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cmd/compile: aggressive IMUL rewrites on AMD64 sometimes lead to performance regressions #25358

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quasilyte opened this issue May 11, 2018 · 3 comments
Open

cmd/compile: aggressive IMUL rewrites on AMD64 sometimes lead to performance regressions #25358

quasilyte opened this issue May 11, 2018 · 3 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Performance
Milestone
Unplanned

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@quasilyte
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quasilyte commented May 11, 2018 •
edited 

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.
@quasilyte quasilyte changed the title cmd/compile: aggressive IMUL rewrites sometimes lead to performance regressions cmd/compile: aggressive IMUL rewrites on AMD64 sometimes lead to performance regressions May 11, 2018
@josharian
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Duplicate of #21735?

@quasilyte
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quasilyte commented May 11, 2018 •
edited

Maybe.

I'm reporting regression and it hopefully can be fixed.
Shouldn't be unnoticed.

At the very least it adds related benchmark that can be used to check the results.

@bradfitz
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/cc @randall77

@bradfitz bradfitz added Performance NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels May 11, 2018
@bradfitz bradfitz modified the milestones: Go1.11, Unplanned May 11, 2018
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 13, 2022
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Performance
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