Added VariableUse expression to tree IR.

pkg/compiler/lib/src/dart_backend/backend_ast_emitter.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 backend_ast_emitter;
 
 import '../tree_ir/tree_ir_nodes.dart' as tree;
 import 'backend_ast_nodes.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
@@ skipping 518 matching lines @@
     // Try to pull into initializer.
     if (context.firstStatement == stmt && isFirstOccurrence && isDeclaredHere) {
       if (isNullLiteral(definition)) definition = null;
       context.addDeclaration(stmt.variable, definition);
       context.firstStatement = stmt.next;
       visitStatement(stmt.next, context);
       return;
     }
 
     // Emit a variable declaration if we are required to do so.
-    // This is to ensure that a fresh closure variable is created.
+    // For captured variables, this ensures that a fresh variable is created.
     if (stmt.isDeclaration) {
       assert(isFirstOccurrence);
       assert(isDeclaredHere);
       if (isNullLiteral(definition)) definition = null;
       VariableDeclaration decl = new VariableDeclaration(name, definition)
                                      ..element = stmt.variable.element;
       context.declaredVariables.add(stmt.variable);
       context.addStatement(new VariableDeclarations([decl]));
       visitStatement(stmt.next, context);
       return;
@@ skipping 274 matching lines @@
                               visitExpression(exp.right, context));
   }
 
   @override
   Expression visitNot(tree.Not exp,
                       BuilderContext<Statement> context) {
     return new UnaryOperator('!', visitExpression(exp.operand, context));
   }
 
   @override
+  Expression visitVariableUse(tree.VariableUse exp,
+                                     BuilderContext<Statement> context) {

[Kevin Millikin (Google), 2015/02/26 12:43:17]

Indentation is messed up.

[asgerf, 2015/02/27 12:05:19]

Done.

+    return visitVariable(exp.variable, context);
+  }
+
   Expression visitVariable(tree.Variable exp,

[Kevin Millikin (Google), 2015/02/26 12:43:17]

I'd probably get rid of this visitVariable method --- it's not required by the
superclass tree.Visitor1, and it isn't actually called for all Variables in the
input (it's not called for FunctionDefinition parameters).

Instead, I'd put a method on the BuilderContext and call it explicitly in the
two places where visitVariable is currently called.

[asgerf, 2015/02/27 12:05:19]

Done.

                            BuilderContext<Statement> context) {
     return new Identifier(context.getVariableName(exp))
                ..element = exp.element;
   }
 
   FunctionExpression makeSubFunction(tree.FunctionDefinition function,
                                      BuilderContext<Statement> context) {
     return emit(function, new BuilderContext<Statement>.inner(context));
   }
 
@@ skipping 381 matching lines @@
     visitStatement(definition.body);
     environment = oldEnvironment;
     shadowedParameters = oldShadow;
 
     for (int i=0; i<definition.parameters.length; i++) {
       tree.Variable param = definition.parameters[i];
       if (hasShadowedUse.remove(param)) {
         tree.Variable newParam = new tree.Variable(definition.element,
             param.element);
         definition.parameters[i] = newParam;
-        definition.body = new tree.Assign(param, newParam, definition.body);
+        definition.body = new tree.Assign(param, new tree.VariableUse(newParam),
+            definition.body);
         newParam.writeCount = 1; // Being a parameter counts as a write.
+        param.writeCount--; // Not a parameter anymore.

[asgerf, 2015/02/25 12:40:30]

This was technically a bug, although the reference counts are not used after
this phase, so it never manifested.

       }
     }
   }
 
+  @override
   visitVariable(tree.Variable variable) {
     if (shadowedParameters.contains(variable)) {
       hasShadowedUse.add(variable);
     }
   }
 
 }
 
 // TODO(johnniwinther): Remove this when the dart `backend_ast` does not need
 // [Element] for entities.
 class _SyntheticLocalVariableElement extends modelx.VariableElementX
     implements LocalVariableElement {
 
   _SyntheticLocalVariableElement(String name,
                                  ExecutableElement enclosingElement,
                                  modelx.VariableList variables)
       : super(name, ElementKind.VARIABLE, enclosingElement, variables, null);
 
   ExecutableElement get executableContext => enclosingElement;
 
   ExecutableElement get memberContext => executableContext.memberContext;
 
   bool get isLocal => true;
 
   LibraryElement get implementationLibrary => enclosingElement.library;
 }