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cmd/compile: store pairing on arm64 misses some cases #71987

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randall77 opened this issue Feb 26, 2025 · 1 comment
Open

cmd/compile: store pairing on arm64 misses some cases #71987

randall77 opened this issue Feb 26, 2025 · 1 comment
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BugReport Issues describing a possible bug in the Go implementation. compiler/runtime Issues related to the Go compiler and/or runtime. help wanted NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. Performance
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Backlog

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@randall77
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randall77 commented Feb 26, 2025 •
edited by gabyhelp
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After CL 633075, this program:

package main

type T struct{ a, b, c int }
type TT struct{ i, j T }

func f(x *TT) {
	x.j = T{}
	x.i = T{}
}

Compiles to:

MOVD	ZR, 24(R0)
STP	(ZR, ZR), 32(R0)
MOVD	ZR, (R0)
STP	(ZR, ZR), 8(R0)

It would be better to compile to 3 STPs. Because the pairing is chosen greedily we get stuck in a local maximum that isn't optimal. Not sure what to do about it yet.

(Note that if we assign i and j in order, we do get 3 STPs.)
@randall77 randall77 added this to the Backlog milestone Feb 26, 2025
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Feb 26, 2025
@gabyhelp gabyhelp added the BugReport Issues describing a possible bug in the Go implementation. label Feb 26, 2025
@zigo101
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zigo101 commented Feb 28, 2025

Similar to duplicate arguments in fmt print function calls.

@prattmic prattmic added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Feb 28, 2025
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BugReport Issues describing a possible bug in the Go implementation. compiler/runtime Issues related to the Go compiler and/or runtime. help wanted NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. Performance
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Go Compiler / Runtime
Status: Todo
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@prattmic @randall77 @gopherbot @zigo101 @gabyhelp