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.
