Bug 123638 – FTL should use a simple optimization pipeline by default

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Filip Pizlo]

My experiments show a 20% speed-up on imagine-gaussian-blur

[Filip Pizlo]

Created attachment 215764 [details]
the patch

[Nadav Rotem]

270        llvm->AddInstructionCombiningPass(modulePasses);
271        llvm->AddPromoteMemoryToRegisterPass(modulePasses);

I imagine that you are running instcombine and constantprop before mem2reg because the code you generate does not have too many allocas. Have you considered running earlyCSE instead of GVN ?

Have you considered adding LICM or JumpThreading ?

[Geoffrey Garen]

Comment on attachment 215764 [details]
the patch

View in context: https://bugs.webkit.org/attachment.cgi?id=215764&action=review

r=me

> Source/JavaScriptCore/ftl/FTLCompile.cpp:271
> +        llvm->AddPromoteMemoryToRegisterPass(modulePasses);

Shouldn't mem2reg always go first? (My understanding is that it's a simple transformation that eliminates a lot of dummy code, and relies only on convention and not on any other optimizations.)

[Nadav Rotem]

mem2reg should go first, unless we know that FTL generates all of its computations in registers. I know that this is the case for all of the arithmetic calculations but I am not sure about the other stuff.

[Filip Pizlo]

(In reply to comment #4)
> mem2reg should go first, unless we know that FTL generates all of its computations in registers. I know that this is the case for all of the arithmetic calculations but I am not sure about the other stuff.

Y'all have a point.  LowerDFGToLLVM produces very few alloca's so it probably doesn't matter *too* much.  I'll changed it.

[Filip Pizlo]

Landed in http://trac.webkit.org/changeset/158482