[turbofan] GraphReducer is more "fixpointish" now.

src/compiler/graph-reducer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/graph-reducer.h"
 
 #include <functional>
 
 #include "src/compiler/graph-inl.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 GraphReducer::GraphReducer(Graph* graph)
     : graph_(graph), reducers_(graph->zone()) {}
 
 
 static bool NodeIdIsLessThan(const Node* node, NodeId id) {
   return node->id() < id;
 }
 
 
 void GraphReducer::ReduceNode(Node* node) {
-  ZoneVector<Reducer*>::iterator skip = reducers_.end();
   static const unsigned kMaxAttempts = 16;
   bool reduce = true;
   for (unsigned attempts = 0; attempts <= kMaxAttempts; ++attempts) {
     if (!reduce) return;
     reduce = false;  // Assume we don't need to rerun any reducers.
     int before = graph_->NodeCount();
     for (ZoneVector<Reducer*>::iterator i = reducers_.begin();
          i != reducers_.end(); ++i) {
-      if (i == skip) continue;  // Skip this reducer.
       Reduction reduction = (*i)->Reduce(node);
       Node* replacement = reduction.replacement();
       if (replacement == NULL) {
         // No change from this reducer.
       } else if (replacement == node) {
         // {replacement == node} represents an in-place reduction.
-        // Rerun all the reducers except the current one for this node,
-        // as now there may be more opportunities for reduction.
+        // Rerun all the reducers for this node, as now there may be more
+        // opportunities for reduction.
         reduce = true;
-        skip = i;
         break;
       } else {
         if (node == graph_->start()) graph_->SetStart(replacement);
         if (node == graph_->end()) graph_->SetEnd(replacement);
         // If {node} was replaced by an old node, unlink {node} and assume that
         // {replacement} was already reduced and finish.
         if (replacement->id() < before) {
           node->ReplaceUses(replacement);
           node->Kill();
           return;
         }
         // Otherwise, {node} was replaced by a new node. Replace all old uses of
         // {node} with {replacement}. New nodes created by this reduction can
         // use {node}.
         node->ReplaceUsesIf(
             std::bind2nd(std::ptr_fun(&NodeIdIsLessThan), before), replacement);
         // Unlink {node} if it's no longer used.
         if (node->uses().empty()) {
           node->Kill();
         }
         // Rerun all the reductions on the {replacement}.
-        skip = reducers_.end();
         node = replacement;
         reduce = true;
         break;
       }
     }
   }
 }
 
 
 // A helper class to reuse the node traversal algorithm.
@@ skipping 12 matching lines @@
   // Perform a post-order reduction of all nodes starting from the end.
   graph()->VisitNodeInputsFromEnd(&visitor);
 }
 
 
 // TODO(titzer): partial graph reductions.
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8