Avoid creating new HThis at each closure access.

lib/compiler/implementation/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.
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
   SourceString mapOperatorToMethodName(Operator op) {
     String name = op.source.stringValue;
@@ skipping 372 matching lines @@
    */
   HInstruction readLocal(Element element) {
     if (isAccessedDirectly(element)) {
       if (directLocals[element] == null) {
         builder.compiler.internalError("Cannot find value $element",
                                        element: element);
       }
       return directLocals[element];
     } else if (isStoredInClosureField(element)) {
       Element redirect = redirectionMapping[element];
-      // We must not use the [LocalsHandler.readThis()] since that could
-      // point to a captured this which would be stored in a closure-field
-      // itself.
-      HInstruction receiver = new HThis();
-      builder.add(receiver);
+      HInstruction receiver = readLocal(closureData.closureElement);
       HInstruction fieldGet = new HFieldGet(redirect, receiver);
       builder.add(fieldGet);
       return fieldGet;
     } else if (isBoxed(element)) {
       Element redirect = redirectionMapping[element];
       // In the function that declares the captured variable the box is
       // accessed as direct local. Inside the nested closure the box is
       // accessed through a closure-field.
       // Calling [readLocal] makes sure we generate the correct code to get
       // the box.
@@ skipping 45 matching lines @@
 
   /**
    * Sets the [element] to [value]. If the element is boxed or stored in a
    * closure then the method generates code to set the value.
    */
   void updateLocal(Element element, HInstruction value) {
     if (isAccessedDirectly(element)) {
       directLocals[element] = value;
     } else if (isStoredInClosureField(element)) {
       Element redirect = redirectionMapping[element];
-      // We must not use the [LocalsHandler.readThis()] since that could
-      // point to a captured this which would be stored in a closure-field
-      // itself.
-      HInstruction receiver = new HThis();
-      builder.add(receiver);
+      HInstruction receiver = readLocal(closureData.closureElement);
       builder.add(new HFieldSet(redirect.name, receiver, value));
     } else if (isBoxed(element)) {
       Element redirect = redirectionMapping[element];
       // The box itself could be captured, or be local. A local variable that
       // is captured will be boxed, but the box itself will be a local.
       // Inside the closure the box is stored in a closure-field and cannot
       // be accessed directly.
       assert(redirect.enclosingElement.kind == ElementKind.VARIABLE);
       HInstruction box = readLocal(redirect.enclosingElement);
       builder.add(new HFieldSet(redirect, box, value));
@@ skipping 2915 matching lines @@
                                    <HInstruction>[target, input],
                                    HType.STRING));
     return builder.pop();
   }
 
   HInstruction result(Node node) {
     flushLiterals(node);
     return prefix;
   }
 }