Reland r20974: Unify and simplify the FastCloneShallowArrayStub

src/hydrogen-gvn.cc

 // Copyright 2013 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 "hydrogen.h"
 #include "hydrogen-gvn.h"
 #include "v8.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 845 matching lines @@
         dominators->Store(changes, instr);
         if (FLAG_trace_gvn) {
           HeapStringAllocator allocator;
           StringStream stream(&allocator);
           stream.Add("Instruction i%d changes ", instr->id());
           side_effects_tracker_.PrintSideEffectsTo(&stream, changes);
           stream.Add("\n");
           stream.OutputToStdOut();
         }
       }
-      if (instr->CheckFlag(HValue::kUseGVN)) {
+      if (instr->CheckFlag(HValue::kUseGVN) &&
+          !instr->CheckFlag(HValue::kCantBeReplaced)) {
         ASSERT(!instr->HasObservableSideEffects());
         HInstruction* other = map->Lookup(instr);
         if (other != NULL) {
           ASSERT(instr->Equals(other) && other->Equals(instr));
           TRACE_GVN_4("Replacing instruction i%d (%s) with i%d (%s)\n",
                       instr->id(),
                       instr->Mnemonic(),
                       other->id(),
                       other->Mnemonic());
           if (instr->HasSideEffects()) removed_side_effects_ = true;
@@ skipping 27 matching lines @@
                                                       dominated);
         successor_map->Kill(side_effects_on_all_paths);
         successor_dominators->Kill(side_effects_on_all_paths);
       }
     }
     current = next;
   }
 }
 
 } }  // namespace v8::internal