dart2js cps: Generate increment and compound operators.

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart

 // Copyright (c) 2014, 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.
 
 library tree_ir.optimization.statement_rewriter;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 import '../../io/source_information.dart';
 import '../../elements/elements.dart';
@@ skipping 740 matching lines @@
     }
     return node;
   }
 
   Expression visitTypeOperator(TypeOperator node) {
     _rewriteList(node.typeArguments);
     node.value = visitExpression(node.value);
     return node;
   }
 
+  bool sameVariable(Expression e1, Expression e2) {
+    return e1 is VariableUse && e2 is VariableUse && e1.variable == e2.variable;
+  }
+
+  bool isCompoundableBuiltin(Expression e) {
+    return e is ApplyBuiltinOperator &&
+           e.arguments.length == 2 &&
+           isCompoundableOperator(e.operator);
+  }
+
+  void destroyVariableUse(VariableUse node) {
+    --node.variable.readCount;
+  }
+
   Expression visitSetField(SetField node) {
     allowRhsPropagation.add(true);
     node.value = visitExpression(node.value);
+    if (isCompoundableBuiltin(node.value)) {
+      ApplyBuiltinOperator rhs = node.value;
+      Expression left = rhs.arguments[0];
+      Expression right = rhs.arguments[1];
+      if (left is GetField &&
+          left.field == node.field &&
+          sameVariable(left.object, node.object)) {
+        destroyVariableUse(left.object);
+        node.compound = rhs.operator;
+        node.value = right;
+      }
+    }
     node.object = visitExpression(node.object);
     allowRhsPropagation.removeLast();
     return node;
   }
 
   Expression visitGetField(GetField node) {
     node.object = visitExpression(node.object);
     return node;
   }
 
@@ skipping 53 matching lines @@
   }
 
   Expression visitGetIndex(GetIndex node) {
     node.index = visitExpression(node.index);
     node.object = visitExpression(node.object);
     return node;
   }
 
   Expression visitSetIndex(SetIndex node) {
     node.value = visitExpression(node.value);
+    if (isCompoundableBuiltin(node.value)) {
+      ApplyBuiltinOperator rhs = node.value;
+      Expression left = rhs.arguments[0];
+      Expression right = rhs.arguments[1];
+      if (left is GetIndex &&
+          sameVariable(left.object, node.object) &&
+          sameVariable(left.index, node.index)) {
+        destroyVariableUse(left.object);
+        destroyVariableUse(left.index);
+        node.compound = rhs.operator;
+        node.value = right;
+      }
+    }
     node.index = visitExpression(node.index);
     node.object = visitExpression(node.object);
     return node;
   }
 
   /// True if [operator] is a binary operator that always has the same value
   /// if its arguments are swapped.
   bool isSymmetricOperator(BuiltinOperator operator) {
     switch (operator) {
       case BuiltinOperator.StrictEq:
@@ skipping 469 matching lines @@
   VariableUseCallback callback;
 
   VariableUseVisitor(this.callback);
 
   visitVariableUse(VariableUse use) => callback(use);
 
   static void visit(Expression node, VariableUseCallback callback) {
     new VariableUseVisitor(callback).visitExpression(node);
   }
 }