dart2js CPS: Remove an invalid assertion in shrinking reductions.

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 527 matching lines @@
   if (trueBody is! InvokeContinuation) return false;
   Continuation falseCont = branch.falseContinuation.definition;
   Expression falseBody = _unfoldDeadRefinements(falseCont.body);
   if (falseBody is! InvokeContinuation) return false;
   InvokeContinuation trueInvoke = trueBody;
   InvokeContinuation falseInvoke = falseBody;
   if (trueInvoke.continuation.definition !=
       falseInvoke.continuation.definition) {
     return false;
   }
-  assert(trueInvoke.arguments.length == falseInvoke.arguments.length);
   // Matching zero arguments should be adequate, since isomorphic true and false
   // invocations should result in redundant phis which are removed elsewhere.
-  if (trueInvoke.arguments.isNotEmpty) return false;
-  return true;
+  //
+  // Note that the argument lists are not necessarily the same length here,
+  // because we could be looking for new redexes in the middle of performing a
+  // dead parameter reduction, where some but not all of the invocations have
+  // been rewritten.  In that case, we will find the redex (once) after both
+  // of these invocations have been rewritten.
+  return trueInvoke.arguments.isEmpty && falseInvoke.arguments.isEmpty;
 }
 
 bool _isDeadParameter(Parameter parameter) {
   if (_isParameterRemoved(parameter)) return false;
 
   // We cannot remove function parameters as an intraprocedural optimization.
   if (parameter.parent is! Continuation || parameter.hasAtLeastOneUse) {
     return false;
   }
 
@@ skipping 139 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";
 }