[BUG] -Wuninitialized: initialize variable with itself

[Andrew Pinski]

On Sun, Nov 13, 2022 at 10:36 AM Alejandro Colomar via Gcc
<gcc@gcc.gnu.org> wrote:
>
> Hi,
>
> While discussing some idea for a new feature, I tested the following example
> program:
>
>
>      int main(void)
>      {
>          int i = i;
>          return i;
>      }

This is NOT a bug but a documented way of having the warning not being there.
See https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/Warning-Options.html#index-Winit-self
https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/Warning-Options.html#index-Wuninitialized
"If you want to warn about code that uses the uninitialized value of
the variable in its own initializer, use the -Winit-self option."

Thanks,
Andrew Pinski

>
>
> It seems obvious that it should give a warning, and in Clang it does:
>
>
>      $ clang --version | head -n1
>      Debian clang version 14.0.6
>
>      $ clang -Wall -Wextra foo.c
>      foo.c:3:10: warning: variable 'i' is uninitialized when used within its own
> initialization [-Wuninitialized]
>              int i = i;
>                  ~   ^
>      1 warning generated.
>
>
> But for GCC it looks fine:
>
>      $ gcc --version | head -n1
>      gcc (Debian 12.2.0-9) 12.2.0
>
>      $ gcc -Wall -Wextra foo.c
>      $
>
>
> Until you enable the analyzer, which catches the uninitialized use:
>
>
>      $ gcc -fanalyzer foo.c
>      foo.c: In function ‘main’:
>      foo.c:3:13: warning: use of uninitialized value ‘i’ [CWE-457]
> [-Wanalyzer-use-of-uninitialized-value]
>          3 |         int i = i;
>            |             ^
>        ‘main’: events 1-2
>          |
>          |    3 |         int i = i;
>          |      |             ^
>          |      |             |
>          |      |             (1) region created on stack here
>          |      |             (2) use of uninitialized value ‘i’ here
>          |
>
>
>
> I expect that GCC should be able to detect this bug with a simple warning.  The
> analyzer is quite unreadable compared to normal warnings.
>
> Cheers,
> Alex
>
> --
> <http://www.alejandro-colomar.es/>