On Fri, Nov 7, 2025 at 5:32 PM Robin Dapp <[email protected]> wrote:
>
> Hi,
>
> In can_vec_perm_const_p if we cannot directly permute a vector mode we
> try to pun it with a byte mode. qimode_for_vec_perm checks gets the
> mode size and uses that as number of elements for the new QImode vector.
>
> This doesn't work for RVV mask vectors, though: First, their
> precision might be smaller than a byte and second, there is no
> way to easily pun them. The most common way would be a vector select
> from {0, 0, ...} and {1, 1, ...} vectors. Therefore this patch checks
> if the perm's innermode precision is a multiple of QImode's precision.
>
> I hit this during testing of a riscv backend patch related to
> gather/scatter (to be upstreamed soon). It manifests in around 10-20
> FAILs in the test suite so I figured we don't need a separate test.
>
> Bootstrapped and regtested on x86 and power10. Regtested on aarch64 and
> riscv64.
OK.
> Regards
> Robin
>
> gcc/ChangeLog:
>
> * optabs-query.cc (qimode_for_vec_perm): Check if QImode's
> precision divides the inner mode's precision.
> ---
> gcc/optabs-query.cc | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/optabs-query.cc b/gcc/optabs-query.cc
> index 5335d0d8401..484d7c2e205 100644
> --- a/gcc/optabs-query.cc
> +++ b/gcc/optabs-query.cc
> @@ -358,7 +358,9 @@ can_conditionally_move_p (machine_mode mode)
> opt_machine_mode
> qimode_for_vec_perm (machine_mode mode)
> {
> - if (GET_MODE_INNER (mode) != QImode)
> + if (GET_MODE_INNER (mode) != QImode
> + && multiple_p (GET_MODE_PRECISION (GET_MODE_INNER (mode)),
> + GET_MODE_PRECISION (QImode)))
> return related_vector_mode (mode, QImode, GET_MODE_SIZE (mode));
> return opt_machine_mode ();
> }
> --
> 2.51.0
>
