[Bug c++/57132] New: spurious warning: division by zero [-Wdiv-by-zero] in if (m) res %=m;

[Bug c++/57132] New: spurious warning: division by zero [-Wdiv-by-zero] in if (m) res %=m;

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57132

             Bug #: 57132
           Summary: spurious warning: division by zero [-Wdiv-by-zero] in
                    if (m) res %=m;
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


the following code is "copied" from line 131 of
libstdc++v3//include/bits/random.h


cat divzero.cc 
using UI = unsigned int;
template<UI m, UI a>
struct mod{
  static UI calc(UI x) {
    UI res = a*x;
    if (m) res %=m;
    return res;
  }

};


#include<iostream>
int main() {
   std::cout << mod<3,2>::calc(7) << std::endl;
   std::cout << mod<0,2>::calc(7) << std::endl;

};
pb-d-128-141-131-94:bugs48 innocent$ c++  -std=c++11 divzero.cc -Wall 
divzero.cc: In instantiation of ‘static UI mod<m, a>::calc(UI) [with unsigned
int m = 0u; unsigned int a = 2u; UI = unsigned int]’:
divzero.cc:16:27:   required from here
divzero.cc:6:16: warning: division by zero [-Wdiv-by-zero]
     if (m) res %=m;
                ^
pb-d-128-141-131-94:bugs48 innocent$ c++ -v
Using built-in specs.
COLLECT_GCC=c++
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-apple-darwin12.3.0/4.9.0/lto-wrapper
Target: x86_64-apple-darwin12.3.0
Configured with: ./configure --disable-multilib --disable-bootstrap
--enable-lto -disable-libitm --enable-languages=c,c++,fortran,lto --no-create
--no-recursion
Thread model: posix
gcc version 4.9.0 20130428 (experimental) [trunk revision 198366] (GCC)
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From: "paolo.carlini at oracle dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/57092] [4.8/4.9 Regression] Using decltype of function pointer type to define a data member causes compiler crash
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW092

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.8.1

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-01 09:24:35 UTC ---
Fixed mainline and 4.8.1.

[Bug c++/57132] spurious warning: division by zero [-Wdiv-by-zero] in if (m) res %=m;

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57132

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2013-05-01
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.9.0
     Ever Confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-01 09:53:58 UTC ---
Can be fixed like PR11586, a straightforward patchlet.

[Bug c++/57132] spurious warning: division by zero [-Wdiv-by-zero] in if (m) res %=m;

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57132

Paolo Carlini <paolo.carlini at oracle dot com> changed:

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

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2013-05-01 19:20:24 UTC ---
Fixed for 4.9.0.

[Bug c++/57132] spurious warning: division by zero [-Wdiv-by-zero] in if (m) res %=m;

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57132

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Feb 26 21:28:08 2014
New Revision: 208183

URL: http://gcc.gnu.org/viewcvs?rev=208183&root=gcc&view=rev
Log:
    PR c++/59231
    PR c++/11586
    PR c++/14710
    PR c++/57132
gcc/
    * c-common.c (shorten_compare): Don't check
    c_inhibit_evaluation_warnings.
gcc/cp/
    * pt.c (struct warning_sentinel): New.
    (tsubst_copy_and_build): Use it instead of
    c_inhibit_evaluation_warnings.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wsign-compare-7.C
Modified:
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c-common.c
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/g++.dg/cilk-plus/AN/array_test2_tplt.cc
    trunk/gcc/testsuite/g++.dg/cpp0x/overflow1.C