Revert r15649 and fix for loop dominator propagation in GVN.

src/hydrogen-gvn.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 601 matching lines @@
   return AllowCodeMotion() && !instr->block()->IsDeoptimizing();
 }
 
 
 GVNFlagSet
 HGlobalValueNumberingPhase::CollectSideEffectsOnPathsToDominatedBlock(
     HBasicBlock* dominator, HBasicBlock* dominated) {
   GVNFlagSet side_effects;
   for (int i = 0; i < dominated->predecessors()->length(); ++i) {
     HBasicBlock* block = dominated->predecessors()->at(i);
-    if (dominator->block_id() <= block->block_id() &&
+    if (dominator->block_id() < block->block_id() &&
         block->block_id() < dominated->block_id() &&
         visited_on_paths_.Add(block->block_id())) {
       side_effects.Add(block_side_effects_[block->block_id()]);
       if (block->IsLoopHeader()) {
         side_effects.Add(loop_side_effects_[block->block_id()]);
       }
       side_effects.Add(CollectSideEffectsOnPathsToDominatedBlock(
           dominator, block));
     }
   }
@@ skipping 133 matching lines @@
     HValueMap* map = current->map();
     HSideEffectMap* dominators = current->dominators();
 
     TRACE_GVN_2("Analyzing block B%d%s\n",
                 block->block_id(),
                 block->IsLoopHeader() ? " (loop header)" : "");
 
     // If this is a loop header kill everything killed by the loop.
     if (block->IsLoopHeader()) {
       map->Kill(loop_side_effects_[block->block_id()]);
+      dominators->Kill(loop_side_effects_[block->block_id()]);
     }
 
     // Go through all instructions of the current block.
     for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
       HInstruction* instr = it.Current();
       if (instr->CheckFlag(HValue::kTrackSideEffectDominators)) {
         for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
           HValue* other = dominators->at(i);
           GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
           GVNFlag depends_on_flag = HValue::DependsOnFlagFromInt(i);
@@ skipping 62 matching lines @@
                                                       dominated);
         successor_map->Kill(side_effects_on_all_paths);
         successor_dominators->Kill(side_effects_on_all_paths);
       }
     }
     current = next;
   }
 }
 
 } }  // namespace v8::internal