dart2js cps: More aggressive operator specialization.

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';
+import '../world.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;
+  World get classWorld => typeSystem.classWorld;
 
   Map<Primitive, Primitive> refinementFor = <Primitive, Primitive>{};
 
   UpdateRefinements(this.typeSystem);
 
   void rewrite(FunctionDefinition node) {
     visit(node);
   }
 
   Expression traverseLetPrim(LetPrim node) {
     Expression next = node.body;
     visit(node.primitive);
     return next;
   }
 
-  visitNullCheck(NullCheck node) {
+  visitReceiverCheck(ReceiverCheck node) {
     if (refine(node.value)) {
+      // Update the type if the input has changed.
       Primitive value = node.value.definition;
-      if (value.type.isNullable) {
-        // Update the type if the input has changed.
-        node.type = value.type.nonNullable();
+      if (value.type.needsNoSuchMethodHandling(node.selector, classWorld)) {
+        node.type = typeSystem.receiverTypeFor(node.selector, value.type);
       } else {
+        // Check is no longer needed.
         node..replaceUsesWith(value)..destroy();
         LetPrim letPrim = node.parent;
         letPrim.remove();
         return;
       }
     }
-    // Use the NullCheck as a refinement.
+    // Use the ReceiverCheck as a refinement.
     Primitive value = node.effectiveDefinition;
     Primitive old = refinementFor[value];
     refinementFor[value] = node;
     pushAction(() {
       refinementFor[value] = old;
     });
   }
 
   visitRefinement(Refinement node) {
     if (refine(node.value)) {
@@ skipping 18 matching lines @@
     if (def is Primitive) {
       Primitive refinement = refinementFor[def.effectiveDefinition];
       if (refinement != null && refinement != ref.definition) {
         ref.changeTo(refinement);
         return true;
       }
     }
     return false;
   }
 }