Make sure polymorphic element access creates non-replaying phis.

src/hydrogen.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 5574 matching lines @@
           external_elements, checked_key, val,
           mapcompare, elements_kind, is_store);
     }
     *has_side_effects |= access->HasObservableSideEffects();
     // The caller will use has_side_effects and add a correct Simulate.
     access->SetFlag(HValue::kHasNoObservableSideEffects);
     if (position != RelocInfo::kNoPosition) access->set_position(position);
     if (!is_store) {
       Push(access);
     }
+    NoObservableSideEffectsScope scope(this);
     current_block()->GotoNoSimulate(join);
     set_current_block(other_map);
   }
 
   // Deopt if none of the cases matched.
   NoObservableSideEffectsScope scope(this);
   FinishExitWithHardDeoptimization(join);
   set_current_block(join);
   return is_store ? NULL : Pop();
 }
@@ skipping 4110 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal