[Bug tree-optimization/105237] Missing uninitialized warning in self-initialization case

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105237

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-04-12
             Blocks|                            |24639

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
If you enable optimization (inlining in this case) the warning is shown:

> gcc-11 -S t2.c -Wall -O
t2.c: In function 'test':
t2.c:2:28: warning: 'n' is used uninitialized [-Wuninitialized]
    2 | int negate(int n) { return -n; }
      |                            ^~
t2.c:8:13: note: 'n' was declared here
    8 |         int n = negate(n); // n used before initialization
      |             ^

without optimization we are confused by the loop and limited flow analysis.

The

 int n = n;

case is a GCC extension to silence uninit diagnostics


Confirmed at -O0.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639
[Bug 24639] [meta-bug] bug to track all Wuninitialized issues