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* [Bug tree-optimization/99756] New: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional
@ 2021-03-24 23:48 msebor at gcc dot gnu.org
2021-03-24 23:51 ` [Bug tree-optimization/99756] " msebor at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-03-24 23:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99756
Bug ID: 99756
Summary: bogus -Wmaybe-uninitialized with a use conditional
that's a subset of a defining conditional
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The following code triggers a spurious -Wmaybe-uninitialized. There are two
underlying problems: one is a limitation of the uninitialized pass and another
is a missed optimization opportunity described in PR 99755 (the second test for
k results in another read from it instead of reusing the value read previously
in the first conditional).
$ cat t.c && gcc -O2 -S -Wall t.c
extern int a[], i, j, k;
void f (void)
{
int x;
if (i > 1 && j > 2 && k > 3)
x = i + 1;
if (i == 2 && j == 3 && k == 4)
a[x] = 0; // { dg-bogus "Wmaybe-uninitialized" }
}
t.c: In function ‘f3’:
t.c:28:10: warning: ‘x’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
28 | a[x] = 0; // { dg-bogus "Wmaybe-uninitialized" }
| ~~~~~^~~
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/99756] bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional
2021-03-24 23:48 [Bug tree-optimization/99756] New: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional msebor at gcc dot gnu.org
@ 2021-03-24 23:51 ` msebor at gcc dot gnu.org
2021-11-30 12:12 ` aldyh at gcc dot gnu.org
2021-12-18 11:47 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-03-24 23:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99756
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
Depends on| |99755
Blocks| |24639
Known to fail| |10.2.0, 11.0, 4.1.0, 4.8.4,
| |4.9.4, 5.5.0, 6.4.0, 7.2.0,
| |8.3.0, 9.1.0
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The spurious warning goes as far back as GCC 4.1. It can be avoided either by
improving the optimization or by changing tree-ssa-uninit.c.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
[Bug 24639] [meta-bug] bug to track all Wuninitialized issues
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99755
[Bug 99755] failure to fold a conditional that's a subset of another expression
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/99756] bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional
2021-03-24 23:48 [Bug tree-optimization/99756] New: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional msebor at gcc dot gnu.org
2021-03-24 23:51 ` [Bug tree-optimization/99756] " msebor at gcc dot gnu.org
@ 2021-11-30 12:12 ` aldyh at gcc dot gnu.org
2021-12-18 11:47 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: aldyh at gcc dot gnu.org @ 2021-11-30 12:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99756
Aldy Hernandez <aldyh at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
CC| |aldyh at gcc dot gnu.org
Resolution|--- |FIXED
--- Comment #2 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Fixed in trunk by one of the various improvements to the jump threader:
abulafia:~/bld/t/gcc$ ./cc1 a.c -O2 -Wall -quiet
abulafia:~/bld/t/gcc$ ./cc1 a.c -O2 -Wall -quiet -fno-thread-jumps
a.c: In function ‘f’:
a.c:10:10: warning: ‘x’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
10 | a[x] = 0; // { dg-bogus "Wmaybe-uninitialized" }
| ~~~~~^~~
a.c:5:7: note: ‘x’ was declared here
5 | int x;
| ^
abulafia:~/bld/t/gcc$
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/99756] bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional
2021-03-24 23:48 [Bug tree-optimization/99756] New: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional msebor at gcc dot gnu.org
2021-03-24 23:51 ` [Bug tree-optimization/99756] " msebor at gcc dot gnu.org
2021-11-30 12:12 ` aldyh at gcc dot gnu.org
@ 2021-12-18 11:47 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-12-18 11:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99756
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.0
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-03-24 23:48 [Bug tree-optimization/99756] New: bogus -Wmaybe-uninitialized with a use conditional that's a subset of a defining conditional msebor at gcc dot gnu.org
2021-03-24 23:51 ` [Bug tree-optimization/99756] " msebor at gcc dot gnu.org
2021-11-30 12:12 ` aldyh at gcc dot gnu.org
2021-12-18 11:47 ` pinskia at gcc dot gnu.org
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