 Tf -208.0385 -9.9627 Td[(controlflow-recursive)]TJ/F42 8.9664 Tf 98.8532 0 Td[(.)]TJ/F26 7.9701 Tf -106.5743 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(The)-384(implementation)-384(does)-383(not)-384(currently)-384(trace)]TJ/F33 8.9664 Tf 168.5649 0 Td[(eval)]TJ/F42 8.9664 Tf 22.2705 0 Td[(and)-384(some)]TJ -190.8354 -9.9626 Td[(other)-483(functions)-482(implemented)-483(in)-483(C.)-483(Because)]TJ/F33 8.9664 Tf 169.6644 0 Td[(date-format-)]TJ -169.6644 -9.9626 Td[(tofte)]TJ/F42 8.9664 Tf 27.0327 0 Td[(and)]TJ/F33 8.9664 Tf 16.4436 0 Td[(date-format-xparb)]TJ/F42 8.9664 Tf 83.5202 0 Td[(use)-390(such)-390(functions)-390(in)-390(their)]TJ -126.9965 -9.9627 Td[(main)-250(loops,)-250(we)-250(do)-250(not)-250(trace)-250(them.)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(The)-400(implementation)-399(does)-400(not)-399(currently)-400(trace)-400(through)-399(re)15(gular)]TJ 0 -9.9626 Td[(e)15(xpression)]TJ/F33 8.9664 Tf 41.7528 0 Td[(replace)]TJ/F42 8.9664 Tf 36.4895 0 Td[(operations.)-395(The)-394(replace)-395(function)-394(can)-395(be)]TJ -78.2423 -9.9627 Td[(passed)-271(a)-270(function)-271(object)-271(used)-270(to)-271(compute)-271(the)-271(replacement)-270(te)15(xt.)]TJ 0 -9.9626 Td[(Our)-374(implementation)-373(currently)-374(does)-373(not)-374(trace)-374(functions)-373(called)]TJ 0 -9.9626 Td[(as)-239(replace)-240(functions.)-239(The)-239(run)-239(time)-240(of)]TJ/F33 8.9664 Tf 133.2945 0 Td[(string-unpack-code)]TJ/F42 8.9664 Tf 86.877 0 Td[(is)]TJ -220.1715 -9.9627 Td[(dominated)-250(by)-250(such)-250(a)]TJ/F33 8.9664 Tf 76.2046 0 Td[(replace)]TJ/F42 8.9664 Tf 35.1927 0 Td[(call.)]TJ/F26 7.9701 Tf 143.8953 274.109 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(T)80(w)10(o)-405(programs)-406(trace)-405(well,)-405(b)20(ut)-406(ha)20(v)15(e)-405(a)-406(long)-405(compilation)-405(time.)]TJ/F33 8.9664 Tf 0 -9.9626 Td[(access-nbody)]TJ/F42 8.9664 Tf 58.1911 0 Td[(forms)-190(a)-190(lar)18(ge)-190(number)-190(of)-190(traces)-190(\05081\051.)]TJ/F33 8.9664 Tf 127.5367 0 Td[(crypto-md5)]TJ/F42 8.9664 Tf -185.7278 -9.9627 Td[(forms)-297(one)-297(v)14(e)1(ry)-298(long)-297(trace.)-297(W)80(e)-298(e)15(xpec)1(t)-298(to)-297(impro)15(v)15(e)-297(performance)]TJ 0 -9.9626 Td[(on)-273(this)-274(programs)-273(by)-274(impro)15(ving)-273(the)-274(compilation)-273(speed)-274(of)-273(nano-)]TJ 0 -9.9626 Td[(jit.)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(Some)-450(programs)-450(trace)-449(v)15(ery)-450(well,)-450(and)-450(speed)-450(up)-449(compared)-450(to)]TJ 0 -9.9626 Td[(the)-360(interpreter)40(,)-361(b)20(ut)-360(are)-360(not)-361(as)-360(f)10(ast)-360(as)-360(SFX)-361(and/or)-360(V8,)-360(namely)]TJ/F33 8.9664 Tf 0 -9.9627 Td[(bitops-bits-in-byte)]TJ/F42 8.9664 Tf 89.4386 0 Td[(,)]TJ/F33 8.9664 Tf 9.5155 0 Td[(bitops-nsieve-bits)]TJ/F42 8.9664 Tf 84.7313 0 Td[(,)]TJ/F33 8.9664 Tf 9.5155 0 Td[(access-)]TJ -193.2009 -9.9626 Td[(fannkuch)]TJ/F42 8.9664 Tf 37.6584 0 Td[(,)]TJ/F33 8.9664 Tf 5.113 0 Td[(access-nsieve)]TJ/F42 8.9664 Tf 61.1948 0 Td[(,)-320(and)]TJ/F33 8.9664 Tf 20.9319 0 Td[(crypto-aes)]TJ/F42 8.9664 Tf 47.0729 0 Td[(.)-320(The)-320(reason)-321(is)]TJ -171.971 -9.9627 Td[(not)-452(clear)40(,)-451(b)20(ut)-452(all)-451(of)-452(these)-451(programs)-452(ha)20(v)15(e)-451(nested)-452(loops)-451(with)]TJ 0 -9.9626 Td[(small)-259(bodies,)-258(so)-259(we)-259(suspec)1(t)-259(that)-259(the)-258(implementation)-259(has)-259(a)-258(rela-)]TJ 0 -9.9626 Td[(ti)25(v)15(ely)-242(high)-243(cost)-242(for)-242(calling)-242(nested)-243(traces.)]TJ/F33 8.9664 Tf 146.5825 0 Td[(string-fasta)]TJ/F42 8.9664 Tf 58.6602 0 Td[(traces)]TJ -205.2427 -9.9627 Td[(well,)-226(b)20(ut)-226(its)-226(run)-227(time)-226(is)-226(dominated)-226(by)-226(string)-226(processing)-226(b)20(uiltins,)]TJ 0 -9.9626 Td[(which)-258(are)-257(unaf)25(fected)-258(by)-258(tracing)-257(and)-258(seem)-258(to)-257(be)-258(less)-258(ef)25(\002cient)-257(in)]TJ 0 -9.9627 Td[(SpiderMonk)10(e)15(y)-250(than)-250(in)-250(the)-250(tw)10(o)-250(other)-250(VMs.)]TJ/F41 8.9664 Tf -0.9963 -20.1597 Td[(Detailed)-232(perf)25(ormance)-231(metrics.)]TJ/F42 8.9664 Tf 117.8007 0 Td[(In)-232(Figure)-231(11)-232(we)-232(sho)25(w)-232(the)-231(frac-)]TJ -129.7558 -9.9626 Td[(tion)-257(of)-257(instructions)-257(interprete)1(d)-257(and)-257(the)-257(fraction)-257(of)-257(instructions)-257(e)15(x)15(e-)]TJ 0 -9.9627 Td[(cuted)-225(as)-225(nati)25(v)15(e)-225(code.)-225(This)-224(\002gure)-225(sho)25(ws)-225(that)-225(for)-225(man)15(y)-225(programs,)-225(we)]TJ 0 -9.9626 Td[(are)-250(able)-250(to)-250(e)15(x)15(ecute)-250(almost)-250(all)-250(the)-250(code)-250(nati)25(v)15(ely)65(.)]TJ 11.9551 -9.9627 Td[(Figure)-281(12)-280(breaks)-281(do)25(wn)-280(the)-281(total)-280(e)15(x)15(ecution)-281(time)-280(into)-281(four)-280(acti)25(v-)]TJ -11.9551 -9.9626 Td[(ities:)-330(interpreting)-330(bytecodes)-330(while)-330(not)-330(recording,)-331(recording)-330(traces)]TJ 0 -9.9626 Td[(\050including)-394(time)-394(tak)10(en)-395(to)-394(interpret)-394(the)-394(recorded)-394(trace\051,)-395(compiling)]TJ 0 -9.9627 Td[(traces)-250(to)-250(nati)25(v)15(e)-250(code,)-250(and)-250(e)15(x)15(ecuting)-250(nati)25(v)15(e)-250(code)-250(traces.)]TJ 11.9551 -9.9626 Td[(These)-405(detailed)-404(metrics)-405(allo)25(w)-404(us)-405(to)-405(estimate)-404(parameters)-405(for)-404(a)]TJ -11.9551 -9.9627 Td[(simple)-358(model)-358(of)-359(tracing)-358(performance.)-358(These)-358(estimates)-358(should)-359(be)]TJ 0 -9.9626 Td[(considered)-395(v)15(ery)-395(rough,)-396(as)-395(the)-395(v)25(alues)-395(observ)15(ed)-395(on)-396(the)-395(indi)25(vidual)]TJ 0 -9.9626 Td[(benchmarks)-423(ha)20(v)15(e)-423(lar)18(ge)-423(standard)-423(de)25(viations)-423(\050on)-423(the)-423(order)-423(of)-423(the)]TJ
ET
BT
/F42 8.9664 Tf 166.5633 713.0262 Td[(Loops)-1333(T)35(rees)-1334(T)35(races)-1333(Aborts)-1333(Flushes)-1334(T)35(re)1(es/Loop)-1334(T)35(races/T)35(ree)-1333(T)35(races/Loop)-1333(Speedup)]TJ
ET
1 0 0 1 65.4416 709.6388 cm
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1 0 0 1 -65.4416 -709.6388 cm
BT
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1 0 0 1 54 439.3225 cm
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1 0 0 1 -54 -439.3225 cm
BT
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Td[(ator)-260(has)-260(told)-261(us)-260(that)-260(LuaJIT)-260(has)-260(a)-261(similar)-260(design)-260(to)-260(our)-260(system,)-261(b)20(ut)]TJ 0 -9.9626 Td[(will)-335(use)-335(a)-335(less)-334(aggressi)25(v)15(e)-335(type)-335(speculation)-335(\050e.g.,)-335(using)-335(a)-335(\003oating-)]TJ 0 -9.9627 Td[(point)-324(representation)-325(for)-324(all)-325(number)-324(v)25(alues\051)-324(and)-325(does)-324(not)-325(generate)]TJ 0 -9.9626 Td[(nested)-250(traces)-250(for)-250(nested)-250(loops.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(General)-431(trace)-432(optimization.)]TJ/F42 8.9664 Tf 112.4579 0 Td[(General)-431(trace)-432(optimization)-431(has)]TJ -124.4131 -9.9627 Td[(a)-465(longer)-466(history)-465(that)-466(has)-465(treated)-466(mostly)-465(nati)25(v)15(e)-466(code)-465(and)-466(typed)]TJ 0 -9.9626 Td[(languages)-254(lik)10(e)-254(Ja)20(v)25(a.)-254(Thus,)-253(these)-254(systems)-254(ha)20(v)15(e)-254(focused)-254(less)-254(on)-254(type)]TJ 0 -9.9627 Td[(specialization)-250(and)-250(more)-250(on)-250(other)-250(optimizations.)]TJ 11.9552 -9.9626 Td[(Dynamo)-325(\0507\051)-325(by)-325(Bala)-324(et)-325(al,)-325(introduced)-325(nati)25(v)15(e)-325(code)-325(tracing)-324(as)-325(a)]TJ -11.9552 -9.9626 Td[(replacement)-314(for)-314(pro\002le-guided)-314(optimization)-314(\050PGO\051.)-314(A)-315(major)-314(goal)]TJ 0 -9.9627 Td[(w)10(as)-457(to)-456(perform)-457(PGO)-456(online)-457(so)-457(that)-456(the)-457(pro\002le)-456(w)10(as)-457(speci\002c)-457(to)]TJ 0 -9.9626 Td[(the)-273(current)-272(e)15(x)15(ecution.)-273(Dynamo)-272(used)-273(loop)-272(headers)-273(as)-272(candidate)-273(hot)]TJ 0 -9.9627 Td[(traces,)-250(b)20(ut)-250(did)-250(not)-250(try)-250(to)-250(create)-250(loop)-250(traces)-250(speci\002cally)65(.)]TJ 11.9552 -9.9626 Td[(T)35(race)-355(trees)-354(were)-355(originally)-355(proposed)-355(by)-355(Gal)-354(et)-355(al.)-355(\05011\051)-355(in)-354(the)]TJ -11.9552 -9.9626 Td[(conte)15(xt)-357(of)-357(Ja)20(v)25(a,)-356(a)-357(statically)-357(typed)-357(language.)-356(Their)-357(trace)-357(trees)-357(ac-)]TJ 0 -9.9627 Td[(tually)-311(inlined)-312(parts)-311(of)-311(outer)-312(loops)-311(within)-312(the)-311(inner)-311(loops)-312(\050because)]TJ
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Td[(Chambers)-374(et.)-374(al)-373(\0509\051)-374(pioneered)-374(the)-374(idea)-374(of)-374(compiling)-373(multiple)]TJ -11.9552 -9.9626 Td[(v)15(ersions)-320(of)-320(a)-320(procedure)-320(specialized)-320(for)-320(the)-320(input)-320(types)-321(in)-320(the)-320(lan-)]TJ 0 -9.9627 Td[(guage)-391(Self.)-392(In)-391(one)-392(implementation,)-391(the)15(y)-392(generated)-391(a)-392(specialized)]TJ 0 -9.9626 Td[(method)-213(online)-213(each)-213(time)-213(a)-213(method)-213(w)10(as)-213(called)-213(with)-214(ne)25(w)-213(input)-213(types.)]TJ 0 -9.9627 Td[(In)-364(another)40(,)-365(the)15(y)-364(used)-364(an)-365(of)25(\003ine)-364(whole-program)-364(static)-364(analysis)-365(to)]TJ 0 -9.9626 Td[(infer)-302(input)-302(types)-301(and)-302(constant)-302(recei)25(v)15(er)-302(types)-301(at)-302(call)-302(sites.)-302(Interest-)]TJ 0 -9.9626 Td[(ingly)65(,)-250(the)-250(tw)10(o)-250(techniques)-250(produced)-250(nearly)-250(the)-250(same)-250(performance.)]TJ 11.9552 -9.9627 Td[(Salib)-223(\05017\051)-222(designed)-223(a)-223(type)-223(inference)-222(algorithm)-223(for)-223(Python)-222(based)]TJ -11.9552 -9.9626 Td[(on)-239(the)-239(Cartesian)-240(Produc)1(t)-240(Algorithm)-239(and)-239(used)-239(the)-239(results)-240(to)-239(special-)]TJ 0 -9.9627 Td[(ize)-250(on)-250(types)-250(and)-250(translate)-250(the)-250(program)-250(to)-250(C++.)]TJ 11.9552 -9.9626 Td[(McClosk)10(e)15(y)-430(\05014\051)-431(has)-430(w)10(ork)-430(in)-431(progress)-430(based)-431(on)-430(a)-430(language-)]TJ -11.9552 -9.9626 Td[(independent)-473(t)1(ype)-473(inference)-473(that)-472(is)-473(used)-472(to)-473(generate)-472(ef)25(\002cient)-473(C)]TJ 0 -9.9627 Td[(implementations)-250(of)-250(Ja)20(v)25(aScript)-250(and)-250(Python)-250(programs.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Nati)10(v)10(e)-268(code)-269(generation)-268(by)-268(inter)10(pr)18(eters.)]TJ/F42 8.9664 Tf 152.2911 0 Td[(The)-268(traditional)-269(inter)20(-)]TJ -164.2463 -9.9627 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ET
BT
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/F41 8.9664 Tf 54 570.7786 Td[(Figur)18(e)-350(3.)-500(LIR)-349(snippet)-350(f)25(or)-349(sample)-350(pr)18(ogram.)]TJ/F42 8.9664 Tf 173.1706 0 Td[(This)-350(is)-349(the)-350(LIR)-349(recorded)-350(for)-349(line)-350(5)-350(of)-349(the)-350(sample)-349(program)-350(in)-349(Figure)-350(1.)-350(The)-349(LIR)-350(encodes)]TJ -173.1706 -9.9626 Td[(the)-328(semantics)-328(in)-328(SSA)-328(form)-328(using)-327(temporary)-328(v)25(ariables.)-328(The)-328(LIR)-328(also)-328(encodes)-328(all)-328(the)-328(stores)-328(that)-328(the)-327(interpreter)-328(w)10(ould)-328(do)-328(to)-328(its)-328(data)-328(stack.)]TJ 0 -9.9627 Td[(Sometimes)-255(these)-256(stores)-255(can)-256(be)-255(optimized)-256(a)15(w)10(ay)-255(as)-255(the)-256(stack)-255(locations)-256(are)-255(li)25(v)15(e)-256(only)-255(on)-256(e)15(xits)-255(to)-255(the)-256(interpreter)55(.)-255(Finally)65(,)-256(the)-255(LIR)-256(records)-255(guards)]TJ 0 -9.9626 Td[(and)-250(side)-250(e)15(xits)-250(to)-250(v)15(erify)-250(the)-250(assumptions)-250(made)-250(in)-250(this)-250(recording:)-250(that)]TJ/F33 8.9664 Tf 244.2951 0 Td[(primes)]TJ/F42 8.9664 Tf 30.4854 0 Td[(is)-250(an)-250(array)-250(and)-250(that)-250(the)-250(call)-250(to)-250(set)-250(its)-250(element)-250(succeeds.)]TJ/F33 8.9664 Tf -274.7805 -26.1519 Td[(mov)-525(edx,)-525(ebx\050748\051)-3150(//)-525(load)-525(primes)-525(from)-525(the)-525(trace)-525(activation)-525(record)]TJ 0 -9.9627 Td[(mov)-525(edi\0500\051,)-525(edx)-4200(//)-525(\050*\051)-525(store)-525(primes)-525(to)-525(interpreter)-525(stack)]TJ 0 -9.9626 Td[(mov)-525(esi,)-525(ebx\050764\051)-3150(//)-525(load)-525(k)-525(from)-525(the)-525(trace)-525(activation)-525(record)]TJ 0 -9.9627 Td[(mov)-525(edi\0508\051,)-525(esi)-4200(//)-525(\050*\051)-525(store)-525(k)-525(to)-525(interpreter)-525(stack)]TJ 0 -9.9626 Td[(mov)-525(edi\05016\051,)-525(0)-4725(//)-525(\050*\051)-525(store)-525(false)-525(to)-525(interpreter)-525(stack)]TJ 0 -9.9626 Td[(mov)-525(eax,)-525(edx\0504\051)-4200(//)-525(\050*\051)-525(load)-525(object)-525(class)-525(word)-525(for)-525(primes)]TJ 0 -9.9627 Td[(and)-525(eax,)-525(-4)-6300(//)-525(\050*\051)-525(mask)-525(out)-525(object)-525(class)-525(tag)-525(for)-525(primes)]TJ 0 -9.9626 Td[(cmp)-525(eax,)-525(Array)-4725(//)-525(\050*\051)-525(test)-525(whether)-525(primes)-525(is)-525(an)-525(array)]TJ 0 -9.9627 Td[(jne)-525(side_exit_1)-4200(//)-525(\050*\051)-525(side)-525(exit)-525(if)-525(primes)-525(is)-525(not)-525(an)-525(array)]TJ 0 -9.9626 Td[(sub)-525(esp,)-525(8)-6825(//)-525(bump)-525(stack)-525(for)-525(call)-525(alignment)-525(convention)]TJ 0 -9.9626 Td[(push)-525(false)-6825(//)-525(push)-525(last)-525(argument)-525(for)-525(call)]TJ 0 -9.9627 Td[(push)-525(esi)-7875(//)-525(push)-525(first)-525(argument)-525(for)-525(call)]TJ 0 -9.9626 Td[(call)-525(js_Array_set)-3150(//)-525(call)-525(function)-525(to)-525(set)-525(array)-525(element)]TJ 0 -9.9627 Td[(add)-525(esp,)-525(8)-6825(//)-525(clean)-525(up)-525(extra)-525(stack)-525(space)]TJ 0 -9.9626 Td[(mov)-525(ecx,)-525(ebx)-5775(//)-525(\050*\051)-525(created)-525(by)-525(register)-525(allocator)]TJ 0 -9.9626 Td[(test)-525(eax,)-525(eax)-5250(//)-525(\050*\051)-525(test)-525(return)-525(value)-525(of)-525(js_Array_set)]TJ 0 -9.9627 Td[(je)-525(side_exit_2)-4725(//)-525(\050*\051)-525(side)-525(exit)-525(if)-525(call)-525(failed)]TJ 0 -9.9626 Td[(...)]TJ 0 -9.9627 Td[(side_exit_1:)]TJ 0 -9.9626 Td[(mov)-525(ecx,)-525(ebp\050-4\051)-3675(//)-525(restore)-525(ecx)]TJ 0 -9.9626 Td[(mov)-525(esp,)-525(ebp)-5775(//)-525(restore)-525(esp)]TJ 0 -9.9627 Td[(jmp)-525(epilog)-6825(//)-525(jump)-525(to)-525(ret)-525(statement)]TJ
ET
1 0 0 1 54 292.2431 cm
q
[]0 d
0 J
0.3288 w
0 0.1644 m
502.1171 0.1644 l
S
Q
1 0 0 1 -54 -292.2431 cm
BT
/F41 8.9664 Tf 54 282.0803 Td[(Figur)18(e)-224(4.)-500(x86)-224(snippet)-223(f)25(or)-224(sample)-224(pr)18(ogram.)]TJ/F42 8.9664 Tf 163.9137 0 Td[(This)-224(is)-224(the)-223(x86)-224(code)-224(compiled)-224(from)-224(the)-224(LIR)-223(snippet)-224(in)-224(Figure)-224(3.)-224(Most)-224(LIR)-223(instructions)-224(compile)]TJ -163.9137 -9.9627 Td[(to)-308(a)-307(single)-308(x86)-307(instruction.)-308(Instructions)-307(mark)10(ed)-308(with)]TJ/F33 8.9664 Tf 193.5674 0 Td[(\050*\051)]TJ/F42 8.9664 Tf 16.8795 0 Td[(w)10(ould)-308(be)-307(omitted)-308(by)-307(an)-308(idealized)-307(compiler)-308(that)-307(kne)25(w)-308(that)-307(none)-308(of)-307(the)-308(side)-307(e)15(xits)]TJ -210.4469 -9.9626 Td[(w)10(ould)-263(e)25(v)15(er)-263(be)-263(tak)10(en.)-263(The)-263(17)-263(instructions)-263(generated)-263(by)-263(the)-263(compiler)-263(compare)-263(f)10(a)20(v)20(orably)-263(with)-263(the)-263(100+)-263(instructions)-263(that)-263(the)-263(interpreter)-263(w)10(ould)]TJ 0 -9.9627 Td[(e)15(x)15(ecute)-250(for)-250(the)-250(same)-250(code)-250(snippet,)-250(including)-250(4)-250(indirect)-250(jumps.)]TJ/F41 8.9664 Tf 11.9552 -29.8365 Td[(i=2.)]TJ/F42 8.9664 Tf 17.8463 0 Td[(This)-392(is)-393(the)-392(\002rst)-392(iteration)-393(of)-392(the)-392(outer)-393(loop.)-392(The)-393(loop)-392(on)]TJ -29.8015 -9.9626 Td[(lines)-265(4-5)-265(becomes)-264(hot)-265(on)-265(its)-265(second)-264(iteration,)-265(so)-265(T)35(raceMonk)10(e)15(y)-265(en-)]TJ 0 -9.9627 Td[(ters)-359(recording)-359(mode)-360(on)-359(line)-359(4.)-359(In)-359(recording)-360(m)1(ode,)-360(T)35(raceMonk)10(e)15(y)]TJ 0 -9.9626 Td[(records)-257(the)-257(code)-258(along)-257(the)-257(trace)-257(in)-257(a)-257(lo)25(w-le)25(v)15(el)-258(compiler)-257(intermedi-)]TJ 0 -9.9627 Td[(ate)-258(representation)-257(we)-258(call)]TJ/F46 8.9664 Tf 93.8904 0 Td[(LIR)]TJ/F42 8.9664 Tf 13.4495 0 Td[(.)-258(The)-257(LIR)-258(trace)-257(encodes)-258(all)-258(the)-257(oper)20(-)]TJ -107.3399 -9.9626 Td[(ations)-266(performed)-265(and)-266(the)-266(types)-265(of)-266(all)-266(operands.)-266(The)-265(LIR)-266(trace)-266(also)]TJ 0 -9.9626 Td[(encodes)]TJ/F46 8.9664 Tf 31.4698 0 Td[(guar)37(ds)]TJ/F42 8.9664 Tf 24.5767 0 Td[(,)-289(which)-289(are)-288(checks)-289(that)-289(v)15(erify)-289(that)-288(the)-289(control)-289(\003o)25(w)]TJ -56.0465 -9.9627 Td[(and)-370(types)-369(are)-370(identical)-370(to)-369(those)-370(observ)15(ed)-369(during)-370(trace)-370(recording.)]TJ 0 -9.9626 Td[(Thus,)-306(on)-306(later)-306(e)15(x)15(ecutions,)-307(if)-306(and)-306(only)-306(if)-306(all)-306(guards)-306(are)-307(passed,)-306(the)]TJ 0 -9.9627 Td[(trace)-250(has)-250(the)-250(required)-250(program)-250(semantics.)]TJ 11.9552 -9.9626 Td[(T)35(raceMonk)10(e)15(y)-442(stops)-442(recording)-443(when)-442(e)15(x)15(ecution)-442(returns)-442(to)-442(the)]TJ -11.9552 -9.9626 Td[(loop)-282(header)-282(or)-282(e)15(xits)-282(the)-281(loop.)-282(In)-282(this)-282(case,)-282(e)15(x)15(ecution)-282(returns)-282(to)-282(the)]TJ 0 -9.9627 Td[(loop)-250(header)-250(on)-250(line)-250(4.)]TJ 11.9552 -9.9626 Td[(After)-276(recording)-275(is)-276(\002nished,)-275(T)35(raceMonk)10(e)15(y)-276(compiles)-275(the)-276(trace)-275(to)]TJ -11.9552 -9.9627 Td[(nati)25(v)15(e)-321(code)-322(using)-321(the)-322(recorded)-321(type)-322(information)-321(for)-322(optimization.)]TJ 0 -9.9626 Td[(The)-439(result)-439(is)-439(a)-439(nati)25(v)15(e)-439(code)-439(fragment)-439(that)-439(can)-439(be)-440(entered)-439(if)-439(the)]TJ 263.0137 149.4396 Td[(interpreter)-282(PC)-282(and)-283(the)-282(types)-282(of)-283(v)25(alues)-282(match)-282(those)-282(observ)15(ed)-283(when)]TJ 0 -9.9626 Td[(trace)-392(recording)-393(w)10(as)-392(started.)-392(The)-392(\002rst)-393(trace)-392(in)-392(our)-392(e)15(xample,)]TJ/F29 8.9664 Tf 223.6818 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9963 Td[(45)]TJ/F42 8.9664 Tf 7.804 0.9963 Td[(,)]TJ -236.8618 -9.9627 Td[(co)15(v)15(ers)-238(lines)-239(4)-238(and)-238(5.)-238(This)-239(trace)-238(can)-238(be)-239(entered)-238(if)-238(the)-239(PC)-238(is)-238(at)-238(line)-239(4,)]TJ/F33 8.9664 Tf 0 -9.9626 Td[(i)]TJ/F42 8.9664 Tf 6.774 0 Td[(and)]TJ/F33 8.9664 Tf 15.0142 0 Td[(k)]TJ/F42 8.9664 Tf 6.774 0 Td[(are)-230(inte)15(gers,)-231(and)]TJ/F33 8.9664 Tf 60.5897 0 Td[(primes)]TJ/F42 8.9664 Tf 30.3105 0 Td[(is)-230(an)-231(object.)-230(After)-231(compiling)]TJ/F29 8.9664 Tf 104.2194 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9963 Td[(45)]TJ/F42 8.9664 Tf 7.804 0.9963 Td[(,)]TJ -236.8618 -9.9627 Td[(T)35(raceMonk)10(e)15(y)-250(returns)-250(to)-250(the)-250(interpreter)-250(and)-250(loops)-250(back)-250(to)-250(line)-250(1.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(i=3.)]TJ/F42 8.9664 Tf 17.3136 0 Td[(No)25(w)-333(the)-333(loop)-333(header)-333(at)-333(line)-333(1)-333(has)-333(become)-333(hot,)-332(so)-333(T)35(race-)]TJ -29.2688 -9.9626 Td[(Monk)10(e)15(y)-390(starts)-391(recording.)-390(When)-391(recording)-390(reaches)-391(line)-390(4,)-391(T)35(race-)]TJ 0 -9.9627 Td[(Monk)10(e)15(y)-307(observ)15(es)-307(that)-308(it)-307(has)-307(reached)-307(an)-308(inner)-307(loop)-307(header)-307(that)-308(al-)]TJ 0 -9.9626 Td[(ready)-332(has)-331(a)-332(compiled)-331(trace,)-332(so)-331(T)35(raceMonk)10(e)15(y)-332(attempts)-332(to)-331(nest)-332(the)]TJ 0 -9.9627 Td[(inner)-255(loop)-254(inside)-255(the)-254(current)-255(trace.)-255(The)-254(\002rst)-255(step)-254(is)-255(to)-255(ca)1(ll)-255(the)-255(inner)]TJ 0 -9.9626 Td[(trace)-209(as)-209(a)-208(subroutine.)-209(This)-209(e)15(x)15(ecutes)-209(the)-209(loop)-208(on)-209(line)-209(4)-209(to)-209(completion)]TJ 0 -9.9626 Td[(and)-255(then)-256(returns)-255(to)-255(the)-256(recorder)55(.)-255(T)35(raceMonk)10(e)15(y)-256(v)15(eri\002es)-255(that)-255(the)-256(call)]TJ 0 -9.9627 Td[(w)10(as)-232(successful)-232(and)-232(then)-232(records)-233(the)-232(call)-232(to)-232(the)-232(inner)-232(trace)-232(as)-233(part)-232(of)]TJ 0 -9.9626 Td[(the)-279(current)-279(trace.)-279(Recor)1(ding)-279(continues)-279(until)-279(e)15(x)15(ecution)-279(reaches)-279(line)]TJ 0 -9.9627 Td[(1,)-320(and)-321(at)-320(which)-321(point)-320(T)35(raceMonk)10(e)15(y)-320(\002nishes)-321(and)-320(compiles)-320(a)-321(trace)]TJ 0 -9.9626 Td[(for)-250(the)-250(outer)-250(loop,)]TJ/F29 8.9664 Tf 66.9873 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(16)]TJ/F42 8.9664 Tf 7.804 0.9962 Td[(.)]TJ
ET
BT
/F41 8.9664 Tf 65.9552 712.0299 Td[(i=4.)]TJ/F42 8.9664 Tf 16.3253 0 Td[(On)-223(this)-222(iteration,)-223(T)35(raceMonk)10(e)15(y)-223(calls)]TJ/F29 8.9664 Tf 132.214 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9963 Td[(16)]TJ/F42 8.9664 Tf 7.804 0.9963 Td[(.)-223(Because)]TJ/F33 8.9664 Tf 36.1115 0 Td[(i=4)]TJ/F42 8.9664 Tf 14.1219 0 Td[(,)-223(the)]TJ/F33 8.9664 Tf -223.9079 -9.9627 Td[(if)]TJ/F42 8.9664 Tf 12.3342 0 Td[(statement)-326(on)-325(line)-326(2)-325(is)-326(tak)10(en.)-326(This)-325(branch)-326(w)10(as)-325(not)-326(tak)10(en)-325(in)-326(the)]TJ -12.3342 -9.9626 Td[(original)-231(trace,)-231(so)-232(this)-231(causes)]TJ/F29 8.9664 Tf 102.2519 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(16)]TJ/F42 8.9664 Tf 9.8771 0.9962 Td[(to)-231(f)10(ail)-231(a)-232(guard)-231(and)-231(tak)10(e)-231(a)-231(side)-232(e)15(xit.)]TJ -117.505 -9.9626 Td[(The)-304(e)15(xit)-304(is)-303(not)-304(yet)-304(hot,)-304(so)-304(T)35(raceMonk)10(e)15(y)-303(returns)-304(to)-304(the)-304(interpreter)40(,)]TJ 0 -9.9627 Td[(which)-250(e)15(x)15(ecutes)-250(the)-250(continue)-250(statement.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(i=5.)]TJ/F42 8.9664 Tf 16.3435 0 Td[(T)35(raceMonk)10(e)15(y)-225(calls)]TJ/F29 8.9664 Tf 70.2197 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9963 Td[(16)]TJ/F42 8.9664 Tf 7.804 0.9963 Td[(,)-225(which)-225(in)-224(turn)-225(calls)-225(the)-224(nested)-225(trace)]TJ/F29 8.9664 Tf -111.6984 -9.9627 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(45)]TJ/F42 8.9664 Tf 7.804 0.9962 Td[(.)]TJ/F29 8.9664 Tf 5.3921 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(16)]TJ/F42 8.9664 Tf 10.9544 0.9962 Td[(loops)-351(back)-352(to)-351(its)-351(o)25(wn)-352(header)40(,)-351(starting)-351(the)-352(ne)15(xt)-351(iteration)]TJ -34.9025 -9.9626 Td[(without)-250(e)25(v)15(er)-250(returning)-250(to)-250(the)-250(monitor)55(.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(i=6.)]TJ/F42 8.9664 Tf 16.5046 0 Td[(On)-243(this)-242(iteration,)-243(the)-243(side)-243(e)15(xit)-242(on)-243(line)-243(2)-242(is)-243(tak)10(en)-243(ag)5(ain.)-243(This)]TJ -28.4598 -9.9627 Td[(time,)-352(the)-352(side)-352(e)15(xit)-351(becomes)-352(hot,)-352(so)-352(a)-352(trace)]TJ/F29 8.9664 Tf 159.7422 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(23)]TJ/F30 5.9776 Tf 7.3058 0 Td[(;)]TJ/F28 5.9776 Tf 2.2693 0 Td[(1)]TJ/F42 8.9664 Tf 7.3061 0.9962 Td[(is)-352(recorded)-352(that)]TJ -181.9994 -9.9626 Td[(co)15(v)15(ers)-258(line)-257(3)-258(and)-257(returns)-258(to)-257(the)-258(loop)-257(header)55(.)-258(Thus,)-258(the)-257(end)-258(of)]TJ/F29 8.9664 Tf 220.0013 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9963 Td[(23)]TJ/F30 5.9776 Tf 7.3058 0 Td[(;)]TJ/F28 5.9776 Tf 2.2692 0 Td[(1)]TJ/F42 8.9664 Tf -234.9523 -8.9664 Td[(jumps)-313(directly)-314(to)-313(the)-314(start)-313(of)]TJ/F29 8.9664 Tf 107.0194 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(16)]TJ/F42 8.9664 Tf 7.8039 0.9962 Td[(.)-313(The)-314(side)-313(e)15(xit)-314(is)-313(patched)-314(so)-313(that)]TJ -120.1993 -9.9626 Td[(on)-250(future)-250(iterations,)-250(it)-250(jumps)-250(directly)-250(to)]TJ/F29 8.9664 Tf 142.9581 0 Td[(T)]TJ/F28 5.9776 Tf 5.376 -0.9962 Td[(23)]TJ/F30 5.9776 Tf 7.3058 0 Td[(;)]TJ/F28 5.9776 Tf 2.2692 0 Td[(1)]TJ/F42 8.9664 Tf 4.1511 0.9962 Td[(.)]TJ -150.105 -9.9626 Td[(At)-193(this)-192(point,)-193(T)35(raceMonk)10(e)15(y)-192(has)-193(compiled)-193(enough)-192(traces)-193(to)-192(co)15(v)15(er)]TJ -11.9552 -9.9627 Td[(the)-397(entire)-397(nested)-397(loop)-397(st)1(ructure,)-397(so)-397(the)-397(rest)-397(of)-397(the)-397(program)-397(runs)]TJ 0 -9.9626 Td[(entirely)-250(as)-250(nati)25(v)15(e)-250(code.)]TJ/F41 10.9589 Tf 0 -27.0984 Td[(3.)-1000(T)74(race)-250(T)74(r)18(ees)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(In)-371(this)-370(section,)-371(we)-370(describe)-371(traces,)-370(trace)-371(trees,)-370(and)-371(ho)25(w)-370(the)15(y)-371(are)]TJ 0 -9.9626 Td[(formed)-243(at)-244(run)-243(time.)-244(Although)-243(our)-244(techniques)-243(apply)-244(to)-243(an)15(y)-244(dynamic)]TJ 0 -9.9627 Td[(language)-349(interpreter)40(,)-350(we)-349(will)-350(describe)-349(them)-350(assuming)-349(a)-350(bytecode)]TJ 0 -9.9626 Td[(interpreter)-250(to)-250(k)10(eep)-250(the)-250(e)15(xposition)-250(simple.)]TJ/F41 8.9664 Tf 0 -20.7223 Td[(3.1)-1000(T)74(races)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(A)]TJ/F46 8.9664 Tf 9.4995 0 Td[(tr)15(ace)]TJ/F42 8.9664 Tf 21.3178 0 Td[(is)-338(sim)1(ply)-338(a)-338(program)-337(path,)-338(which)-337(may)-338(cross)-337(function)-338(call)]TJ -30.8173 -9.9626 Td[(boundaries.)-281(T)35(raceMonk)10(e)15(y)-281(focuses)-280(on)]TJ/F46 8.9664 Tf 137.2694 0 Td[(loop)-281(tr)15(aces)]TJ/F42 8.9664 Tf 40.2395 0 Td[(,)-281(that)-281(originate)-281(at)]TJ -177.5089 -9.9627 Td[(a)-284(loop)-284(edge)-284(and)-284(represent)-283(a)-284(single)-284(iteration)-284(through)-284(the)-284(associated)]TJ 0 -9.9626 Td[(loop.)]TJ 11.9552 -9.9627 Td[(Similar)-368(to)-368(an)-368(e)15(xtended)-368(basic)-368(block,)-368(a)-368(trace)-368(is)-367(only)-368(entered)-368(at)]TJ -11.9552 -9.9626 Td[(the)-282(top,)-282(b)20(ut)-281(may)-282(ha)20(v)15(e)-282(man)15(y)-282(e)15(xits.)-282(In)-281(contrast)-282(to)-282(an)-282(e)15(xtended)-282(basic)]TJ 0 -9.9626 Td[(block,)-381(a)-381(trace)-381(can)-382(contain)-381(join)-381(nodes.)-381(Since)-381(a)-381(trace)-382(al)10(w)10(ays)-381(only)]TJ 0 -9.9627 Td[(follo)25(ws)-212(one)-213(single)-212(path)-212(through)-212(the)-213(original)-212(program,)-212(ho)25(we)25(v)15(er)40(,)-213(join)]TJ 0 -9.9626 Td[(nodes)-397(are)-397(not)-397(recognizable)-397(as)-397(such)-397(in)-397(a)-397(trace)-397(and)-398(ha)20(v)15(e)-397(a)-397(single)]TJ 0 -9.9627 Td[(predecessor)-250(node)-250(lik)10(e)-250(re)15(gular)-250(nodes.)]TJ 11.9552 -9.9626 Td[(A)]TJ/F46 8.9664 Tf 8.6978 0 Td[(typed)-248(tr)15(ace)]TJ/F42 8.9664 Tf 42.1603 0 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Td[(is)-261(of)-261(type)]TJ/F33 8.9664 Tf 35.9115 0 Td[(int)]TJ/F42 8.9664 Tf 16.4626 0 Td[(and)-261(the)-261(v)25(alue)-261(of)]TJ/F33 8.9664 Tf 59.9329 0 Td[(b)]TJ/F42 8.9664 Tf -234.3961 -9.9626 Td[(is)-267(of)-266(type)]TJ/F33 8.9664 Tf 36.06 0 Td[(boolean)]TJ/F42 8.9664 Tf 32.9511 0 Td[(.)-267(The)-266(entry)-267(type)-266(map)-267(is)-266(much)-267(lik)10(e)-266(the)-267(signature)]TJ -69.0111 -9.9627 Td[(of)-250(a)-250(function.)]TJ 11.9552 -9.9626 Td[(In)-368(this)-367(paper)40(,)-368(we)-367(only)-368(discuss)-367(typed)-368(loop)-368(traces,)-367(and)-368(we)-367(will)]TJ -11.9552 -9.9627 Td[(refer)-344(to)-343(them)-344(simply)-344(as)-343(\223traces\224.)-344(The)-344(k)10(e)15(y)-344(property)-343(of)-344(typed)-344(loop)]TJ 0 -9.9626 Td[(traces)-267(is)-266(that)-267(the)15(y)-267(can)-267(be)-266(compiled)-267(to)-267(ef)25(\002cient)-266(machine)-267(code)-267(using)]TJ 0 -9.9626 Td[(the)-250(same)-250(techniques)-250(used)-250(for)-250(typed)-250(languages.)]TJ 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Td[(and)-275(conditional)-275(e)15(xits.)-275(T)80(ype)-274(con)40(v)15(ersions,)-275(such)-275(as)-275(inte)15(ger)-275(to)-275(double,)]TJ 0 -9.9627 Td[(are)-443(represented)-443(by)-444(function)-443(calls.)-443(This)-443(mak)10(es)-443(the)-443(LIR)-443(used)-444(by)]TJ 0 -9.9626 Td[(T)35(raceMonk)10(e)15(y)-390(independent)-390(of)-391(the)-390(concrete)-390(type)-390(system)-390(and)-391(type)]TJ 0 -9.9626 Td[(con)40(v)15(ersion)-368(rules)-368(of)-368(the)-368(source)-368(language.)-368(The)-368(LIR)-368(operations)-368(are)]TJ 0 -9.9627 Td[(generic)-221(enough)-220(that)-221(the)-221(back)10(end)-221(compiler)-220(is)-221(language)-221(independent.)]TJ 0 -9.9626 Td[(Figure)-250(3)-250(sho)25(ws)-250(an)-250(e)15(xample)-250(LIR)-250(trace.)]TJ 11.9552 -9.9627 Td[(Bytecode)-452(interpreters)-453(typically)-452(represent)-452(v)25(alues)-453(in)-452(a)-452(v)25(arious)]TJ -11.9552 -9.9626 Td[(comple)15(x)-304(data)-303(structures)-304(\050e.g.,)-303(hash)-304(tables\051)-303(in)-304(a)-304(box)15(ed)-303(format)-304(\050i.e.,)]TJ 0 -9.9626 Td[(with)-311(attached)-311(type)-311(tag)-311(bits\051.)-311(Since)-311(a)-311(trace)-312(i)1(s)-312(intended)-311(to)-311(represent)]TJ 0 -9.9627 Td[(ef)25(\002cient)-332(code)-333(that)-332(eliminates)-332(all)-332(that)-333(comple)15(xity)65(,)-332(our)-332(traces)-333(oper)20(-)]TJ 0 -9.9626 Td[(ate)-340(on)-339(unbox)15(ed)-340(v)25(alues)-340(in)-340(simpl)1(e)-340(v)25(ariables)-340(and)-340(arrays)-339(as)-340(much)-340(as)]TJ 0 -9.9627 Td[(possible.)]TJ 274.9689 643.5866 Td[(A)-297(trace)-297(records)-297(a)1(ll)-297(its)-297(intermediate)-297(v)25(alues)-297(in)-297(a)-297(small)-296(acti)25(v)25(ation)]TJ -11.9552 -9.9627 Td[(record)-275(area.)-275(T)80(o)-275(mak)10(e)-275(v)25(ariable)-275(accesses)-275(f)10(ast)-275(on)-275(trace,)-275(the)-275(trace)-275(also)]TJ 0 -9.9626 Td[(imports)-300(local)-301(and)-300(global)-301(v)25(ariables)-300(by)-300(unboxing)-301(them)-300(and)-301(cop)10(ying)]TJ 0 -9.9626 Td[(them)-384(to)-384(its)-384(acti)25(v)25(ation)-383(record.)-384(Thus,)-384(the)-384(trace)-384(can)-384(read)-384(and)-384(write)]TJ 0 -9.9627 Td[(these)-201(v)25(ariables)-201(wit)1(h)-201(simple)-201(loads)-201(and)-201(stores)-200(from)-201(a)-201(nati)25(v)15(e)-201(acti)25(v)25(ation)]TJ 0 -9.9626 Td[(recording,)-434(independently)-435(of)-434(the)-435(boxing)-434(mechanism)-435(used)-434(by)-435(the)]TJ 0 -9.9627 Td[(interpreter)55(.)-378(When)-379(the)-378(trace)-378(e)15(xits,)-378(the)-379(VM)-378(box)15(es)-378(the)-378(v)25(alues)-379(from)]TJ 0 -9.9626 Td[(this)-266(nati)25(v)15(e)-265(storage)-266(location)-265(and)-266(copies)-265(them)-266(back)-266(to)-265(the)-266(interpreter)]TJ 0 -9.9626 Td[(structures.)]TJ 11.9552 -9.9627 Td[(F)15(or)-584(e)25(v)15(ery)-583(control-\003o)25(w)-584(branch)-583(in)-584(the)-583(source)-584(program,)-583(the)]TJ -11.9552 -9.9626 Td[(recorder)-229(generates)-229(conditional)-229(e)15(xit)-229(LIR)-230(inst)1(ructions.)-230(These)-229(instruc-)]TJ 0 -9.9627 Td[(tions)-325(e)15(xit)-324(from)-325(the)-324(trace)-325(if)-324(required)-325(control)-324(\003o)25(w)-325(is)-324(dif)25(ferent)-325(from)]TJ 0 -9.9626 Td[(what)-310(it)-310(w)10(as)-310(at)-310(trac)1(e)-310(recording,)-310(ensuring)-310(that)-310(the)-310(trace)-310(instructions)]TJ 0 -9.9626 Td[(are)-416(run)-415(only)-416(if)-415(the)15(y)-416(are)-416(supposed)-415(to.)-416(W)80(e)-416(call)-415(these)-416(instructions)]TJ/F46 8.9664 Tf 0 -9.9627 Td[(guar)37(d)]TJ/F42 8.9664 Tf 23.5724 0 Td[(instructions.)]TJ -11.6172 -9.9626 Td[(Most)-198(of)-199(our)-198(traces)-199(represent)-198(loops)-198(and)-199(end)-198(with)-199(the)-198(special)]TJ/F33 8.9664 Tf 208.319 0 Td[(loop)]TJ/F42 8.9664 Tf -220.2742 -9.9627 Td[(LIR)-306(instruction.)-305(This)-306(is)-305(just)-306(an)-306(unconditional)-305(branch)-306(to)-305(the)-306(top)-306(of)]TJ 0 -9.9626 Td[(the)-250(trace.)-250(Such)-250(traces)-250(return)-250(only)-250(via)-250(guards.)]TJ 11.9552 -9.9626 Td[(No)25(w)65(,)-325(we)-325(describe)-325(the)-326(k)10(e)15(y)-325(optimizations)-325(that)-325(are)-325(performed)-325(as)]TJ -11.9552 -9.9627 Td[(part)-320(of)-320(recording)-320(LIR.)-320(All)-320(of)-321(thes)1(e)-321(optimizations)-320(reduce)-320(comple)15(x)]TJ 0 -9.9626 Td[(dynamic)-396(language)-396(constructs)-397(to)-396(simple)-396(typed)-396(constructs)-396(by)-397(spe-)]TJ 0 -9.9627 Td[(cializing)-238(for)-239(the)-238(current)-239(trace.)-238(Each)-238(optimization)-239(requires)-238(guard)-239(in-)]TJ 0 -9.9626 Td[(structions)-342(to)-342(v)15(erify)-342(their)-342(assumptions)-342(about)-342(the)-342(state)-343(a)1(nd)-343(e)15(xit)-342(the)]TJ 0 -9.9626 Td[(trace)-250(if)-250(necessary)65(.)]TJ/F41 8.9664 Tf 11.9552 -9.9627 Td[(T)74(ype)-250(specialization.)]TJ/F42 8.9664 Tf 0 -9.9626 Td[(All)-369(LIR)-369(primiti)26(v)14(e)1(s)-369(apply)-369(to)-369(operands)-369(of)-369(speci\002c)-369(type)1(s.)-369(Thus,)]TJ -11.9552 -9.9627 Td[(LIR)-435(traces)-435(are)-435(necessarily)-435(type-specialized,)-435(and)-435(a)-436(compiler)-435(can)]TJ 0 -9.9626 Td[(easily)-430(produc)1(e)-430(a)-430(translation)-429(that)-430(requires)-429(no)-430(type)-429(dispatches.)-430(A)]TJ 0 -9.9626 Td[(typical)-291(byt)1(ecode)-291(interpreter)-291(carri)1(es)-291(tag)-291(bits)-290(along)-291(with)-290(each)-291(v)25(alue,)]TJ 0 -9.9627 Td[(and)-241(to)-241(perform)-240(an)15(y)-241(operation,)-241(must)-241(check)-240(the)-241(tag)-241(bits,)-241(dynamically)]TJ 0 -9.9626 Td[(dispatch,)-478(mask)-478(out)-478(the)-478(tag)-478(bits)-478(to)-478(reco)15(v)15(er)-479(the)-478(untagged)-478(v)25(alue,)]TJ 0 -9.9627 Td[(perform)-233(the)-234(operation,)-233(and)-233(then)-234(reappl)1(y)-234(tags.)-233(LIR)-233(omits)-234(e)25(v)15(erything)]TJ 0 -9.9626 Td[(e)15(xcept)-250(the)-250(operation)-250(itself.)]TJ 11.9552 -9.9626 Td[(A)-244(potential)-244(problem)-244(is)-244(that)-244(some)-244(operations)-243(can)-244(produce)-244(v)25(alues)]TJ -11.9552 -9.9627 Td[(of)-368(unpredictable)-368(types.)-369(F)15(or)-368(e)15(xample,)-368(reading)-368(a)-368(property)-368(from)-369(an)]TJ 0 -9.9626 Td[(object)-411(could)-410(yield)-411(a)-410(v)25(alue)-411(of)-411(an)15(y)-410(type,)-411(not)-411(ne)1(cessarily)-411(the)-411(type)]TJ 0 -9.9627 Td[(observ)15(ed)-340(during)-341(rec)1(ording.)-341(The)-340(recorder)-340(emits)-340(guard)-341(instructions)]TJ 0 -9.9626 Td[(that)-284(conditionally)-284(e)15(xit)-284(if)-284(the)-284(operation)-284(yields)-284(a)-284(v)25(alue)-285(of)-284(a)-284(dif)25(ferent)]TJ 0 -9.9626 Td[(type)-462(from)-463(that)-462(seen)-462(during)-463(recording.)-462(These)-462(guard)-463(instructions)]TJ 0 -9.9627 Td[(guarantee)-285(that)-285(as)-285(long)-286(as)-285(e)15(x)15(ecution)-285(is)-285(on)-285(trace,)-285(the)-285(types)-286(of)-285(v)25(alues)]TJ 0 -9.9626 Td[(match)-283(those)-283(of)-283(the)-283(typed)-283(trace.)-283(When)-283(the)-283(VM)-283(observ)15(es)-284(a)-283(side)-283(e)15(xit)]TJ 0 -9.9627 Td[(along)-283(such)-283(a)-283(type)-284(guard,)-283(a)-283(ne)25(w)-283(typed)-283(trace)-283(is)-284(recorded)-283(originating)]TJ 0 -9.9626 Td[(at)-265(the)-265(side)-266(e)15(xit)-265(location,)-265(capturing)-265(the)-266(ne)25(w)-265(type)-265(of)-265(the)-265(operation)-266(in)]TJ 0 -9.9626 Td[(question.)]TJ/F41 8.9664 Tf 11.9552 -9.9627 Td[(Repr)18(esentation)-424(specialization:)-425(objects.)]TJ/F42 8.9664 Tf 153.4538 0 Td[(In)-425(Ja)20(v)25(aS)1(cript,)-425(name)]TJ -165.409 -9.9626 Td[(lookup)-352(semantics)-352(are)-352(comple)15(x)-352(and)-352(potentially)-352(e)15(xpensi)25(v)15(e)-352(because)]TJ 0 -9.9627 Td[(the)15(y)-263(include)-263(features)-263(lik)10(e)-263(object)-263(inheritance)-263(and)]TJ/F33 8.9664 Tf 174.6448 0 Td[(eval)]TJ/F42 8.9664 Tf 18.8292 0 Td[(.)-263(T)80(o)-263(e)25(v)25(aluate)]TJ -193.474 -9.9626 Td[(an)-362(object)-363(property)-362(read)-362(e)15(xpression)-363(li)1(k)10(e)]TJ/F33 8.9664 Tf 147.2531 0 Td[(o.x)]TJ/F42 8.9664 Tf 14.1219 0 Td[(,)-362(the)-363(interpreter)-362(must)]TJ -161.375 -9.9626 Td[(search)-283(the)-283(property)-283(map)-283(of)]TJ/F33 8.9664 Tf 99.8342 0 Td[(o)]TJ/F42 8.9664 Tf 7.2455 0 Td[(and)-283(all)-283(of)-283(its)-283(prototypes)-283(and)-283(parents.)]TJ -107.0797 -9.9627 Td[(Property)-351(maps)-351(can)-351(be)-351(implemented)-351(with)-351(dif)25(ferent)-351(data)-351(structures)]TJ 0 -9.9626 Td[(\050e.g.,)-358(per)20(-object)-359(hash)-358(tables)-358(or)-358(shared)-359(hash)-358(tables\051,)-358(so)-358(the)-359(search)]TJ 0 -9.9627 Td[(process)-420(also)-421(must)-420(dispatch)-420(on)-421(t)1(he)-421(representation)-420(of)-420(each)-421(object)]TJ 0 -9.9626 Td[(found)-210(during)-209(search.)-210(T)35(raceMonk)10(e)15(y)-210(can)-209(simply)-210(observ)15(e)-209(the)-210(result)-210(of)]TJ 0 -9.9626 Td[(the)-312(search)-311(process)-312(and)-312(record)-311(the)-312(simplest)-312(possible)-311(LIR)-312(to)-312(access)]TJ 0 -9.9627 Td[(the)-220(property)-220(v)25(alue.)-219(F)15(or)-220(e)15(xample,)-220(the)-220(search)-220(might)-219(\002nds)-220(the)-220(v)25(alue)-220(of)]TJ/F33 8.9664 Tf 0 -9.9626 Td[(o.x)]TJ/F42 8.9664 Tf 16.242 0 Td[(in)-236(the)-237(prototype)-236(of)]TJ/F33 8.9664 Tf 68.2496 0 Td[(o)]TJ/F42 8.9664 Tf 4.7073 0 Td[(,)-236(which)-237(uses)-236(a)-237(shared)-236(hash-table)-237(represen-)]TJ -89.1989 -9.9627 Td[(tation)-232(that)-233(places)]TJ/F33 8.9664 Tf 62.5359 0 Td[(x)]TJ/F42 8.9664 Tf 6.7923 0 Td[(in)-233(sl)1(ot)-233(2)-233(of)-232(a)-233(property)-232(v)15(ector)55(.)-233(Then)-232(the)-233(recorded)]TJ -69.3282 -9.9626 Td[(can)-226(generate)-226(LIR)-226(that)-226(reads)]TJ/F33 8.9664 Tf 99.7654 0 Td[(o.x)]TJ/F42 8.9664 Tf 16.1497 0 Td[(with)-226(just)-226(tw)10(o)-226(or)-227(three)-226(loads:)-226(one)-226(to)]TJ -115.9151 -9.9626 Td[(get)-225(the)-225(prototype,)-224(possibly)-225(one)-225(to)-225(get)-225(the)-224(property)-225(v)25(alue)-225(v)15(ector)40(,)-225(and)]TJ 0 -9.9627 Td[(one)-262(more)-261(to)-262(get)-262(slot)-261(2)-262(from)-262(the)-261(v)15(ector)55(.)-262(This)-262(is)-261(a)-262(v)25(ast)-262(simpli\002cation)]TJ 0 -9.9626 Td[(and)-261(speedup)-262(compared)-261(to)-261(the)-262(original)-261(interpreter)-261(code.)-262(Inheritance)]TJ 0 -9.9627 Td[(relationships)-307(and)-307(object)-306(representations)-307(can)-307(change)-307(during)-307(e)15(x)15(ecu-)]TJ 0 -9.9626 Td[(tion,)-287(so)-288(the)-287(simpli\002ed)-287(code)-288(require)1(s)-288(guard)-287(instructions)-287(that)-288(ensure)]TJ 0 -9.9626 Td[(the)-200(object)-200(representation)-200(is)-199(the)-200(same.)-200(In)-200(T)35(raceMonk)10(e)15(y)65(,)-200(objects')-200(rep-)]TJ
ET
BT
/F42 8.9664 Tf 54 712.0299 Td[(resentations)-385(are)-384(assigned)-385(an)-385(inte)15(ger)-385(k)10(e)15(y)-384(called)-385(the)]TJ/F46 8.9664 Tf 190.5798 0 Td[(object)-385(shape)]TJ/F42 8.9664 Tf 46.282 0 Td[(.)]TJ -236.8618 -9.9627 Td[(Thus,)-250(the)-250(guard)-250(is)-250(a)-250(simple)-250(equality)-250(check)-250(on)-250(the)-250(object)-250(shape.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Repr)18(esentation)-452(specialization:)-452(numbers.)]TJ/F42 8.9664 Tf 161.1756 0 Td[(Ja)20(v)25(aScript)-452(has)-452(no)]TJ -173.1308 -9.9626 Td[(inte)15(ger)-374(type,)-374(only)-375(a)-374(Number)-374(type)-374(that)-375(is)-374(the)-374(set)-374(of)-374(64-bit)-375(IEEE-)]TJ 0 -9.9627 Td[(754)-469(\003oating-pointer)-469(numbers)-468(\050\223doubles\224\051.)-469(But)-469(man)15(y)-469(Ja)20(v)25(aScript)]TJ 0 -9.9626 Td[(operators,)-258(in)-258(particular)-258(array)-258(accesses)-258(and)-258(bitwise)-258(operators,)-258(really)]TJ 0 -9.9627 Td[(operate)-296(on)-296(inte)15(gers,)-296(so)-296(the)15(y)-296(\002rst)-296(con)40(v)15(ert)-296(the)-296(number)-296(to)-296(an)-296(inte)15(ger)40(,)]TJ 0 -10.3249 Td[(and)-373(then)-372(con)40(v)15(ert)-373(an)15(y)-373(inte)15(ger)-373(result)-372(back)-373(to)-373(a)-372(double.)]TJ/F42 5.9776 Tf 196.896 3.809 Td[(1)]TJ/F42 8.9664 Tf 6.8289 -3.809 Td[(Clearly)65(,)-373(a)]TJ -203.7249 -9.9626 Td[(Ja)20(v)25(aScript)-279(VM)-280(that)-279(w)10(ants)-280(to)-280(be)-279(f)10(ast)-280(must)-279(\002nd)-280(a)-279(w)10(ay)-280(to)-279(operate)-280(on)]TJ 0 -9.9627 Td[(inte)15(gers)-250(directly)-250(and)-250(a)20(v)20(oid)-250(these)-250(con)40(v)15(ersions.)]TJ 11.9552 -9.9626 Td[(In)-310(T)35(raceMonk)10(e)15(y)65(,)-310(we)-309(support)-310(tw)10(o)-310(representations)-310(for)-309(numbers:)]TJ -11.9552 -9.9627 Td[(inte)15(gers)-350(and)-351(doubles.)-350(The)-351(interpreter)-350(uses)-350(inte)15(ger)-351(representations)]TJ 0 -9.9626 Td[(as)-225(much)-225(as)-225(it)-225(can,)-225(switching)-225(for)-225(results)-225(that)-225(can)-225(only)-225(be)-225(represented)]TJ 0 -9.9626 Td[(as)-291(doubles.)-290(When)-291(a)-290(trace)-291(is)-291(started,)-290(some)-291(v)25(alues)-290(may)-291(be)-291(imported)]TJ 0 -9.9627 Td[(and)-369(represented)-369(as)-369(inte)15(gers.)-369(Some)-369(operations)-370(on)-369(inte)15(gers)-369(require)]TJ 0 -9.9626 Td[(guards.)-292(F)15(or)-292(e)15(xample,)-292(adding)-291(tw)10(o)-292(inte)15(gers)-292(can)-292(produce)-292(a)-292(v)25(alue)-292(too)]TJ 0 -9.9627 Td[(lar)18(ge)-250(for)-250(the)-250(inte)15(ger)-250(representation.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Function)-411(inlining)15(.)]TJ/F42 8.9664 Tf 73.2653 0 Td[(LIR)-411(traces)-411(can)-411(cross)-411(function)-411(boundaries)]TJ -85.2205 -9.9626 Td[(in)-326(either)-325(direction,)-326(achie)25(ving)-325(function)-326(inlining.)-325(Mo)15(v)15(e)-326(instructions)]TJ 0 -9.9627 Td[(need)-292(to)-293(be)-292(recorded)-292(for)-293(function)-292(entry)-292(and)-293(e)15(xit)-292(to)-292(cop)10(y)-293(ar)18(guments)]TJ 0 -9.9626 Td[(in)-225(and)-226(return)-225(v)25(alues)-226(out)1(.)-226(These)-225(mo)15(v)15(e)-226(statements)-225(are)-225(then)-226(optimized)]TJ 0 -9.9627 Td[(a)15(w)10(ay)-305(by)-304(the)-305(compiler)-304(using)-305(cop)10(y)-305(propag)5(ation.)-304(In)-305(order)-304(to)-305(be)-305(able)]TJ 0 -9.9626 Td[(to)-421(return)-421(to)-420(the)-421(interpreter)40(,)-421(the)-421(trace)-421(must)-420(also)-421(generate)-421(LIR)-421(to)]TJ 0 -9.9626 Td[(record)-384(that)-383(a)-384(call)-383(frame)-384(has)-383(been)-384(entered)-383(and)-384(e)15(xited.)-383(The)-384(frame)]TJ 0 -9.9627 Td[(entry)-463(and)-464(e)15(xit)-463(LIR)-463(sa)20(v)15(es)-463(just)-464(enough)-463(information)-463(to)-463(allo)25(w)-464(the)]TJ 0 -9.9626 Td[(intepreter)-324(call)-323(stack)-324(to)-324(be)-323(restored)-324(later)-324(and)-324(is)-323(much)-324(simpler)-324(than)]TJ 0 -9.9627 Td[(the)-362(interpreter')55(s)-362(standard)-362(call)-361(code.)-362(If)-362(the)-362(function)-362(being)-362(entered)]TJ 0 -9.9626 Td[(is)-317(not)-318(constant)-317(\050which)-317(in)-318(Ja)20(v)25(aScript)-317(includes)-318(an)15(y)-317(call)-317(by)-318(function)]TJ 0 -9.9626 Td[(name\051,)-301(the)-301(recorder)-301(must)-301(also)-300(emit)-301(LIR)-301(to)-301(guard)-301(that)-301(the)-301(function)]TJ 0 -9.9627 Td[(is)-250(the)-250(same.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Guards)-485(and)-484(side)-485(exits.)]TJ/F42 8.9664 Tf 95.3529 0 Td[(Each)-485(optimization)-484(described)-485(abo)15(v)15(e)]TJ -107.3081 -9.9627 Td[(requires)-419(one)-418(or)-419(more)-418(guards)-419(to)-418(v)15(erify)-419(the)-419(assumptions)-418(made)-419(in)]TJ 0 -9.9626 Td[(doing)-260(the)-260(optimization.)-260(A)-261(guard)-260(is)-260(just)-260(a)-260(group)-260(of)-261(LIR)-260(instructions)]TJ 0 -9.9626 Td[(that)-384(performs)-385(a)-384(test)-385(and)-384(conditional)-385(e)15(xit.)-384(The)-384(e)15(xit)-385(branches)-384(to)-385(a)]TJ/F46 8.9664 Tf 0 -9.9627 Td[(side)-372(e)20(xit)]TJ/F42 8.9664 Tf 30.551 0 Td[(,)-372(a)-373(small)-372(of)25(f-trace)-372(piece)-373(of)-372(LIR)-372(that)-372(returns)-373(a)-372(pointer)-372(to)]TJ -30.551 -9.9626 Td[(a)-416(structure)-416(that)-416(describes)-416(the)-416(reason)-416(for)-416(the)-416(e)15(xit)-416(along)-416(with)-416(the)]TJ 0 -9.9627 Td[(interpreter)-239(PC)-239(at)-239(the)-239(e)15(xit)-239(point)-239(and)-239(an)15(y)-239(other)-240(dat)1(a)-240(needed)-239(to)-239(restore)]TJ 0 -9.9626 Td[(the)-250(interpreter')55(s)-250(state)-250(structures.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Aborts.)]TJ/F42 8.9664 Tf 31.7673 0 Td[(Some)-349(constructs)-349(are)-349(dif)25(\002cult)-349(to)-349(record)-349(in)-349(LIR)-348(traces.)]TJ -43.7225 -9.9627 Td[(F)15(or)-376(e)15(xample,)]TJ/F33 8.9664 Tf 51.5401 0 Td[(eval)]TJ/F42 8.9664 Tf 22.1969 0 Td[(or)-376(calls)-375(to)-376(e)15(xternal)-375(functions)-376(can)-375(change)-376(the)]TJ -73.737 -9.9626 Td[(program)-427(state)-427(in)-427(unpredictable)-427(w)10(ays,)-427(making)-427(it)-428(dif)25(\002c)1(ult)-428(for)-427(the)]TJ 0 -9.9627 Td[(tracer)-344(to)-343(kno)25(w)-344(the)-344(current)-343(type)-344(map)-344(in)-344(order)-343(to)-344(continue)-344(tracing.)]TJ 0 -9.9626 Td[(A)-272(tracing)-272(implementation)-272(can)-272(also)-272(ha)20(v)15(e)-272(an)15(y)-272(number)-273(of)-272(other)-272(limi-)]TJ 0 -9.9626 Td[(tations,)-272(e.g.,a)-271(small-memory)-272(de)25(vice)-271(may)-272(limit)-272(the)-271(length)-272(of)-272(traces.)]TJ 0 -9.9627 Td[(When)-313(an)15(y)-313(situation)-313(occurs)-312(that)-313(pre)25(v)15(ents)-313(the)-313(implementation)-313(from)]TJ 0 -9.9626 Td[(continuing)-211(trace)-211(recording,)-211(the)-211(implementation)]TJ/F46 8.9664 Tf 169.0923 0 Td[(aborts)]TJ/F42 8.9664 Tf 24.8109 0 Td[(trace)-211(record-)]TJ -193.9032 -9.9627 Td[(ing)-250(and)-250(returns)-250(to)-250(the)-250(trace)-250(monitor)55(.)]TJ/F41 8.9664 Tf 0 -24.4515 Td[(3.2)-1000(T)74(race)-250(T)74(r)18(ees)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(Especially)-376(simple)-376(loops,)-375(namely)-376(those)-376(where)-376(control)-376(\003o)25(w)65(,)-376(v)25(alue)]TJ 0 -9.9626 Td[(types,)-244(v)25(alue)-245(representations,)-244(and)-245(inlined)-244(functions)-245(are)-244(all)-245(in)40(v)25(ariant,)]TJ 0 -9.9626 Td[(can)-311(be)-311(represented)-312(by)-311(a)-311(single)-311(trace.)-312(But)-311(most)-311(loops)-311(ha)20(v)15(e)-311(at)-312(least)]TJ 0 -9.9627 Td[(some)-361(v)25(ariation,)-361(and)-361(so)-361(the)-360(program)-361(will)-361(tak)10(e)-361(side)-361(e)15(xits)-361(from)-361(the)]TJ 0 -9.9626 Td[(main)-341(trace.)-342(When)-341(a)-342(side)-341(e)15(xit)-342(becomes)-341(hot,)-342(T)35(raceMonk)10(e)15(y)-341(starts)-342(a)]TJ 0 -9.9627 Td[(ne)25(w)]TJ/F46 8.9664 Tf 17.021 0 Td[(br)15(anc)15(h)-257(tr)15(ace)]TJ/F42 8.9664 Tf 48.0385 0 Td[(from)-257(that)-258(point)-257(and)-257(patches)-258(the)-257(side)-257(e)15(xit)-257(to)-258(jump)]TJ -65.0595 -9.9626 Td[(directly)-235(to)-235(that)-234(trace.)-235(In)-235(this)-235(w)10(ay)65(,)-235(a)-234(single)-235(trace)-235(e)15(xpands)-235(on)-235(demand)]TJ 0 -9.9626 Td[(to)-250(a)-250(single-entry)65(,)-250(multiple-e)15(xit)]TJ/F46 8.9664 Tf 110.6079 0 Td[(tr)15(ace)-250(tr)37(ee)]TJ/F42 8.9664 Tf 34.1434 0 Td[(.)]TJ -132.7961 -9.9627 Td[(This)-280(section)-280(e)15(xplains)-280(ho)25(w)-281(trace)-280(trees)-280(are)-280(formed)-280(during)-280(e)15(x)15(ecu-)]TJ -11.9552 -9.9626 Td[(tion.)-267(The)-267(goal)-267(is)-267(to)-267(form)-267(trace)-267(trees)-267(during)-267(e)15(x)15(ecution)-267(that)-267(co)15(v)15(er)-267(all)]TJ 0 -9.9627 Td[(the)-250(hot)-250(paths)-250(of)-250(the)-250(program.)]TJ
ET
1 0 0 1 54 95.3424 cm
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0.3288 w
0 0.1644 m
119.5517 0.1644 l
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1 0 0 1 -54 -95.3424 cm
BT
/F42 5.9776 Tf 54 89.1889 Td[(1)]TJ/F42 7.9701 Tf 4.4832 -2.8128 Td[(Arrays)-246(are)-247(actually)-246(w)10(orse)-246(than)-247(this:)-246(if)-246(the)-247(inde)15(x)-246(v)25(alue)-246(is)-247(a)-246(number)40(,)-246(it)-247(must)]TJ -4.4832 -8.9664 Td[(be)-249(con)40(v)15(erted)-250(from)-249(a)-250(double)-249(to)-249(a)-250(string)-249(for)-250(the)-249(property)-249(access)-250(operator)40(,)-249(and)]TJ 0 -8.9664 Td[(then)-250(to)-250(an)-250(inte)15(ger)-250(internally)-250(to)-250(the)-250(array)-250(implementation.)]TJ/F41 8.9664 Tf 274.9689 643.5866 Td[(Starting)-230(a)-231(tr)18(ee.)]TJ/F42 8.9664 Tf 59.0707 0 Td[(T)35(ree)-230(trees)-231(al)10(w)10(ays)-230(start)-230(at)-231(loop)-230(headers,)-230(because)]TJ -71.0259 -9.9627 Td[(the)15(y)-225(are)-225(a)-225(natural)-226(place)-225(to)-225(look)-225(for)-225(hot)-225(paths.)-225(In)-226(T)35(raceMonk)10(e)15(y)65(,)-225(loop)]TJ 0 -9.9626 Td[(headers)-402(are)-402(easy)-402(to)-402(detect\226the)-402(bytecode)-402(compiler)-403(ensur)1(es)-403(that)-402(a)]TJ 0 -9.9627 Td[(bytecode)-289(is)-289(a)-288(loop)-289(header)-289(if)25(f)-289(it)-289(is)-289(the)-288(tar)18(get)-289(of)-289(a)-289(backw)10(ard)-289(branch.)]TJ 0 -9.9626 Td[(T)35(raceMonk)10(e)15(y)-265(starts)-265(a)-265(tree)-266(when)-265(a)-265(gi)25(v)15(en)-265(loop)-265(header)-265(has)-266(bee)1(n)-266(e)15(x)15(e-)]TJ 0 -9.9626 Td[(cuted)-275(a)-276(certain)-275(number)-276(of)-275(times)-276(\0502)-275(in)-276(the)-275(current)-276(implementation\051.)]TJ 0 -9.9627 Td[(Starting)-283(a)-284(tree)-283(just)-284(means)-283(starting)-284(recordi)1(ng)-284(a)-283(trace)-284(for)-283(the)-284(current)]TJ 0 -9.9626 Td[(point)-221(and)-220(type)-221(map)-221(and)-220(marking)-221(the)-221(trace)-221(as)-220(the)-221(root)-221(of)-220(a)-221(tree.)-221(Each)]TJ 0 -9.9627 Td[(tree)-233(is)-234(associated)-233(with)-233(a)-234(loop)-233(header)-233(and)-234(type)-233(map,)-234(so)-233(there)-233(may)-234(be)]TJ 0 -9.9626 Td[(se)25(v)15(eral)-250(trees)-250(for)-250(a)-250(gi)25(v)15(en)-250(loop)-250(header)55(.)]TJ/F41 8.9664 Tf 11.9552 -9.9626 Td[(Closing)-250(the)-250(loop.)]TJ/F42 8.9664 Tf 66.2608 0 Td[(T)35(race)-250(recording)-250(can)-250(end)-250(in)-250(se)25(v)15(eral)-250(w)10(ays.)]TJ -66.2608 -9.9627 Td[(Ideally)65(,)-310(the)-310(trace)-310(reaches)-310(the)-310(loop)-310(header)-310(where)-310(it)-310(started)-310(with)]TJ -11.9552 -9.9626 Td[(the)-369(same)-369(type)-369(map)-370(as)-369(on)-369(entry)65(.)-369(This)-369(is)-369(called)-369(a)]TJ/F46 8.9664 Tf 180.5073 0 Td[(type-stable)]TJ/F42 8.9664 Tf 42.654 0 Td[(loop)]TJ -223.1613 -9.9627 Td[(iteration.)-372(In)-372(this)-372(case,)-372(the)-373(end)-372(of)-372(the)-372(trace)-372(can)-372(jump)-372(right)-373(to)-372(the)]TJ 0 -9.9626 Td[(be)15(ginning,)-264(as)-265(all)-264(the)-265(v)25(alue)-264(representations)-265(are)-264(e)15(xactly)-265(as)-264(needed)-265(to)]TJ 0 -9.9626 Td[(enter)-294(the)-294(trace.)-294(The)-294(jump)-294(can)-294(e)25(v)15(en)-294(skip)-294(the)-294(usual)-294(code)-294(that)-294(w)10(ould)]TJ 0 -9.9627 Td[(cop)10(y)-276(out)-276(the)-276(state)-275(at)-276(the)-276(end)-276(of)-276(the)-276(trace)-276(and)-275(cop)10(y)-276(it)-276(back)-276(in)-276(to)-276(the)]TJ 0 -9.9626 Td[(trace)-250(acti)25(v)25(ation)-250(record)-250(to)-250(enter)-250(a)-250(trace.)]TJ 11.9552 -9.9627 Td[(In)-374(certain)-375(cases)-374(the)-375(trace)-374(might)-374(reach)-375(the)-374(loop)-375(header)-374(with)-374(a)]TJ -11.9552 -9.9626 Td[(dif)25(ferent)-235(type)-235(map.)-235(This)-235(scenario)-235(is)-235(sometime)-235(observ)15(ed)-235(for)-235(the)-235(\002rst)]TJ 0 -9.9626 Td[(iteration)-217(of)-217(a)-217(loop.)-217(Some)-217(v)25(ariables)-217(inside)-217(the)-217(loop)-217(might)-217(initially)-217(be)]TJ/F46 8.9664 Tf 0 -9.9627 Td[(unde\002ned)]TJ/F42 8.9664 Tf 34.8612 0 Td[(,)-203(before)-203(the)15(y)-203(are)-204(set)-203(to)-203(a)-203(concrete)-203(type)-203(during)-203(the)-204(\002rst)-203(loop)]TJ -34.8612 -9.9626 Td[(iteration.)-411(When)-410(recording)-411(such)-410(an)-411(iteration,)-411(t)1(he)-411(recorder)-411(cannot)]TJ 0 -9.9627 Td[(link)-273(the)-273(trace)-274(back)-273(to)-273(its)-273(o)25(wn)-274(loop)-273(header)-273(since)-273(it)-273(is)]TJ/F46 8.9664 Tf 188.5515 0 Td[(type-unstable)]TJ/F42 8.9664 Tf 48.3103 0 Td[(.)]TJ -236.8618 -9.9626 Td[(Instead,)-264(the)-263(iteration)-264(is)-263(terminated)-264(with)-263(a)-264(side)-263(e)15(xit)-264(that)-263(will)-264(al)10(w)10(ays)]TJ 0 -9.9626 Td[(f)10(ail)-339(and)-338(return)-339(to)-338(the)-339(interpreter)55(.)-339(At)-338(the)-339(same)-338(time)-339(a)-339(ne)25(w)-338(trace)-339(is)]TJ 0 -9.9627 Td[(recorded)-368(with)-369(the)-368(ne)25(w)-368(type)-369(map.)-368(Ev)15(ery)-369(time)-368(an)-368(additional)-369(type-)]TJ 0 -9.9626 Td[(unstable)-235(trace)-236(is)-236(adde)1(d)-236(to)-236(a)-235(re)15(gion,)-236(its)-235(e)15(xit)-236(type)-235(map)-236(is)-235(compared)-236(to)]TJ 0 -9.9627 Td[(the)-306(entry)-307(m)1(ap)-307(of)-306(all)-306(e)15(xisting)-306(traces)-307(in)-306(case)-306(the)15(y)-306(complement)-307(each)]TJ 0 -9.9626 Td[(other)55(.)-316(W)40(ith)-316(this)-316(approach)-315(we)-316(are)-316(able)-316(to)-316(co)15(v)15(er)-316(type-unstable)-316(loop)]TJ 0 -9.9626 Td[(iterations)-250(as)-250(long)-250(the)15(y)-250(e)25(v)15(entually)-250(form)-250(a)-250(stable)-250(equilibrium.)]TJ 11.9552 -9.9627 Td[(Finally)65(,)-333(the)-334(trace)-333(might)-333(e)15(xit)-334(the)-333(loop)-333(before)-334(reaching)-333(the)-333(loop)]TJ -11.9552 -9.9626 Td[(header)40(,)-242(for)-242(e)15(xample)-243(because)-242(e)15(x)15(ecution)-242(reaches)-242(a)]TJ/F33 8.9664 Tf 175.5107 0 Td[(break)]TJ/F42 8.9664 Tf 25.7082 0 Td[(or)]TJ/F33 8.9664 Tf 9.6407 0 Td[(return)]TJ/F42 8.9664 Tf -210.8596 -9.9627 Td[(statement.)-298(In)-298(this)-297(case,)-298(the)-298(VM)-298(simply)-298(ends)-297(the)-298(trace)-298(with)-298(an)-298(e)15(xit)]TJ 0 -9.9626 Td[(to)-250(the)-250(trace)-250(monitor)55(.)]TJ 11.9552 -9.9626 Td[(As)-354(mentioned)-353(pre)25(viously)65(,)-354(we)-353(may)-354(speculati)25(v)15(ely)-353(chose)-354(to)-353(rep-)]TJ -11.9552 -9.9627 Td[(resent)-284(certain)-284(Number)20(-typed)-284(v)25(alues)-285(as)-284(inte)15(gers)-284(on)-284(trace.)-284(W)80(e)-284(do)-285(so)]TJ 0 -9.9626 Td[(when)-337(we)-336(observ)15(e)-337(that)-336(Number)20(-typed)-337(v)25(ariables)-337(c)1(ontain)-337(an)-337(inte)15(ger)]TJ 0 -9.9627 Td[(v)25(alue)-293(at)-293(trace)-293(entry)65(.)-293(If)-292(during)-293(trace)-293(recording)-293(the)-293(v)25(ariable)-293(is)-293(une)15(x-)]TJ 0 -9.9626 Td[(pectedly)-322(assigned)-322(a)-322(non-inte)15(ger)-322(v)25(alue,)-322(we)-322(ha)20(v)15(e)-322(to)-322(widen)-322(the)-322(type)]TJ 0 -9.9626 Td[(of)-253(the)-252(v)25(ariable)-253(to)-253(a)-253(double.)-252(As)-253(a)-253(result,)-253(the)-252(recorded)-253(trace)-253(becomes)]TJ 0 -9.9627 Td[(inherently)-402(type-unstable)-402(since)-402(it)-402(starts)-402(with)-402(an)-403(i)1(nte)15(ger)-403(v)25(alue)-402(b)20(ut)]TJ 0 -9.9626 Td[(ends)-287(with)-287(a)-288(double)-287(v)25(alue.)-287(This)-287(represents)-287(a)-288(mis-speculat)1(ion,)-288(since)]TJ 0 -9.9627 Td[(at)-247(trace)-247(entry)-247(we)-246(specialized)-247(the)-247(Number)20(-typed)-247(v)25(alue)-247(to)-247(an)-247(inte)15(ger)40(,)]TJ 0 -9.9626 Td[(assuming)-213(that)-213(at)-214(the)-213(loop)-213(edge)-213(we)-214(w)10(ould)-213(ag)5(ain)-213(\002nd)-213(an)-213(inte)15(ger)-214(v)25(alue)]TJ 0 -9.9626 Td[(in)-255(the)-255(v)25(ariable,)-256(allo)25(wing)-255(us)-255(to)-255(close)-256(the)-255(loop.)-255(T)80(o)-255(a)20(v)20(oid)-255(future)-256(spec-)]TJ 0 -9.9627 Td[(ulati)25(v)15(e)-309(f)10(ai)1(lures)-309(in)40(v)20(olving)-309(this)-308(v)25(ariable,)-309(and)-308(to)-309(obtain)-308(a)-309(type-stable)]TJ 0 -9.9626 Td[(trace)-227(we)-227(note)-227(the)-227(f)10(act)-227(that)-227(the)-227(v)25(ariable)-227(in)-227(question)-227(as)-227(been)-227(observ)15(ed)]TJ 0 -9.9627 Td[(to)-264(sometimes)-264(hold)-264(non-inte)15(ger)-264(v)25(alues)-264(in)-264(an)-265(advisory)-264(data)-264(structure)]TJ 0 -9.9626 Td[(which)-250(we)-250(call)-250(the)-250(\223oracle\224.)]TJ 11.9552 -9.9626 Td[(When)-296(compiling)-296(loops,)-295(we)-296(consult)-296(the)-296(oracle)-296(before)-295(specializ-)]TJ -11.9552 -9.9627 Td[(ing)-355(v)25(alues)-356(to)-355(inte)15(gers.)-356(Speculation)-355(to)25(w)10(ards)-356(inte)15(gers)-355(is)-356(performed)]TJ 0 -9.9626 Td[(only)-363(if)-362(no)-363(adv)15(erse)-362(information)-363(is)-362(kno)25(wn)-363(to)-362(the)-363(oracle)-362(about)-363(that)]TJ 0 -9.9627 Td[(particular)-297(v)25(ariable.)-297(Whene)25(v)15(er)-298(we)-297(accidentally)-297(compile)-297(a)-297(loop)-298(that)]TJ 0 -9.9626 Td[(is)-388(type-unstable)-388(due)-388(to)-388(mis-speculation)-388(of)-388(a)-389(Number)20(-typed)-388(v)25(ari-)]TJ 0 -9.9626 Td[(able,)-331(we)-331(immediately)-331(trigger)-331(the)-331(recording)-331(of)-331(a)-331(ne)25(w)-331(trace,)-331(which)]TJ 0 -9.9627 Td[(based)-255(on)-255(the)-255(no)25(w)-256(updated)-255(oracle)-255(information)-255(will)-255(start)-255(with)-255(a)-256(dou-)]TJ 0 -9.9626 Td[(ble)-250(v)25(alue)-250(and)-250(thus)-250(become)-250(type)-250(stable.)]TJ/F41 8.9664 Tf 11.9552 -9.9627 Td[(Extending)-423(a)-424(tr)18(ee.)]TJ/F42 8.9664 Tf 72.2432 0 Td[(Side)-423(e)15(xits)-424(lead)-423(to)-424(di)1(f)25(ferent)-424(paths)-423(through)]TJ -84.1984 -9.9626 Td[(the)-300(loop,)-300(or)-300(paths)-300(with)-300(dif)25(ferent)-300(types)-300(or)-301(representations)1(.)-301(Thus,)-300(to)]TJ 0 -9.9626 Td[(completely)-218(co)15(v)15(er)-218(the)-217(loop,)-218(the)-218(VM)-218(must)-218(record)-217(traces)-218(starting)-218(at)-218(all)]TJ 0 -9.9627 Td[(side)-263(e)15(xits.)-263(These)-263(traces)-263(are)-263(recorded)-263(much)-263(lik)10(e)-264(root)-263(traces:)-263(there)-263(is)]TJ 0 -9.9626 Td[(a)-217(counter)-217(for)-218(each)-217(side)-217(e)15(xit,)-217(and)-218(when)-217(the)-217(counter)-217(reaches)-217(a)-218(hotness)]TJ 0 -9.9627 Td[(threshold,)-286(recording)-286(starts.)-286(Recording)-286(stops)-286(e)15(xactly)-286(as)-286(for)-287(the)-286(root)]TJ 0 -9.9626 Td[(trace,)-250(using)-250(the)-250(loop)-250(header)-250(of)-250(the)-250(root)-250(trace)-250(as)-250(the)-250(tar)18(get)-250(to)-250(reach.)]TJ
ET
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/F42 8.9664 Tf 65.9552 712.0299 Td[(Our)-263(implementation)-263(does)-263(not)-263(e)15(xtend)-263(at)-263(all)-263(side)-263(e)15(xits.)-263(It)-263(e)15(xtends)]TJ -11.9552 -9.9627 Td[(only)-223(if)-224(the)-223(side)-223(e)15(xit)-224(is)-223(for)-223(a)-224(control-\003o)25(w)-223(branch,)-223(and)-224(only)-223(if)-223(the)-224(side)]TJ 0 -9.9626 Td[(e)15(xit)-252(does)-252(not)-251(lea)20(v)15(e)-252(the)-252(loop.)-252(In)-252(particular)-252(we)-251(do)-252(not)-252(w)10(ant)-252(to)-252(e)15(xtend)]TJ 0 -9.9626 Td[(a)-362(trace)-361(tree)-362(along)-362(a)-361(path)-362(that)-362(leads)-361(to)-362(an)-362(outer)-361(loop,)-362(because)-362(we)]TJ 0 -9.9627 Td[(w)10(ant)-250(to)-250(co)15(v)15(er)-250(such)-250(paths)-250(in)-250(an)-250(outer)-250(tree)-250(through)-250(tree)]TJ/F46 8.9664 Tf 192.623 0 Td[(nesting)]TJ/F42 8.9664 Tf 25.9036 0 Td[(.)]TJ/F41 8.9664 Tf -218.5266 -17.5342 Td[(3.3)-1000(Blacklisting)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(Sometimes,)-463(a)-463(program)-463(follo)25(ws)-463(a)-463(path)-463(that)-463(cannot)-463(be)-463(compiled)]TJ 0 -9.9627 Td[(into)-309(a)-309(trace,)-309(usually)-308(because)-309(of)-309(limitations)-309(in)-309(the)-309(implementation.)]TJ 0 -9.9626 Td[(T)35(raceMonk)10(e)15(y)-362(does)-362(not)-362(currently)-362(support)-362(recording)-363(thro)25(wing)-362(and)]TJ 0 -9.9626 Td[(catching)-266(of)-265(arbitrary)-266(e)15(xceptions.)-265(This)-266(design)-265(trade)-266(of)25(f)-265(w)10(as)-266(chosen,)]TJ 0 -9.9627 Td[(because)-396(e)15(xceptions)-395(are)-396(usually)-396(rare)-396(in)-395(Ja)20(v)25(aScript.)-396(Ho)25(we)25(v)15(er)40(,)-396(if)-396(a)]TJ 0 -9.9626 Td[(program)-430(opts)-429(to)-430(use)-430(e)15(xceptions)-430(intensi)25(v)15(ely)65(,)-429(we)-430(w)10(ould)-430(suddenly)]TJ 0 -9.9627 Td[(incur)-309(a)-309(punishing)-310(runt)1(ime)-310(o)15(v)15(erhead)-309(if)-309(we)-309(repeatedly)-309(try)-310(to)-309(record)]TJ 0 -9.9626 Td[(a)-371(trace)-371(for)-371(this)-371(path)-370(and)-371(repeatedly)-371(f)10(ail)-371(to)-371(do)-371(so,)-371(since)-371(we)-371(abort)]TJ 0 -9.9626 Td[(tracing)-250(e)25(v)15(ery)-250(time)-250(we)-250(observ)15(e)-250(an)-250(e)15(xception)-250(being)-250(thro)25(wn.)]TJ 11.9552 -9.9627 Td[(As)-221(a)-220(result,)-221(if)-220(a)-221(hot)-220(loop)-221(contains)-221(traces)-220(that)-221(al)10(w)10(ays)-220(f)10(ail,)-221(the)-220(VM)]TJ -11.9552 -9.9626 Td[(could)-306(potentially)-305(run)-306(much)-306(more)-305(slo)25(wly)-306(than)-305(the)-306(base)-306(interpreter:)]TJ 0 -9.9627 Td[(the)-251(VM)-251(repeatedly)-251(spends)-251(t)1(ime)-251(trying)-251(to)-251(record)-251(traces,)-251(b)20(ut)-251(is)-251(ne)25(v)15(er)]TJ 0 -9.9626 Td[(able)-289(to)-289(run)-288(an)15(y)65(.)-289(T)80(o)-289(a)20(v)20(oid)-289(this)-289(problem,)-288(whene)25(v)15(er)-289(the)-289(VM)-289(is)-289(about)]TJ 0 -9.9626 Td[(to)-231(start)-231(tracing,)-231(it)-231(must)-230(try)-231(to)-231(predict)-231(whether)-231(it)-231(will)-231(\002nish)-231(the)-231(trace.)]TJ 11.9552 -9.9627 Td[(Our)-426(prediction)-427(algorithm)-426(is)-427(based)-426(on)]TJ/F46 8.9664 Tf 143.4761 0 Td[(blac)20(klisting)]TJ/F42 8.9664 Tf 45.4898 0 Td[(traces)-426(that)]TJ -200.9211 -9.9626 Td[(ha)20(v)15(e)-212(been)-212(tried)-212(and)-212(f)10(ailed.)-212(When)-212(the)-212(VM)-212(f)10(ails)-212(to)-212(\002nish)-212(a)-212(trace)-212(start-)]TJ 0 -9.9627 Td[(ing)-214(at)-214(a)-213(gi)25(v)15(en)-214(point,)-214(the)-214(VM)-213(records)-214(that)-214(a)-213(f)10(ailure)-214(has)-214(occurred.)-214(The)]TJ 0 -9.9626 Td[(VM)-193(also)-193(sets)-192(a)-193(counter)-193(so)-193(that)-193(it)-193(will)-193(not)-192(try)-193(to)-193(record)-193(a)-193(trace)-193(starting)]TJ 0 -9.9626 Td[(at)-319(that)-320(point)-319(until)-319(it)-320(is)-319(passed)-319(a)-320(fe)25(w)-319(more)-319(times)-320(\05032)-319(in)-319(our)-320(imple-)]TJ 0 -9.9627 Td[(mentation\051.)-345(This)]TJ/F46 8.9664 Tf 63.2261 0 Td[(bac)20(k)10(of)18(f)]TJ/F42 8.9664 Tf 30.3714 0 Td[(counter)-345(gi)25(v)15(es)-346(t)1(emporary)-346(conditions)-345(that)]TJ -93.5975 -9.9626 Td[(pre)25(v)15(ent)-318(tracing)-318(a)-319(chance)-318(to)-318(end.)-318(F)15(or)-319(e)15(xample,)-318(a)-318(loop)-318(may)-319(beha)20(v)15(e)]TJ 0 -9.9627 Td[(dif)25(ferently)-205(during)-206(startup)-205(than)-205(during)-206(its)-205(steady-state)-205(e)15(x)15(ecution.)-206(Af-)]TJ 0 -9.9626 Td[(ter)-316(a)-315(gi)25(v)15(en)-316(number)-315(of)-316(f)10(ailures)-315(\0502)-316(in)-315(our)-316(implementation\051,)-315(the)-316(VM)]TJ 0 -9.9626 Td[(marks)-241(the)-240(fragment)-241(as)-240(blacklisted,)-241(which)-240(means)-241(the)-241(VM)-240(will)-241(ne)25(v)15(er)]TJ 0 -9.9627 Td[(ag)5(ain)-250(start)-250(recording)-250(at)-250(that)-250(point.)]TJ 11.9552 -9.9626 Td[(After)-426(implem)1(enting)-426(this)-426(basic)-425(strate)15(gy)65(,)-426(we)-425(observ)15(ed)-426(that)-425(for)]TJ -11.9552 -9.9627 Td[(small)-275(loops)-276(that)-275(get)-275(blacklisted,)-275(the)-276(system)-275(can)-275(spend)-275(a)-276(noticeable)]TJ 0 -9.9626 Td[(amount)-239(of)-239(time)-239(just)-239(\002nding)-239(the)-239(loop)-239(fragment)-239(and)-239(determining)-239(that)]TJ 0 -9.9626 Td[(it)-238(has)-238(been)-239(blacklisted.)-238(W)80(e)-238(no)25(w)-238(a)20(v)20(oid)-239(that)-238(problem)-238(by)-238(patching)-239(the)]TJ 0 -9.9627 Td[(bytecode.)-291(W)80(e)-290(de\002ne)-291(an)-291(e)15(xtra)-290(no-op)-291(bytecode)-291(that)-290(indicates)-291(a)-291(loop)]TJ 0 -9.9626 Td[(header)55(.)-327(The)-326(VM)-327(calls)-326(into)-327(the)-327(trace)-326(monitor)-327(e)25(v)15(ery)-326(time)-327(the)-327(inter)20(-)]TJ 0 -9.9627 Td[(preter)-356(e)15(x)15(ecutes)-356(a)-356(loop)-357(header)-356(no-op.)-356(T)80(o)-356(blacklist)-356(a)-357(fragm)1(ent,)-357(we)]TJ 0 -9.9626 Td[(simply)-319(replace)-318(the)-319(loop)-319(header)-318(no-op)-319(with)-319(a)-318(re)15(gular)-319(no-op.)-319(Thus,)]TJ 0 -9.9626 Td[(the)-250(interpreter)-250(will)-250(ne)25(v)15(er)-250(ag)5(ain)-250(e)25(v)15(en)-250(call)-250(into)-250(the)-250(trace)-250(monitor)55(.)]TJ 11.9552 -9.9627 Td[(There)-220(is)-220(a)-219(related)-220(problem)-220(we)-220(ha)20(v)15(e)-219(not)-220(yet)-220(solv)15(ed,)-220(which)-219(occurs)]TJ -11.9552 -9.9626 Td[(when)-250(a)-250(loop)-250(meets)-250(all)-250(of)-250(these)-250(conditions:)]TJ/F26 7.9701 Tf 5.2303 -13.9462 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(The)-250(VM)-250(can)-250(form)-250(at)-250(least)-250(one)-250(root)-250(trace)-250(for)-250(the)-250(loop.)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(There)-395(is)-395(at)-395(least)-395(one)-396(hot)-395(side)-395(e)15(xit)-395(for)-395(which)-395(the)-395(VM)-395(cannot)]TJ 0 -9.9626 Td[(complete)-250(a)-250(trace.)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(The)-250(loop)-250(body)-250(is)-250(short.)]TJ -0.9963 -14.8443 Td[(In)-216(this)-217(case,)-216(the)-216(VM)-217(will)-216(repeatedly)-216(pass)-216(the)-217(loop)-216(header)40(,)-216(search)]TJ -11.9551 -9.9626 Td[(for)-471(a)-472(trace,)-471(\002nd)-472(it,)-471(e)15(x)15(ecute)-471(it,)-472(and)-471(f)10(all)-472(back)-471(to)-471(the)-472(interpreter)55(.)]TJ 0 -9.9627 Td[(W)40(ith)-399(a)-399(short)-399(loop)-399(body)65(,)-398(the)-399(o)15(v)15(erhead)-399(of)-399(\002nding)-399(and)-399(calling)-399(the)]TJ 0 -9.9626 Td[(trace)-342(is)-343(high,)-342(and)-343(causes)-342(performance)-343(to)-342(be)-342(e)25(v)15(en)-343(slo)25(wer)-342(than)-343(the)]TJ 0 -9.9627 Td[(basic)-417(interpreter)55(.)-418(So)-417(f)10(ar)40(,)-417(in)-418(this)-417(situation)-418(we)-417(ha)20(v)15(e)-417(impro)15(v)15(ed)-418(the)]TJ 0 -9.9626 Td[(implementation)-442(so)-442(that)-442(the)-441(VM)-442(can)-442(complete)-442(the)-442(branch)-442(trace.)]TJ 0 -9.9626 Td[(But)-390(it)-390(is)-390(hard)-391(to)-390(guarantee)-390(that)-390(this)-390(situation)-390(will)-391(ne)26(v)14(e)1(r)-391(happen.)]TJ 0 -9.9627 Td[(As)-358(future)-358(w)10(ork,)-358(this)-358(situation)-358(could)-358(be)-358(a)20(v)20(oided)-359(by)-358(detecting)-358(and)]TJ 0 -9.9626 Td[(blacklisting)-406(loops)-406(for)-406(which)-405(the)-406(a)20(v)15(erage)-406(trace)-406(call)-406(e)15(x)15(ecutes)-406(fe)25(w)]TJ 0 -9.9627 Td[(bytecodes)-250(before)-250(returning)-250(to)-250(the)-250(interpreter)55(.)]TJ/F41 10.9589 Tf 0 -22.5155 Td[(4.)-1000(Nested)-250(T)74(race)-250(T)74(r)18(ee)-250(F)25(ormation)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(Figure)-220(7)-220(sho)25(ws)-220(basic)-220(trace)-219(tree)-220(compilation)-220(\05011\051)-220(applied)-220(to)-220(a)-220(nested)]TJ 0 -9.9627 Td[(loop)-363(where)-364(the)-363(inner)-363(loop)-364(contains)-363(tw)10(o)-364(paths.)-363(Usually)65(,)-363(the)-364(inner)]TJ 0 -9.9626 Td[(loop)-239(\050with)-239(header)-239(at)]TJ/F29 8.9664 Tf 73.8141 0 Td[(i)]TJ/F28 5.9776 Tf 3.1534 -0.9962 Td[(2)]TJ/F42 8.9664 Tf 4.151 0.9962 Td[(\051)-239(becomes)-239(hot)-239(\002rst,)-239(and)-239(a)-239(trace)-240(tree)-239(is)-239(rooted)]TJ -81.1185 -9.9626 Td[(at)-310(that)-310(point.)-309(F)15(or)-310(e)15(xample,)-310(the)-310(\002rst)-310(recorded)-309(trace)-310(may)-310(be)-310(a)-310(c)15(ycle)]TJ
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-220.1756 -10.3994 Td[(\050on)-402(geometric)-403(a)20(v)15(erage\051,)-402(this)-403(na)]TJ 116.2073 0.0448 Td[(\250)]TJ 0.2466 -0.0448 Td[(\021v)15(e)-402(strate)15(gy)-403(yields)]TJ/F29 8.9664 Tf 71.322 0 Td[(O)]TJ/F27 8.9664 Tf 7.2682 0 Td[(\050)]TJ/F29 8.9664 Tf 3.5838 0 Td[(n)]TJ/F30 5.9776 Tf 5.559 3.809 Td[(k)]TJ/F27 8.9664 Tf 4.5731 -3.809 Td[(\051)]TJ/F42 8.9664 Tf 7.1926 0 Td[(traces,)]TJ -215.9526 -9.9626 Td[(which)-250(can)-250(easily)-250(\002ll)-250(the)-250(trace)-250(cache.)]TJ 11.9552 -9.9627 Td[(In)-406(order)-406(to)-405(e)15(x)14(e)1(cute)-406(programs)-406(with)-406(nested)-406(loops)-406(ef)25(\002cientl)1(y)64(,)-405(a)]TJ -11.9552 -9.9626 Td[(tracing)-215(system)-214(needs)-215(a)-214(technique)-215(for)-214(co)15(v)15(ering)-215(the)-215(nested)-214(loops)-215(with)]TJ 0 -9.9627 Td[(nati)25(v)15(e)-250(code)-250(without)-250(e)15(xponential)-250(trace)-250(duplication.)]TJ/F41 8.9664 Tf 0 -18.3527 Td[(4.1)-1000(Nesting)-250(Algorithm)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(The)-286(k)10(e)15(y)-286(insight)-287(is)-286(that)-286(if)-286(each)-286(loop)-287(is)-286(represented)-286(by)-286(its)-286(o)25(wn)-287(trace)]TJ 0 -9.9626 Td[(tree,)-297(the)-298(code)-297(for)-297(each)-297(loop)-298(can)-297(be)-297(contained)-298(only)-297(in)-297(its)-297(o)25(wn)-298(tree,)]TJ 0 -9.9627 Td[(and)-228(outer)-227(loop)-228(paths)-228(will)-228(not)-227(be)-228(duplicated.)-228(Another)-228(k)10(e)15(y)-227(f)10(act)-228(is)-228(that)]TJ 0 -9.9626 Td[(we)-239(are)-240(not)-239(tracing)-239(arbitrary)-240(bytec)1(odes)-240(that)-239(might)-239(ha)20(v)15(e)-240(irreduceable)]TJ 0 -9.9626 Td[(control)-317(\003o)25(w)-318(graphs,)-317(b)20(ut)-317(rather)-318(byt)1(ecodes)-318(produced)-317(by)-317(a)-318(compiler)]TJ 0 -9.9627 Td[(for)-320(a)-320(language)-320(with)-319(structured)-320(control)-320(\003o)25(w)65(.)-320(Thus,)-320(gi)25(v)15(en)-320(tw)10(o)-320(loop)]TJ 0 -9.9626 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Td[(must)-242(be)-243(an)]TJ -200.3898 -9.9626 Td[(inner)-250(loop)-250(of)]TJ/F29 8.9664 Tf 48.5616 0 Td[(L)]TJ/F30 5.9776 Tf 6.2709 -0.9963 Td[(R)]TJ/F42 8.9664 Tf 8.2738 0.9963 Td[(because)-250(we)-250(stop)-250(the)-250(trace)-250(when)-250(we)-250(e)15(xit)-250(a)-250(loop.)]TJ/F26 7.9701 Tf -57.876 -14.2558 Td[(\017)]TJ/F42 8.9664 Tf 7.7212 -0.8982 Td[(If)]TJ/F29 8.9664 Tf 8.6997 0 Td[(L)]TJ/F30 5.9776 Tf 6.2709 -0.9962 Td[(O)]TJ/F42 8.9664 Tf 9.0035 0.9962 Td[(has)-304(a)-305(type-)1(matching)-305(compiled)-304(trace)-304(tree,)-304(we)-305(call)]TJ/F29 8.9664 Tf 179.4346 0 Td[(L)]TJ/F30 5.9776 Tf 6.2709 -0.9962 Td[(O)]TJ/F42 8.9664 Tf 9.0035 0.9962 Td[(as)]TJ -218.6831 -9.9626 Td[(a)-274(nested)-274(trace)-274(tree.)-274(If)-274(the)-274(call)-274(succeeds,)-273(then)-274(we)-274(record)-274(the)-274(call)]TJ 0 -9.9626 Td[(in)-260(the)-261(trace)-260(for)]TJ/F29 8.9664 Tf 55.1491 0 Td[(L)]TJ/F30 5.9776 Tf 6.2709 -0.9963 Td[(R)]TJ/F42 8.9664 Tf 6.0322 0.9963 Td[(.)-260(On)-261(future)-260(e)15(x)15(ecutions,)-261(the)-260(trace)-260(for)]TJ/F29 8.9664 Tf 130.1102 0 Td[(L)]TJ/F30 5.9776 Tf 6.2709 -0.9963 Td[(R)]TJ/F42 8.9664 Tf 8.3673 0.9963 Td[(will)]TJ -212.2006 -9.9626 Td[(call)-250(the)-250(inner)-250(trace)-250(directly)65(.)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(If)]TJ/F29 8.9664 Tf 8.9629 0 Td[(L)]TJ/F30 5.9776 Tf 6.2709 -0.9963 Td[(O)]TJ/F42 8.9664 Tf 9.2667 0.9963 Td[(does)-334(not)-333(ha)20(v)15(e)-334(a)-333(type-matching)-334(compiled)-334(trace)-333(tree)-334(yet,)]TJ -24.5005 -9.9626 Td[(we)-386(ha)20(v)15(e)-385(to)-386(obtain)-385(it)-386(before)-385(we)-386(are)-385(able)-386(to)-385(proceed.)-386(In)-385(order)]TJ 0 -9.9627 Td[(to)-319(do)-318(this,)-319(we)-318(simply)-319(abort)-318(recording)-319(the)-319(\002rst)-318(trace.)-319(The)-318(trace)]TJ 0 -9.9626 Td[(monitor)-366(will)-366(see)-365(the)-366(inner)-366(loop)-366(header)40(,)-366(and)-366(wi)1(ll)-366(immediately)]TJ 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8.9664 Tf 6.1689 0 Td[(copies)-288(of)-289(the)-288(innermost)-288(loop.)-288(As)-289(long)-288(as)]TJ/F29 8.9664 Tf -92.252 -9.9626 Td[(m)]TJ/F42 8.9664 Tf 10.3604 0 Td[(is)-250(close)-250(to)-250(1,)-250(the)-250(resulting)-250(trace)-250(trees)-250(will)-250(be)-250(tractable.)]TJ 1.5948 -9.9627 Td[(An)-197(important)-197(detail)-197(is)-196(that)-197(the)-197(call)-197(to)-197(the)-197(inner)-197(trace)-197(tree)-196(must)-197(act)]TJ -11.9552 -9.9626 Td[(lik)10(e)-237(a)-237(function)-237(call)-237(site:)-236(it)-237(must)-237(return)-237(to)-237(the)-237(same)-237(point)-237(e)25(v)15(ery)-237(time.)]TJ 0 -9.9626 Td[(The)-289(goal)-289(of)-289(nesting)-289(is)-289(to)-289(mak)10(e)-289(inner)-290(and)-289(outer)-289(loops)-289(independent;)]TJ 0 -9.9627 Td[(thus)-358(when)-358(the)-358(inner)-359(tree)-358(is)-358(called,)-358(it)-358(must)-358(e)15(xit)-358(to)-358(the)-359(same)-358(point)]TJ 0 -9.9626 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Td[(the)-299(inner)-299(tree)-299(is)-300(not)-299(ready)65(,)-299(this)-299(is)-299(probably)-299(a)-300(temporary)-299(condition.)]TJ 0 -9.9627 Td[(Thus,)-279(we)-278(should)-279(not)-279(count)-278(such)-279(aborts)-279(to)25(w)10(ard)-278(blacklisting)-279(as)-279(long)]TJ 0 -9.9626 Td[(as)-250(we)-250(are)-250(able)-250(to)-250(b)20(uild)-250(up)-250(more)-250(traces)-250(for)-250(the)-250(inner)-250(tree.)]TJ 11.9552 -9.9626 Td[(In)-325(our)-326(implementation,)-325(when)-326(an)-325(outer)-326(tree)-325(aborts)-325(on)-326(the)-325(inner)]TJ -11.9552 -9.9627 Td[(tree,)-353(we)-354(increment)-353(the)-353(outer)-354(tree')55(s)-353(blacklist)-354(counter)-353(as)-353(usual)-354(and)]TJ 0 -9.9626 Td[(back)-313(of)25(f)-312(on)-313(compiling)-313(it.)-313(When)-312(the)-313(inner)-313(tree)-313(\002nis)1(hes)-313(a)-313(trace,)-313(we)]TJ 0 -9.9627 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Td[(,)-470(is)-470(separate)-470(from)-470(the)-470(VM)-470(and)-470(can)-470(be)-471(used)-470(for)-470(other)]TJ -33.1392 -9.9626 Td[(applications.)]TJ
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/F41 8.9664 Tf 54 712.0299 Td[(5.1)-1000(Optimizations)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(Because)-429(traces)-429(are)-429(in)-430(SSA)-429(form)-429(and)-429(ha)20(v)15(e)-429(no)-429(join)-430(points)-429(or)]TJ/F29 8.9664 Tf 230.6326 0 Td[(\036)]TJ/F42 8.9664 Tf 5.485 0 Td[(-)]TJ -236.1176 -9.9626 Td[(nodes,)-433(certa)1(in)-433(optimizations)-433(a)1(re)-433(easy)-433(to)-432(implement.)-433(In)-432(order)-433(to)]TJ 0 -9.9627 Td[(get)-286(good)-286(startup)-287(performance,)-286(the)-286(optimizations)-286(must)-286(run)-287(quickly)65(,)]TJ 0 -9.9626 Td[(so)-433(we)-434(chose)-433(a)-433(small)-433(set)-434(of)-433(optimizations.)-433(W)80(e)-433(implemented)-434(the)]TJ 0 -9.9627 Td[(optimizations)-269(as)-269(pipelined)-270(\002lters)-269(so)-269(that)-269(the)15(y)-270(can)-269(be)-269(turned)-269(on)-270(and)]TJ 0 -9.9626 Td[(of)25(f)-305(independently)65(,)-305(and)-305(yet)-305(all)-305(run)-305(in)-305(just)-305(tw)10(o)-306(l)1(oop)-306(passes)-305(o)15(v)15(er)-305(the)]TJ 0 -9.9626 Td[(trace:)-250(one)-250(forw)10(ard)-250(and)-250(one)-250(backw)10(ard.)]TJ 11.9552 -9.9627 Td[(Ev)15(ery)-360(time)-361(the)-360(trace)-360(recorder)-361(emits)-360(a)-360(LIR)-361(instruction,)-360(the)-360(in-)]TJ -11.9552 -9.9626 Td[(struction)-423(is)-424(immediately)-423(passed)-423(to)-424(the)-423(\002rst)-424(\002lter)-423(in)-423(the)-424(forw)10(ard)]TJ 0 -9.9627 Td[(pipeline.)-377(Thus,)-377(forw)10(ard)-377(\002lte)1(r)-377(optimizations)-377(are)-377(performed)-377(as)-377(the)]TJ 0 -9.9626 Td[(trace)-287(is)-287(recorded.)-288(Each)-287(\002lter)-287(may)-287(pass)-288(each)-287(instruction)-287(to)-287(the)-288(ne)15(xt)]TJ 0 -9.9626 Td[(\002lter)-336(unchanged,)-336(write)-336(a)-337(dif)25(ferent)-336(instruction)-336(to)-336(the)-336(ne)15(xt)-336(\002lter)40(,)-337(or)]TJ 0 -9.9627 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Td[(On)-377(ISAs)-377(without)-377(\003oating-point)-377(instructions,)-376(a)-377(soft-\003oat)-377(\002lter)]TJ 0 -9.9626 Td[(con)40(v)15(erts)-248(\003oating-point)-249(LIR)-248(instructions)-249(to)-248(sequences)-249(of)-248(inte)15(ger)]TJ 0 -9.9627 Td[(instructions.)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(CSE)-250(\050constant)-250(sube)15(xpression)-250(elimination\051,)]TJ/F26 7.9701 Tf -7.7211 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(e)15(xpression)-264(simpli\002cation,)-264(including)-264(constant)-263(folding)-264(and)-264(a)-264(fe)25(w)]TJ 0 -9.9626 Td[(algebraic)-250(identities)-250(\050e.g.,)]TJ/F29 8.9664 Tf 90.6399 0 Td[(a)]TJ/F31 8.9664 Tf 6.9298 0 Td[(\000)]TJ/F29 8.9664 Tf 9.2154 0 Td[(a)]TJ/F27 8.9664 Tf 7.4418 0 Td[(=)-286(0)]TJ/F42 8.9664 Tf 14.3351 0 Td[(\051,)-250(and)]TJ/F26 7.9701 Tf -136.2831 -13.0495 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(source)-512(language)-511(semantic-speci\002c)-512(e)15(xpression)-511(simpli\002cation,)]TJ 0 -9.9626 Td[(primarily)-228(algebraic)-228(identit)1(ies)-228(that)-228(allo)25(w)]TJ/F42 7.1731 Tf 142.6987 0 Td[(D)-62(O)-61(U)-62(B)-62(L)-61(E)]TJ/F42 8.9664 Tf 33.559 0 Td[(to)-228(be)-228(replaced)]TJ -176.2577 -9.9627 Td[(with)]TJ/F42 7.1731 Tf 18.6812 0 Td[(I)-62(N)-62(T)]TJ/F42 8.9664 Tf 13.0548 0 Td[(.)-281(F)15(or)-280(e)15(xample,)-280(LIR)-281(that)-280(con)40(v)15(erts)-281(an)]TJ/F42 7.1731 Tf 131.1187 0 Td[(I)-62(N)-62(T)]TJ/F42 8.9664 Tf 15.5699 0 Td[(to)-280(a)]TJ/F42 7.1731 Tf 16.2111 0 Td[(D)-62(O)-61(U)-62(B)-62(L)-61(E)]TJ/F42 8.9664 Tf -194.6357 -9.9626 Td[(and)-250(then)-250(back)-250(ag)5(ain)-250(w)10(ould)-250(be)-250(remo)15(v)15(ed)-250(by)-250(this)-250(\002lter)55(.)]TJ -0.9963 -17.335 Td[(When)-311(trace)-311(recording)-311(is)-311(completed,)-311(nanojit)-311(runs)-311(the)-311(backw)10(ard)]TJ -11.9551 -9.9626 Td[(optimization)-337(\002lters.)-337(These)-338(are)-337(used)-337(for)-337(optimizations)-337(that)-338(require)]TJ 0 -9.9627 Td[(backw)10(ard)-401(program)-400(analysis.)-401(When)-400(running)-401(the)-400(backw)10(ard)-401(\002lters,)]TJ 0 -9.9626 Td[(nanojit)-216(reads)-215(one)-216(LIR)-216(instruction)-216(at)-215(a)-216(time,)-216(and)-216(t)1(he)-216(reads)-216(are)-216(passed)]TJ 0 -9.9627 Td[(through)-250(the)-250(pipeline.)]TJ 11.9551 -9.9626 Td[(W)80(e)-250(currently)-250(apply)-250(three)-250(backw)10(ard)-250(\002lters:)]TJ/F26 7.9701 Tf -6.7248 -16.4368 Td[(\017)]TJ/F42 8.9664 Tf 7.7211 -0.8982 Td[(Dead)-221(data-stack)-222(store)-221(elimination.)-222(The)-221(LIR)-221(trace)-222(encodes)-221(man)15(y)]TJ 0 -9.9626 Td[(stores)-278(to)-278(locations)-278(in)-278(the)-278(interpreter)-278(stack.)-277(But)-278(these)-278(v)25(alues)-278(are)]TJ 0 -9.9627 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-9.9626 Td[(erator\051.)-371(By)-371(the)-371(time)-371(the)-371(allocator)-371(has)-371(reached)-371(an)-371(instruction)-371(lik)10(e)]TJ/F29 8.9664 Tf 0 -9.9626 Td[(v)]TJ/F28 5.9776 Tf 4.4762 -0.9963 Td[(3)]TJ/F27 8.9664 Tf 7.0642 0.9963 Td[(=)]TJ/F29 8.9664 Tf 10.0807 0 Td[(add)-270(v)]TJ/F28 5.9776 Tf 21.335 -0.9963 Td[(1)]TJ/F29 8.9664 Tf 4.1511 0.9963 Td[(;)-172(v)]TJ/F28 5.9776 Tf 8.572 -0.9963 Td[(2)]TJ/F42 8.9664 Tf 4.151 0.9963 Td[(,)-271(it)-270(has)-271(already)-271(assigned)-270(a)-271(re)15(gister)-271(to)]TJ/F29 8.9664 Tf 133.5763 0 Td[(v)]TJ/F28 5.9776 Tf 4.4762 -0.9963 Td[(3)]TJ/F42 8.9664 Tf 4.151 0.9963 Td[(.)-271(If)]TJ/F29 8.9664 Tf 13.0676 0 Td[(v)]TJ/F28 5.9776 Tf 4.4763 -0.9963 Td[(1)]TJ/F42 8.9664 Tf 6.5783 0.9963 Td[(and)]TJ/F29 8.9664 Tf -226.156 -9.9627 Td[(v)]TJ/F28 5.9776 Tf 4.4763 -0.9962 Td[(2)]TJ/F42 8.9664 Tf 6.4242 0.9962 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9.638 0.9962 Td[(be)-290(the)-290(last)]TJ -202.0246 -9.9626 Td[(instruction)-258(before)-257(the)-258(current)-258(where)-257(each)]TJ/F29 8.9664 Tf 149.8021 0 Td[(v)]TJ/F42 8.9664 Tf 7.1087 0 Td[(is)-258(referred)-257(to.)-258(Then)-258(the)]TJ 112.6402 644.5828 Td[(T)80(ag)]TJ
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Td[(the)-318(interpreter)40(,)-319(with)-318(an)-319(additional)-318(runtime)-319(check)-318(to)-319(see)-318(whether)-319(a)]TJ 0 -9.9626 Td[(recorder)-250(is)-250(currently)-250(acti)25(v)15(e.)]TJ 11.9552 -9.9626 Td[(While)-244(separating)-244(the)-244(interpreter)-244(from)-244(the)-244(recorder)-244(reduces)-244(indi-)]TJ -11.9552 -9.9627 Td[(vidual)-215(code)-216(comple)15(xity)65(,)-215(it)-215(also)-216(requires)-215(careful)-215(implementation)-216(and)]TJ 0 -9.9626 Td[(e)15(xtensi)25(v)15(e)-250(testing)-250(to)-250(achie)25(v)15(e)-250(semantic)-250(equi)25(v)25(alence.)]TJ 11.9552 -9.9627 Td[(In)-302(some)-301(cases)-302(achie)25(ving)-301(this)-302(equi)25(v)25(alence)-302(is)-301(dif)25(\002cult)-302(since)-301(Spi-)]TJ -11.9552 -9.9626 Td[(derMonk)10(e)15(y)-313(follo)25(ws)-312(a)]TJ/F46 8.9664 Tf 80.1794 0 Td[(fat-bytecode)]TJ/F42 8.9664 Tf 47.1246 0 Td[(design,)-313(which)-312(w)10(as)-313(found)-313(to)-313(be)]TJ -127.304 -9.9626 Td[(bene\002cial)-250(to)-250(pure)-250(interpreter)-250(performance.)]TJ 11.9552 -9.9627 Td[(In)-428(f)10(at-bytecode)-427(designs,)-428(indi)25(vidual)-428(bytecodes)-428(can)-427(implement)]TJ -11.9552 -9.9626 Td[(comple)15(x)-446(processing)-446(\050e.g.,)-446(the)]TJ/F33 8.9664 Tf 114.2213 0 Td[(getprop)]TJ/F42 8.9664 Tf 36.9499 0 Td[(bytecode,)-446(which)-446(imple-)]TJ -151.1712 -9.9627 Td[(ments)-221(full)-221(Ja)20(v)25(aScript)-222(property)-221(v)25(alue)-221(access,)-221(including)-222(s)1(pecial)-222(cases)]TJ 0 -9.9626 Td[(for)-250(cached)-250(and)-250(dense)-250(array)-250(access\051.)]TJ 11.9552 -9.9626 Td[(F)15(at)-461(bytecodes)-461(ha)20(v)15(e)-461(tw)10(o)-461(adv)25(antages:)-461(fe)25(wer)-461(bytecodes)-461(means)]TJ -11.9552 -9.9627 Td[(lo)25(wer)-255(dispatch)-255(cost,)-255(and)-255(bigger)-255(bytecode)-256(impleme)1(ntations)-256(gi)25(v)15(e)-255(the)]TJ 0 -9.9626 Td[(compiler)-250(more)-250(opportunities)-250(to)-250(optimize)-250(the)-250(interpreter)55(.)]TJ 11.9552 -9.9627 Td[(F)15(at)-436(bytecodes)-436(are)-435(a)-436(problem)-436(for)-436(T)35(raceMonk)10(e)15(y)-436(because)-435(the)15(y)]TJ -11.9552 -9.9626 Td[(require)-408(the)-408(recorder)-409(to)-408(reimplement)-408(the)-408(same)-408(special)-409(c)1(ase)-409(logic)]TJ 0 -9.9626 Td[(in)-433(the)-433(same)-433(w)10(ay)65(.)-433(Also,)-433(the)-433(adv)25(antages)-433(are)-434(reduced)-433(because)-433(\050a\051)]TJ 0 -9.9627 Td[(dispatch)-374(costs)-374(are)-374(eliminated)-374(entirely)-374(in)-374(compiled)-374(traces,)-374(\050b\051)-374(the)]TJ 0 -9.9626 Td[(traces)-456(contain)-457(only)-456(one)-457(special)-456(case,)-456(not)-457(the)-456(interpreter')55(s)-457(lar)18(ge)]TJ 0 -9.9627 Td[(chunk)-282(of)-281(code,)-282(and)-281(\050c\051)-282(T)35(raceMonk)10(e)15(y)-281(spends)-282(less)-282(time)-281(running)-282(the)]TJ 0 -9.9626 Td[(base)-250(interpreter)55(.)]TJ 11.9552 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Td[(f)10(at)-288(bytecodes)-288(that)-287(recurse)-288(back)-288(into)-288(the)-287(interpreter)40(,)-288(for)-288(e)15(xample)-288(to)]TJ 0 -9.9626 Td[(con)40(v)15(ert)-287(an)-288(object)-287(into)-288(a)-287(primiti)25(v)15(e)-288(v)25(alue)-287(by)-288(in)40(v)20(oking)-287(a)-288(well-kno)25(wn)]TJ 0 -9.9627 Td[(method)-250(on)-250(the)-250(object,)-250(since)-250(it)-250(lets)-250(us)-250(inline)-250(this)-250(function)-250(call.)]TJ 11.9552 -9.9626 Td[(It)-269(is)-270(important)-269(to)-270(note)-269(that)-270(we)-269(split)-270(f)10(at)-269(opcodes)-269(into)-270(thinner)-269(op-)]TJ -11.9552 -9.9626 Td[(codes)-256(only)-257(during)-256(recording.)-257(When)-256(running)-256(purely)-257(interpretati)25(v)15(ely)]TJ 0 -9.9627 Td[(\050i.e.)-259(code)-259(that)-259(has)-259(been)-259(blacklisted\051,)-259(the)-259(interpreter)-260(direct)1(ly)-260(and)-259(ef-)]TJ 0 -9.9626 Td[(\002ciently)-250(e)15(x)15(ecutes)-250(the)-250(f)10(at)-250(opcodes.)]TJ/F41 8.9664 Tf 0 -31.8805 Td[(6.4)-1000(Pr)18(eemption)]TJ/F42 8.9664 Tf 0 -13.9477 Td[(SpiderMonk)10(e)15(y)65(,)-223(lik)10(e)-223(man)15(y)-223(VMs,)-223(needs)-223(to)-223(preempt)-224(the)-223(user)-223(program)]TJ 0 -9.9626 Td[(periodically)65(.)-441(The)-440(main)-441(reasons)-440(are)-441(to)-441(pre)25(v)15(ent)-440(in\002nitely)-441(looping)]TJ 0 -9.9626 Td[(scripts)-250(from)-250(locking)-250(up)-250(the)-250(host)-250(system)-250(and)-250(to)-250(schedule)-250(GC.)]TJ 11.9552 -9.9627 Td[(In)-274(the)-274(interpreter)40(,)-274(this)-274(had)-274(been)-274(implemented)-274(by)-273(setting)-274(a)-274(\223pre-)]TJ -11.9552 -9.9626 Td[(empt)-357(no)25(w\224)-358(\003ag)-357(that)-357(w)10(as)-357(check)10(ed)-358(on)-357(e)25(v)15(ery)-357(backw)10(ard)-357(jump.)-358(This)]TJ 0 -9.9627 Td[(strate)15(gy)-244(carried)-245(o)15(v)15(er)-244(into)-245(T)35(raceMonk)10(e)15(y:)-244(the)-245(VM)-244(inserts)-245(a)-244(guard)-245(on)]TJ 0 -9.9626 Td[(the)-342(preemption)-342(\003ag)-343(at)-342(e)25(v)15(ery)-342(loop)-342(edge.)-343(W)80(e)-342(measured)-342(less)-342(than)-343(a)]TJ 0 -9.9626 Td[(1%)-327(increase)-327(in)-327(runtime)-327(on)-327(most)-327(benchmarks)-327(for)-327(this)-327(e)15(xtra)-327(guard.)]TJ 0 -9.9627 Td[(In)-237(practice,)-236(the)-237(cost)-237(is)-236(detectable)-237(only)-237(for)-237(programs)-236(with)-237(v)15(ery)-237(short)]TJ 0 -9.9626 Td[(loops.)]TJ 11.9552 -9.9627 Td[(W)80(e)-390(tested)-390(and)-391(rejected)-390(a)-390(solution)-390(that)-391(a)20(v)20(oided)-390(the)-390(guards)-390(by)]TJ -11.9552 -9.9626 Td[(compiling)-361(the)-362(loop)-361(edge)-361(as)-362(a)1(n)-362(unconditional)-361(jump,)-361(and)-362(patching)]TJ 0 -9.9626 Td[(the)-412(jump)-412(tar)18(get)-412(to)-412(an)-412(e)15(xit)-412(routine)-412(when)-412(preemption)-412(is)-412(required.)]TJ 0 -9.9627 Td[(This)-394(solution)-395(can)-394(mak)10(e)-394(the)-395(normal)-394(case)-395(slightly)-394(f)10(aster)40(,)-394(b)20(ut)-395(then)]TJ 0 -9.9626 Td[(preemption)-256(becomes)-257(v)15(ery)-256(slo)25(w)65(.)-256(The)-257(implementation)-256(w)10(as)-256(also)-257(v)15(ery)]TJ 0 -9.9627 Td[(comple)15(x,)-201(especially)-200(trying)-201(to)-201(restart)-201(e)15(x)15(ecution)-200(after)-201(the)-201(preemption.)]TJ
ET