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cmd/compile: eliminate stores to unread auto variables

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This is a crude compiler pass to eliminate stores to auto variables
that are only ever written to.

Eliminates an unnecessary store to x from the following code:

func f() int {
	var x := 1
	return *(&x)
}

Fixes #19765.

Change-Id: If2c63a8ae67b8c590b6e0cc98a9610939a3eeffa
Reviewed-on: https://go-review.googlesource.com/38746
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Michael Munday 2017-03-29 14:01:41 -04:00
parent 18b48afec9
commit 744ebfde04
8 changed files with 158 additions and 23 deletions
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1
src/cmd/compile/internal/ssa/compile.go
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@ -356,6 +356,7 @@ var passes = [...]pass{
{name: "tighten", fn: tighten}, // move values closer to their uses
{name: "lower", fn: lower, required: true},
{name: "lowered cse", fn: cse},
{name: "elim unread autos", fn: elimUnreadAutos},
{name: "lowered deadcode", fn: deadcode, required: true},
{name: "checkLower", fn: checkLower, required: true},
{name: "late phielim", fn: phielim},