Smi arrays are only guaranteed to be initialized in non-holey case

src/hydrogen-instructions.h

 // Copyright 2012 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.
 
 #ifndef V8_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include "src/v8.h"
 
 #include "src/allocation.h"
@@ skipping 6963 matching lines @@
     ASSERT_EQ(index, 2);
     return RequiredValueRepresentation(elements_kind_, store_mode_);
   }
 
   static Representation RequiredValueRepresentation(
       ElementsKind kind, StoreFieldOrKeyedMode mode) {
     if (IsDoubleOrFloatElementsKind(kind)) {
       return Representation::Double();
     }
 
+    if (kind == FAST_SMI_ELEMENTS && SmiValuesAre32Bits() &&
+        mode == STORE_TO_INITIALIZED_ENTRY) {
+      return Representation::Integer32();
+    }
+
     if (IsFastSmiElementsKind(kind)) {
-      if (SmiValuesAre32Bits() && mode == STORE_TO_INITIALIZED_ENTRY) {
-        return Representation::Integer32();
-      }
       return Representation::Smi();
     }
 
     return IsExternalArrayElementsKind(kind) ||
                    IsFixedTypedArrayElementsKind(kind)
                ? Representation::Integer32()
                : Representation::Tagged();
   }
 
   bool is_external() const {
@@ skipping 855 matching lines @@
 };
 
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_