cmd/gc: returning a function parameter causes escape

[bradfitz]

The buf below shouldn't escape to the heap.

package main

func nothing() {
}

func f(b []byte) []byte { // leaking param: b
        b[0] = 'H'
        b[1] = 'i'
        nothing() // (force f to not inline.)
        return b[:2]
}

func main() {
        var buf [10]byte // moved to heap: buf
        hi := f(buf[:]) // buf escapes to heap
        for i, c := range hi {
                println(i, c)
        }
}

$ go tool 6g -s -m e.go
e.go:3: can inline nothing
e.go:9: inlining call to nothing
e.go:14: moved to heap: buf
e.go:6: leaking param: b
e.go:15: buf escapes to heap

[rsc]

Comment 1:

That is exactly what I'm working on. I am probably going to have to
change gears for a week or two, but it's at the top of my compiler
work list.

Status changed to Accepted.

[rsc]

Comment 2:

http://golang.org/cl/6339053/ is supposed to fix this. lvd may look into why
it's broken, or if he doesn't get to it I will.

[rsc]

Comment 3:

Labels changed: added priority-later, removed priority-triage.

[rsc]

Comment 4:

Labels changed: added go1.1.

[lvdlvd]

Comment 5:

should be fixed by
https://code.google.com/p/go/source/detail?r=7df8438a2c4156e915d3065baf1a00732cb39b13

[bradfitz]

Comment 6:

Verified the example at top doesn't example.

Status changed to Fixed.

Attachments:

1. e.go (731 bytes)