add & fix bug207: rewritten if condition

was discarding initialization work.

R=ken
OCL=35454
CL=35457

src/cmd/gc/walk.c

@@ -356,7 +356,7 @@ walkstmt(Node **np)
 		walkstmtlist(n->ninit);
 		if(n->ntest != N) {
 			walkstmtlist(n->ntest->ninit);
-			walkexpr(&n->ntest, &n->ntest->ninit);
+			walkexpr(&n->ntest, &n->ninit);
 		}
 		walkstmt(&n->nincr);
 		walkstmtlist(n->nbody);
@@ -364,7 +364,7 @@ walkstmt(Node **np)
 
 	case OIF:
 		walkstmtlist(n->ninit);
-		walkexpr(&n->ntest, &n->ntest->ninit);
+		walkexpr(&n->ntest, &n->ninit);
 		walkstmtlist(n->nbody);
 		walkstmtlist(n->nelse);
 		break;
@@ -455,6 +455,13 @@ walkexpr(Node **np, NodeList **init)
 	if(n == N)
 		return;
 
+	if(init == &n->ninit) {
+		// not okay to use n->ninit when walking n,
+		// because we might replace n with some other node
+		// and would lose the init list.
+		fatal("walkexpr init == &n->ninit");
+	}
+
 	// annoying case - not typechecked
 	if(n->op == OKEY) {
 		walkexpr(&n->left, init);

test/fixedbugs/bug207.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// used to panic because 6g didn't generate
+// the code to fill in the ... argument to fmt.Sprint.
+
+package main
+
+import "fmt"
+
+type T struct {
+	a, b, c, d, e []int;
+}
+
+var t T
+
+func main() {
+	if fmt.Sprint("xxx", t) != "yyy" { 
+	}
+}