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cmd/compile: ARM's MOVWnop causes regalloc to insert unnecessary copies #37096

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josharian opened this issue Feb 6, 2020 · 1 comment
Open

cmd/compile: ARM's MOVWnop causes regalloc to insert unnecessary copies #37096

josharian opened this issue Feb 6, 2020 · 1 comment
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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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Backlog

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@josharian
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MOVWnop is a nop/copy designed to ensure type safety. It generates no code. However, it is not free; regalloc sometimes makes a copy of a value to provide to MOVWnop, since it doesn't know that MOVWnop doesn't modify its argument.

I noticed this while tracking down regressions due to changes in rewrite rule order application.

I don't know what the best approach to fixing it is. Suggestions?

cc @cherrymui
@josharian josharian added this to the Backlog milestone Feb 6, 2020
@cagedmantis cagedmantis added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Feb 7, 2020
@cagedmantis
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/cc @randall77 @griesemer

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jul 13, 2022
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Labels
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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Go Compiler / Runtime
Status: Triage Backlog
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Backlog
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@josharian @cagedmantis @gopherbot