https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92080
--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> --- On Thu, 21 Mar 2024, liuhongt at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92080 > > Hongtao Liu <liuhongt at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |liuhongt at gcc dot gnu.org > > --- Comment #7 from Hongtao Liu <liuhongt at gcc dot gnu.org> --- > Another simple case is > > typedef int v4si __attribute__((vector_size(16))); > typedef short v8hi __attribute__((vector_size(16))); > > v8hi a; > v4si b; > void > foo () > { > b = __extension__(v4si){0, 0, 0, 0}; > a = __extension__(v8hi){0, 0, 0, 0, 0, 0, 0, 0}; > } > > GCC generates 2 pxor > > foo(): > vpxor xmm0, xmm0, xmm0 > vmovdqa XMMWORD PTR b[rip], xmm0 > vpxor xmm0, xmm0, xmm0 > vmovdqa XMMWORD PTR a[rip], xmm0 > ret If we were to expose that vpxor before postreload we'd likely CSE but we have 5: xmm0:V4SI=const_vector REG_EQUIV const_vector 6: [`b']=xmm0:V4SI 7: xmm0:V8HI=const_vector REG_EQUIV const_vector 8: [`a']=xmm0:V8HI until the very end. But since we have the same mode size on the xmm0 sets CSE could easily handle (integral) constants by hashing/comparing on their byte representation rather than by using the RTX structure. OTOH as we mostly have special constants allowed in the IL like this treating all-zeros and all-ones specially might be good enough ...
