dart2js cps: Add path-sensitive types by inserting refinement IR nodes.

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

Index: pkg/compiler/lib/src/cps_ir/remove_refinements.dart
diff --git a/pkg/compiler/lib/src/cps_ir/remove_refinements.dart b/pkg/compiler/lib/src/cps_ir/remove_refinements.dart
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+// Copyright (c) 2015, 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 cps_ir.optimization.remove_refinements;
+
+import 'optimizers.dart' show Pass;
+import 'shrinking_reductions.dart' show ParentVisitor;
+import 'cps_ir_nodes.dart';
+
+/// Removes all [Refinement] nodes from the IR.
+///
+/// This simplifies subsequent passes that don't rely on path-sensitive
+/// type information but depend on equality between primitives.
+class RemoveRefinements extends RecursiveVisitor implements Pass {
+  String get passName => 'Remove refinement nodes';
+
+  void rewrite(FunctionDefinition node) {
+    new ParentVisitor().visit(node);
+    visit(node);
+  }
+
+  @override
+  Expression traverseLetPrim(LetPrim node) {
+    if (node.primitive is Refinement) {
+      Refinement refinement = node.primitive;
+      refinement.value.definition.substituteFor(refinement);
+      refinement.value.unlink();
+      InteriorNode parent = node.parent;
+      parent.body = node.body;
+      node.body.parent = parent;
+    }
+    return node.body;
+  }
+}