https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77287
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|rtl-optimization |target
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
clang can now produce:
mov eax, dword ptr [esp + 16]
mov ecx, dword ptr [esp + 28]
vmovdqu xmm0, xmmword ptr [ecx + 32]
vmovdqu xmm1, xmmword ptr [eax]
vpackuswb xmm2, xmm1, xmm0
vpsubw xmm0, xmm1, xmm0
vpaddw xmm0, xmm0, xmm2
vpackuswb xmm0, xmm0, xmm0
vpackuswb xmm0, xmm0, xmm0
vpextrd eax, xmm0, 1
ret
I suspect if the back-end is able to "fold" at the gimple level the builtins
into gimple, GCC will do a much better job.
Currently we have stuff like:
_27 = __builtin_ia32_vextractf128_si256 (_28, 0);
_26 = __builtin_ia32_vec_ext_v4si (_27, 1); [tail call]
I think both are just a BIT_FIELD_REF really and even more can be simplified to
just one bitfield extraction rather than what we do now:
vpackuswb %ymm1, %ymm0, %ymm0
vpextrd $1, %xmm0, %eax
Plus it looks like with __builtin_ia32_vextractf128_si256 (_28, 0), clang is
able to remove half of the code due to only needing 128 bytes stuff :).
