[jxors]

The memory operand version tends to be as slow or slower than the manual implementation, so LLVM is right to avoid it.

[cmovq]

Right, it has much worse throughput:

Memory: https://uica.uops.info/tmp/f022a3c0a70e4ae5ab3588ebe65fd2a5_...

Register: https://uica.uops.info/tmp/e80e60e0c4914955b11dc6590711c1b8_...