https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94865
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Missing match.pd patterns also include a no-op comb of insertion of an
extracted element at the same position
(simplify
(bit_insert @0 (BIT_FIELD_REF @0 @size @pos) @pos)
(if (size matches)
@0)
in addition to the requested
(simplify
(bit_insert @0 (BIT_FIELD_REF @1 @rsize @rpos) @ipos)
(if (@0 and @1 are vectors compatible for a vec_perm)
(vec_perm @0 @1 { shuffle-mask }))
