gc: bug281 - bad overlap in stack copy

Fixes issue 807.

R=ken2
CC=golang-dev
http://codereview.appspot.com/1283041

1 files changed, 32 insertions, 0 deletions

diff --git a/src/cmd/5g/cgen.c b/src/cmd/5g/cgen.c
index cf701a50a..8072c3ceb 100644
--- a/src/cmd/5g/cgen.c
+++ b/src/cmd/5g/cgen.c
@@ -1053,11 +1053,32 @@ stkof(Node *n)
 {
 	Type *t;
 	Iter flist;
+	int32 off;
 
 	switch(n->op) {
 	case OINDREG:
 		return n->xoffset;
 
+	case ODOT:
+		t = n->left->type;
+		if(isptr[t->etype])
+			break;
+		off = stkof(n->left);
+		if(off == -1000 || off == 1000)
+			return off;
+		return off + n->xoffset;
+
+	case OINDEX:
+		t = n->left->type;
+		if(!isfixedarray(t))
+			break;
+		off = stkof(n->left);
+		if(off == -1000 || off == 1000)
+			return off;
+		if(isconst(n->right, CTINT))
+			return off + t->type->width * mpgetfix(n->right->val.u.xval);
+		return 1000;
+		
 	case OCALLMETH:
 	case OCALLINTER:
 	case OCALLFUNC:
@@ -1106,6 +1127,17 @@ sgen(Node *n, Node *res, int32 w)
 	osrc = stkof(n);
 	odst = stkof(res);
 
+	if(osrc != -1000 && odst != -1000 && (osrc == 1000 || odst == 1000)) {
+		// osrc and odst both on stack, and at least one is in
+		// an unknown position.  Could generate code to test
+		// for forward/backward copy, but instead just copy
+		// to a temporary location first.
+		tempname(&tmp, n->type);
+		sgen(n, &tmp, w);
+		sgen(&tmp, res, w);
+		return;
+	}
+
 	if(osrc % 4 != 0 || odst %4 != 0)
 		fatal("sgen: non word(4) aligned offset src %d or dst %d", osrc, odst);