https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114801
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> --- 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)? 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); + } 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...