Add CPS IR transformation to make the JavaScript backend specific semantics explicit in the tree.

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

Index: pkg/compiler/lib/src/cps_ir/constant_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/constant_propagation.dart b/pkg/compiler/lib/src/cps_ir/constant_propagation.dart
index fc9ebba0fed2f353a69aade7efe5ce42d1bc860f..ee4ec054cd4cf8af8b2a7afe75e3ae1350d37b93 100644
--- a/pkg/compiler/lib/src/cps_ir/constant_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/constant_propagation.dart
@@ -28,7 +28,7 @@ class ConstantPropagator implements Pass {
 
     // Set all parent pointers.
 
-    new _ParentVisitor().visit(root);
+    new ParentVisitor().visit(root);
 
     // Analyze. In this phase, the entire term is analyzed for reachability
     // and the constant status of each expression.
@@ -603,6 +603,13 @@ class _ConstPropagationVisitor extends Visitor {
     Branch branch = node.parent;
     visitBranch(branch);
   }
+
+  // JavaScript specific nodes.
+
+  void visitIdentical(Identical node) {
+    setReachable(node.left.definition);

[Kevin Millikin (Google), 2014/11/25 14:27:23]

I need to understand the code in this file a bit better.  But I think the safe
thing here is to have:

void visitIdentical(Identical node) {
  setValue(node, _ConstnessLattice.NonConst);
}

[karlklose, 2014/11/25 14:38:46]

I am not sure if it is okay to not set the parameters as reachable.

I added the call to mark the node itself as non-constant.

+    setReachable(node.right.definition);
+  }
 }
 
 /// Represents the constant-state of a variable at some point in the program.