[Bug target/49244] __sync or __atomic builtins will not emit 'lock bts/btr/btc'

[dhowells at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49244

--- Comment #10 from dhowells at redhat dot com <dhowells at redhat dot com> ---
A partial optimisation could be made if the mask is constant and only contains
one bit (or/xor) or only lacks one bit (and).  That is the most common case in
the kernel by far, but it would still leave instances where the bit number is
dynamic.