Reland r20974: Unify and simplify the FastCloneShallowArrayStub

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index fcf46554ea0b5188991323cb77d0fcb1046e466b..34eafa99ffb3be462b068edddbef8c191b3141b8 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -619,6 +619,10 @@ class HValue : public ZoneObject {
     // flag.
     kUint32,
     kHasNoObservableSideEffects,
+    // Indicates an instruction shouldn't be replaced by optimization, this flag
+    // is useful to set in cases where recomputing a value is cheaper than
+    // extending the value's live range and spilling it.
+    kCantBeReplaced,
     // Indicates the instruction is live during dead code elimination.
     kIsLive,
 
@@ -6257,6 +6261,7 @@ class HLoadNamedField V8_FINAL : public HTemplateInstruction<2> {
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   bool CanBeReplacedWith(HValue* other) const {
+    if (!CheckFlag(HValue::kCantBeReplaced)) return false;
     if (!type().Equals(other->type())) return false;
     if (!representation().Equals(other->representation())) return false;
     if (!other->IsLoadNamedField()) return true;