https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85945
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the problem is that validate_subreg etc. has a restriction like:
/* Subregs involving floating point modes are not allowed to
change size. Therefore (subreg:DI (reg:DF) 0) is fine, but
(subreg:SI (reg:DF) 0) isn't. */
but lower-subreg.c doesn't take that into account in:
/* We only try to decompose single word subregs of multi-word
registers. When we find one, we return -1 to avoid iterating
over the inner register.
??? This doesn't allow, e.g., DImode subregs of TImode values
on 32-bit targets. We would need to record the way the
pseudo-register was used, and only decompose if all the uses
were the same number and size of pieces. Hopefully this
doesn't happen much. */
if (outer_words == 1 && inner_words > 1)
{
bitmap_set_bit (decomposable_context, regno);
iter.skip_subrtxes ();
continue;
}
and decompose_register creates concat with a word sized integral pseudos in it.
