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go/test/fixedbugs/issue51913.go

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cmd/compile/internal/staticinit: make staticopy safe Currently, cmd/compile optimizes `var a = true; var b = a` into `var a = true; var b = true`. But this may not be safe if we need to initialize any other global variables between `a` and `b`, and the initialization involves calling a user-defined function that reassigns `a`. This CL changes staticinit to keep track of the initialization expressions that we've seen so far, and to stop applying the staticcopy optimization once we've seen an initialization expression that might have modified another global variable within this package. To help identify affected initializers, this CL adds a -d=staticcopy flag to warn when a staticcopy is suppressed and turned into a dynamic copy. Currently, `go build -gcflags=all=-d=staticcopy std` reports only four instances: ``` encoding/xml/xml.go:1600:5: skipping static copy of HTMLEntity+0 with map[string]string{...} encoding/xml/xml.go:1869:5: skipping static copy of HTMLAutoClose+0 with []string{...} net/net.go:661:5: skipping static copy of .stmp_31+0 with poll.ErrNetClosing net/http/transport.go:2566:5: skipping static copy of errRequestCanceled+0 with ~R0 ``` Fixes #51913. Change-Id: Iab41cf6f84c44f7f960e4e62c28a8aeaade4fbcf Reviewed-on: https://go-review.googlesource.com/c/go/+/395541 Auto-Submit: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> Reviewed-by: David Chase <drchase@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Heschi Kreinick <heschi@google.com>
2022-03-24 13:27:39 -06:00
// 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.
package main
var _ = func() int {
a = false
return 0
}()
var a = true
var b = a
func main() {
if b {
panic("FAIL")
}
}