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* [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary
@ 2024-03-06 11:27 overdijk at gmail dot com
2024-03-06 11:28 ` [Bug tree-optimization/114253] " overdijk at gmail dot com
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: overdijk at gmail dot com @ 2024-03-06 11:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114253
Bug ID: 114253
Summary: False positive maybe-uninitialized with std::optional
and ternary
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: overdijk at gmail dot com
Target Milestone: ---
The following warning is reported:
> mwe.cpp: In function ‘int main()’:
> mwe.cpp:26:13: warning: ‘pid’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> kill_pid(*pid);
> ~~~~~~~~^~~~~~
When compiling this minimum working example:
````````````````````
#include <string>
#include <optional>
std::optional<int> get_pid()
{
return std::nullopt;
}
void kill_pid(int)
{
}
int main()
{
std::string s;
volatile bool is_running = true;
std::optional<int> pid = is_running ? get_pid() : std::nullopt;
kill_pid(0);
if (pid)
kill_pid(*pid); // no warning
if (pid)
kill_pid(*pid); // warning: 'pid' may be used uninitialized in this
function [-Wmaybe-uninitialized]
}
````````````````````
With the following compiler command line:
$ g++ -std=c++17 -O1 -fPIC -Wmaybe-uninitialized mwe.cpp
I think it is a false positive, since *pid is only used after verifying that it
is valid.
If any of these changes are made, the warning is no longer reported:
* Replace std::optional<int> by a plain int*
* Remove the std::string variable (or replace it by something simple such as
int)
* Remove the first or second call to kill_pid
* Changing the ternary (e.g. `is_running ? std::optional<int>{999} :
std::nullopt`)
* Removing -O1 or -fPIC from the command line (a higher optimization level is
fine)
I observed it with gcc 8.3.0, but it can be reproduced with gcc 8.1 through
13.2 as can be seen on godbolt:
https://godbolt.org/z/TYqYdfc77
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/114253] False positive maybe-uninitialized with std::optional and ternary
2024-03-06 11:27 [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary overdijk at gmail dot com
@ 2024-03-06 11:28 ` overdijk at gmail dot com
2024-03-06 11:31 ` overdijk at gmail dot com
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: overdijk at gmail dot com @ 2024-03-06 11:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114253
--- Comment #1 from Frank Overdijk <overdijk at gmail dot com> ---
Created attachment 57629
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57629&action=edit
Preprocessed minimum working example
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/114253] False positive maybe-uninitialized with std::optional and ternary
2024-03-06 11:27 [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary overdijk at gmail dot com
2024-03-06 11:28 ` [Bug tree-optimization/114253] " overdijk at gmail dot com
@ 2024-03-06 11:31 ` overdijk at gmail dot com
2024-03-06 11:43 ` rguenth at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: overdijk at gmail dot com @ 2024-03-06 11:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114253
--- Comment #2 from Frank Overdijk <overdijk at gmail dot com> ---
Created attachment 57630
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57630&action=edit
Verbose compiler output
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/114253] False positive maybe-uninitialized with std::optional and ternary
2024-03-06 11:27 [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary overdijk at gmail dot com
2024-03-06 11:28 ` [Bug tree-optimization/114253] " overdijk at gmail dot com
2024-03-06 11:31 ` overdijk at gmail dot com
@ 2024-03-06 11:43 ` rguenth at gcc dot gnu.org
2024-03-07 3:14 ` pinskia at gcc dot gnu.org
2024-03-07 3:21 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-03-06 11:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114253
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Known to work| |7.5.0
Blocks| |24639
Last reconfirmed| |2024-03-06
Known to fail| |12.3.1, 13.2.1, 14.0
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
[Bug 24639] [meta-bug] bug to track all Wuninitialized issues
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/114253] False positive maybe-uninitialized with std::optional and ternary
2024-03-06 11:27 [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary overdijk at gmail dot com
` (2 preceding siblings ...)
2024-03-06 11:43 ` rguenth at gcc dot gnu.org
@ 2024-03-07 3:14 ` pinskia at gcc dot gnu.org
2024-03-07 3:21 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-07 3:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114253
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
VIEW_CONVERT_EXPR<bool>(pid$4_26)
Where I have seen this before ...
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/114253] False positive maybe-uninitialized with std::optional and ternary
2024-03-06 11:27 [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary overdijk at gmail dot com
` (3 preceding siblings ...)
2024-03-07 3:14 ` pinskia at gcc dot gnu.org
@ 2024-03-07 3:21 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-03-07 3:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114253
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
```
<bb 6> [local count: 1073741824]:
# pid_16 = PHI <pid_25(4), pid_24(D)(5)>
# pid$4_26 = PHI <pid$4_10(4), 0(5)>
kill_pid (0);
goto <bb 8>; [100.00%]
<bb 7> [count: 0]:
<L13>:
goto <bb 15>; [100.00%]
<bb 8> [local count: 1073741824]:
_12 = VIEW_CONVERT_EXPR<bool>(pid$4_26);
if (_12 != 0)
goto <bb 9>; [33.00%]
else
goto <bb 16>; [67.00%]
<bb 9> [local count: 354334800]:
kill_pid (pid_16);
goto <bb 11>; [100.00%]
```
Funny if we turn off SRA we get:
```
<bb 8> [local count: 354334800]:
_2 = MEM[(int &)&pid];
kill_pid (_2);
goto <bb 10>; [100.00%]
<bb 9> [count: 0]:
<L14>:
goto <bb 14>; [100.00%]
<bb 10> [local count: 536870912]:
kill_pid (_2);
<bb 17> [local count: 536870912]:
goto <bb 12>; [100.00%]
```
(note bb9/bb17 here looks to be landing pads for EH).
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2024-03-07 3:21 UTC | newest]
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2024-03-06 11:27 [Bug tree-optimization/114253] New: False positive maybe-uninitialized with std::optional and ternary overdijk at gmail dot com
2024-03-06 11:28 ` [Bug tree-optimization/114253] " overdijk at gmail dot com
2024-03-06 11:31 ` overdijk at gmail dot com
2024-03-06 11:43 ` rguenth at gcc dot gnu.org
2024-03-07 3:14 ` pinskia at gcc dot gnu.org
2024-03-07 3:21 ` pinskia at gcc dot gnu.org
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