You have the optimizer disabled and the functions are no-ops. Additionally, masking that way makes the XOR no longer a no-op, so only one masking operation is n

You have the optimizer disabled and the functions are no-ops. Additionally, masking that way makes the XOR no longer a no-op, so only one masking operation is necessary -- but it seems that GCC already knows this trick: https://godbolt.org/z/qxMvcbrc8 https://godbolt.org/z/qxMvcbrc8