[Bug c/56020] New: FE_INVALID flag not set on comparison with NAN (unordered)

["vincent-gcc at vinc17 dot net" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56020

             Bug #: 56020
           Summary: FE_INVALID flag not set on comparison with NAN
                    (unordered)
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincent-gcc@vinc17.net


GCC doesn't set the FE_INVALID flag on comparison with NAN (<=, >=, <, >), e.g.
with:

#include <stdio.h>
#include <math.h>
#include <fenv.h>

#pragma STDC FENV_ACCESS ON

int main (void)
{
  double d = NAN;
  int err;

  feclearexcept (FE_INVALID);
  d <= 0.0;
  err = ! fetestexcept(FE_INVALID);
  if (err)
    printf ("The FE_INVALID flag is not set\n");
  return err;
}

$ gcc-snapshot --version
gcc (Debian 20130113-1) 4.8.0 20130113 (experimental) [trunk revision 195136]
[...]
$ gcc-snapshot -std=c99 -Wall nancmp.c -o nancmp -lm
nancmp.c:5:0: warning: ignoring #pragma STDC FENV_ACCESS [-Wunknown-pragmas]
 #pragma STDC FENV_ACCESS ON
 ^
nancmp.c: In function 'main':
nancmp.c:13:3: warning: statement with no effect [-Wunused-value]
   d <= 0.0;
   ^
$ ./nancmp
The FE_INVALID flag is not set

The "statement with no effect" warning would also be incorrect once this bug is
fixed.