[Bug c/56705] New: 4.8-20130319 misdiagnoses initialized var (regression from 4.7.2)

[Bug c/56705] New: 4.8-20130319 misdiagnoses initialized var (regression from 4.7.2)

[eggert at gnu dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56705

             Bug #: 56705
           Summary: 4.8-20130319 misdiagnoses initialized var (regression
                    from 4.7.2)
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: eggert@gnu.org


Created attachment 29711
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29711
test program, abstracted from Emacs source code

This is GCC 4.8-20130319, x86-64, compiled on Fedora 17.
I ran into this problem when building a test version of Emacs.
Compiling the attached program with:

gcc -std=gnu99 -S -Wall -Werror -O3 t.i

yields the following diagnostic.

t.i: In function 'egetenv':
t.i:195:9: error: 'value' may be used uninitialized in this function
[-Werror=maybe-uninitialized]
   char *value;
         ^

The diagnostic appears to be incorrect, as
there's no path through egetenv where 'value'
may be unused.

The diagnostic is not generated by GCC 4.7.2.

Removing the seemingly-unrelated function Fgetenv_internal
makes the diagnostic go away.

[Bug middle-end/56705] 4.8-20130319 misdiagnoses initialized var (regression from 4.7.2)

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56705

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-03-24 08:15:48 UTC ---
Looks like a missing jump threading which is causing this warning to show up:
  <bb 24>:
  # _48 = PHI <0(28), prephitmp_80(31), 0(23)>
  # value_89 = PHI <value_84(D)(28), value_93(31), value_84(D)(23)>

  <bb 25>:
  # _16 = PHI <prephitmp_107(30), _48(24)>
  # value_85 = PHI <value_45(30), value_89(24)>
  if (_16 != 0)
    goto <bb 27>;
  else
    goto <bb 26>;

  <bb 26>:

  <bb 27>:
  # _1 = PHI <value_85(25), 0B(26)>
  return _1;

[Bug middle-end/56705] 4.8-20130319 misdiagnoses initialized var (regression from 4.7.2)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56705

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic,
                   |                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-03-25
     Ever Confirmed|0                           |1
      Known to fail|                            |4.8.0

[Bug middle-end/56705] 4.8-20130319 misdiagnoses initialized var (regression from 4.7.2)

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56705

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Jeffrey A. Law <law at redhat dot com> ---
Appears to be fixed on the trunk.