dart2js cps: Maintain parent pointers instead of recomputing them.

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

 // 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 dart2js.cps_ir.share_interceptors;
 
 import 'optimizers.dart';
 import 'cps_ir_nodes.dart';
 import 'loop_hierarchy.dart';
 import '../constants/values.dart';
 
 /// Removes redundant `getInterceptor` calls.
 /// 
 /// The pass performs three optimizations for interceptors:
 ///- pull interceptors out of loops
 ///- replace interceptors with constants
 ///- share interceptors when one is in scope of the other
-class ShareInterceptors extends RecursiveVisitor implements Pass {
+class ShareInterceptors extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Share interceptors';
 
   /// The innermost loop containing a given primitive.
   final Map<Primitive, Continuation> loopHeaderFor =
       <Primitive, Continuation>{};
 
   /// An interceptor currently in scope for a given primitive.
   final Map<Primitive, Primitive> interceptorFor =
       <Primitive, Primitive>{};
 
@@ skipping 79 matching lines @@
       if (existing != null) {
         existing.substituteFor(interceptor);
         interceptor.destroy();
         node.remove();
         return next;
       }
 
       // The interceptor could not be shared. Replace it with a constant.
       Constant constantPrim = new Constant(constant);
       node.primitive = constantPrim;
+      constantPrim.parent = node;
       constantPrim.hint = interceptor.hint;
       constantPrim.type = interceptor.type;
       constantPrim.substituteFor(interceptor);
       interceptor.destroy();
       sharedConstantFor[constant] = constantPrim;
     } else {
       interceptorFor[input] = interceptor;
     }
 
     // Determine the outermost loop where the input to the interceptor call
@@ skipping 58 matching lines @@
       }
     }
     return c1;
   }
 
   int getDepth(Continuation loop) {
     if (loop == null) return -1;
     return loopHierarchy.loopDepth[loop];
   }
 }