[Bug c/56607] New: [4.8 regression] GCC fails to warn on division by zero

[Bug c/56607] New: [4.8 regression] GCC fails to warn on division by zero

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

             Bug #: 56607
           Summary: [4.8 regression] GCC fails to warn on division by zero
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ppluzhnikov@google.com


Test:

typedef unsigned long size_t;

#ifdef TEST1
int ShouldntCompile ()
{
  return 1 / ((sizeof(int) / 3) - 1);
}
#endif

#ifdef TEST2
int WontCompile ()
{
  const int x = (sizeof(int) / 3) - 1;
  return 1 / x;
}
#endif

Using gcc-4.7:
gcc -Werror -c -DTEST1 as.c ; echo $?

as.c: In function 'ShouldntCompile':
as.c:6:12: error: division by zero [-Werror=div-by-zero]
cc1: all warnings being treated as errors
1

g++ -Werror -c -DTEST1 as.c ; echo $?
# same as above

gcc -Werror -c -DTEST2 as.c ; echo $?
0   # problem

g++ -Werror -c -DTEST2 as.c ; echo $?

as.c: In function 'int WontCompile()':
as.c:14:14: error: division by zero [-Werror=div-by-zero]
cc1plus: all warnings being treated as errors
1


Using gcc-4.8 (r196619):


gcc -Werror -c -DTEST1 as.c; echo $?

as.c: In function 'ShouldntCompile':
as.c:6:12: error: division by zero [-Werror=div-by-zero]
   return 1 / ((sizeof(int) / 3) - 1);
            ^
cc1: all warnings being treated as errors
1


g++ -Werror -c -DTEST1 as.c; echo $?
0  # 4.8 regression, used to warn.


gcc -Werror -c -DTEST2 as.c ; echo $?
0   # still a problem


g++ -Werror -c -DTEST2 as.c; echo $?

as.c: In function 'int WontCompile()':
as.c:14:14: error: division by zero [-Werror=div-by-zero]
   return 1 / x;
              ^
cc1plus: all warnings being treated as errors
1

[Bug c++/56607] [4.8 regression] GCC fails to warn on division by zero

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-03-13
          Component|c                           |c++
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org
     Ever Confirmed|0                           |1
   Target Milestone|---                         |4.8.0

[Bug c++/56607] [4.8 regression] GCC fails to warn on division by zero

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jakub at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-13 08:35:26 UTC ---
Created attachment 29660
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29660
gcc48-pr56607.patch

For the C++ warning regression, here is an untested fix, but wonder if we
shouldn't defer it for 4.8.1.

[Bug c++/56607] [4.8 regression] GCC fails to warn on division by zero

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
   Target Milestone|4.8.0                       |4.8.1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-13 09:50:12 UTC ---
Let's defer it.

[Bug c++/56607] [4.8 regression] GCC fails to warn on division by zero

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> 2013-03-13 14:18:34 UTC ---
The patch is OK for 4.8.1.

[Bug c++/56607] [4.8/4.9 regression] GCC fails to warn on division by zero

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-16 19:35:48 UTC ---
Author: jakub
Date: Sat Mar 16 19:35:41 2013
New Revision: 196704

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=196704
Log:
    PR c++/56607
    * typeck.c (cp_build_binary_op): When calling warn_for_div_by_zero,
    pass op1 through maybe_constant_value first.

    * g++.dg/warn/Wdiv-by-zero-2.C: New test.
    * c-c++-common/pr56607.c: New test.

Added:
    trunk/gcc/testsuite/c-c++-common/pr56607.c
    trunk/gcc/testsuite/g++.dg/warn/Wdiv-by-zero-2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/56607] [4.8/4.9 regression] GCC fails to warn on division by zero

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-22 15:59:09 UTC ---
Author: jakub
Date: Fri Mar 22 15:54:37 2013
New Revision: 196973

URL: http://gcc.gnu.org/viewcvs?rev=196973&root=gcc&view=rev
Log:
    Backported from mainline
    2013-03-16  Jakub Jelinek  <jakub@redhat.com>

    PR c++/56607
    * typeck.c (cp_build_binary_op): When calling warn_for_div_by_zero,
    pass op1 through maybe_constant_value first.

    * g++.dg/warn/Wdiv-by-zero-2.C: New test.
    * c-c++-common/pr56607.c: New test.

Added:
    branches/gcc-4_8-branch/gcc/testsuite/c-c++-common/pr56607.c
    branches/gcc-4_8-branch/gcc/testsuite/g++.dg/warn/Wdiv-by-zero-2.C
Modified:
    branches/gcc-4_8-branch/gcc/cp/ChangeLog
    branches/gcc-4_8-branch/gcc/cp/typeck.c
    branches/gcc-4_8-branch/gcc/testsuite/ChangeLog

[Bug c++/56607] [4.8/4.9 regression] GCC fails to warn on division by zero

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56607

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-22 15:59:30 UTC ---
Fixed.