dart2js cps: Compile some loops as 'for' loops.

pkg/compiler/lib/src/tree_ir/tree_ir_nodes.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_nodes;
 
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
 import '../elements/elements.dart';
 import '../io/source_information.dart' show SourceInformation;
@@ skipping 478 matching lines @@
   }
 
   Statement get next => null;
   void set next(Statement s) => throw 'UNREACHABLE';
 
   accept(StatementVisitor visitor) => visitor.visitWhileTrue(this);
   accept1(StatementVisitor1 visitor, arg) => visitor.visitWhileTrue(this, arg);
 }
 
 /**
- * A while loop with a condition. If the condition is false, control resumes
- * at the [next] statement.
+ * A loop with a condition and update expressions. If there are any update
+ * expressions, this generates a for loop, otherwise a while loop.
+ * 
+ * When the condition is false, control resumes at the [next] statement.
  *
  * It is NOT valid to target this statement with a [Break].
  * The only way to reach [next] is for the condition to evaluate to false.
  *
  * [WhileCondition] statements are introduced in the [LoopRewriter] and is
  * assumed not to occur before then.
  */
 class WhileCondition extends Loop {

[Kevin Millikin (Google), 2015/08/13 11:32:47]

Strange that While has updates.  Maybe we call it For.

[asgerf, 2015/08/13 12:06:42]

Renamed.

   final Label label;
   Expression condition;
+  List<Expression> updates;
   Statement body;
   Statement next;
 
-  WhileCondition(this.label, this.condition, this.body,
+  WhileCondition(this.label,
+                 this.condition,
+                 this.updates,
+                 this.body,
                  this.next) {
     assert(label.binding == null);
     label.binding = this;
   }
 
   accept(StatementVisitor visitor) => visitor.visitWhileCondition(this);
   accept1(StatementVisitor1 visitor, arg) {
     return visitor.visitWhileCondition(this, arg);
   }
 }
@@ skipping 610 matching lines @@
     visitStatement(node.thenStatement);
     visitStatement(node.elseStatement);
   }
 
   visitWhileTrue(WhileTrue node) {
     visitStatement(node.body);
   }
 
   visitWhileCondition(WhileCondition node) {
     visitExpression(node.condition);
+    node.updates.forEach(visitExpression);
     visitStatement(node.body);
     visitStatement(node.next);
   }
 
   visitExpressionStatement(ExpressionStatement inputNode) {
     // Iterate over chains of expression statements to avoid deep recursion.
     Statement node = inputNode;
     while (node is ExpressionStatement) {
       ExpressionStatement stmt = node;
       visitExpression(stmt.expression);
@@ skipping 211 matching lines @@
     return node;
   }
 
   visitWhileTrue(WhileTrue node) {
     node.body = visitStatement(node.body);
     return node;
   }
 
   visitWhileCondition(WhileCondition node) {
     node.condition = visitExpression(node.condition);
+    _replaceExpressions(node.updates);
     node.body = visitStatement(node.body);
     node.next = visitStatement(node.next);
     return node;
   }
 
   visitExpressionStatement(ExpressionStatement node) {
     // Iterate over chains of expression statements to avoid deep recursion.
     Statement first = node;
     while (true) {
       node.expression = visitExpression(node.expression);
@@ skipping 140 matching lines @@
 
   /// Number of uses of the current fallthrough target.
   int get useCount => _stack.last.useCount;
 
   /// Indicate that a statement will fall through to the current fallthrough
   /// target.
   void use() {
     ++_stack.last.useCount;
   }
 }