https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101062
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Eric Botcazou from comment #6)
> > Does Ada allow bitfields in unions and if yes, what does it want for those?
>
> Yes, it does, and I don't think there is any specific need so the default
> should be OK like for structures.
I also think since there's at most a single active union member the default
should work.
Now, it looks to me this is rather an issue that the access is larger than
the object and thus a general bug - at least I don't see how it should only
manifest with bitfields in unions?
Note we do
if (TREE_CODE (to) == COMPONENT_REF
&& DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1)))
get_bit_range (&bitregion_start, &bitregion_end, to, &bitpos, &offset);
/* The C++ memory model naturally applies to byte-aligned fields.
However, if we do not have a DECL_BIT_FIELD_TYPE but BITPOS or
BITSIZE are not byte-aligned, there is no need to limit the range
we can access. This can occur with packed structures in Ada. */
else if (maybe_gt (bitsize, 0)
&& multiple_p (bitsize, BITS_PER_UNIT)
&& multiple_p (bitpos, BITS_PER_UNIT))
{
bitregion_start = bitpos;
bitregion_end = bitpos + bitsize - 1;
}
but if we assume that for DECL_BIT_FIELD_TYPE there's a representative
then we miss the else if, so - maybe get_bit_range should return whether
it handled things or the else if part should be done unconditionally
in case bitregion_start/end is not {0,0}?
