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 <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:ed8e7ece850bab599c15db3d43041b70d9e99237 commit r12-9124-ged8e7ece850bab599c15db3d43041b70d9e99237 Author: Jakub Jelinek <ja...@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 <ja...@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)
