Fix receiver refining optimization in the presence of null: any Object method can be called on the null object.

R=karlklose@google.com

Review URL: https://codereview.chromium.org//23353002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@26418 260f80e4-7a28-3924-810f-c04153c831b5

sdk/lib/_internal/compiler/implementation/types/flat_type_mask.dart

@@ -21,8 +21,6 @@ class FlatTypeMask implements TypeMask {
   FlatTypeMask(DartType base, int kind, bool isNullable)
       : this.internal(base, (kind << 1) | (isNullable ? 1 : 0));
 
-  FlatTypeMask.empty()
-      : this.internal(null, (EMPTY << 1) | 1);
   FlatTypeMask.exact(DartType base)
       : this.internal(base, (EXACT << 1) | 1);
   FlatTypeMask.subclass(DartType base)
@@ -31,6 +29,7 @@ class FlatTypeMask implements TypeMask {
       : this.internal(base, (SUBTYPE << 1) | 1);
 
   const FlatTypeMask.nonNullEmpty(): base = null, flags = 0;
+  const FlatTypeMask.empty() : base = null, flags = 1;
 
   FlatTypeMask.nonNullExact(DartType base)
       : this.internal(base, EXACT << 1);

sdk/lib/_internal/compiler/implementation/types/type_mask.dart

@@ -13,7 +13,7 @@ abstract class TypeMask {
   factory TypeMask(DartType base, int kind, bool isNullable)
       => new FlatTypeMask(base, kind, isNullable);
 
-  factory TypeMask.empty() => new FlatTypeMask.empty();
+  const factory TypeMask.empty() = FlatTypeMask.empty;
 
   factory TypeMask.exact(DartType base) => new FlatTypeMask.exact(base);
   factory TypeMask.subclass(DartType base) => new FlatTypeMask.subclass(base);

sdk/lib/_internal/compiler/implementation/universe/function_set.dart

@@ -220,6 +220,9 @@ class FullFunctionSetQuery extends FunctionSetQuery {
               : [cls];
         })
         .map((cls) {
+          if (compiler.backend.isNullImplementation(cls)) {
+            return const TypeMask.empty();
+          }
           return compiler.world.hasSubclasses(cls)
               ? new TypeMask.nonNullSubclass(cls.rawType)
               : new TypeMask.nonNullExact(cls.rawType);

sdk/lib/_internal/lib/interceptors.dart

@@ -365,7 +365,7 @@ class JSBool extends Interceptor implements bool {
 /**
  * The interceptor class for [Null].
  *
- * This class defines implementations for *all* methods on [Object] since the
+ * This class defines implementations for *all* methods on [Object] since
  * the methods on Object assume the receiver is non-null.  This means that
  * JSNull will always be in the interceptor set for methods defined on Object.
  */

tests/compiler/dart2js/mock_compiler.dart

@@ -154,6 +154,8 @@ const String DEFAULT_INTERCEPTORSLIB = r'''
   class JSNull extends Interceptor {
     bool operator==(other) => identical(null, other);
     get hashCode => throw "JSNull.hashCode not implemented.";
+    String toString() => 'Null';
+    Type get runtimeType => null;
   }
   class JSBool extends Interceptor implements bool {
   }

tests/compiler/dart2js/simple_inferrer_test.dart

@@ -441,6 +441,14 @@ testSpecialization2() {
   return a;
 }
 
+testSpecialization3() {
+  var a = returnDynamic() ? null : 42;
+  a.toString();
+  // Test that calling an [Object] method on [a] will not lead to
+  // infer that [a] is not null;
+  return a;
+}
+
 testReturnInvokeDynamicGetter() => new A().myFactory();
 
 var topLevelConstList = const [42];
@@ -582,6 +590,7 @@ main() {
   testCascade2();
   testSpecialization1();
   testSpecialization2();
+  testSpecialization3();
 }
 """;
 
@@ -706,4 +715,5 @@ void main() {
       typesTask.rawTypeOf(findElement(compiler, 'CascadeHelper'))));
   checkReturn('testSpecialization1', typesTask.numType);
   checkReturn('testSpecialization2', typesTask.dynamicType);
+  checkReturn('testSpecialization3', typesTask.intType.nullable());
 }

tests/language/refine_receiver_null_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Regression test for dart2js that used to infer that code following
+// a dynamic call could assume the receiver is not null. This does not
+// work for Object methods.
+
+import "package:expect/expect.dart";
+import "compiler_annotations.dart";
+
+main() {
+  var a = true ? null : 42;
+  a.toString();
+  foo(a);
+}
+
+@DontInline()
+foo(a) {
+  var f = () => 42;
+  Expect.throws(() => a + 42, (e) => e is NoSuchMethodError);
+}