dart2dart: Restore loops with conditions and updates in backend.

sdk/lib/_internal/compiler/implementation/dart_backend/dart_codegen.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 dart_codegen;
 
 import 'dart_tree.dart' as tree;
 import 'dart_printer.dart';
 import 'dart_tree_printer.dart' show TreePrinter;
 import '../tree/tree.dart' as frontend;
@@ skipping 194 matching lines @@
       // Fall through to break target
     } else if (fall is tree.Break && fall.target == stmt.target) {
       // Fall through to equivalent break
     } else {
       usedLabels.add(stmt.target);
       statementBuffer.add(new Break(stmt.target.name));
     }
   }
 
   void visitContinue(tree.Continue stmt) {
-    statementBuffer.add(new Continue(stmt.target.name));
+    tree.Statement fall = fallthrough;
+    if (stmt.target.binding == fall) {
+      // Fall through to continue target
+    } else if (fall is tree.Continue && fall.target == stmt.target) {
+      // Fall through to equivalent continue
+    } else {
+      usedLabels.add(stmt.target);
+      statementBuffer.add(new Continue(stmt.target.name));
+    }
   }
 
   void visitIf(tree.If stmt) {
     Expression condition = visitExpression(stmt.condition);
     List<Statement> savedBuffer = statementBuffer;
     List<Statement> thenBuffer = statementBuffer = <Statement>[];
     visitStatement(stmt.thenStatement);
     List<Statement> elseBuffer = statementBuffer = <Statement>[];
     visitStatement(stmt.elseStatement);
     savedBuffer.add(
         new If(condition, new Block(thenBuffer), new Block(elseBuffer)));
     statementBuffer = savedBuffer;
   }
 
-  void visitWhile(tree.While stmt) {
-    Expression condition = new Literal(new dart2js.BoolConstant(true));
+  void visitWhileTrue(tree.WhileTrue stmt) {
+    List<Expression> updates = stmt.updates.reversed
+                                           .map(visitExpression)
+                                           .toList(growable:false);
+
     List<Statement> savedBuffer = statementBuffer;
+    tree.Statement savedFallthrough = fallthrough;
     statementBuffer = <Statement>[];
-    tree.Statement savedFallthrough = fallthrough;
-    fallthrough = stmt.body;
+    fallthrough = stmt;
+
     visitStatement(stmt.body);
-    savedBuffer.add(
-        new LabeledStatement(
-            stmt.label.name,
-            new While(condition, new Block(statementBuffer))));
+    Statement body = new Block(statementBuffer);
+    Statement statement = new For(null, null, updates, body);
+    if (usedLabels.remove(stmt.label.name)) {
+      statement = new LabeledStatement(stmt.label.name, statement);
+    }
+    savedBuffer.add(statement);
+
     statementBuffer = savedBuffer;
     fallthrough = savedFallthrough;
   }
 
+  void visitWhileCondition(tree.WhileCondition stmt) {
+    Expression condition = visitExpression(stmt.condition);
+    List<Expression> updates = stmt.updates.reversed
+                                           .map(visitExpression)
+                                           .toList(growable:false);
+
+    List<Statement> savedBuffer = statementBuffer;
+    tree.Statement savedFallthrough = fallthrough;
+    statementBuffer = <Statement>[];
+    fallthrough = stmt;
+
+    visitStatement(stmt.body);
+    Statement body = new Block(statementBuffer);
+    Statement statement;
+    if (updates.isEmpty) {
+      // while(E) is the same as for(;E;), but the former is nicer
+      statement = new While(condition, body);
+    } else {
+      statement = new For(null, condition, updates, body);
+    }
+    if (usedLabels.remove(stmt.label.name)) {
+      statement = new LabeledStatement(stmt.label.name, statement);
+    }
+    savedBuffer.add(statement);
+
+    statementBuffer = savedBuffer;
+    fallthrough = savedFallthrough;
+
+    visitStatement(stmt.next);
+  }
+
   Expression visitConstant(tree.Constant exp) {
     return emitConstant(exp.value);
   }
 
   Expression visitLiteralList(tree.LiteralList exp) {
     return new LiteralList(
         exp.values.map(visitExpression).toList(growable: false));
   }
 
   Expression visitLiteralMap(tree.LiteralMap exp) {
@@ skipping 175 matching lines @@
       if (constant is dart2js.ConstructedConstant && constant.isLiteralSymbol) {
         dart2js.StringConstant nameConstant = constant.fields[0];
         String nameString = nameConstant.value.slowToString();
         return new LiteralSymbol(nameString);
       } else {
         throw "Unsupported constant: $constant";
       }
     }
   }
 }
+