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cmd/compile: optimize small runtime.memequal calls #37275

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josharian opened this issue Feb 18, 2020 · 2 comments
Open

cmd/compile: optimize small runtime.memequal calls #37275

josharian opened this issue Feb 18, 2020 · 2 comments
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NeedsFix The path to resolution is known, but the work has not been done. Performance
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Unplanned

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@josharian
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In the SSA backend, we could optimize a call to runtime.memequal in which the length is small and one argument points to a readonly data symbol. We could replace it by reading the readonly data and checking the bytes of the other argument directly.

This is similar to the optimization in walk.go for comparing against a constant string, and could potentially supercede it. The optimization in walk.go doesn't always trigger. An example is using strings.HasPrefix to check for a constant prefix; the call gets inlined, but walk.go isn't able to do the optimization because its analysis isn't powerful enough.

Low priority.
@josharian josharian added this to the Backlog milestone Feb 18, 2020
@josharian josharian modified the milestones: Backlog, Unplanned Feb 18, 2020
@toothrot toothrot added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Feb 18, 2020
@toothrot
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/cc @randall77 @griesemer

@josharian josharian added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. labels Feb 18, 2020
@gopherbot
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Change https://golang.org/cl/328291 mentions this issue: cmd/compile: inline memequal(x, const, sz) for small sizes

gopherbot pushed a commit that referenced this issue Oct 6, 2021
@kels-ng @cherrymui
cmd/compile: inline memequal(x, const, sz) for small sizes
810b08b 
This CL adds late expanded memequal(x, const, sz) inlining for 2, 4, 8
bytes size. This PoC is using the same method as CL 248404.
This optimization fires about 100 times in Go compiler (1675 occurrences
reduced to 1574, so -6%).
Also, added unit-tests to codegen/comparisions.go file.

Updates #37275

Change-Id: Ia52808d573cb706d1da8166c5746ede26f46c5da
Reviewed-on: https://go-review.googlesource.com/c/go/+/328291
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Trust: David Chase <drchase@google.com>
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@toothrot @josharian @gopherbot