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cmd/compile: missed opportunity to coalesce loads that compare with constants #43248

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josharian opened this issue Dec 17, 2020 · 0 comments
Open

cmd/compile: missed opportunity to coalesce loads that compare with constants #43248

josharian opened this issue Dec 17, 2020 · 0 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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@josharian
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josharian commented Dec 17, 2020 •
edited 

func f(x *[16]byte) bool {
	return x[0] == 0 && x[1] == 0 &&
		x[2] == 0 && x[3] == 0 &&
		x[4] == 0 && x[5] == 0 &&
		x[6] == 0 && x[7] == 0 &&
		x[8] == 0 && x[9] == 0 &&
		x[10] == 0xff && x[11] == 0xff
}

This could compile on amd64 to something like MOVQ to load the first 8 bytes, TESTQ to check whether the first 8 bytes are zero, MOVL to load the next 4 bytes, CMPL to test those bytes. Instead, we currently generate a series of 12 CMPBs.

Low priority.
@josharian josharian added this to the Unplanned milestone Dec 17, 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 Dec 21, 2020
@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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