[release-branch.go1.17] cmd/compile: do not use special literal assignment if LHS is address-taken

A composite literal assignment

x = T{field: v}

may be compiled to

x = T{}
x.field = v

We already do not use this form is RHS uses LHS. If LHS is
address-taken, RHS may uses LHS implicitly, e.g.

v = &x.field
x = T{field: *v}

The lowering above would change the value of RHS (*v).

Updates #52953.
Fixes #52960.

Change-Id: I3f798e00598aaa550b8c17182c7472fef440d483
Reviewed-on: https://go-review.googlesource.com/c/go/+/407014
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
(cherry picked from commit 1c77137d4fdfbb3e7e8d9efaab3bab5ee736a19d)
Reviewed-on: https://go-review.googlesource.com/c/go/+/419451
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Cherry Mui 2022-05-18 11:58:53 -04:00
parent 489c148578
commit d9242f7a8c
2 changed files with 36 additions and 1 deletions

View File

@ -621,6 +621,12 @@ func oaslit(n *ir.AssignStmt, init *ir.Nodes) bool {
// not a special composite literal assignment
return false
}
if x.Addrtaken() {
// If x is address-taken, the RHS may (implicitly) uses LHS.
// Not safe to do a special composite literal assignment
// (which may expand to multiple assignments).
return false
}
switch n.Y.Op() {
default:
@ -629,7 +635,7 @@ func oaslit(n *ir.AssignStmt, init *ir.Nodes) bool {
case ir.OSTRUCTLIT, ir.OARRAYLIT, ir.OSLICELIT, ir.OMAPLIT:
if ir.Any(n.Y, func(y ir.Node) bool { return ir.Uses(y, x) }) {
// not a special composite literal assignment
// not safe to do a special composite literal assignment if RHS uses LHS.
return false
}
anylit(n.Y, n.X, init)

View File

@ -0,0 +1,29 @@
// run
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Issue 52953: miscompilation for composite literal assignment
// when LHS is address-taken.
package main
type T struct {
Field1 bool
}
func main() {
var ret T
ret.Field1 = true
var v *bool = &ret.Field1
ret = T{Field1: *v}
check(ret.Field1)
}
//go:noinline
func check(b bool) {
if !b {
panic("FAIL")
}
}