dart2js cps: Debugging utility and fix idempotency in shrinking reducer.

pkg/compiler/lib/src/js_backend/codegen/task.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.
 
 /// Generate code using the cps-based IR pipeline.
 library code_generator_task;
 
 import 'glue.dart';
 import 'codegen.dart';
 import 'unsugar.dart';
@@ skipping 85 matching lines @@
     return reporter.withCurrentElement(element, () {
       try {
         // TODO(karlklose): remove this fallback when we do not need it for
         // testing anymore.
         if (false) {
           reporter.log('Using SSA compiler for platform element $element');
           return fallbackCompiler.compile(work);
         }
 
         if (tracer != null) {
-          tracer.traceCompilation(element.name, null);
+          tracer.traceCompilation('$element', null);
         }
         cps.FunctionDefinition cpsFunction = compileToCpsIr(element);
         optimizeCpsBeforeInlining(cpsFunction);
         applyCpsPass(inliner, cpsFunction);
         optimizeCpsAfterInlining(cpsFunction);
         cpsIntegrityChecker = null;
         tree_ir.FunctionDefinition treeFunction = compileToTreeIr(cpsFunction);
         treeFunction = optimizeTreeIr(treeFunction);
         return compileToJavaScript(work, treeFunction);
       } on CodegenBailout catch (e) {
         String message = "Unable to compile $element with the new compiler.\n"
             "  Reason: ${e.message}";
         reporter.internalError(element, message);
       }
     });
   }
 
   void giveUp(String reason) {
     throw new CodegenBailout(null, reason);
   }
 
   void traceGraph(String title, var irObject) {
     if (tracer != null) {
       tracer.traceGraph(title, irObject);
     }
   }
 
+  String stringify(cps.FunctionDefinition node) {
+    return new SExpressionStringifier().withTypes().visit(node);
+  }
+
+  /// For debugging purposes, replace a call to [applyCpsPass] with a call
+  /// to [debugCpsPass] to check that this pass is idempotent.
+  ///
+  /// This runs [pass] followed by shrinking reductions, and then checks that
+  /// one more run of [pass] does not change the IR.  The intermediate shrinking
+  /// reductions pass is omitted if [pass] itself is shrinking reductions.
+  ///
+  /// If [targetName] is given, functions whose name contains that substring
+  /// will be dumped out if the idempotency test fails.
+  void debugCpsPass(cps_opt.Pass makePass(),
+                    cps.FunctionDefinition cpsFunction,
+                    [String targetName]) {
+    String original = stringify(cpsFunction);
+    cps_opt.Pass pass = makePass();
+    pass.rewrite(cpsFunction);
+    assert(checkCpsIntegrity(cpsFunction, pass.passName));
+    if (pass is! ShrinkingReducer) {
+      new ShrinkingReducer().rewrite(cpsFunction);
+    }
+    String before = stringify(cpsFunction);
+    makePass().rewrite(cpsFunction);
+    String after = stringify(cpsFunction);
+    if (before != after) {
+      print('SExpression changed for ${cpsFunction.element}');
+      if (targetName != null && '${cpsFunction.element}'.contains(targetName)) {
+        print(original);
+        print('\n-->\n');
+        print(before);
+        print('\n-->\n');
+        print(after);
+        compiler.outputProvider('original', 'dump')..add(original)..close();
+        compiler.outputProvider('before', 'dump')..add(before)..close();
+        compiler.outputProvider('after', 'dump')..add(after)..close();
+      }
+    }
+    traceGraph(pass.passName, cpsFunction);
+    dumpTypedIr(pass.passName, cpsFunction);
+  }
+
   void applyCpsPass(cps_opt.Pass pass, cps.FunctionDefinition cpsFunction) {
     cpsOptimizationTask.measureSubtask(pass.passName, () {
       pass.rewrite(cpsFunction);
     });
     traceGraph(pass.passName, cpsFunction);
     dumpTypedIr(pass.passName, cpsFunction);
     assert(checkCpsIntegrity(cpsFunction, pass.passName));
   }
 
   cps.FunctionDefinition compileToCpsIr(AstElement element) {
@@ skipping 164 matching lines @@
         treeOptimizationTask]
       ..addAll(fallbackCompiler.tasks);
   }
 
   js.Node attachPosition(js.Node node, AstElement element) {
     return node.withSourceInformation(
         sourceInformationFactory.createBuilderForContext(element)
             .buildDeclaration(element));
   }
 }