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randall77 opened this issue Jan 13, 2025 · 3 comments
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cmd/compile: get rid of write barrier on slicing #71251

randall77 opened this issue Jan 13, 2025 · 3 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. Implementation Issues describing a semantics-preserving change to the Go implementation. Performance
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Unplanned

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@randall77
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type S struct {
	a []byte
}

func f(s *S) {
	s.a = s.a[1:]
}

The write barrier in f seems unnecessary. We're always writing back to s.a a pointer to the same object that used to be there.
Noticed while looking at #71246.
@randall77 randall77 added compiler/runtime Issues related to the Go compiler and/or runtime. Performance labels Jan 13, 2025
@randall77 randall77 added this to the Unplanned milestone Jan 13, 2025
@gabyhelp
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@gabyhelp gabyhelp added the Implementation Issues describing a semantics-preserving change to the Go implementation. label Jan 13, 2025
@randall77
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Maybe we can't do this? See the comment at #14855 (comment). Russ is afraid that in the presence of races we can't do the pointer write without the write barrier, as we may lose track of some write that happened between the read of s.a.ptr and the write of s.a.ptr+1.

@randall77
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Probably a dup of #24314. There's even a CL, CL 105258.
@aclements

@randall77 randall77 mentioned this issue Jan 15, 2025
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