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* [Bug c/99944] New: incorrect maybe-uninitialized warning on variable defined as an array
@ 2021-04-06 20:59 vincent-gcc at vinc17 dot net
2021-04-07 7:25 ` [Bug c/99944] " rguenth at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: vincent-gcc at vinc17 dot net @ 2021-04-06 20:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99944
Bug ID: 99944
Summary: incorrect maybe-uninitialized warning on variable
defined as an array
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent-gcc at vinc17 dot net
Target Milestone: ---
Consider the following testcase derived from the initial testcase of PR85777
and its cleaned-up testcase (which is actually a bit different since an enum
was replaced by an int, and it matters here).
int d;
int h(void);
void e1(void)
{
int f[2];
int g = 0;
if (d)
g++;
if (d == 1)
f[g++] = 2;
(void) (f[0] || (g && h()));
}
void e2(void)
{
enum { a } f[2];
int g = 0;
if (d)
g++;
if (d == 1)
f[g++] = a;
(void) (f[0] || (g && h()));
}
With a GCC snapshot built a few hour ago from the master branch:
cventin% gcc --version
gcc (GCC) 11.0.1 20210406 (experimental)
[...]
cventin% gcc -Werror=maybe-uninitialized -O2 -c file.c
file.c: In function ‘e1’:
file.c:11:3: error: ‘f[0]’ may be used uninitialized
[-Werror=maybe-uninitialized]
11 | (void) (f[0] || (g && h()));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
file.c: In function ‘e2’:
file.c:21:3: error: ‘*(unsigned int *)(&f[0])’ may be used uninitialized
[-Werror=maybe-uninitialized]
21 | (void) (f[0] || (g && h()));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
The error for e1 is correct, but not the one for e2 (for e2, previous GCC
versions were outputting ‘f’ instead of ‘*(unsigned int *)(&f[0])’, but this is
about the same thing).
cventin% gcc -Werror=maybe-uninitialized -O2 -c file.c -fsanitize=undefined
file.c: In function ‘e1’:
file.c:11:12: error: ‘f’ may be used uninitialized
[-Werror=maybe-uninitialized]
11 | (void) (f[0] || (g && h()));
| ~^~~
file.c:5:7: note: ‘f’ declared here
5 | int f[2];
| ^
file.c: In function ‘e2’:
file.c:21:12: error: ‘f’ may be used uninitialized
[-Werror=maybe-uninitialized]
21 | (void) (f[0] || (g && h()));
| ~^~~
file.c:15:14: note: ‘f’ declared here
15 | enum { a } f[2];
| ^
cc1: some warnings being treated as errors
Here, with the option -fsanitize=undefined added, both errors are incorrect.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/99944] incorrect maybe-uninitialized warning on variable defined as an array
2021-04-06 20:59 [Bug c/99944] New: incorrect maybe-uninitialized warning on variable defined as an array vincent-gcc at vinc17 dot net
@ 2021-04-07 7:25 ` rguenth at gcc dot gnu.org
2021-04-07 7:41 ` vincent-gcc at vinc17 dot net
2021-04-14 16:38 ` [Bug c/99944] poor format of array reference in -Wuninitialized msebor at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-04-07 7:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99944
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
What's not correct with the diagnostic? The obfuscated printing of f[0]? Or
the misplaced caret?
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/99944] incorrect maybe-uninitialized warning on variable defined as an array
2021-04-06 20:59 [Bug c/99944] New: incorrect maybe-uninitialized warning on variable defined as an array vincent-gcc at vinc17 dot net
2021-04-07 7:25 ` [Bug c/99944] " rguenth at gcc dot gnu.org
@ 2021-04-07 7:41 ` vincent-gcc at vinc17 dot net
2021-04-14 16:38 ` [Bug c/99944] poor format of array reference in -Wuninitialized msebor at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: vincent-gcc at vinc17 dot net @ 2021-04-07 7:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99944
--- Comment #2 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Richard Biener from comment #1)
> What's not correct with the diagnostic? The obfuscated printing of f[0]?
Hmm... for the *(unsigned int *)(&f[0]) case, it is correct after all, though
it should just say f[0].
But in the case with -fsanitize=undefined, gcc says that f may be used
uninitialized. But f is automatically initialized; it is f[0] that may be used
uninitialized.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/99944] poor format of array reference in -Wuninitialized
2021-04-06 20:59 [Bug c/99944] New: incorrect maybe-uninitialized warning on variable defined as an array vincent-gcc at vinc17 dot net
2021-04-07 7:25 ` [Bug c/99944] " rguenth at gcc dot gnu.org
2021-04-07 7:41 ` vincent-gcc at vinc17 dot net
@ 2021-04-14 16:38 ` msebor at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-04-14 16:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99944
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |msebor at gcc dot gnu.org
Severity|normal |minor
Summary|incorrect |poor format of array
|maybe-uninitialized warning |reference in
|on variable defined as an |-Wuninitialized
|array |
Last reconfirmed| |2021-04-14
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
So the issues here are that a) the MEM_REF isn't formatted as neatly as it
could be, and b) that the warning says 'f' when it should mention 'f[0]'. Let
me confirm this on that basis.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-04-14 16:38 UTC | newest]
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2021-04-06 20:59 [Bug c/99944] New: incorrect maybe-uninitialized warning on variable defined as an array vincent-gcc at vinc17 dot net
2021-04-07 7:25 ` [Bug c/99944] " rguenth at gcc dot gnu.org
2021-04-07 7:41 ` vincent-gcc at vinc17 dot net
2021-04-14 16:38 ` [Bug c/99944] poor format of array reference in -Wuninitialized msebor at gcc dot gnu.org
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