On Thu, 13 Oct 2022, Andre Vieira (lists) wrote:
> Added some extra comments to describe what is going on there.
Just to note I was confused and DECL_FIELD_OFFSET can indeed be
different (but then are guaranteed to be constant), so the patch
looks correct.
> On 13/10/2022 09:14, Richard Biener wrote:
> > On Wed, 12 Oct 2022, Andre Vieira (lists) wrote:
> >
> >> Hi,
> >>
> >> The bitposition calculation for the bitfield lowering in loop if conversion
> >> was not
> >> taking DECL_FIELD_OFFSET into account, which meant that it would result in
> >> wrong bitpositions for bitfields that did not end up having representations
> >> starting at the beginning of the struct.
> >>
> >> Bootstrappend and regression tested on aarch64-none-linux-gnu and
> >> x86_64-pc-linux-gnu.
> > + {
> > + tree bf_pos = fold_build2 (MULT_EXPR, bitsizetype,
> > + DECL_FIELD_OFFSET (field_decl),
> > + build_int_cst (bitsizetype, 8));
> > + bf_pos = fold_build2 (PLUS_EXPR, bitsizetype, bf_pos,
> > + DECL_FIELD_BIT_OFFSET (field_decl));
> > + tree rep_pos = fold_build2 (MULT_EXPR, bitsizetype,
> > + DECL_FIELD_OFFSET (rep_decl),
> > + build_int_cst (bitsizetype, 8));
> > + rep_pos = fold_build2 (PLUS_EXPR, bitsizetype, rep_pos,
> > + DECL_FIELD_BIT_OFFSET (rep_decl));
> >
> > you can use the invariant that DECL_FIELD_OFFSET of rep_decl
> > and field_decl are always the same. Also please use BITS_PER_UNIT
> > instead of '8'.
> >
> > Richard.
>
--
Richard Biener <rguent...@suse.de>
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