https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96789
--- Comment #29 from Kewen Lin <linkw at gcc dot gnu.org> --- (In reply to Hongtao.liu from comment #28) > > Probably you can try to tweak it in ix86_add_stmt_cost? when the statement > > Yes, it's the place. > > > is UB to UH conversion statement, further check if the def of the input UB > > is MEM. > > Only if there's no multi-use for UB. More generally, it's quite difficult to > guess later optimizations for the purpose of more accurate vectorization > cost model, :(. Yeah, it's hard sadly. The generic cost modeling is rough, ix86_add_stmt_cost is more fine-grain (at least than what we have on Power :)), if you want to check it more, it seems doable in target specific hook finish_cost where you can get the whole vinfo object, but it could end up with very heavy analysis and might not be worthy. Do you mind to check if it can also fix this degradation on x86 to run FRE and DSE just after cunroll? I found it worked for Power, hoped it can help there too.
