Rewrite for-in loop as indexing loop for JavaScript indexable arrays

pkg/compiler/lib/src/js_backend/backend.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 js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 284 matching lines @@
   ClassElement jsUInt31Class;
 
   Element jsIndexableLength;
   Element jsArrayTypedConstructor;
   Element jsArrayRemoveLast;
   Element jsArrayAdd;
   Element jsStringSplit;
   Element jsStringToString;
   Element jsStringOperatorAdd;
   Element objectEquals;
+  Element cachedCheckConcurrentModificationError;
 
   ClassElement typeLiteralClass;
   ClassElement mapLiteralClass;
   ClassElement constMapLiteralClass;
   ClassElement typeVariableClass;
   ConstructorElement mapLiteralConstructor;
   ConstructorElement mapLiteralConstructorEmpty;
   Element mapLiteralUntypedMaker;
   Element mapLiteralUntypedEmptyMaker;
 
@@ skipping 1339 matching lines @@
   }
 
   Element getThrowTypeError() {
     return findHelper('throwTypeError');
   }
 
   Element getThrowAbstractClassInstantiationError() {
     return findHelper('throwAbstractClassInstantiationError');
   }
 
+  Element getCheckConcurrentModificationError() {
+    if (cachedCheckConcurrentModificationError == null) {
+      cachedCheckConcurrentModificationError =
+          findHelper('checkConcurrentModificationError');
+    }
+    return cachedCheckConcurrentModificationError;
+  }
+
+  Element getThrowConcurrentModificationError() {
+    return findHelper('throwConcurrentModificationError');
+  }
+
   Element getStringInterpolationHelper() {
     return findHelper('S');
   }
 
   Element getWrapExceptionHelper() {
     return findHelper(r'wrapException');
   }
 
   Element getThrowExpressionHelper() {
     return findHelper('throwExpression');
@@ skipping 1069 matching lines @@
       backend.compiler.world.allTypedefs.add(type.element);
     }
     backend.customElementsAnalysis.registerTypeLiteral(type, registry);
   }
 
   void onStackTraceInCatch(Registry registry) {
     assert(registry.isForResolution);
     registerBackendStaticInvocation(backend.getTraceFromException(), registry);
   }
 
+  void onSyncForIn(Registry registry) {
+    assert(registry.isForResolution);
+    // The SSA builder recognizes certain for-in loops and can generate calls to
+    // throwConcurrentModificationError.
+    registerBackendStaticInvocation(
+        backend.getCheckConcurrentModificationError(), registry);
+  }
 
   void onTypeVariableExpression(Registry registry) {
     assert(registry.isForResolution);
     registerBackendStaticInvocation(backend.getSetRuntimeTypeInfo(), registry);
     registerBackendStaticInvocation(backend.getGetRuntimeTypeInfo(), registry);
     backend.registerGetRuntimeTypeArgument(registry);
     registerBackendInstantiation(backend.compiler.listClass, registry);
     registerBackendStaticInvocation(backend.getRuntimeTypeToString(), registry);
     registerBackendStaticInvocation(backend.getCreateRuntimeType(), registry);
   }
@@ skipping 123 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }