[Bug target/101891] Adjust -fzero-call-used-regs to always use XOR

[arjan at linux dot intel.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101891

Arjan van de Ven <arjan at linux dot intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arjan at linux dot intel.com

--- Comment #7 from Arjan van de Ven <arjan at linux dot intel.com> ---
from a performance angle, the xor-only sequence is not so great at all; modern
CPUs are really good at eliminating mov's so that's why the code originally was
added to do a combo of xor and mov..

I can understand the security versus performance tradeoff.
(the original tuning was done to basically make it entirely free, so that it
could just be always enabled)