code review 10026046: cmd/gc: properly race-instrument for loops

cmd/gc: properly race-instrument for loops
Instrumentation of ntest expression should go to ntest->init.
Same for nincr.
Fixes issue 5340.

[dvyukov, 2013-06-06 11:57:16]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://dvyukov%40google.com@code.google.com/p/go/

[DMorsing, 2013-06-06 15:05:36]

This code has the same problems as https://codereview.appspot.com/9910043/

I'll send in a new version for this issue today.

Proof of concept that causes gc to go into an infinite loop with this patch:
package main

type iface interface {
        Foo() *struct{ b bool }
}

type Int int

func (i Int) Foo() *struct{ b bool } {
        return &struct{ b bool }{false}
}

func main() {
        var t Int
        // interface conversion causes nodes to be put on init list
        for iface(t).Foo().b {
        }
}

[dvyukov, 2013-06-06 15:16:39]

On 2013/06/06 15:05:36, DMorsing wrote:
> This code has the same problems as https://codereview.appspot.com/9910043/
> 
> I'll send in a new version for this issue today.
> 
> Proof of concept that causes gc to go into an infinite loop with this patch:
> package main
> 
> type iface interface {
>         Foo() *struct{ b bool }
> }
> 
> type Int int
> 
> func (i Int) Foo() *struct{ b bool } {
>         return &struct{ b bool }{false}
> }
> 
> func main() {
>         var t Int
>         // interface conversion causes nodes to be put on init list
>         for iface(t).Foo().b {
>         }
> }


Thanks!
Then I am waiting for your updated version, and will update this CL the same
way.

[DMorsing, 2013-06-11 20:35:47]

9910043 is in now. Pinging this CL so it doesn't get lost.

[dvyukov, 2013-06-13 10:54:30]

Hello golang-dev@googlegroups.com, daniel.morsing@gmail.com (cc:
golang-dev@googlegroups.com),

Please take another look.

[dvyukov, 2013-06-13 10:56:21]

On 2013/06/13 10:54:30, dvyukov wrote:
> Hello mailto:golang-dev@googlegroups.com, mailto:daniel.morsing@gmail.com (cc:
> mailto:golang-dev@googlegroups.com),
> 
> Please take another look.

Daniel,

I've refactored you code slightly, so that now it's possible to write:
racewalknode(&n->right, &n->right->ninit, wr, 0);
and it will do the right thing.

I've also added your test that should cause infinite loop before.

[DMorsing, 2013-06-13 11:12:04]

LGTM.

[dvyukov, 2013-06-13 12:04:05]

*** Submitted as https://code.google.com/p/go/source/detail?r=ff86470c2f3c ***

cmd/gc: properly race-instrument for loops
Instrumentation of ntest expression should go to ntest->init.
Same for nincr.
Fixes issue 5340.

R=golang-dev, daniel.morsing
CC=golang-dev
https://codereview.appspot.com/10026046