From: Russ Cox <rsc@golang.org>
Date: Fri, 14 Feb 2014 02:11:50 +0000 (-0500)
Subject: cmd/gc: fix liveness for addressed results
X-Git-Tag: go1.3beta1~710
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=824e918ca4f799c4105ef1b96d81894a137a1b29;p=gostls13.git

cmd/gc: fix liveness for addressed results

Was spuriously marking results live on entry to function.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/63640043
---

diff --git a/src/cmd/gc/plive.c b/src/cmd/gc/plive.c
index 4e3eadcd74..bd14610864 100644
--- a/src/cmd/gc/plive.c
+++ b/src/cmd/gc/plive.c
@@ -668,8 +668,15 @@ progeffects(Prog *prog, Array *vars, Bvec *uevar, Bvec *varkill, Bvec *avarinit)
 			node = *(Node**)arrayget(vars, i);
 			switch(node->class & ~PHEAP) {
 			case PPARAM:
-			case PPARAMOUT:
 				bvset(uevar, i);
+			case PPARAMOUT:
+				// If the result had its address taken, it is being tracked
+				// by the avarinit code, which does not use uevar.
+				// If we added it to uevar too, we'd not see any kill
+				// and decide that the varible was live entry, which it is not.
+				// So only use uevar in the non-addrtaken case.
+				if(!node->addrtaken)
+					bvset(uevar, i);
 				break;
 			}
 		}
diff --git a/test/live.go b/test/live.go
index c0ea131294..c3dbc55c0a 100644
--- a/test/live.go
+++ b/test/live.go
@@ -86,3 +86,12 @@ func f6() (_, y string) {
 	y = "hello"
 	return
 }
+
+// confusion about addressed results used to cause "live at entry to f7: x".
+
+func f7() (x string) {
+	_ = &x
+	x = "hello"
+	return
+}
+