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.