Emit read-modify-write of fields as assignment op.

sdk/lib/_internal/compiler/implementation/ssa/codegen.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 SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
@@ skipping 1669 matching lines @@
     Element element = node.element;
     world.registerFieldSetter(element);
     String name = backend.namer.instanceFieldPropertyName(element);
     use(node.receiver);
     js.Expression receiver = pop();
     use(node.value);
     push(new js.Assignment(new js.PropertyAccess.field(receiver, name), pop()),
         node);
   }
 
+  visitReadModifyWrite(HReadModifyWrite node) {
+    Element element = node.element;
+    world.registerFieldSetter(element);
+    String name = backend.namer.instanceFieldPropertyName(element);
+    use(node.receiver);
+    js.Expression fieldReference = new js.PropertyAccess.field(pop(), name);
+    if (node.isPreOp) {
+      push(new js.Prefix(node.jsOp, fieldReference), node);
+    } else if (node.isPostOp) {
+      push(new js.Postfix(node.jsOp, fieldReference), node);
+    } else {
+      use(node.value);
+      push(new js.Assignment.compound(fieldReference, node.jsOp, pop()), node);
+    }
+  }
+
   visitLocalGet(HLocalGet node) {
     use(node.receiver);
   }
 
   visitLocalSet(HLocalSet node) {
     use(node.value);
     assignVariable(variableNames.getName(node.receiver), pop());
   }
 
   void registerForeignTypes(HForeign node) {
@@ skipping 969 matching lines @@
   js.PropertyAccess accessHelper(String name) {
     Element helper = compiler.findHelper(name);
     if (helper == null) {
       // For mocked-up tests.
       return js.js('(void 0).$name');
     }
     world.registerStaticUse(helper);
     return backend.namer.elementAccess(helper);
   }
 }