[Bug c/57029] New: GCC doesn't set the inexact flag on inexact compile-time int-to-float conversion

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57029

             Bug #: 57029
           Summary: GCC doesn't set the inexact flag on inexact
                    compile-time int-to-float conversion
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincent-gcc@vinc17.net


GCC doesn't set the inexact flag on inexact compile-time int-to-float
conversion:

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

#pragma STDC FENV_ACCESS ON

void test1 (void)
{
  volatile float c;

  c = 0x7fffffbf;
  printf ("c = %a, inexact = %d\n", c, fetestexcept (FE_INEXACT));
}

void test2 (void)
{
  volatile float c;
  volatile int i = 0x7fffffbf;

  c = i;
  printf ("c = %a, inexact = %d\n", c, fetestexcept (FE_INEXACT));
}

int main (void)
{
  test1 ();
  test2 ();
  return 0;
}

Under Linux/x86_64:

$ gcc -std=c99 -O3 conv-int-flt-inex.c -o conv-int-flt-inex -lm
$ ./conv-int-flt-inex
c = 0x1.fffffep+30, inexact = 0
c = 0x1.fffffep+30, inexact = 32

Ditto without optimizations.

Note: the STDC FENV_ACCESS pragma is currently not supported (PR 34678), but I
don't think it is directly related (this is not an instruction ordering
problem...).

This bug has been found from:

  http://gcc.gnu.org/ml/gcc-help/2013-04/msg00164.html