dart2js CPS: During shrinking reductions, mark deleted branches as deleted.

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

 // Copyright (c) 2014, 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.shrinking_reductions;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /**
@@ skipping 114 matching lines @@
         break;
       case _ReductionKind.ETA_CONT:
         _reduceEtaCont(task);
         break;
       case _ReductionKind.DEAD_PARAMETER:
         _reduceDeadParameter(task);
         break;
       case _ReductionKind.BRANCH:
         _reduceBranch(task);
         break;
-      default:
-        assert(false);
     }
   }
 
   /// Applies the dead-val reduction:
   ///   letprim x = V in E -> E (x not free in E).
   void _reduceDeadVal(_ReductionTask task) {
     if (_isRemoved(task.node)) return;
     assert(_isDeadVal(task.node));
 
     LetPrim deadLet = task.node;
@@ skipping 484 matching lines @@
   _RemovalVisitor(this.worklist);
 
   void processLetPrim(LetPrim node) {
     node.parent = null;
   }
 
   void processContinuation(Continuation node) {
     node.parent = null;
   }
 
+  void processBranch(Branch node) {
+    node.parent = null;
+  }
+
   void processReference(Reference reference) {
     reference.unlink();
 
     if (reference.definition is Primitive) {
       Primitive primitive = reference.definition.unrefined;
       Node parent = primitive.parent;
       // The parent might be the deleted sentinel, or it might be a
       // Continuation or FunctionDefinition if the primitive is an argument.
       if (parent is LetPrim && _isDeadVal(parent)) {
         worklist.add(new _ReductionTask(_ReductionKind.DEAD_VAL, parent));
@@ skipping 49 matching lines @@
     assert(node is Continuation || node is LetPrim || node is Parameter ||
            node is Branch);
   }
 
   bool operator==(_ReductionTask that) {
     return (that.kind == this.kind && that.node == this.node);
   }
 
   String toString() => "$kind: $node";
 }