Try aligning unboxed double array backing store in allocation or scavenge promotion.

src/ia32/stub-cache-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4012 matching lines @@
     __ bind(&value_is_smi);
 
     // Check for the empty array, and preallocate a small backing store if
     // possible.
     __ mov(edi, FieldOperand(edx, JSObject::kElementsOffset));
     __ cmp(edi, Immediate(masm->isolate()->factory()->empty_fixed_array()));
     __ j(not_equal, &check_capacity);
 
     int size = FixedDoubleArray::SizeFor(JSArray::kPreallocatedArrayElements);
     __ AllocateInNewSpace(size, edi, ebx, ecx, &prepare_slow, TAG_OBJECT);
+
     // Restore the key, which is known to be the array length.
     __ mov(ecx, Immediate(0));
 
     // eax: value
     // ecx: key
     // edx: receiver
     // edi: elements
     // Initialize the new FixedDoubleArray. Leave elements unitialized for
     // efficiency, they are guaranteed to be initialized before use.
     __ mov(FieldOperand(edi, JSObject::kMapOffset),
@@ skipping 35 matching lines @@
     __ jmp(ic_slow, RelocInfo::CODE_TARGET);
   }
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32