cps-ir: Split up main codegen and add a bailout exception to print out

pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart

 // Copyright (c) 2013, 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.
 
 part of dart2js.ir_builder;
 
 /**
  * This task iterates through all resolved elements and builds [ir.Node]s. The
  * nodes are stored in the [nodes] map and accessible through [hasIr] and
  * [getIr].
@@ skipping 23 matching lines @@
   ir.FunctionDefinition getIr(Element element) => nodes[element.implementation];
 
   ir.FunctionDefinition buildNode(AstElement element) {
     if (!canBuild(element)) return null;
     TreeElements elementsMapping = element.resolvedAst.elements;
     element = element.implementation;
     return compiler.withCurrentElement(element, () {
       SourceFile sourceFile = elementSourceFile(element);
       IrBuilderVisitor builder =
           new IrBuilderVisitor(elementsMapping, compiler, sourceFile);
-      ir.FunctionDefinition function;
-      function = builder.buildFunction(element);
-
-      return function;
+      return builder.buildFunction(element);
     });
   }
 
   void buildNodes() {
     measure(() {
       Set<Element> resolved = compiler.enqueuer.resolution.resolvedElements;
       resolved.forEach((AstElement element) {
         ir.FunctionDefinition functionDefinition = buildNode(element);
         if (functionDefinition != null) {
           nodes[element] = functionDefinition;
@@ skipping 821 matching lines @@
     node.visitChildren(this);
   }
 
   visitFunctionExpression(ast.FunctionExpression node) {
     FunctionElement oldFunction = currentFunction;
     currentFunction = elements[node];
     visit(node.body);
     currentFunction = oldFunction;
   }
 }