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Each"},{"wmode":0,"bbox":{"x":317,"y":151,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":159,"text":"tree is associated with a loop header and type map, so there may be"},{"wmode":0,"bbox":{"x":317,"y":161,"w":130,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":169,"text":"several trees for a given loop header."},{"wmode":0,"bbox":{"x":328,"y":170,"w":64,"h":11},"font":{"name":"TACTGM+NimbusRomNo9L-Medi","family":"serif","weight":"bold","style":"normal","size":8},"x":328,"y":179,"text":"Closing the loop."},{"wmode":0,"bbox":{"x":392,"y":171,"w":148,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":392,"y":179,"text":" Trace recording can end in several ways."},{"wmode":0,"bbox":{"x":328,"y":181,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":328,"y":189,"text":"Ideally, the trace reaches the loop header where it started with"},{"wmode":0,"bbox":{"x":317,"y":191,"w":177,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":199,"text":"the same type map as on entry. This is called a"},{"wmode":0,"bbox":{"x":494,"y":191,"w":42,"h":10},"font":{"name":"FCXRUF+NimbusRomNo9L-ReguItal","family":"serif","weight":"normal","style":"italic","size":8},"x":494,"y":199,"text":" type-stable"},{"wmode":0,"bbox":{"x":536,"y":191,"w":19,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":536,"y":199,"text":" loop"},{"wmode":0,"bbox":{"x":317,"y":201,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":209,"text":"iteration. In this case, the end of the trace can jump right to the"},{"wmode":0,"bbox":{"x":317,"y":211,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":219,"text":"beginning, as all the value representations are exactly as needed to"},{"wmode":0,"bbox":{"x":317,"y":221,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":229,"text":"enter the trace. The jump can even skip the usual code that would"},{"wmode":0,"bbox":{"x":317,"y":231,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":239,"text":"copy out the state at the end of the trace and copy it back in to the"},{"wmode":0,"bbox":{"x":317,"y":241,"w":137,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":249,"text":"trace activation record to enter a trace."},{"wmode":0,"bbox":{"x":328,"y":251,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":328,"y":259,"text":"In certain cases the trace might reach the loop header with a"},{"wmode":0,"bbox":{"x":317,"y":260,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":269,"text":"different type map. This scenario is sometime observed for the first"},{"wmode":0,"bbox":{"x":317,"y":270,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":279,"text":"iteration of a loop. Some variables inside the loop might initially be"},{"wmode":0,"bbox":{"x":317,"y":280,"w":34,"h":10},"font":{"name":"FCXRUF+NimbusRomNo9L-ReguItal","family":"serif","weight":"normal","style":"italic","size":8},"x":317,"y":289,"text":"undefined"},{"wmode":0,"bbox":{"x":351,"y":280,"w":204,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":351,"y":289,"text":", before they are set to a concrete type during the first loop"},{"wmode":0,"bbox":{"x":317,"y":290,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":299,"text":"iteration. When recording such an iteration, the recorder cannot"},{"wmode":0,"bbox":{"x":317,"y":300,"w":186,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":309,"text":"link the trace back to its own loop header since it is"},{"wmode":0,"bbox":{"x":503,"y":300,"w":50,"h":10},"font":{"name":"FCXRUF+NimbusRomNo9L-ReguItal","family":"serif","weight":"normal","style":"italic","size":8},"x":503,"y":309,"text":" type-unstable"},{"wmode":0,"bbox":{"x":553,"y":300,"w":2,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":553,"y":309,"text":"."},{"wmode":0,"bbox":{"x":317,"y":310,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":319,"text":"Instead, the iteration is terminated with a side exit that will always"},{"wmode":0,"bbox":{"x":317,"y":320,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":329,"text":"fail and return to the interpreter. At the same time a new trace is"},{"wmode":0,"bbox":{"x":317,"y":330,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":338,"text":"recorded with the new type map. Every time an additional type-"},{"wmode":0,"bbox":{"x":317,"y":340,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":348,"text":"unstable trace is added to a region, its exit type map is compared to"},{"wmode":0,"bbox":{"x":317,"y":350,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":358,"text":"the entry map of all existing traces in case they complement each"},{"wmode":0,"bbox":{"x":317,"y":360,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":368,"text":"other. With this approach we are able to cover type-unstable loop"},{"wmode":0,"bbox":{"x":317,"y":370,"w":213,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":378,"text":"iterations as long they eventually form a stable equilibrium."},{"wmode":0,"bbox":{"x":328,"y":380,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":328,"y":388,"text":"Finally, the trace might exit the loop before reaching the loop"},{"wmode":0,"bbox":{"x":317,"y":390,"w":173,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":398,"text":"header, for example because execution reaches a"},{"wmode":0,"bbox":{"x":490,"y":392,"w":25,"h":8},"font":{"name":"RRLDLB+CMTT9","family":"monospace","weight":"normal","style":"normal","size":8},"x":490,"y":398,"text":" break"},{"wmode":0,"bbox":{"x":516,"y":390,"w":9,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":516,"y":398,"text":" or"},{"wmode":0,"bbox":{"x":525,"y":392,"w":30,"h":8},"font":{"name":"RRLDLB+CMTT9","family":"monospace","weight":"normal","style":"normal","size":8},"x":525,"y":398,"text":" return"},{"wmode":0,"bbox":{"x":317,"y":400,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":408,"text":"statement. In this case, the VM simply ends the trace with an exit"},{"wmode":0,"bbox":{"x":317,"y":410,"w":72,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":418,"text":"to the trace monitor."},{"wmode":0,"bbox":{"x":328,"y":420,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":328,"y":428,"text":"As mentioned previously, we may speculatively chose to rep-"},{"wmode":0,"bbox":{"x":317,"y":430,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":438,"text":"resent certain Number-typed values as integers on trace. We do so"},{"wmode":0,"bbox":{"x":317,"y":440,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":448,"text":"when we observe that Number-typed variables contain an integer"},{"wmode":0,"bbox":{"x":317,"y":450,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":458,"text":"value at trace entry. If during trace recording the variable is unex-"},{"wmode":0,"bbox":{"x":317,"y":460,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":468,"text":"pectedly assigned a non-integer value, we have to widen the type"},{"wmode":0,"bbox":{"x":317,"y":470,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":478,"text":"of the variable to a double. As a result, the recorded trace becomes"},{"wmode":0,"bbox":{"x":317,"y":480,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":488,"text":"inherently type-unstable since it starts with an integer value but"},{"wmode":0,"bbox":{"x":317,"y":490,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":498,"text":"ends with a double value. This represents a mis-speculation, since"},{"wmode":0,"bbox":{"x":317,"y":500,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":508,"text":"at trace entry we specialized the Number-typed value to an integer,"},{"wmode":0,"bbox":{"x":317,"y":510,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":518,"text":"assuming that at the loop edge we would again find an integer value"},{"wmode":0,"bbox":{"x":317,"y":520,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":528,"text":"in the variable, allowing us to close the loop. To avoid future spec-"},{"wmode":0,"bbox":{"x":317,"y":529,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":538,"text":"ulative failures involving this variable, and to obtain a type-stable"},{"wmode":0,"bbox":{"x":317,"y":539,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":548,"text":"trace we note the fact that the variable in question as been observed"},{"wmode":0,"bbox":{"x":317,"y":549,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":558,"text":"to sometimes hold non-integer values in an advisory data structure"},{"wmode":0,"bbox":{"x":317,"y":559,"w":97,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":568,"text":"which we call the “oracle”."},{"wmode":0,"bbox":{"x":328,"y":569,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":328,"y":578,"text":"When compiling loops, we consult the oracle before specializ-"},{"wmode":0,"bbox":{"x":317,"y":579,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":588,"text":"ing values to integers. Speculation towards integers is performed"},{"wmode":0,"bbox":{"x":317,"y":589,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":598,"text":"only if no adverse information is known to the oracle about that"},{"wmode":0,"bbox":{"x":317,"y":599,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":607,"text":"particular variable. Whenever we accidentally compile a loop that"},{"wmode":0,"bbox":{"x":317,"y":609,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":617,"text":"is type-unstable due to mis-speculation of a Number-typed vari-"},{"wmode":0,"bbox":{"x":317,"y":619,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":627,"text":"able, we immediately trigger the recording of a new trace, which"},{"wmode":0,"bbox":{"x":317,"y":629,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":637,"text":"based on the now updated oracle information will start with a dou-"},{"wmode":0,"bbox":{"x":317,"y":639,"w":137,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":647,"text":"ble value and thus become type stable."},{"wmode":0,"bbox":{"x":328,"y":649,"w":68,"h":11},"font":{"name":"TACTGM+NimbusRomNo9L-Medi","family":"serif","weight":"bold","style":"normal","size":8},"x":328,"y":657,"text":"Extending a tree."},{"wmode":0,"bbox":{"x":397,"y":649,"w":158,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":397,"y":657,"text":" Side exits lead to different paths through"},{"wmode":0,"bbox":{"x":317,"y":659,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":667,"text":"the loop, or paths with different types or representations. Thus, to"},{"wmode":0,"bbox":{"x":317,"y":669,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":677,"text":"completely cover the loop, the VM must record traces starting at all"},{"wmode":0,"bbox":{"x":317,"y":679,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":687,"text":"side exits. These traces are recorded much like root traces: there is"},{"wmode":0,"bbox":{"x":317,"y":689,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":697,"text":"a counter for each side exit, and when the counter reaches a hotness"},{"wmode":0,"bbox":{"x":317,"y":699,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":317,"y":707,"text":"threshold, recording starts. 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Also, if the writes and reads are very close"},{"wmode":0,"bbox":{"x":54,"y":363,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":371,"text":"in the dynamic instruction stream, we have found that current"},{"wmode":0,"bbox":{"x":54,"y":373,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":381,"text":"x86 processors often incur penalties of 6 cycles or more (e.g., if"},{"wmode":0,"bbox":{"x":54,"y":383,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":391,"text":"the instructions use different base registers with equal values, the"},{"wmode":0,"bbox":{"x":54,"y":393,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":401,"text":"processor may not be able to detect that the addresses are the same"},{"wmode":0,"bbox":{"x":54,"y":403,"w":43,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":411,"text":"right away)."},{"wmode":0,"bbox":{"x":65,"y":413,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":65,"y":421,"text":"The alternate solution is to recompile an entire trace tree, thus"},{"wmode":0,"bbox":{"x":54,"y":423,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":431,"text":"achieving inter-trace register allocation (10). The disadvantage is"},{"wmode":0,"bbox":{"x":54,"y":433,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":441,"text":"that tree recompilation takes time quadratic in the number of traces."},{"wmode":0,"bbox":{"x":54,"y":443,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":451,"text":"We believe that the cost of recompiling a trace tree every time"},{"wmode":0,"bbox":{"x":54,"y":453,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":461,"text":"a branch is added would be prohibitive. That problem might be"},{"wmode":0,"bbox":{"x":54,"y":463,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":471,"text":"mitigated by recompiling only at certain points, or only for very"},{"wmode":0,"bbox":{"x":54,"y":473,"w":58,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":481,"text":"hot, stable trees."},{"wmode":0,"bbox":{"x":65,"y":483,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":65,"y":491,"text":"In the future, multicore hardware is expected to be common,"},{"wmode":0,"bbox":{"x":54,"y":493,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":501,"text":"making background tree recompilation attractive. In a closely re-"},{"wmode":0,"bbox":{"x":54,"y":503,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":511,"text":"lated project (13) background recompilation yielded speedups of"},{"wmode":0,"bbox":{"x":54,"y":513,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":521,"text":"up to 1.25x on benchmarks with many branch traces. We plan to"},{"wmode":0,"bbox":{"x":54,"y":522,"w":189,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":531,"text":"apply this technique to TraceMonkey as future work."}]},{"type":"text","bbox":{"x":54,"y":541,"w":84,"h":11},"lines":[{"wmode":0,"bbox":{"x":54,"y":541,"w":11,"h":11},"font":{"name":"TACTGM+NimbusRomNo9L-Medi","family":"serif","weight":"bold","style":"normal","size":8},"x":54,"y":550,"text":"6.3"},{"wmode":0,"bbox":{"x":74,"y":541,"w":63,"h":11},"font":{"name":"TACTGM+NimbusRomNo9L-Medi","family":"serif","weight":"bold","style":"normal","size":8},"x":74,"y":550,"text":"Trace Recording"}]},{"type":"text","bbox":{"x":54,"y":555,"w":239,"h":170},"lines":[{"wmode":0,"bbox":{"x":54,"y":555,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":564,"text":"The job of the trace recorder is to emit LIR with identical semantics"},{"wmode":0,"bbox":{"x":54,"y":565,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":574,"text":"to the currently running interpreter bytecode trace. A good imple-"},{"wmode":0,"bbox":{"x":54,"y":575,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":584,"text":"mentation should have low impact on non-tracing interpreter per-"},{"wmode":0,"bbox":{"x":54,"y":585,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":594,"text":"formance and a convenient way for implementers to maintain se-"},{"wmode":0,"bbox":{"x":54,"y":595,"w":71,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":604,"text":"mantic equivalence."},{"wmode":0,"bbox":{"x":65,"y":605,"w":227,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":65,"y":613,"text":"In our implementation, the only direct modification to the inter-"},{"wmode":0,"bbox":{"x":54,"y":615,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":623,"text":"preter is a call to the trace monitor at loop edges. In our benchmark"},{"wmode":0,"bbox":{"x":54,"y":625,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":633,"text":"results (see Figure 12) the total time spent in the monitor (for all"},{"wmode":0,"bbox":{"x":54,"y":635,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":643,"text":"activities) is usually less than 5%, so we consider the interpreter"},{"wmode":0,"bbox":{"x":54,"y":645,"w":239,"h":10},"font":{"name":"KUYGUP+NimbusRomNo9L-Regu","family":"serif","weight":"normal","style":"normal","size":8},"x":54,"y":653,"text":"impact requirement met. 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