dart2js cps: Support async/await by rewriting the JavaScript AST.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 435b4bbecdad2b69f0d54d0e9d5c1d4632d5ab91..a1ba74f70cd04597f3dde51bba1428291591b45e 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -5,15 +5,17 @@
 part of ssa;
 
 class SsaFunctionCompiler implements FunctionCompiler {
-  SsaCodeGeneratorTask generator;
-  SsaBuilderTask builder;
-  SsaOptimizerTask optimizer;
+  final SsaCodeGeneratorTask generator;
+  final SsaBuilderTask builder;
+  final SsaOptimizerTask optimizer;
+  final JavaScriptBackend backend;
 
   SsaFunctionCompiler(JavaScriptBackend backend,
                       SourceInformationStrategy sourceInformationFactory)
       : generator = new SsaCodeGeneratorTask(backend, sourceInformationFactory),
         builder = new SsaBuilderTask(backend, sourceInformationFactory),
-        optimizer = new SsaOptimizerTask(backend);
+        optimizer = new SsaOptimizerTask(backend),
+        backend = backend;
 
   /// Generates JavaScript code for `work.element`.
   /// Using the ssa builder, optimizer and codegenerator.
@@ -23,55 +25,7 @@ class SsaFunctionCompiler implements FunctionCompiler {
     Element element = work.element;
     js.Expression result = generator.generateCode(work, graph);
     if (element is FunctionElement) {
-      JavaScriptBackend backend = builder.backend;
-
-      AsyncRewriterBase rewriter = null;
-      js.Name name = backend.namer.methodPropertyName(element);
-      if (element.asyncMarker == AsyncMarker.ASYNC) {
-        rewriter = new AsyncRewriter(
-            backend.compiler,
-            backend.compiler.currentElement,
-            asyncHelper:
-                backend.emitter.staticFunctionAccess(backend.getAsyncHelper()),
-            newCompleter: backend.emitter.staticFunctionAccess(
-                backend.getCompleterConstructor()),
-            safeVariableName: backend.namer.safeVariablePrefixForAsyncRewrite,
-            bodyName: backend.namer.deriveAsyncBodyName(name));
-      } else if (element.asyncMarker == AsyncMarker.SYNC_STAR) {
-        rewriter = new SyncStarRewriter(
-            backend.compiler,
-            backend.compiler.currentElement,
-            endOfIteration: backend.emitter.staticFunctionAccess(
-                backend.getEndOfIteration()),
-            newIterable: backend.emitter.staticFunctionAccess(
-                backend.getSyncStarIterableConstructor()),
-            yieldStarExpression: backend.emitter.staticFunctionAccess(
-                backend.getYieldStar()),
-            uncaughtErrorExpression: backend.emitter.staticFunctionAccess(
-                backend.getSyncStarUncaughtError()),
-            safeVariableName: backend.namer.safeVariablePrefixForAsyncRewrite,
-            bodyName: backend.namer.deriveAsyncBodyName(name));
-      }
-      else if (element.asyncMarker == AsyncMarker.ASYNC_STAR) {
-        rewriter = new AsyncStarRewriter(
-            backend.compiler,
-            backend.compiler.currentElement,
-            asyncStarHelper: backend.emitter.staticFunctionAccess(
-                backend.getAsyncStarHelper()),
-            streamOfController: backend.emitter.staticFunctionAccess(
-                backend.getStreamOfController()),
-            newController: backend.emitter.staticFunctionAccess(
-                backend.getASyncStarControllerConstructor()),
-            safeVariableName: backend.namer.safeVariablePrefixForAsyncRewrite,
-            yieldExpression: backend.emitter.staticFunctionAccess(
-                backend.getYieldSingle()),
-            yieldStarExpression: backend.emitter.staticFunctionAccess(
-                backend.getYieldStar()),
-            bodyName: backend.namer.deriveAsyncBodyName(name));
-      }
-      if (rewriter != null) {
-        result = rewriter.rewrite(result);
-      }
+      result = backend.rewriteAsync(element, result);
     }
     return result;
   }