Use HInstructionIterator more broadly for hydrogen.

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 379 matching lines @@
 void HGlobalValueNumberer::ComputeBlockSideEffects() {
   // The Analyze phase of GVN can be called multiple times. Clear loop side
   // effects before computing them to erase the contents from previous Analyze
   // passes.
   for (int i = 0; i < loop_side_effects_.length(); ++i) {
     loop_side_effects_[i].RemoveAll();
   }
   for (int i = graph_->blocks()->length() - 1; i >= 0; --i) {
     // Compute side effects for the block.
     HBasicBlock* block = graph_->blocks()->at(i);
-    HInstruction* instr = block->first();
     int id = block->block_id();
     GVNFlagSet side_effects;
-    while (instr != NULL) {
+    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+      HInstruction* instr = it.Current();
       side_effects.Add(instr->ChangesFlags());
       if (instr->IsSoftDeoptimize()) {
         block_side_effects_[id].RemoveAll();
         side_effects.RemoveAll();
         break;
       }
-      instr = instr->next();
     }
     block_side_effects_[id].Add(side_effects);
 
     // Loop headers are part of their loop.
     if (block->IsLoopHeader()) {
       loop_side_effects_[id].Add(side_effects);
     }
 
     // Propagate loop side effects upwards.
     if (block->HasParentLoopHeader()) {
@@ skipping 427 matching lines @@
                                                       dominated);
         successor_map->Kill(side_effects_on_all_paths);
         successor_dominators->Kill(side_effects_on_all_paths);
       }
     }
     current = next;
   }
 }
 
 } }  // namespace v8::internal