There's actually dozens and dozens of such instructions on x86 and x86-64. So the question shouldn't really be if there is an instruction, it's whether the one

There's actually dozens and dozens of such instructions on x86 and x86-64. So the question shouldn't really be if there is an instruction, it's whether the one you're using is the most performant for your given CPU. Old Linux kernels would actually calculate CPU speed, and whether 16-bit, 32-bit, FPU, MMX memory copies were fastest and pick one for the kernel to use.