> 1. is easy, see patch below. 2. is much harder - we need to
> compute the bit-offset relative to the bitfield group start,
> thus in get_bit_range we do
> /* Compute the adjustment to bitpos from the offset of the field
> relative to the representative. */
> offset = size_diffop (DECL_FIELD_OFFSET (field),
> DECL_FIELD_OFFSET (repr));
> bitoffset = (tree_low_cst (offset, 1) * BITS_PER_UNIT
> + tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1)
> - tree_low_cst (DECL_FIELD_BIT_OFFSET (repr), 1));
> and we cannot generally assume offset is zero (well, maybe we could
> arrange that though, at least we could assert that for all fields
> in a bitfield group DECL_FIELD_OFFSET is the same?).
> Any suggestion? Apart from trying to make sure that offset will
> be zero by construction? Or by simply not handling bitfields
> properly that start at a variable offset?
Computing the offset in stor-layout.c and storing it in DECL_INITIAL?
> The finish_bitfield_representative hunk implements the fix for 1.,
> the rest the proposed zero-by-construction solution for 2.