https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82447
--- Comment #6 from amker at gcc dot gnu.org --- (In reply to Jakub Jelinek from comment #5) > (In reply to amker from comment #4) > > (In reply to Jakub Jelinek from comment #2) > > > Indeed. But when the body is: > > > sum += a[size - 1 - i]; > > > while base 128U with step -1U is considered, it isn't found as the > > > cheapest > > > for some reason either. > > > > On 64-bit targets, candidate [128, -1] is added in unsigned int type, while > > address IV has pointer type. IVOPTs simply skips the candidate because it > > has smaller precision than the IV use. > > Yeah, but can't we also add [128UL, -1UL] candidate if we see there are IVs > of that bitsize? Conversion from that to the unsigned int IV is cheap. Yes we can. For constant niters loop, currently it's ivcanon adding the counting down IV, I mentioned during cauldron that we may want to get rid of iv_canonicalization by adding all necessary IV candidates in IVOTPs.
