Comparing 32- and 64-bit
You are using int64_t, so most of your code gets compiled into the same machine code regardless of the bitness of the target. Also, A^A = 0, so the compiler might be optimizing your entire for loop with a single call to memset with zero.

I would recommend that you move different values around instead of xoring the same values together, and I would recommend that you use int32_t for the 32-bit version, and int64_t for the 64-bit version.