dart2js cps: Retain refinement nodes and update refinements after GVN.

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

+library dart2js.cps_ir.update_refinements;
+
+import 'cps_ir_nodes.dart';
+import 'optimizers.dart' show Pass;
+import 'type_mask_system.dart';
+
+/// Updates all references to use the most refined version in scope.
+///
+/// [GVN] and [RedundantJoinElimination], and possibly other passes, can create
+/// references that don't use the best refinement in scope. This pass improves
+/// the refinement information.
+///
+//
+// TODO(asgerf): Could be done during GVN for another adjacent pass.
+//   It is easier to measure performance and rearrange passes when it has its
+//   own pass, but we can merge it with an adjacent pass later.
+//
+class UpdateRefinements extends TrampolineRecursiveVisitor implements Pass {
+  String get passName => 'Update refinements';
+
+  final TypeMaskSystem typeSystem;
+
+  Map<Primitive, Refinement> refinementFor = <Primitive, Refinement>{};
+
+  UpdateRefinements(this.typeSystem);
+
+  void rewrite(FunctionDefinition node) {
+    visit(node);
+  }
+
+  Expression traverseLetPrim(LetPrim node) {
+    visit(node.primitive);
+    return node.body;
+  }
+
+  @override
+  visitRefinement(Refinement node) {
+    if (refine(node.value)) {
+      // Update the type if the input has changed.
+      node.type = typeSystem.intersection(node.value.definition.type,
+          node.refineType);
+    }
+    Primitive value = node.effectiveDefinition;
+    Refinement old = refinementFor[value];
+    refinementFor[value] = node;
+    pushAction(() {
+      refinementFor[value] = old;
+    });
+  }
+
+  @override
+  processReference(Reference ref) {
+    refine(ref);
+  }
+
+  bool refine(Reference ref) {
+    Definition def = ref.definition;
+    if (def is Primitive) {
+      Refinement refinement = refinementFor[def.effectiveDefinition];
+      if (refinement != null && refinement != ref.definition) {
+        ref.changeTo(refinement);
+        return true;
+      }
+    }
+    return false;
+  }
+}