On Tue, 30 Aug 2022, Richard Sandiford wrote:
> Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > On Tue, 30 Aug 2022, Tamar Christina wrote:
> >
> >> Hi All,
> >>
> >> This initializes regnum to 0 for when undefined_p.
> >> 0 is the right default as it's supposed to get the lowpart
> >> when undefined.
> >>
> >> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> >>
> >> Ok for master?
> >
> > OK.
>
> I'm not sure this is the right fix. We were still supposed to use the
> correct byte offset in the undefined case.
>
> Is the attached OK? Tested on aarch64-linux-gnu.
OK.
Thanks,
Richard.
> Thanks,
> Richard
>
> ----------------------
>
> store_bit_field_1 tries to convert a field assignment into a subreg
> assignment. Normally it must check that the field occupies a full
> word (or more specifically, a full REGMODE_NATURAL_SIZE chunk),
> so that writing to the subreg doesn't clobber any other fields.
> But it can skip that check if the structure is known to be in
> an undefined state.
>
> The idea was that, in the undefined case, we could rely on
> simplify_gen_subreg to do the check for a valid subreg, rather
> than having to repeat the required endianness logic in the caller.
>
> Before the addition of the undefined case, the code could use
> regnum * regsize to get the byte offset, where regnum came from
> checking that the start was word-aligned. In the undefined case
> we need to calculate the byte offset explicitly.
>
> gcc/
> * expmed.cc (store_bit_field_1): Fix byte offset calculation
> for undefined structures.
> ---
> gcc/expmed.cc | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/expmed.cc b/gcc/expmed.cc
> index 8d7418be418..6c02c3bb850 100644
> --- a/gcc/expmed.cc
> +++ b/gcc/expmed.cc
> @@ -794,7 +794,7 @@ store_bit_field_1 (rtx str_rtx, poly_uint64 bitsize,
> poly_uint64 bitnum,
> words or to cope with mode punning between equal-sized modes.
> In the latter case, use subreg on the rhs side, not lhs. */
> rtx sub;
> - HOST_WIDE_INT regnum;
> + poly_uint64 bytenum;
> poly_uint64 regsize = REGMODE_NATURAL_SIZE (GET_MODE (op0));
> if (known_eq (bitnum, 0U)
> && known_eq (bitsize, GET_MODE_BITSIZE (GET_MODE (op0))))
> @@ -808,13 +808,13 @@ store_bit_field_1 (rtx str_rtx, poly_uint64 bitsize,
> poly_uint64 bitnum,
> return true;
> }
> }
> - else if (((constant_multiple_p (bitnum, regsize * BITS_PER_UNIT,
> ®num)
> - && multiple_p (bitsize, regsize * BITS_PER_UNIT))
> - || undefined_p)
> + else if (multiple_p (bitnum, BITS_PER_UNIT, &bytenum)
> + && (undefined_p
> + || (multiple_p (bitnum, regsize * BITS_PER_UNIT)
> + && multiple_p (bitsize, regsize * BITS_PER_UNIT)))
> && known_ge (GET_MODE_BITSIZE (GET_MODE (op0)), bitsize))
> {
> - sub = simplify_gen_subreg (fieldmode, op0, GET_MODE (op0),
> - regnum * regsize);
> + sub = simplify_gen_subreg (fieldmode, op0, GET_MODE (op0), bytenum);
> if (sub)
> {
> if (reverse)
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
