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* [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
@ 2022-02-09 11:43 asolokha at gmx dot com
2022-02-09 12:03 ` [Bug rtl-optimization/104459] " rguenth at gcc dot gnu.org
` (8 more replies)
0 siblings, 9 replies; 10+ messages in thread
From: asolokha at gmx dot com @ 2022-02-09 11:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Bug ID: 104459
Summary: [9/10/11/12 Regression] '-fcompare-debug' failure w/
-O2 -funswitch-loops -fno-tree-dce
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: compare-debug-failure
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: asolokha at gmx dot com
Target Milestone: ---
gcc 12.0.1 20220206 snapshot (g:8eb329e963593342855b6072e5692659107337b7) fails
-fcompare-debug check when compiling the following testcase w/ -O2
-funswitch-loops -fno-tree-dce:
void
foo (int x, int y)
{
unsigned int a;
for (;;)
{
short int *p = (short int *) &x;
unsigned int q = 0;
a /= 2;
if (a)
{
q -= y;
while (q)
{
}
}
if (x)
{
for (q = 0; q != 1; q += 2)
{
unsigned int n;
n = *p ? 0 : q;
y += n < 1;
n = a || *p;
if (n % x == 0)
y /= x;
}
}
}
}
% gcc-12.0.1 -O2 -fcompare-debug -funswitch-loops -fno-tree-dce -c rfygrmu3.c
gcc-12.0.1: error: rfygrmu3.c: '-fcompare-debug' failure
--- rfygrmu3.c.gkd 2022-02-09 18:38:41.086339468 +0700
+++ rfygrmu3.gk.c.gkd 2022-02-09 18:38:41.117339440 +0700
@@ -32,7 +32,7 @@
(pc))) "rfygrmu3.c":20:10# {*jcc}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(int_list:REG_BR_PROB 118111604 (nil)))
- -> 18)
+ -> 19)
(code_label # 0 0 4 4 (nil) [1 uses])
(note # 0 0 [bb 4] NOTE_INSN_BASIC_BLOCK)
(insn:TI # 0 0 4 (set (reg/v:SI 36 r8 [orig:89 a ] [89])
@@ -79,7 +79,7 @@
(nil)
-> 3)
(barrier # 0 0)
-(code_label # 0 0 7 18 (nil) [1 uses])
+(code_label # 0 0 7 19 (nil) [1 uses])
(note # 0 0 [bb 7] NOTE_INSN_BASIC_BLOCK)
(insn:TI # 0 0 7 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:HI 5 di [orig:94 x ] [94])
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
@ 2022-02-09 12:03 ` rguenth at gcc dot gnu.org
2022-02-09 18:56 ` jakub at gcc dot gnu.org
` (7 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-02-09 12:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Target Milestone|--- |9.5
Last reconfirmed| |2022-02-09
Component|debug |rtl-optimization
Priority|P3 |P2
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. On the GIMPLE level there are no differences. The compare fail
might be spurious though.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
2022-02-09 12:03 ` [Bug rtl-optimization/104459] " rguenth at gcc dot gnu.org
@ 2022-02-09 18:56 ` jakub at gcc dot gnu.org
2022-02-09 19:07 ` jakub at gcc dot gnu.org
` (6 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-02-09 18:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The divergence starts during jump_after_combine.
With -g0, cfg_layout_merge_blocks is called on
(note 53 51 56 13 [bb 13] NOTE_INSN_BASIC_BLOCK)
and
(code_label 56 53 57 14 8 (nil) [0 uses])
(note 57 56 79 14 [bb 14] NOTE_INSN_BASIC_BLOCK)
while with -g on:
(note 91 89 92 13 [bb 13] NOTE_INSN_BASIC_BLOCK)
(debug_insn 92 91 93 13 (var_location:SI n (clobber (const_int 0 [0])))
"pr104459.c":29:17 -1
(nil))
(debug_insn 93 92 135 13 (debug_marker) "pr104459.c":31:17 -1
(nil))
(debug_insn 135 93 96 13 (var_location:SI D#3 (clobber (const_int 0 [0]))) -1
(nil))
(debug_insn 96 135 97 13 (var_location:SI y (debug_expr:SI D#3))
"pr104459.c":31:19 -1
(nil))
and
(code_label 97 96 98 14 8 (nil) [0 uses])
(note 98 97 99 14 [bb 14] NOTE_INSN_BASIC_BLOCK)
(debug_insn 99 98 100 14 (var_location:SI y (clobber (const_int 0 [0]))) -1
(nil))
(debug_insn 100 99 102 14 (debug_marker) "pr104459.c":22:33 -1
(nil))
(debug_insn 102 100 133 14 (var_location:SI q (clobber (const_int 0 [0])))
"pr104459.c":22:33 -1
(nil))
That function calls update_bb_for_insn_chain for note 98 through 102 for -g and
note 57 through note 57 for -g0.
547 end = NEXT_INSN (end);
548 for (insn = begin; insn != end; insn = NEXT_INSN (insn))
549 if (!BARRIER_P (insn))
550 df_insn_change_bb (insn, bb);
which means that for -g0 df_insn_change_bb isn't called, while for -g it is.
df_insn_change_bb in turn calls df_set_bb_dirty and that sets bb(14)->flags |=
BB_MODIFIED.
Unfortunately, cfgcleanup.cc uses the BB_MODIFIED flag to decide on some stuff:
try_forward_edges has:
bool may_thread = first_pass || (b->flags & BB_MODIFIED) != 0;
and
may_thread |= (target->flags & BB_MODIFIED) != 0;
and try_crossjump_bb has:
/* If nothing changed since the last attempt, there is nothing
we can do. */
if (!first_pass
&& !((e->src->flags & BB_MODIFIED)
|| (fallthru->src->flags & BB_MODIFIED)))
continue;
and
/* If nothing changed since the last attempt, there is nothing
we can do. */
if (!first_pass
&& !((e->src->flags & BB_MODIFIED)
|| (e2->src->flags & BB_MODIFIED)))
continue;
Seems this has been introduced in
https://gcc.gnu.org/legacy-ml/gcc-patches/2010-08/txt00014.txt
but before that we were using equally problematic df_get_bb_dirty.
As BB_MODIFIED is only used in those places:
cfgcleanup.cc: bool may_thread = first_pass || (b->flags & BB_MODIFIED) !=
0;
cfgcleanup.cc: may_thread |= (target->flags & BB_MODIFIED) != 0;
cfgcleanup.cc: && !((e->src->flags & BB_MODIFIED)
cfgcleanup.cc: || (fallthru->src->flags & BB_MODIFIED)))
cfgcleanup.cc: && !((e->src->flags & BB_MODIFIED)
cfgcleanup.cc: || (e2->src->flags & BB_MODIFIED)))
df-core.cc: bb->flags |= BB_MODIFIED;
I think best would be to introduce df_set_bb_dirty_for_debug or similar variant
to df_set_bb_dirty that wouldn't set the BB_MODIFIED flag, and use that in
df_insn_change_bb.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
2022-02-09 12:03 ` [Bug rtl-optimization/104459] " rguenth at gcc dot gnu.org
2022-02-09 18:56 ` jakub at gcc dot gnu.org
@ 2022-02-09 19:07 ` jakub at gcc dot gnu.org
2022-02-09 19:13 ` jakub at gcc dot gnu.org
` (5 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-02-09 19:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
On the other side, df-scan.cc does in 3 other spots:
/* By adding the ref directly, df_insn_rescan my not find any
differences even though the block will have changed. So we need
to mark the block dirty ourselves. */
if (!DEBUG_INSN_P (DF_REF_INSN (ref)))
df_set_bb_dirty (bb);
and
/* The block must be marked as dirty now, rather than later as in
df_insn_rescan and df_notes_rescan because it may not be there at
rescanning time and the mark would blow up.
DEBUG_INSNs do not make a block's data flow solution dirty (at
worst the LUIDs are no longer contiguous). */
if (bb != NULL && NONDEBUG_INSN_P (insn))
df_set_bb_dirty (bb);
and
if (!DEBUG_INSN_P (insn))
df_set_bb_dirty (bb);
so I wonder if another fix wouldn't be just not call df_set_bb_dirty on
DEBUG_INSN_P in df_insn_change_bb. But what do I know about df :(.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
` (2 preceding siblings ...)
2022-02-09 19:07 ` jakub at gcc dot gnu.org
@ 2022-02-09 19:13 ` jakub at gcc dot gnu.org
2022-02-11 10:24 ` cvs-commit at gcc dot gnu.org
` (4 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-02-09 19:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |aoliva at gcc dot gnu.org
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
See e.g. https://gcc.gnu.org/legacy-ml/gcc-patches/2010-10/msg00059.html
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
` (3 preceding siblings ...)
2022-02-09 19:13 ` jakub at gcc dot gnu.org
@ 2022-02-11 10:24 ` cvs-commit at gcc dot gnu.org
2022-02-11 11:00 ` [Bug rtl-optimization/104459] [9/10/11 " jakub at gcc dot gnu.org
` (3 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-02-11 10:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:
https://gcc.gnu.org/g:18c8086d65f3d539e065ea7c97e3de6f3bbdf684
commit r12-7194-g18c8086d65f3d539e065ea7c97e3de6f3bbdf684
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Feb 11 11:21:24 2022 +0100
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.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [9/10/11 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
` (4 preceding siblings ...)
2022-02-11 10:24 ` cvs-commit at gcc dot gnu.org
@ 2022-02-11 11:00 ` jakub at gcc dot gnu.org
2022-05-27 9:47 ` [Bug rtl-optimization/104459] [10/11 " rguenth at gcc dot gnu.org
` (2 subsequent siblings)
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-02-11 11:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[9/10/11/12 Regression] |[9/10/11 Regression]
|'-fcompare-debug' failure |'-fcompare-debug' failure
|w/ -O2 -funswitch-loops |w/ -O2 -funswitch-loops
|-fno-tree-dce |-fno-tree-dce
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed on the trunk. I'll prefer to wait quite a long before considering to
backport this though.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [10/11 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
` (5 preceding siblings ...)
2022-02-11 11:00 ` [Bug rtl-optimization/104459] [9/10/11 " jakub at gcc dot gnu.org
@ 2022-05-27 9:47 ` rguenth at gcc dot gnu.org
2022-06-28 10:48 ` jakub at gcc dot gnu.org
2023-07-07 10:42 ` [Bug rtl-optimization/104459] [11 " rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-05-27 9:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.5 |10.4
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [10/11 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
` (6 preceding siblings ...)
2022-05-27 9:47 ` [Bug rtl-optimization/104459] [10/11 " rguenth at gcc dot gnu.org
@ 2022-06-28 10:48 ` jakub at gcc dot gnu.org
2023-07-07 10:42 ` [Bug rtl-optimization/104459] [11 " rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: jakub at gcc dot gnu.org @ 2022-06-28 10:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.4 |10.5
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.
^ permalink raw reply [flat|nested] 10+ messages in thread
* [Bug rtl-optimization/104459] [11 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce
2022-02-09 11:43 [Bug debug/104459] New: [9/10/11/12 Regression] '-fcompare-debug' failure w/ -O2 -funswitch-loops -fno-tree-dce asolokha at gmx dot com
` (7 preceding siblings ...)
2022-06-28 10:48 ` jakub at gcc dot gnu.org
@ 2023-07-07 10:42 ` rguenth at gcc dot gnu.org
8 siblings, 0 replies; 10+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-07-07 10:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104459
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.5 |11.5
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.
^ permalink raw reply [flat|nested] 10+ messages in thread
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2022-02-09 12:03 ` [Bug rtl-optimization/104459] " rguenth at gcc dot gnu.org
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