Reland r20974: Unify and simplify the FastCloneShallowArrayStub

src/hydrogen-gvn.cc

Index: src/hydrogen-gvn.cc
diff --git a/src/hydrogen-gvn.cc b/src/hydrogen-gvn.cc
index f9d1b408a7f7840b0a618340f2488845b3b1ba49..b32b90951a95f991cadcfe2b4ee7f5a94064337e 100644
--- a/src/hydrogen-gvn.cc
+++ b/src/hydrogen-gvn.cc
@@ -863,7 +863,8 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
           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) {