Add and use ElementsKind side effect

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 65fc4df4bd8ec35883577a8c4899332a1736dafe..3770254ac5d1e27c65070d4ecae9ed599f0f0258 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -183,6 +183,7 @@ class LChunkBuilder;
   V(Calls)                                     \
   V(InobjectFields)                            \
   V(BackingStoreFields)                        \
+  V(ElementsKind)                              \
   V(ArrayElements)                             \
   V(DoubleArrayElements)                       \
   V(SpecializedArrayElements)                  \
@@ -621,8 +622,14 @@ class HValue: public ZoneObject {
   void SetAllSideEffects() { flags_ |= AllSideEffects(); }
   void ClearAllSideEffects() { flags_ &= ~AllSideEffects(); }
   bool HasSideEffects() const { return (flags_ & AllSideEffects()) != 0; }
+  bool HasObservableSideEffects() const {
+    return (flags_ & ObservableSideEffects()) != 0;
+  }
 
   int ChangesFlags() const { return flags_ & ChangesFlagsMask(); }
+  int ObservableChangesFlags() const {
+    return flags_ & ChangesFlagsMask() & ObservableSideEffects();
+  }
 
   Range* range() const { return range_; }
   bool HasRange() const { return range_ != NULL; }
@@ -702,6 +709,12 @@ class HValue: public ZoneObject {
     return ChangesFlagsMask() & ~(1 << kChangesOsrEntries);
   }
 
+  // A flag mask of all side effects that can make observable changes in
+  // an executing program (i.e. are not safe to repeat, move or remove);
+  static int ObservableSideEffects() {
+    return ChangesFlagsMask() & ~(1 << kChangesElementsKind);
+  }
+
   // Remove the matching use from the use list if present.  Returns the
   // removed list node or NULL.
   HUseListNode* RemoveUse(HValue* value, int index);
@@ -1739,7 +1752,7 @@ class HElementsKind: public HUnaryOperation {
   explicit HElementsKind(HValue* value) : HUnaryOperation(value) {
     set_representation(Representation::Integer32());
     SetFlag(kUseGVN);
-    SetFlag(kDependsOnMaps);
+    SetFlag(kDependsOnElementsKind);
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
@@ -1866,6 +1879,7 @@ class HLoadElements: public HUnaryOperation {
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetFlag(kDependsOnMaps);
+    SetFlag(kDependsOnElementsKind);
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
@@ -3915,7 +3929,7 @@ class HTransitionElementsKind: public HTemplateInstruction<1> {
         transitioned_map_(transitioned_map) {
     SetOperandAt(0, object);
     SetFlag(kUseGVN);
-    SetFlag(kDependsOnMaps);
+    SetFlag(kChangesElementsKind);
     set_representation(Representation::Tagged());
   }