https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96789
--- Comment #19 from Kewen Lin <linkw at gcc dot gnu.org> --- (In reply to rguent...@suse.de from comment #17) > On Fri, 18 Sep 2020, linkw at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96789 > > > > --- Comment #15 from Kewen Lin <linkw at gcc dot gnu.org> --- > > (In reply to rguent...@suse.de from comment #14) > > > On Fri, 18 Sep 2020, linkw at gcc dot gnu.org wrote: > > > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96789 > > > > > > > > --- Comment #13 from Kewen Lin <linkw at gcc dot gnu.org> --- > > > > > 2) on Power, the conversion from unsigned char to unsigned short is > > > > > nop > > > > > conversion, when we counting scalar cost, it's counted, then add > > > > > costs 32 > > > > > totally onto scalar cost. Meanwhile, the conversion from unsigned > > > > > short to > > > > > signed short should be counted but it's not (need to check why > > > > > further). > > > > > > > > UH to SH conversion is true when calling vect_nop_conversion_p, so it's > > > > not > > > > even put into the cost vector. > > > > > > > > tree_nop_conversion_p's comments saying: > > > > > > > > /* Return true iff conversion from INNER_TYPE to OUTER_TYPE generates > > > > no instruction. */ > > > > > > > > I may miss something here, but UH to SH conversion does need one > > > > explicit > > > > extend instruction *extsh*, the precision/mode equality check looks > > > > wrong for > > > > this conversion. > > > > > > Well, it isn't a RTL predicate and it only needs extension because > > > there's never a HImode pseudo but always SImode subregs. > > > > Thanks Richi! Should we take care of this case? or neglect this kind of > > extension as "no instruction"? I was intent to handle it in target specific > > code, but it isn't recorded into cost vector while it seems too heavy to do > > the > > bb_info slp_instances revisits in finish_cost. > > I think it's not something we should handle on GIMPLE. Got it! For else if (vect_nop_conversion_p (stmt_info)) continue; Is it a good idea to change it to call record_stmt_cost like the others? 1) introduce one vect_cost_for_stmt enum type eg: nop_stmt 2) builtin_vectorization_cost return zero for it by default as before. 3) targets can adjust the cost according to its need
