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cmd/compile: stores to unused variables on the stack not eliminated #19765

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mundaym opened this issue Mar 29, 2017 · 2 comments

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@mundaym
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commented Mar 29, 2017

I am trying to replace math.Float64bits and friends with register to register moves and noticed that stores to variables on the stack aren't eliminated when their all their uses have been optimized away. Is there an existing issue for this?

For example, on tip (6e9ec14):

package main

var Sink int

func main() {
	x := 1
	Sink = *(&x)
}

Compiles to:

   	00000 (/tmp/main.go:5)	TEXT	"".main(SB)
   	00001 (/tmp/main.go:5)	FUNCDATA	$0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
   	00002 (/tmp/main.go:5)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
v7	00003 (/tmp/main.go:6)	MOVQ	$1, "".x-8(SP)
v13	00004 (/tmp/main.go:7)	MOVQ	$1, "".Sink(SB)
b1	00005 (/tmp/main.go:8)	RET
   	00006 (<unknown line number>)	END

The MOVQ $1, "".x-8(SP) could be eliminated by the compiler but isn't.

@randall77

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commented Mar 29, 2017

Kind of a dup of #13095

@gopherbot

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commented Mar 29, 2017

CL https://golang.org/cl/38746 mentions this issue.

@gopherbot gopherbot closed this in 744ebfd Aug 24, 2017

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