cmd/gc: logical operators should produce untyped bool for untyped

operands

Fixes #6671 for cmd/gc.

Change-Id: I4907655b6e243960f2ceb544c63ea16513c7bd68
Reviewed-on: https://go-review.googlesource.com/1251Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/gc/typecheck.c

@@ -644,6 +644,13 @@ reswitch:
 				n->left = l;
 				n->right = r;
 			}
+		} else if(n->op == OANDAND || n->op == OOROR) {
+			if(l->type == r->type)
+				t = l->type;
+			else if(l->type == idealbool)
+				t = r->type;
+			else if(r->type == idealbool)
+				t = l->type;
 		// non-comparison operators on ideal bools should make them lose their ideal-ness
 		} else if(t == idealbool)
 			t = types[TBOOL];
@@ -1438,7 +1445,7 @@ reswitch:
 		}
 		switch(n->op) {
 		case OCONVNOP:
-			if(n->left->op == OLITERAL) {
+			if(n->left->op == OLITERAL && n->type != types[TBOOL]) {
 				r = nod(OXXX, N, N);
 				n->op = OCONV;
 				n->orig = r;

test/fixedbugs/issue3924.go

-// errorcheck
-
-// Copyright 2012 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 foo
-
-type mybool bool
-
-var x, y = 1, 2
-var _ mybool = x < y && x < y // ERROR "cannot use"
-var _ mybool = x < y || x < y // ERROR "cannot use"

test/fixedbugs/issue6671.go

+// errorcheck
+
+// Copyright 2014 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.
+
+// Issue 6671: Logical operators should produce untyped bool for untyped operands.
+
+package p
+
+type mybool bool
+
+func _(x, y int) {
+	type mybool bool
+	var b mybool
+	_ = b
+	b = bool(true)             // ERROR "cannot use"
+	b = true                   // permitted as expected
+	b = bool(true) && true     // ERROR "cannot use"
+	b = true && true           // permitted => && returns an untyped bool
+	b = x < y                  // permitted => x < y returns an untyped bool
+	b = true && x < y          // permitted => result of && returns untyped bool
+	b = x < y && x < y         // permitted => result of && returns untyped bool
+	b = x < y || x < y         // permitted => result of || returns untyped bool
+	var c bool = true && x < y // permitted => result of && is bool
+	c = false || x < y         // permitted => result of || returns untyped bool
+	_ = c
+}