runtime: fix compilation of send select cases

Fixes #2102.

R=fullung, rsc
CC=golang-dev
https://golang.org/cl/4825043

src/cmd/gc/go.h

@@ -1136,7 +1136,7 @@ Sym*	restrictlookup(char *name, Pkg *pkg);
 Node*	safeexpr(Node *n, NodeList **init);
 void	saveerrors(void);
 Node*	cheapexpr(Node *n, NodeList **init);
-Node*	localexpr(Node *n, NodeList **init);
+Node*	localexpr(Node *n, Type *t, NodeList **init);
 int32	setlineno(Node *n);
 void	setmaxarg(Type *t);
 Type*	shallow(Type *t);

src/cmd/gc/select.c

@@ -311,7 +311,7 @@ walkselect(Node *sel)
 			case OSEND:
 				// selectsend(sel *byte, hchan *chan any, elem *any) (selected bool);
 				n->left = safeexpr(n->left, &r->ninit);
-				n->right = localexpr(n->right, &r->ninit);
+				n->right = localexpr(n->right, n->left->type->type, &r->ninit);
 				n->right = nod(OADDR, n->right, N);
 				n->right->etype = 1;  // pointer does not escape
 				typecheck(&n->right, Erv);

src/cmd/gc/subr.c

@@ -2728,12 +2728,12 @@ safeexpr(Node *n, NodeList **init)
 }
 
 static Node*
-copyexpr(Node *n, NodeList **init)
+copyexpr(Node *n, Type *t, NodeList **init)
 {
 	Node *a, *l;
 	
 	l = nod(OXXX, N, N);
-	tempname(l, n->type);
+	tempname(l, t);
 	a = nod(OAS, l, n);
 	typecheck(&a, Etop);
 	walkexpr(&a, init);
@@ -2754,20 +2754,21 @@ cheapexpr(Node *n, NodeList **init)
 		return n;
 	}
 
-	return copyexpr(n, init);
+	return copyexpr(n, n->type, init);
 }
 
 /*
- * return n in a local variable if it is not already.
+ * return n in a local variable of type t if it is not already.
  */
 Node*
-localexpr(Node *n, NodeList **init)
+localexpr(Node *n, Type *t, NodeList **init)
 {
 	if(n->op == ONAME &&
-		 (n->class == PAUTO || n->class == PPARAM || n->class == PPARAMOUT))
+		(n->class == PAUTO || n->class == PPARAM || n->class == PPARAMOUT) &&
+		convertop(n->type, t, nil) == OCONVNOP)
 		return n;
 	
-	return copyexpr(n, init);
+	return copyexpr(n, t, init);
 }
 
 void

src/pkg/runtime/chan_test.go

@@ -10,6 +10,22 @@ import (
 	"testing"
 )
 
+func TestChanSendInterface(t *testing.T) {
+	type mt struct{}
+	m := &mt{}
+	c := make(chan interface{}, 1)
+	c <- m
+	select {
+	case c <- m:
+	default:
+	}
+	select {
+	case c <- m:
+	case c <- &mt{}:
+	default:
+	}
+}
+
 func BenchmarkSelectUncontended(b *testing.B) {
 	const CallsPerSched = 1000
 	procs := runtime.GOMAXPROCS(-1)