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author | Jakub Jelinek <jakub@redhat.com> | 2022-02-11 11:21:24 +0100 |
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committer | Jakub Jelinek <jakub@redhat.com> | 2022-02-11 11:21:24 +0100 |
commit | 18c8086d65f3d539e065ea7c97e3de6f3bbdf684 (patch) | |
tree | 3c9dbf530c21e03043e9326360577c2a89c84a65 /gcc/df-scan.cc | |
parent | 165947fecf4d78c7effb0f1ee15e6942d8dce4ea (diff) | |
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df: Don't set bbs dirty because of debug insn moves [PR104459]
As mentioned in the PR, we get -fcompare-debug failure, which is caused by
cfg_layout_merge_blocks successfully merging two bbs where both bbs
contained just CODE_LABEL, NOTE_INSN_BASIC_BLOCK and in the -g case both
some debug insns at the end. cfg_layout_merge_blocks calls
update_bb_for_insn_chain which for the post-label insns in the second block
(except for BARRIERs) calls df_insn_change_bb. This function changes
the bb of the insns and for notes just punts, but for other insns calls
df_set_bb_dirty. Now the problem is that because there were only debug
insns and notes in the second block, df_set_bb_dirty is called on both
only in the -g case and not with -g0. df_set_bb_dirty these days
sets both the BB_MODIFIED flag and marks the bb as dirty, and the former
is what 6 spots in cfgcleanup.cc use in code-generation decisions,
in this case
may_thread |= (target->flags & BB_MODIFIED) != 0;
in particular. So, with -g may_thread is true while with -g0 it is not
and we diverge from that point onwards.
I've thought about introducing df_set_bb_dirty_nondebug that wouldn't
set BB_MODIFIED but would mark the bb dirty, but then I went through
history and found changes like:
https://gcc.gnu.org/legacy-ml/gcc-patches/2010-10/msg00059.html
so I've also tried just not calling df_set_bb_dirty for debug insns
at all and it passed x86_64-linux and i686-linux
--enable-checking=yes,rtl,extra,df bootstraps/regtests, so perhaps
that works too.
Now that I look at it again, if we don't need those from %d to %d messages
for debug insns in the dump files, another way to fix it would be just to
change the very first line in the hunk from
if (!INSN_P (insn))
to
if (!DEBUG_INSN_P (insn))
Though, df_set_bb_dirty_nondebug which will do everything but
set bb->flags |= BB_MODIFIED is yet another option I can test.
Perhaps even that PR42889 was solely about those 6 decisions in cfgcleanup
(at that point it used df_get_bb_dirty) and not about actually the
recomputation of some of the problems causing different code generations.
2022-02-11 Jakub Jelinek <jakub@redhat.com>
PR rtl-optimization/104459
* df-scan.cc (df_insn_change_bb): Don't call df_set_bb_dirty when
moving DEBUG_INSNs between bbs.
* gcc.dg/pr104459.c: New test.
Diffstat (limited to 'gcc/df-scan.cc')
-rw-r--r-- | gcc/df-scan.cc | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/gcc/df-scan.cc b/gcc/df-scan.cc index 5df70e9..9b2375d 100644 --- a/gcc/df-scan.cc +++ b/gcc/df-scan.cc @@ -1769,13 +1769,15 @@ df_insn_change_bb (rtx_insn *insn, basic_block new_bb) if (!INSN_P (insn)) return; - df_set_bb_dirty (new_bb); + if (!DEBUG_INSN_P (insn)) + df_set_bb_dirty (new_bb); if (old_bb) { if (dump_file) fprintf (dump_file, " from %d to %d\n", old_bb->index, new_bb->index); - df_set_bb_dirty (old_bb); + if (!DEBUG_INSN_P (insn)) + df_set_bb_dirty (old_bb); } else if (dump_file) |