[Bug tree-optimization/52523] New: Missing "uninitialized" warning in simple code

[Bug tree-optimization/52523] New: Missing "uninitialized" warning in simple code

[andreac at unstable dot it]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52523

             Bug #: 52523
           Summary: Missing "uninitialized" warning in simple code
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: andreac@unstable.it


Compiling this code:

#include <iostream>
int main()
{
  int x;
  std::cout << x;
  std::cin >> x;
}

with g++ -Wall uninitialized.cc
give no warning.

But compiling this code:

#include <iostream>
int main()
{
  int x;
  std::cout << x;
}

with g++ -Wall uninitialized.cc
gives:
uninitialized.cc: In function ‘int main()’:
uninitialized.cc:6:17: warning: ‘x’ is used uninitialized in this function
[-Wuninitialized

Tested also on version 4.6.1 and 4.6.2

[Bug tree-optimization/52523] Missing "uninitialized" warning in simple code

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52523

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-03-08
                 CC|                            |manu at gcc dot gnu.org
             Blocks|                            |24639
     Ever Confirmed|0                           |1

--- Comment #1 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-03-08 00:05:22 UTC ---
The SSA dump is a bit obscure to me:

int main() ()
{
  int x;
  int D.21721;
  int x.0;

<bb 2>:
  [pr52523.cc : 5:17] x.0_1 = x;
  [pr52523.cc : 5:17] std::basic_ostream<char>::operator<< ([pr52523.cc : 5]
&cout, x.0_1);

<bb 3>:
  [pr52523.cc : 6:16] std::basic_istream<char>::operator>> ([pr52523.cc : 6]
&cin, &x);

<bb 4>:
  x ={v} {CLOBBER};
  [pr52523.cc : 7:1] D.21721_2 = 0;

<L0>:
  [pr52523.cc : 7:1] return D.21721_2;

<L1>:
  x ={v} {CLOBBER};
  resx 1

}

but I guess that 'std::cin >> x' creates a VOP, and the warning machinery does
not work well with VOPs. See PR19430.

[Bug tree-optimization/52523] Missing "uninitialized" warning (VOP, taking address of var)

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52523

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org
             Status|NEW                         |RESOLVED
           Keywords|                            |diagnostic
         Resolution|---                         |FIXED
   Target Milestone|---                         |11.0
      Known to fail|                            |10.2.0, 4.7.0, 4.8.4,
                   |                            |4.9.4, 5.5.0, 6.4.0, 7.2.0,
                   |                            |8.3.0, 9.1.0

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
GCC 11 (since g:b825a22890740f341eae566af27e18e528cd29a7) diagnoses passing an
uninitialized object by const reference by -Wmaybe-uninitialized:

$ g++ -S -Wall pr52523.C
pr52523.C: In function ‘int main()’:
pr52523.C:6:13: warning: ‘x’ is used uninitialized [-Wuninitialized]
    6 |   std::cout << x;
      |   ~~~~~~~~~~^~~~
pr52523.C:5:7: note: ‘x’ declared here
    5 |   int x;
      |       ^