https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101944
--- Comment #5 from Kewen Lin <linkw at gcc dot gnu.org> --- (In reply to Richard Biener from comment #3) > On x86 we even have > > Vector cost: 136 > Scalar cost: 196 > > note that we seem to vectorize the reduction but that only happens with > -ffast-math, not -O2 -ftree-slp-vectorize? > I don't quite follow this question, may misunderstand it. Yes, -ffast-math is required, now -O2 doesn't implicitly enable vectorization, it needs the explicit slp option. > One issue is the association of > > (diffa * vdw_d * (1 / 6.) + vdw_c * (1 / 4.)) * diffa + vdw_b * (1 / 2.)) * > diffa + vdw_a > > which we fail to reduce as > > diffa*diffa*diffa*(1/6.)*vdw_d + diffa*diffa*(1/4.)*vdw_c + > diffa*(1/2.)*vdw_b + 1.0*vdw_a Good point!
