https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115405
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
It's not visible but I assume that _4 doesn't have _BitInt(17) type?
The
if (known_eq (offset, 0)
&& !reverse
&& poly_int_tree_p (TYPE_SIZE (type), &type_size)
&& known_eq (GET_MODE_BITSIZE (DECL_MODE (base)), type_size))
check tries to assess that no extension is required, does it work if you
adjust that for the _BitInt case?
OTOH the reduce_bit_field handling in VIEW_CONVERT_EXPR expansion looks
misplaced - shouldn't it be before the INTEGRAL_TYPE_P handling?
