cps-ir: Merge variables based on set-based liveness and graph coloring.

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 501 matching lines @@
 
   bool isNullLiteral(Expression exp) => exp is Literal && exp.value.isNull;
 
   @override
   void visitAssign(tree.Assign stmt,
                    BuilderContext<Statement> context) {
     // Try to emit a local function declaration. This is useful for functions
     // that may occur in expression context, but could not be inlined anywhere.
     if (stmt.variable.element is FunctionElement &&
         stmt.value is tree.FunctionExpression &&
-        !context.declaredVariables.contains(stmt.variable)) {
+        !context.declaredVariables.contains(stmt.variable) &&
+        stmt.variable.writeCount == 1) {
       tree.FunctionExpression functionExp = stmt.value;
       FunctionExpression function =
           makeSubFunction(functionExp.definition, context);
       FunctionDeclaration decl = new FunctionDeclaration(function);
       context.addStatement(decl);
       context.declaredVariables.add(stmt.variable);
 
       visitStatement(stmt.next, context);
       return;
     }
@@ skipping 781 matching lines @@
       : 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;
 }