Richard Earnshaw via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> gen_lowpart_general handles forming a lowpart of a MEM by using
> adjust_address to rework and validate a new version of the MEM.
> Do the same for gen_highpart rather than calling simplify_gen_subreg
> for this case.
Looks OK, but what went wrong with the existing code? Did
simplify_gen_subreg refuse to handle a MEM that you wanted
it to handle, or did the validize_mem go wrong for some reason?
Thanks,
Richard
> gcc/ChangeLog:
>
> PR target/102125
> * emit-rtl.c (gen_highpart): Use adjust_address to handle
> MEM rather than calling simplify_gen_subreg.
> ---
> gcc/emit-rtl.c | 23 +++++++++++++----------
> 1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
> index 77ea8948ee8..0ba110879aa 100644
> --- a/gcc/emit-rtl.c
> +++ b/gcc/emit-rtl.c
> @@ -1585,19 +1585,22 @@ gen_highpart (machine_mode mode, rtx x)
> gcc_assert (known_le (msize, (unsigned int) UNITS_PER_WORD)
> || known_eq (msize, GET_MODE_UNIT_SIZE (GET_MODE (x))));
>
> - result = simplify_gen_subreg (mode, x, GET_MODE (x),
> - subreg_highpart_offset (mode, GET_MODE (x)));
> - gcc_assert (result);
> -
> - /* simplify_gen_subreg is not guaranteed to return a valid operand for
> - the target if we have a MEM. gen_highpart must return a valid operand,
> - emitting code if necessary to do so. */
> - if (MEM_P (result))
> + /* gen_lowpart_common handles a lot of special cases due to needing to
> handle
> + paradoxical subregs; it only calls simplify_gen_subreg when certain that
> + it will produce something meaningful. The only case we need to handle
> + specially here is MEM. */
> + if (MEM_P (x))
> {
> - result = validize_mem (result);
> - gcc_assert (result);
> + poly_int64 offset = subreg_highpart_offset (mode, GET_MODE (x));
> + return adjust_address (x, mode, offset);
> }
>
> + result = simplify_gen_subreg (mode, x, GET_MODE (x),
> + subreg_highpart_offset (mode, GET_MODE (x)));
> + /* Since we handle MEM directly above, we should never get a MEM back
> + from simplify_gen_subreg. */
> + gcc_assert (result && !MEM_P (result));
> +
> return result;
> }
>
