gc: do not try to add a key with incorrect type to a hash

Fixes #2623.

R=rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5533043

src/cmd/gc/typecheck.c

@@ -2130,7 +2130,8 @@ typecheckcomplit(Node **np)
 			typecheck(&l->left, Erv);
 			defaultlit(&l->left, t->down);
 			l->left = assignconv(l->left, t->down, "map key");
-			keydup(l->left, hash, nhash);
+			if (l->left->op != OCONV)
+				keydup(l->left, hash, nhash);
 
 			r = l->right;
 			pushtype(r, t->type);

test/fixedbugs/bug397.go

+// errchk $G -e $D/$F.go
+
+// Copyright 2011 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.
+
+package main
+
+// Issue 2623
+var m = map[string]int {
+	"abc":1,
+	1:2, // ERROR "cannot use 1.*as type string in map key"
+}