https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84101
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Segher Boessenkool from comment #6) > I think subreg should deal with this. What do you mean "there aren't > any half of TImode subregs"? insn 10 has it split at the start, and > insn 18 at the end wants it split, too. By that I mean that there aren't any (subreg:DI (reg:TI) [08]) destinations or similar. Admittedly lower-subreg also handles shifts, and a few others, but not vec_concat etc. Plus V2DI move: original cost 4, split cost 4 * 2 so it decides not to do anything about V2DImode (generally the right thing). So, we'd need to pattern recognize a vec_concat from scalar modes (integral only) and the result used (single use) in a subreg to twice that big integral mode and handle it as if it was setting the two halves of the wider reg.
