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7395083136
Currently, order desugars map assignment operations like
m[k] op= r
into
m[k] = m[k] op r
which in turn is transformed during walk into:
tmp := *mapaccess(m, k)
tmp = tmp op r
*mapassign(m, k) = tmp
However, this is suboptimal, as we could instead produce just:
*mapassign(m, k) op= r
One complication though is if "r == 0", then "m[k] /= r" and "m[k] %=
r" will panic, and they need to do so *before* calling mapassign,
otherwise we may insert a new zero-value element into the map.
It would be spec compliant to just emit the "r != 0" check before
calling mapassign (see #23735), but currently these checks aren't
generated until SSA construction. For now, it's simpler to continue
desugaring /= and %= into two map indexing operations.
Fixes #23661.
Change-Id: I46e3739d9adef10e92b46fdd78b88d5aabe68952
Reviewed-on: https://go-review.googlesource.com/91557
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
78 lines
1.2 KiB
Go
78 lines
1.2 KiB
Go
// run
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// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Test to make sure RHS is evaluated before map insert is started.
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// The RHS panics in all of these cases.
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package main
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import "fmt"
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func main() {
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for i, f := range []func(map[int]int){
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f0, f1, f2, f3, f4, f5, f6, f7, f8,
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} {
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m := map[int]int{}
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func() { // wrapper to scope the defer.
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defer func() {
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recover()
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}()
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f(m) // Will panic. Shouldn't modify m.
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fmt.Printf("RHS didn't panic, case f%d\n", i)
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}()
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if len(m) != 0 {
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fmt.Printf("map insert happened, case f%d\n", i)
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}
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}
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}
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func f0(m map[int]int) {
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var p *int
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m[0] = *p
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}
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func f1(m map[int]int) {
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var p *int
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m[0] += *p
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}
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func f2(m map[int]int) {
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var p *int
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sink, m[0] = sink, *p
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}
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func f3(m map[int]int) {
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var p *chan int
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m[0], sink = <-(*p)
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}
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func f4(m map[int]int) {
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var p *interface{}
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m[0], sink = (*p).(int)
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}
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func f5(m map[int]int) {
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var p *map[int]int
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m[0], sink = (*p)[0]
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}
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func f6(m map[int]int) {
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var z int
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m[0] /= z
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}
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func f7(m map[int]int) {
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var a []int
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m[0] = a[0]
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}
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func f8(m map[int]int) {
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var z int
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m[0] %= z
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}
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var sink bool
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