On Mar 1, 2022, Alexandre Oliva <ol...@adacore.com> wrote:
> On Feb 23, 2022, Alexandre Oliva <ol...@adacore.com> wrote:
>> On Feb 21, 2022, Richard Biener <richard.guent...@gmail.com> wrote:
>>>> Ok to revert commit r12-5852-g50e8b0c9bca6cdc57804f860ec5311b641753fbb
>>> OK. Please re-open the bug as appropriate.
>> Thanks. I've reopened it. Here's what I'm installing. I'm not
>> reverting the testcase, since it stopped failing even before the patch
>> was put in.
> And now here's a patch that fixes the underlying issue.
Oops, I missed the important question:
> Undo multi-word optional reloads correctly
> Unlike e.g. remove_inheritance_pseudos, undo_optional_reloads didn't
> deal with subregs, so instead of removing multi-word moves, it
> replaced the reload pseudo with the original pseudo. Besides the
> redundant move, that retained the clobber of the dest, that starts a
> multi-word move. After the remap, the sequence that should have
> become a no-op move starts by clobbering the original pseudo and then
> moving its pieces onto themselves. The problem is the clobber: it
> makes earlier sets of the original pseudo to be regarded as dead: if
> the optional reload sequence was an output reload, the insn for which
> the output reload was attempted may be regarded as dead and deleted.
> I've arranged for undo_optional_reloads to accept SUBREGs and use
> get_regno, like remove_inheritance_pseudo, adjusted its insn-removal
> loop to tolerate iterating over a removed clobber, and added logic to
> catch any left-over reload clobbers that could trigger the problem.
Regstrapped on x86_64-linux-gnu, also tested on various riscv and arm
targets (with gcc-11). Ok to install?
> for gcc/ChangeLog
> * lra-constraints.cc (undo_optional_reloads): Recognize and
> drop insns of multi-word move sequences, tolerate removal
> iteration on an already-removed clobber, and refuse to
> substitute original pseudos into clobbers.
> ---
> gcc/lra-constraints.cc | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
> diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
> index b2c4590153c4c..5cd89e7eeddc2 100644
> --- a/gcc/lra-constraints.cc
> +++ b/gcc/lra-constraints.cc
> @@ -7261,15 +7261,17 @@ undo_optional_reloads (void)
> continue;
> src = SET_SRC (set);
> dest = SET_DEST (set);
> - if (! REG_P (src) || ! REG_P (dest))
> + if ((! REG_P (src) && ! SUBREG_P (src))
> + || (! REG_P (dest) && ! SUBREG_P (dest)))
> continue;
> - if (REGNO (dest) == regno
> + if (get_regno (dest) == (int) regno
> /* Ignore insn for optional reloads itself. */
> - && REGNO (lra_reg_info[regno].restore_rtx) != REGNO (src)
> + && (get_regno (lra_reg_info[regno].restore_rtx)
> + != get_regno (src))
> /* Check only inheritance on last inheritance pass. */
> - && (int) REGNO (src) >= new_regno_start
> + && get_regno (src) >= new_regno_start
> /* Check that the optional reload was inherited. */
> - && bitmap_bit_p (&lra_inheritance_pseudos, REGNO (src)))
> + && bitmap_bit_p (&lra_inheritance_pseudos, get_regno (src)))
> {
> keep_p = true;
> break;
> @@ -7291,18 +7293,22 @@ undo_optional_reloads (void)
> bitmap_copy (insn_bitmap, &lra_reg_info[regno].insn_bitmap);
> EXECUTE_IF_SET_IN_BITMAP (insn_bitmap, 0, uid, bi2)
> {
> + /* We may have already removed a clobber. */
> + if (!lra_insn_recog_data[uid])
> + continue;
> insn = lra_insn_recog_data[uid]->insn;
> if ((set = single_set (insn)) != NULL_RTX)
> {
> src = SET_SRC (set);
> dest = SET_DEST (set);
> - if (REG_P (src) && REG_P (dest)
> - && ((REGNO (src) == regno
> - && (REGNO (lra_reg_info[regno].restore_rtx)
> - == REGNO (dest)))
> - || (REGNO (dest) == regno
> - && (REGNO (lra_reg_info[regno].restore_rtx)
> - == REGNO (src)))))
> + if ((REG_P (src) || SUBREG_P (src))
> + && (REG_P (dest) || SUBREG_P (dest))
> + && ((get_regno (src) == (int) regno
> + && (get_regno (lra_reg_info[regno].restore_rtx)
> + == get_regno (dest)))
> + || (get_regno (dest) == (int) regno
> + && (get_regno (lra_reg_info[regno].restore_rtx)
> + == get_regno (src)))))
> {
> if (lra_dump_file != NULL)
> {
> @@ -7310,7 +7316,7 @@ undo_optional_reloads (void)
> INSN_UID (insn));
> dump_insn_slim (lra_dump_file, insn);
> }
> - delete_move_and_clobber (insn, REGNO (dest));
> + delete_move_and_clobber (insn, get_regno (dest));
> continue;
> }
> /* We should not worry about generation memory-memory
> @@ -7319,6 +7325,11 @@ undo_optional_reloads (void)
> we remove the inheritance pseudo and the optional
> reload. */
> }
> + if (GET_CODE (PATTERN (insn)) == CLOBBER
> + && REG_P (SET_DEST (insn))
> + && get_regno (SET_DEST (insn)) == (int) regno)
> + /* Refuse to remap clobbers to preexisting pseudos. */
> + gcc_unreachable ();
> lra_substitute_pseudo_within_insn
> (insn, regno, lra_reg_info[regno].restore_rtx, false);
> lra_update_insn_regno_info (insn);
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
