[Bug c++/107106] New: Incorrect use of uninitialized value warning

[Bug c++/107106] New: Incorrect use of uninitialized value warning

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107106

            Bug ID: 107106
           Summary: Incorrect use of uninitialized value warning
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlame646 at gmail dot com
  Target Milestone: ---

The following program with `-fanalyzer` flag produces incorrect warning. Demo:
https://godbolt.org/z/YWd4cKbGc


```

#include <string>

std::string square(int num) {
    return std::to_string(num * num);
}

```

The warning says:

```
<source>: In function 'std::string square(int)':
<source>:4:36: warning: use of uninitialized value '<unknown>' [CWE-457]
[-Wanalyzer-use-of-uninitialized-value]
    4 |     return std::to_string(num * num);
      |                                    ^
  'std::string square(int)': events 1-2
    |
    |    3 | std::string square(int num) {
    |      |                           ^
    |      |                           |
    |      |                           (1) region created on stack here
    |    4 |     return std::to_string(num * num);
    |      |                                    ~
    |      |                                    |
    |      |                                    (2) use of uninitialized value
'<unknown>' here
    |
<source>:4:36: warning: use of uninitialized value '<unknown>' [CWE-457]
[-Wanalyzer-use-of-uninitialized-value]
    4 |     return std::to_string(num * num);
      |                                    ^
  'std::string square(int)': events 1-2
    |
    |    3 | std::string square(int num) {
    |      |                           ^
    |      |                           |
    |      |                           (1) region created on stack here
    |    4 |     return std::to_string(num * num);
    |      |                                    ~
    |      |                                    |
    |      |                                    (2) use of uninitialized value
'<unknown>' here
    |
```

On searching for possible dupes, i came across this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13025 that may be related to this
bug.

[Bug analyzer/107106] Incorrect use of uninitialized value warning

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107106

David Malcolm <dmalcolm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-09-30
             Blocks|                            |97110

--- Comment #1 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Thanks for filing this bug; confirmed.

Note that the simpler:

std::string square(int num) {
    return std::to_string(num);
}

also gives the warning.

Note that I recommend *not* using -fanalyzer on C++ code for now; see tracker
bug 97110.  I'm guessing the issue is due to -fanalyzer failing to cope with
exceptions and exception-handling (bug 97111).  In the meantime, this is a test
case that we'll eventually want to get working, so keeping open.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97110
[Bug 97110] [meta-bug] tracker bug for supporting C++ in -fanalyzer

[Bug analyzer/107106] Incorrect use of uninitialized value warning on C++

[jg at jguk dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107106

Jonny Grant <jg at jguk dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jg at jguk dot org

--- Comment #2 from Jonny Grant <jg at jguk dot org> ---
I saw this and checked on latest trunk, just sharing as another test case.
If I have -Wno-analyzer-use-of-uninitialized-value it keeps this one quiet


<source>:7:12: warning: use of uninitialized value '<unknown>' [CWE-457]
[-Wanalyzer-use-of-uninitialized-value]
    7 |     return str;


#include <string>

std::string make_str(const char * str)
{
    return str;
}