From 51266761fdbe1b22fc354d7536123492a51769cf Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Mon, 16 Sep 2013 14:22:37 -0400
Subject: [PATCH] cmd/gc: fix divide by zero error in compiler

Fixes #6399.

R=ken2
CC=golang-dev
https://golang.org/cl/13253055
---
 src/cmd/gc/walk.c           |  2 +-
 test/fixedbugs/issue6399.go | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/fixedbugs/issue6399.go

diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index e9a594d1ef..489b947143 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -1295,7 +1295,7 @@ walkexpr(Node **np, NodeList **init)
 		t = n->type;
 		if(n->esc == EscNone
 			&& smallintconst(l) && smallintconst(r)
-			&& mpgetfix(r->val.u.xval) < (1ULL<<16) / t->type->width) {
+			&& (t->type->width == 0 || mpgetfix(r->val.u.xval) < (1ULL<<16) / t->type->width)) {
 			// var arr [r]T
 			// n = arr[:l]
 			t = aindex(r, t->type); // [r]T
diff --git a/test/fixedbugs/issue6399.go b/test/fixedbugs/issue6399.go
new file mode 100644
index 0000000000..b3d1c855b2
--- /dev/null
+++ b/test/fixedbugs/issue6399.go
@@ -0,0 +1,27 @@
+// compile
+
+package main
+
+type Foo interface {
+	Print()
+}
+
+type Bar struct{}
+
+func (b Bar) Print() {}
+
+func main() {
+	b := make([]Bar, 20)
+	f := make([]Foo, 20)
+	for i := range f {
+		f[i] = b[i]
+	}
+	T(f)
+	_ = make([]struct{}, 1)
+}
+
+func T(f []Foo) {
+	for i := range f {
+		f[i].Print()
+	}
+}