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* [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher
@ 2023-01-19 16:08 vincent-gcc at vinc17 dot net
2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: vincent-gcc at vinc17 dot net @ 2023-01-19 16:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467
Bug ID: 108467
Summary: false positive -Wmaybe-uninitialized warning at -O1 or
higher
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent-gcc at vinc17 dot net
Target Milestone: ---
Consider the following code, derived from MPFR's sub1sp.c (where the issue
occurred since at least GCC 4.9.4 and the warning was silenced with the "sh =
sh" trick via an INITIALIZED() macro):
extern long emin;
extern long emax;
int f(void);
int g(void)
{
int sh, rb, sb;
if (f())
rb = sb = 0;
else
{
sh = f();
sb = f();
rb = f();
}
(0 >= emin && 0 <= emax) || (f(), __builtin_unreachable(), 0);
if (rb == 0 && sb == 0)
return 0;
else
return sh;
}
With gcc-12 (Debian 12.2.0-14) 12.2.0, I get:
$ gcc-12 -O2 -Wmaybe-uninitialized -c tst.c
tst.c: In function ‘g’:
tst.c:23:12: warning: ‘sh’ may be used uninitialized [-Wmaybe-uninitialized]
23 | return sh;
| ^~
tst.c:8:7: note: ‘sh’ was declared here
8 | int sh, rb, sb;
| ^~
The warning also occurs at -O1 and -O3. It disappears if I slightly modify the
code.
Note: During the code reduction, I also got the warning, but with a different
location. However, the code was more complex, and I've already reported
PR108466 about a location issue (where the -Wmaybe-uninitialized is correct).
So I haven't reported an additional issue about the location.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher
2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net
@ 2023-01-19 16:15 ` pinskia at gcc dot gnu.org
2023-01-20 8:28 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-01-19 16:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Known to fail| |4.1.2
Last reconfirmed| |2023-01-19
Status|UNCONFIRMED |NEW
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
After normalization [USE]:
_7 = PHI <0(13), sh_4(8)>
is conditional on:
((NOT (_3 == 0)) AND (emax.3_2 >= 0) AND (emin.2_1 <= 0))
_3 = rb_5 | sb_6;
if (_3 == 0)
Confirmed.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher
2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net
2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org
@ 2023-01-20 8:28 ` rguenth at gcc dot gnu.org
2024-06-15 2:07 ` sjames at gcc dot gnu.org
2024-06-15 9:41 ` vincent-gcc at vinc17 dot net
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-01-20 8:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
There's some special code dealing with checking on a conditional set value
but that's confused by the two-value guard here.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher
2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net
2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org
2023-01-20 8:28 ` rguenth at gcc dot gnu.org
@ 2024-06-15 2:07 ` sjames at gcc dot gnu.org
2024-06-15 9:41 ` vincent-gcc at vinc17 dot net
3 siblings, 0 replies; 5+ messages in thread
From: sjames at gcc dot gnu.org @ 2024-06-15 2:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467
Sam James <sjames at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |sjames at gcc dot gnu.org
--- Comment #3 from Sam James <sjames at gcc dot gnu.org> ---
For 14/15, it seems gone with -O2, but I see it with -Og.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher
2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net
` (2 preceding siblings ...)
2024-06-15 2:07 ` sjames at gcc dot gnu.org
@ 2024-06-15 9:41 ` vincent-gcc at vinc17 dot net
3 siblings, 0 replies; 5+ messages in thread
From: vincent-gcc at vinc17 dot net @ 2024-06-15 9:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467
--- Comment #4 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Sam James from comment #3)
> For 14/15, it seems gone with -O2, but I see it with -Og.
The warning still occurs with -O1 too.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-06-15 9:41 UTC | newest]
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2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net
2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org
2023-01-20 8:28 ` rguenth at gcc dot gnu.org
2024-06-15 2:07 ` sjames at gcc dot gnu.org
2024-06-15 9:41 ` vincent-gcc at vinc17 dot net
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