[Bug tree-optimization/94403] Missed optimization bswap

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94403

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 48147
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48147&action=edit
gcc10-pr94403.patch

Untested fix for the std::byte part.  Not a regression, so will have to wait
for GCC11.  Also, if the testcase doesn't have the assignment of the parameter
into a separate local temporary (i.e. when the parameter itself is
addressable), then it doesn't work either, the loads stay as MEM_REFs instead
of being transformed to BIT_FIELD_REFs on the parameter.