public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
@ 2024-08-19 20:13 zhendong.su at inf dot ethz.ch
2024-08-19 21:16 ` [Bug tree-optimization/116420] [15 Regression] " pinskia at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: zhendong.su at inf dot ethz.ch @ 2024-08-19 20:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
Bug ID: 116420
Summary: wrong code at -O{2,3} with "-fno-forward-propagate
-fno-tree-ch" on x86_64-linux-gnu
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zhendong.su at inf dot ethz.ch
Target Milestone: ---
It appears to be a recent regression as it doesn't reproduce with 14.* and
earlier.
Compiler Explorer: https://godbolt.org/z/zfssY8K95
[524] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/suz-local/software/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/15.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=yes --prefix=/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20240819 (experimental) (GCC)
[525] %
[525] % gcctk -O2 small.c; ./a.out
[526] %
[526] % gcctk -O2 -fno-forward-propagate -fno-tree-ch small.c
[527] % ./a.out
Aborted
[528] % cat small.c
int a, d, e;
char b = -1, c, f;
int main() {
int g;
for (; d < 1; d++) {
g = b;
for (; c; c = g)
;
}
f = g;
for (; e < 1; e++)
if (g >= a)
__builtin_abort();
return 0;
}
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
@ 2024-08-19 21:16 ` pinskia at gcc dot gnu.org
2024-08-19 21:19 ` pinskia at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-08-19 21:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|wrong code at -O{2,3} with |[15 Regression] wrong code
|"-fno-forward-propagate |at -O{2,3} with
|-fno-tree-ch" on |"-fno-forward-propagate
|x86_64-linux-gnu |-fno-tree-ch" on
| |x86_64-linux-gnu
Target| |x86_64-linux-gnu
Target Milestone|--- |15.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug tree-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2024-08-19 21:16 ` [Bug tree-optimization/116420] [15 Regression] " pinskia at gcc dot gnu.org
@ 2024-08-19 21:19 ` pinskia at gcc dot gnu.org
2024-08-20 7:36 ` [Bug rtl-optimization/116420] " rguenth at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-08-19 21:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
CC| |law at gcc dot gnu.org
Last reconfirmed| |2024-08-19
Status|UNCONFIRMED |NEW
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. -fno-ext-dce makes the failure go away.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2024-08-19 21:16 ` [Bug tree-optimization/116420] [15 Regression] " pinskia at gcc dot gnu.org
2024-08-19 21:19 ` pinskia at gcc dot gnu.org
@ 2024-08-20 7:36 ` rguenth at gcc dot gnu.org
2024-08-22 14:07 ` law at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-08-20 7:36 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P1
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
` (2 preceding siblings ...)
2024-08-20 7:36 ` [Bug rtl-optimization/116420] " rguenth at gcc dot gnu.org
@ 2024-08-22 14:07 ` law at gcc dot gnu.org
2024-08-22 14:42 ` law at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: law at gcc dot gnu.org @ 2024-08-22 14:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |law at gcc dot gnu.org
--- Comment #2 from Jeffrey A. Law <law at gcc dot gnu.org> ---
So what's really interesting here is it appears that we're not queuing preds of
the current block for reprocessing during the liveness computation. But it
seems to be specific to a particular pred/succ in a given loop -- the other
loop seems to iterate and reach a fixed point just fine. Weird. But
definitely mine.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
` (3 preceding siblings ...)
2024-08-22 14:07 ` law at gcc dot gnu.org
@ 2024-08-22 14:42 ` law at gcc dot gnu.org
2024-08-22 19:14 ` cvs-commit at gcc dot gnu.org
2024-08-22 19:29 ` law at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: law at gcc dot gnu.org @ 2024-08-22 14:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
--- Comment #3 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Fun.
The DF framework provides us a way to run dataflow problems on sub-graphs.
Naturally a bitmap of interesting blocks is passed into those routines. At a
confluence point, the DF framework will not mark a block for re-processing if
it's not in that set of interesting blocks.
When ext-dce sets up that set of interesting blocks it's using the wrong
counter. ie, it's using n_basic_blocks rather than last_basic_block. If there
are holes in the block indices, some number of blocks won't get marked as
interesting.
In this case the block needing reprocessing has an index higher than
n_basic_blocks. It never gets reprocessed and the newly found live chunks
don't propagate further up the CFG -- ultimately resulting in a pseudo
appearing to have only the low 8 bits live, when in fact the low 32 bits are
actually live.
Testing a pretty obvious fix.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
` (4 preceding siblings ...)
2024-08-22 14:42 ` law at gcc dot gnu.org
@ 2024-08-22 19:14 ` cvs-commit at gcc dot gnu.org
2024-08-22 19:29 ` law at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-08-22 19:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <law@gcc.gnu.org>:
https://gcc.gnu.org/g:c9377734b798d8d311dfd3a5618dc49407703b93
commit r15-3095-gc9377734b798d8d311dfd3a5618dc49407703b93
Author: Jeff Law <jlaw@ventanamicro.com>
Date: Thu Aug 22 12:48:49 2024 -0600
[PR rtl-optimization/116420] Fix interesting block bitmap DF dataflow
The DF framework provides us a way to run dataflow problems on sub-graphs.
Naturally a bitmap of interesting blocks is passed into those routines.
At a
confluence point, the DF framework will not mark a block for re-processing
if
it's not in that set of interesting blocks.
When ext-dce sets up that set of interesting blocks it's using the wrong
counter. ie, it's using n_basic_blocks rather than last_basic_block. If
there
are holes in the block indices, some number of blocks won't get marked as
interesting.
In this case the block needing reprocessing has an index higher than
n_basic_blocks. It never gets reprocessed and the newly found live chunks
don't propagate further up the CFG -- ultimately resulting in a pseudo
appearing to have only the low 8 bits live, when in fact the low 32 bits
are
actually live.
Fixed in the obvious way, by using last_basic_block instead.
Bootstrapped and regression tested on x86_64. Pushing to the trunk.
PR rtl-optimization/116420
gcc/
* ext-dce.cc (ext_dce_init): Fix loop iteration when setting up the
interesting block for DF to analyze.
gcc/testsuite
* gcc.dg/torture/pr116420.c: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/116420] [15 Regression] wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
` (5 preceding siblings ...)
2024-08-22 19:14 ` cvs-commit at gcc dot gnu.org
@ 2024-08-22 19:29 ` law at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: law at gcc dot gnu.org @ 2024-08-22 19:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #5 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Fixed on the trunk.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2024-08-22 19:29 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-08-19 20:13 [Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2024-08-19 21:16 ` [Bug tree-optimization/116420] [15 Regression] " pinskia at gcc dot gnu.org
2024-08-19 21:19 ` pinskia at gcc dot gnu.org
2024-08-20 7:36 ` [Bug rtl-optimization/116420] " rguenth at gcc dot gnu.org
2024-08-22 14:07 ` law at gcc dot gnu.org
2024-08-22 14:42 ` law at gcc dot gnu.org
2024-08-22 19:14 ` cvs-commit at gcc dot gnu.org
2024-08-22 19:29 ` law at gcc dot gnu.org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).