Commit 34db5f0c authored by Matthew Dempsky's avatar Matthew Dempsky

cmd/compile: fix evaluation order for OASOP

Currently, we handle "x op= y" by rewriting as "x = x op y", while
ensuring that any calls or receive operations in 'x' are only
evaluated once. Notably, pointer indirection, indexing operations,
etc. are left alone as it's typically safe to re-evaluate those.

However, those operations were interleaved with evaluating 'y', which
could include function calls that might cause re-evaluation to yield
different memory addresses.

As a fix, simply ensure that we order side-effecting operations in 'y'
before either evaluation of 'x'.

Fixes #21687.

Change-Id: Ib14e77760fda9c828e394e8e362dc9e5319a84b2
Reviewed-on: https://go-review.googlesource.com/60091
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: default avatarDavid Chase <drchase@google.com>
parent d349fa25
...@@ -533,8 +533,9 @@ func orderstmt(n *Node, order *Order) { ...@@ -533,8 +533,9 @@ func orderstmt(n *Node, order *Order) {
// out map read from map write when l is // out map read from map write when l is
// a map index expression. // a map index expression.
t := marktemp(order) t := marktemp(order)
n.Left = orderexpr(n.Left, order, nil) n.Left = orderexpr(n.Left, order, nil)
n.Right = orderexpr(n.Right, order, nil)
n.Left = ordersafeexpr(n.Left, order) n.Left = ordersafeexpr(n.Left, order)
tmp1 := treecopy(n.Left, src.NoXPos) tmp1 := treecopy(n.Left, src.NoXPos)
if tmp1.Op == OINDEXMAP { if tmp1.Op == OINDEXMAP {
......
// run
// Copyright 2017 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 21687: cmd/compile evaluates x twice in "x op= y", which was
// detectable if evaluating y affects x.
package main
func ptrs() (int, int) {
one := 1
two := 2
x := &one
*x += func() int {
x = &two
return 0
}()
return one, two
}
func slices() (int, int) {
one := []int{1}
two := []int{2}
x := one
x[0] += func() int {
x = two
return 0
}()
return one[0], two[0]
}
func maps() (int, int) {
one := map[int]int{0: 1}
two := map[int]int{0: 2}
x := one
x[0] += func() int {
x = two
return 0
}()
return one[0], two[0]
}
var tests = [...]func() (int, int){
ptrs,
slices,
maps,
}
func main() {
bad := 0
for i, f := range tests {
if a, b := f(); a+b != 3 {
println(i, a, b)
bad++
}
}
if bad != 0 {
panic(bad)
}
}
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