| commit | 878a86a129ceb771f677c8391a9f5c891e5be7c3 | [log] [tgz] |
|---|---|---|
| author | Dmitry Vyukov <dvyukov@google.com> | Mon Apr 06 18:17:20 2015 +0300 |
| committer | Dmitry Vyukov <dvyukov@google.com> | Thu Apr 09 09:56:27 2015 +0000 |
| tree | 48798aa4567d214e75a742a136a86de6f6f86e83 | |
| parent | 6e774faed773afa1ff7345e2c2d4367e9510388d [diff] |
cmd/gc: fix escape analysis of closures
Fixes #10353
See test/escape2.go:issue10353. Previously new(int) did not escape to heap,
and so heap-allcated closure was referencing a stack var. This breaks
the invariant that heap must not contain pointers to stack.
Look at the following program:
package main
func main() {
foo(new(int))
bar(new(int))
}
func foo(x *int) func() {
return func() {
println(*x)
}
}
// Models what foo effectively does.
func bar(x *int) *C {
return &C{x}
}
type C struct {
x *int
}
Without this patch escape analysis works as follows:
$ go build -gcflags="-m -m -m -l" esc.go
escflood:1: dst ~r1 scope:foo[0]
escwalk: level:0 depth:0 func literal( l(9) f(1) esc(no) ld(1)) scope:foo[1]
/tmp/live2.go:9: func literal escapes to heap
escwalk: level:0 depth:1 x( l(8) class(PPARAM) f(1) esc(no) ld(1)) scope:foo[1]
/tmp/live2.go:8: leaking param: x to result ~r1
escflood:2: dst ~r1 scope:bar[0]
escwalk: level:0 depth:0 &C literal( l(15) esc(no) ld(1)) scope:bar[1]
/tmp/live2.go:15: &C literal escapes to heap
escwalk: level:-1 depth:1 &C literal( l(15)) scope:bar[0]
escwalk: level:-1 depth:2 x( l(14) class(PPARAM) f(1) esc(no) ld(1)) scope:bar[1]
/tmp/live2.go:14: leaking param: x
/tmp/live2.go:5: new(int) escapes to heap
/tmp/live2.go:4: main new(int) does not escape
new(int) does not escape while being captured by the closure.
With this patch escape analysis of foo and bar works similarly:
$ go build -gcflags="-m -m -m -l" esc.go
escflood:1: dst ~r1 scope:foo[0]
escwalk: level:0 depth:0 &(func literal)( l(9)) scope:foo[0]
escwalk: level:-1 depth:1 func literal( l(9) f(1) esc(no) ld(1)) scope:foo[1]
/tmp/live2.go:9: func literal escapes to heap
escwalk: level:-1 depth:2 x( l(8) class(PPARAM) f(1) esc(no) ld(1)) scope:foo[1]
/tmp/live2.go:8: leaking param: x
escflood:2: dst ~r1 scope:bar[0]
escwalk: level:0 depth:0 &C literal( l(15) esc(no) ld(1)) scope:bar[1]
/tmp/live2.go:15: &C literal escapes to heap
escwalk: level:-1 depth:1 &C literal( l(15)) scope:bar[0]
escwalk: level:-1 depth:2 x( l(14) class(PPARAM) f(1) esc(no) ld(1)) scope:bar[1]
/tmp/live2.go:14: leaking param: x
/tmp/live2.go:4: new(int) escapes to heap
/tmp/live2.go:5: new(int) escapes to heap
Change-Id: Ifd14b7ae3fc11820e3b5eb31eb07f35a22ed0932
Reviewed-on: https://go-review.googlesource.com/8408
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.
For documentation about how to install and use Go, visit https://golang.org/ or load doc/install-source.html in your web browser.
Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.
Please report issues here: https://golang.org/issue/new
Go is the work of hundreds of contributors. We appreciate your help!
To contribute, please read the contribution guidelines: https://golang.org/doc/contribute.html
Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.
If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.
For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:
export GOROOT=$HOME/go export PATH=$PATH:$GOROOT/bin
See https://golang.org/doc/install or doc/install.html for more details.