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cmd/compile: do not use "oaslit" for global

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The compiler did not emit write barrier for assigning global with
struct literal, like global = T{} where T contains pointer.

The relevant code path is:
walkexpr OAS var_ OSTRUCTLIT
    oaslit
        anylit OSTRUCTLIT
            walkexpr OAS var_ nil
            return without adding write barrier
    return true
break (without adding write barrier)

This CL makes oaslit not apply to globals. See also CL
https://go-review.googlesource.com/c/36355/ for an alternative
fix.

The downside of this is that it generates static data for zeroing
struct now. Also this only covers global. If there is any lurking
bug with implicit zeroing other than globals, this doesn't fix.

Fixes #18956.

Change-Id: Ibcd27e4fae3aa38390ffa94a32a9dd7a802e4b37
Reviewed-on: https://go-review.googlesource.com/36410
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Cherry Zhang 2017-02-06 14:24:16 -05:00
parent 1ead0bd1dc
commit 160914e33c
2 changed files with 17 additions and 1 deletions
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2
src/cmd/compile/internal/gc/sinit.go
View File

@ -585,7 +585,7 @@ func isliteral(n *Node) bool {
}
func (n *Node) isSimpleName() bool {
return n.Op == ONAME && n.Addable && n.Class != PAUTOHEAP
return n.Op == ONAME && n.Addable && n.Class != PAUTOHEAP && n.Class != PEXTERN
}
func litas(l *Node, r *Node, init *Nodes) {

16
test/writebarrier.go
View File

@ -220,3 +220,19 @@ func f22(x *int) (y *int) {
*p = x // no barrier
return
}
type T23 struct {
p *int
a int
}
var t23 T23
var i23 int
func f23() {
// zeroing global needs write barrier for the hybrid barrier.
t23 = T23{} // ERROR "write barrier"
// also test partial assignments
t23 = T23{a: 1} // ERROR "write barrier"
t23 = T23{p: &i23} // ERROR "write barrier"
}