cmd/gc: temporary variable from previous scope still live

[phicode]

While debugging a memory problem I found something that looks like temporaries from
previous scopes are sometimes not garbage collected.

In this case disabling compiler optimizations got rid of the leak.

I tried to strip down the problem as much as possible:
http://play.golang.org/p/HR-7R_0f-C

go version: tip (321d42ff40d3)

[ianlancetaylor]

Comment 1:

Labels changed: added repo-main, release-go1.3.

[randall77]

Comment 2:

package main
import (
    "fmt"
    "runtime"
)
func main() {
    report(nil)
    {
        x := make([]byte, 1<<26)
        report(x)
    }
    report(nil)
}
func report(x interface{}) {
    runtime.GC()
    var ms runtime.MemStats
    runtime.ReadMemStats(&ms)
    fmt.Printf("%2d / %2d\n", ms.Alloc/(1<<20), ms.TotalAlloc/(1<<20))
}
$ go tool 6g -S -live ~/go/issue7606.go 
...
/Users/khr/go/issue7606.go:12: live at call to report: x
/Users/khr/go/issue7606.go:14: live at call to report: x
...
Yep, it thinks x is live across the last call to report(), which is wrong.  Might be the
same bug as issue #7602.

[rsc]

Comment 3:

This is because of the new convT2E. The compiler is passing &x to convT2E and it doesn't
know that the pointer does not outlive the call. So it assumes &x is live for the rest
of the function. Added test case to 7345.

Status changed to Duplicate.

Merged into issue #7345.