[Bug tree-optimization/96135] [9/10/11/12 regression] bswap not detected by bswap pass, unexpected results between optimization levels

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96135

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note on the trunk for f and g at -O3 -msse4 (and -O3 on aarch64), GCC produces:
  _21 = VIEW_CONVERT_EXPR<vector(8) char>(i_2(D));
  _22 = VEC_PERM_EXPR <_21, _21, { 7, 6, 5, 4, 3, 2, 1, 0 }>;
  _18 = VIEW_CONVERT_EXPR<long long int>(_22);

But that VEC_PERM_EXPR is a bswap :).

So to fix this at -O3 -msse4, maybe we could just do:
(simplify
 (view_convert (vec_perm @0 @0 vector_cst_byteswap_p @1))
 (if (INTERGAL_TYPE_P (type)))
  (convert (bswap (view_convert @1))))

Note I don't think we want to do the byteswap in the integer registers if we
are going back to the floating point registers.