Fix invalid usage of StoreIC_ArrayLength optimization.

src/x64/ic-x64.cc

Index: src/x64/ic-x64.cc
diff --git a/src/x64/ic-x64.cc b/src/x64/ic-x64.cc
index b3a94227af3a5159fb5649c863f86e8395c0e7a0..020446008f2ba3deb153489cdfdb58d7581d4a66 100644
--- a/src/x64/ic-x64.cc
+++ b/src/x64/ic-x64.cc
@@ -1397,11 +1397,10 @@ void StoreIC::GenerateArrayLength(MacroAssembler* masm) {
   //  -- rsp[0] : return address
   // -----------------------------------
   //
-  // This accepts as a receiver anything JSObject::SetElementsLength accepts
-  // (currently anything except for external and pixel arrays which means
-  // anything with elements of FixedArray type.), but currently is restricted
-  // to JSArray.
-  // Value must be a number, but only smis are accepted as the most common case.
+  // This accepts as a receiver anything JSArray::SetElementsLength accepts
+  // (currently anything except for external arrays which means anything with
+  // elements of FixedArray type).  Value must be a number, but only smis are
+  // accepted as the most common case.
 
   Label miss;
 
@@ -1423,6 +1422,13 @@ void StoreIC::GenerateArrayLength(MacroAssembler* masm) {
   __ CmpObjectType(scratch, FIXED_ARRAY_TYPE, scratch);
   __ j(not_equal, &miss);
 
+  // Check that the array has fast properties, otherwise the length
+  // property might have been redefined.
+  __ movq(scratch, FieldOperand(receiver, JSArray::kPropertiesOffset));
+  __ CompareRoot(FieldOperand(scratch, FixedArray::kMapOffset),
+                 Heap::kHashTableMapRootIndex);
+  __ j(equal, &miss);
+
   // Check that value is a smi.
   __ JumpIfNotSmi(value, &miss);