[Bug middle-end/55873] New: Missed trivial uninitialized use warning

[Bug middle-end/55873] New: Missed trivial uninitialized use warning

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55873

             Bug #: 55873
           Summary: Missed trivial uninitialized use warning
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: steven@gcc.gnu.org


extern int foo (int);
int foo (int c)
{
  int res;
  if (c)
    res = 0;
  return res;
}

res may be used uninitialized if c==0, but the function is "optimized" to
"return 0" before the uninit1 warning pass runs.

[Bug middle-end/55873] Missed trivial uninitialized use warning

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55873

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |WONTFIX

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-04 11:46:06 UTC ---
It's conditionally uninitialized and thus only warned in late uninit pass.
This is a known issue of optimistic constant propagation.

Duplicate of PRxyz.  Never going to be fixed.

[Bug middle-end/55873] Missed trivial uninitialized use warning

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55873

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2013-01-05 12:10:56 UTC ---
PR18501, the most frequently reported Wuninitialized bug.

[Bug middle-end/55873] Missed trivial uninitialized use warning

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55873

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2013-01-05 12:15:35 UTC ---
PR18501, the most frequently reported Wuninitialized bug.

Of course, it is possible to fix it. Clang does warn:

pr18501.c:5:7: warning: variable 'res' is used uninitialized whenever 'if'
condition is false [-Wsometimes-uninitialized]
  if (c)
      ^
pr18501.c:7:10: note: uninitialized use occurs here
  return res;
         ^~~
pr18501.c:5:3: note: remove the 'if' if its condition is always true
  if (c)
  ^~~~~~
pr18501.c:4:10: note: initialize the variable 'res' to silence this warning
  int res;
         ^
          = 0
1 warning generated.

It is just that it probably needs some serious amount of work.