8000 cmd/compile: aggressive IMUL rewrites on AMD64 sometimes lead to performance regressions · Issue #25358 · golang/go · GitHub
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cmd/compile: aggressive IMUL rewrites on AMD64 sometimes lead to performance regressions #25358
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cmd/compile: aggressive IMUL rewrites on AMD64 sometimes lead to performance regressions#25358
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NeedsInvestigationSomeone must examine and confirm this is a valid issue and not a duplicate of an existing one.Performancecompiler/runtimeIssues related to the Go compiler and/or runtime.
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@quasilyte
quasilyte
opened on May 11, 2018
image/draw

name        old time/op  new time/op  delta
CopyOver-4  1.18ms ± 0%  1.52ms ± 0%  +28.49%  (p=0.008 n=5+5)

Bisecting from tip leads to b1df8d6.
This is regression from go1.10.2.
Performance delta is shown for b1df8d6 itself and it's parent (previous commit).

Single IMUL is rewritten into mov+shift+lea.
I can't reliably reproduce those results in free context, but they're stable for CopyOver.

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    NeedsInvestigationSomeone must examine and confirm this is a valid issue and not a duplicate of an existing one.Performancecompiler/runtimeIssues related to the Go compiler and/or runtime.

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