dartj2s: add constructor helpers for map literals with no type parameters.

pkg/compiler/lib/src/ssa/builder.dart

 // Copyright (c) 2012, 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.
 
 part of ssa;
 
 class SsaFunctionCompiler implements FunctionCompiler {
   SsaCodeGeneratorTask generator;
   SsaBuilderTask builder;
   SsaOptimizerTask optimizer;
@@ skipping 5613 matching lines @@
     }
     List<HInstruction> listInputs = <HInstruction>[];
     for (Link<ast.Node> link = node.entries.nodes;
          !link.isEmpty;
          link = link.tail) {
       visit(link.head);
       listInputs.add(pop());
       listInputs.add(pop());
     }
 
-    ConstructorElement constructor;
+    Element constructor;
     List<HInstruction> inputs = <HInstruction>[];
 
     if (listInputs.isEmpty) {
       constructor = backend.mapLiteralConstructorEmpty;
     } else {
       constructor = backend.mapLiteralConstructor;
       HLiteralList keyValuePairs = buildLiteralList(listInputs);
       add(keyValuePairs);
       inputs.add(keyValuePairs);
     }
 
     assert(constructor.isFactoryConstructor);
 
     ConstructorElement functionElement = constructor;
     constructor = functionElement.effectiveTarget;
 
     InterfaceType type = elements.getType(node);
     InterfaceType expectedType =
         functionElement.computeEffectiveTargetType(type);
     expectedType = localsHandler.substInContext(expectedType);
 
     ClassElement cls = constructor.enclosingClass;
 
     if (backend.classNeedsRti(cls)) {
+      List<HInstruction> typeInputs = <HInstruction>[];
       List<DartType> typeVariable = cls.typeVariables;
       expectedType.typeArguments.forEach((DartType argument) {
-        inputs.add(analyzeTypeArgument(argument));
+        typeInputs.add(analyzeTypeArgument(argument));
       });
+      if (typeInputs.every((HInstruction input) => input.isNull())) {

[herhut, 2015/04/14 11:00:14]

Can you add a comment about what this is doing, i.e., that we have lifted this
common pattern to save on size?

[zarah, 2015/04/14 11:27:56]

Done.

+        if (listInputs.isEmpty) {
+          constructor = backend.mapLiteralUntypedEmptyMaker;
+        } else {
+          constructor = backend.mapLiteralUntypedMaker;
+        }
+      } else {
+        inputs.addAll(typeInputs);
+      }
     }
 
+    // If rti is needed and the map literal has no type parameters,
+    // 'constructor' is a static function that forwards the call to the factory
+    // constructor without type parameters.
+    assert(constructor is ConstructorElement || constructor is FunctionElement);
+
     // The instruction type will always be a subtype of the mapLiteralClass, but
     // type inference might discover a more specific type, or find nothing (in
     // dart2js unit tests).
     TypeMask mapType =
         new TypeMask.nonNullSubtype(backend.mapLiteralClass, compiler.world);
     TypeMask returnTypeMask = TypeMaskFactory.inferredReturnTypeForElement(
         constructor, compiler);
     TypeMask instructionType =
         mapType.intersection(returnTypeMask, compiler.world);
 
@@ skipping 1306 matching lines @@
     if (unaliased is TypedefType) throw 'unable to unalias $type';
     unaliased.accept(this, builder);
   }
 
   void visitDynamicType(DynamicType type, SsaBuilder builder) {
     JavaScriptBackend backend = builder.compiler.backend;
     ClassElement cls = backend.findHelper('DynamicRuntimeType');
     builder.push(new HDynamicType(type, new TypeMask.exact(cls, classWorld)));
   }
 }