https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114801
--- Comment #8 from Christophe Lyon <clyon at gcc dot gnu.org> --- (In reply to Jakub Jelinek from comment #5) > Guess the primary question is why there is the gen_lowpart call at all. > Is it that normally the mode of x is already right due to the prototypes of > the builtins, with the exception that gcc likes to promote QImode/HImode > arguments of calls to SImode, so is the intent in that case to just narrow > down SImode back to HImode (seems VALID_MVE_PRED_MODE is only true for > HImode from scalar MODE_INT modes)? > We have mode == V4BImode (could be V16BI or V8BI, it depends on the intrinsic being expanded) and x is HImode. The intent is to generate: (set (reg:V4BI 122) (subreg:V4BI (reg:SI 116 [ _3 ]) 0)) This works if x is not a constant (this is what we have in trunk) > If so, best would be to limit the call to just that case. > So (completely untested): > --- gcc/config/arm/arm-mve-builtins.cc.jj 2024-03-19 09:51:05.203631194 > +0100 > +++ gcc/config/arm/arm-mve-builtins.cc 2024-04-26 15:49:55.380344060 > +0200 > @@ -2100,7 +2100,12 @@ function_expander::add_input_operand (in > mode = GET_MODE (x); > } > else if (VALID_MVE_PRED_MODE (mode)) > - x = gen_lowpart (mode, x); > + { > + if (mode == HImode && GET_MODE (x) != HImode) > + /* GCC promotes QI/HImode arguments to int, undo that > + here. */ > + x = lowpart_subreg (mode, x, SImode); So we won't enter the 'if' since mode != HImode > + } > > m_ops.safe_grow (m_ops.length () + 1, true); > create_input_operand (&m_ops.last (), x, mode); > > I'd hope if the argument is a vector mode x already has that mode...