Open Bug 860923 Opened 11 years ago Updated 2 years ago

[meta] "use asm" should not affect code speed


(Core :: JavaScript Engine, defect)

Other Branch




(Reporter: bhackett1024, Unassigned)


(Depends on 3 open bugs, Blocks 1 open bug)


(Keywords: meta)

asm.js preserves js semantics, and it in principle seems like the speed enhancements made by OdinMonkey should be applicable to vanilla js given enough engineering effort.  I don't know how much of this is actually feasible to do, but it seems a worthy goal to pursue.  This would improve performance by some amount for code that looks nothing like asm.js, and by a lot for code that is very similar to asm.js but includes unsupported features like property accesses.

Note that this would not affect the frontend performance / memory improvements made by asm.js (overhead from constructing JSScripts / baseline code etc.), just the peak performance reached by generated code.
Some numbers from experimenting on fannkuch(10) in the emscripten benchmark suite.  This benchmark involves pretty much no calls so is good for isolating the cost of memory accesses and simple integer operations.  Numbers are an x86/darwin post 804676 non-threadsafe build with the script size limit turned off (most of fannkuch is normally only compiled if off thread compilation is available, due to differing script size thresholds).  Pre 804676 seems to behave similarly.

                  lsra  backtracking
asm.js            600   562
trunk             976   875
  w/memops        803   701
  w/o interrupts  789   640

trunk w/memops adds paths to IonBuilder to generate the same MIR nodes as asm.js for memory loads and stores when possible.

trunk w/o interrupts additionally removes code for interrupt checks at loop headers (code which is not required by asm.js).

This still leaves a 30% gap with lsra, and 14% with backtracking.  This looks to be some combination of worse regalloc due to snapshots keeping things alive longer, and just plain more instructions.  Comparing w/o interrupt w/backtracking to asm.js w/backtracking, the former executes 66m (16%) more spill instructions and 234m (11%) more instructions overall.  Needs more investigating.
Depends on: 864214
Depends on: 864216
Depends on: 864218
Depends on: 864220
Depends on: 865889
Depends on: 866670
Depends on: 870052
Depends on: 870821
Depends on: 870847
Depends on: 871002
Depends on: 886957
Depends on: 886960
Depends on: 891400
Depends on: 891534
Depends on: 898021
Depends on: 898486
Depends on: 902009
Depends on: 902508
Depends on: 932767
Depends on: 1019188
Depends on: 1028580
Assignee: general → nobody
Depends on: 1177139
Severity: normal → S3
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