[Bug c/103491] New: nextafter does not raise "overflow" and "inexact" floating-point exceptions

[Bug c/103491] New: nextafter does not raise "overflow" and "inexact" floating-point exceptions

[pavel.morozkin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103491

            Bug ID: 103491
           Summary: nextafter does not raise "overflow" and "inexact"
                    floating-point exceptions
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pavel.morozkin at gmail dot com
  Target Milestone: ---

Sample code (t0.c):
#include <fenv.h>
#include <math.h>

#pragma STDC FENV_ACCESS ON

int main(void)
{
#if __STDC_IEC_559__ == 1
    double d = 1.0;
    d = nextafter(d, INFINITY);
    return (fetestexcept(FE_INEXACT | FE_INVALID) & (FE_INEXACT | FE_INVALID))
? 0 : 1;
#else
    return 0;
#endif
}

Invocation: gcc -std=c11 -pedantic -Wall -Wextra -lm

Expected a.out exit status: 0

Actual a.out exit status: 1

C11, F.10.8.3 The nextafter functions:
> nextafter(x, y) raises the ‘‘overflow’’ and ‘‘inexact’’ floating-point exceptions for x finite and the function value infinite.

Yes, Pragma STDC * (C99 FP) is unimplemented
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=20785). However, __STDC_IEC_559__
is already 1.

[Bug middle-end/103491] nextafter does not raise "overflow" and "inexact" floating-point exceptions

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103491

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |middle-end
           Keywords|                            |wrong-code

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The -O0 case is a glibc issue and should be reported there as gcc just calls
nextafter function.

The -O1 and above seems like a GCC issue though.

[Bug tree-optimization/103491] nextafter does not raise "overflow" and "inexact" floating-point exceptions

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103491

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-11-30
          Component|middle-end                  |tree-optimization
             Status|UNCONFIRMED                 |NEW
                 CC|                            |jsm28 at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed with -frounding-math and optimization where we simply elide
the nextafter call (and its side-effects).  I think the idea is that
-ftrapping-math should preserve such calls (but that's default on even).
-frounding-math is documented to be required for FENV_ACCESS.

Also confirmed as a glibc bug in 2.31 with -O0 where we call nextafter ().
The manpage isn't too informative on whether your expectation is valid.

[Bug tree-optimization/103491] nextafter does not raise "overflow" and "inexact" floating-point exceptions

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103491

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
This testcase is incorrect.  This call to nextafter has a finite result, 
so it's correct that no exceptions are raised and so an exit status of 1 
from the provided testcase is what should be expected.

A GCC bug could only be demonstrated if the call were elided for arguments 
for which overflow or underflow occurs (such as (DBL_MAX, INFINITY) or 
(DBL_MIN, 0) or (DBL_TRUE_MIN, 0)).  I haven't tested whether that is the 
case.

[Bug tree-optimization/103491] nextafter does not raise "overflow" and "inexact" floating-point exceptions

[pavel.morozkin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103491

--- Comment #4 from Pavel M <pavel.morozkin at gmail dot com> ---
To: joseph@codesourcery.com 
Re: This testcase is incorrect.
Indeed. The F.10.8.3 was misunderstood.