https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96789
--- Comment #14 from rguenther at suse dot de <rguenther at suse dot de> --- 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.