code review 6542058: cmd/gc: fix use of nil interface, slice

src/cmd/5g/cgen.c

Index: src/cmd/5g/cgen.c
===================================================================
--- a/src/cmd/5g/cgen.c
+++ b/src/cmd/5g/cgen.c
@@ -554,6 +554,21 @@
 	while(n->op == OCONVNOP)
 		n = n->left;
 
+	if(isconst(n, CTNIL) && n->type->width > widthptr) {
+		// Use of a nil interface or nil slice.
+		// Create a temporary we can take the address of and read.
+		// The generated code is just going to panic, so it need not
+		// be terribly efficient. See issue 3670.
+		tempname(&n1, n->type);
+		clearfat(&n1);
+		regalloc(&n2, types[tptr], res);
+		gins(ALEAQ, &n1, &n2);
+		gmove(&n2, res);
+		regfree(&n2);
+		goto ret;
+	}
+		
+
 	if(n->addable) {
 		memset(&n1, 0, sizeof n1);
 		n1.op = OADDR;