Fix invalid usage of StoreIC_ArrayLength optimization.

src/arm/ic-arm.cc

Index: src/arm/ic-arm.cc
diff --git a/src/arm/ic-arm.cc b/src/arm/ic-arm.cc
index abbac993df0c8e62dfa08eb90521228af256ad87..219d354c7e8d6e31a62cdee99d659867e7aacfe4 100644
--- a/src/arm/ic-arm.cc
+++ b/src/arm/ic-arm.cc
@@ -1469,11 +1469,10 @@ void StoreIC::GenerateArrayLength(MacroAssembler* masm) {
   //  -- lr    : 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;
 
@@ -1495,6 +1494,13 @@ void StoreIC::GenerateArrayLength(MacroAssembler* masm) {
   __ CompareObjectType(scratch, scratch, scratch, FIXED_ARRAY_TYPE);
   __ b(ne, &miss);
 
+  // Check that the array has fast properties, otherwise the length
+  // property might have been redefined.
+  __ ldr(scratch, FieldMemOperand(receiver, JSArray::kPropertiesOffset));
+  __ ldr(scratch, FieldMemOperand(scratch, FixedArray::kMapOffset));
+  __ CompareRoot(scratch, Heap::kHashTableMapRootIndex);
+  __ b(eq, &miss);
+
   // Check that value is a smi.
   __ JumpIfNotSmi(value, &miss);