[Bug debug/106719] [10/11/12 Regression] '-fcompare-debug' failure w/ -O2 since r10-6038-ge5e07b68187b9a

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106719

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:ed8e7ece850bab599c15db3d43041b70d9e99237

commit r12-9124-ged8e7ece850bab599c15db3d43041b70d9e99237
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Dec 8 14:57:22 2022 +0100

    cfgbuild: Fix DEBUG_INSN handling in find_bb_boundaries [PR106719]

    The following testcase FAILs on aarch64-linux.  We have some atomic
    instruction followed by 2 DEBUG_INSNs (if -g only of course) followed
    by NOTE_INSN_EPILOGUE_BEG followed by some USE insn.
    Now, split3 pass replaces the atomic instruction with a code sequence
    which ends with a conditional jump and the split3 pass calls
    find_many_sub_basic_blocks.
    For -g0, find_bb_boundaries sees the flow_transfer_insn (the new
conditional
    jump), then NOTE_INSN_EPILOGUE_BEG which can live in between basic blocks
    and then the USE insn, so splits block after the NOTE_INSN_EPILOGUE_BEG
    and puts the NOTE in between the blocks.
    For -g, if sees a DEBUG_INSN after the flow_transfer_insn, so sets
    debug_insn to it, then walks over another DEBUG_INSN,
NOTE_INSN_EPILOGUE_BEG
    until it finally sees the USE insn, and triggers the:
              rtx_insn *prev = PREV_INSN (insn);

              /* If the first non-debug inside_basic_block_p insn after a
control
                 flow transfer is not a label, split the block before the debug
                 insn instead of before the non-debug insn, so that the debug
                 insns are not lost.  */
              if (debug_insn && code != CODE_LABEL && code != BARRIER)
                prev = PREV_INSN (debug_insn);
    code I've added for PR81325.  If there are only DEBUG_INSNs, that is
    the right thing to do, but if in between debug_insn and insn there are
    notes which can stay in between basic blocks or simnilarly JUMP_TABLE_DATA
    or their associated CODE_LABELs, it causes -fcompare-debug differences.

    The following patch fixes it by clearing debug_insn if JUMP_TABLE_DATA
    or associated CODE_LABEL is seen (I'm afraid there is no good answer
    what to do with DEBUG_INSNs before those; the code then removes them:
                  /* Clean up the bb field for the insns between the blocks. 
*/
                  for (x = NEXT_INSN (flow_transfer_insn);
                       x != BB_HEAD (fallthru->dest);
                       x = next)
                    {
                      next = NEXT_INSN (x);
                      /* Debug insns should not be in between basic blocks,
                         drop them on the floor.  */
                      if (DEBUG_INSN_P (x))
                        delete_insn (x);
                      else if (!BARRIER_P (x))
                        set_block_for_insn (x, NULL);
                    }
    but if there are NOTEs, the patch just reorders the NOTEs and DEBUG_INSNs,
    such that the NOTEs come first (so that they stay in between basic blocks
    like with -g0) and DEBUG_INSNs after those (so that bb is split before
    them, so they will be in the basic block after NOTE_INSN_BASIC_BLOCK).

    2022-12-08  Jakub Jelinek  <jakub@redhat.com>

            PR debug/106719
            * cfgbuild.cc (find_bb_boundaries): If there are NOTEs in between
            debug_insn (seen after flow_transfer_insn) and insn, move NOTEs
            before all the DEBUG_INSNs and split after NOTEs.  If there are
            other insns like jump table data, clear debug_insn.

            * gcc.dg/pr106719.c: New test.

    (cherry picked from commit d9f9d5d30feb33c359955d7030cc6be50ef6dc0a)