[Bug c/121729] New: DFP FP exception flags not raised as expected

[tydeman at tybor dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121729

            Bug ID: 121729
           Summary: DFP FP exception flags not raised as expected
           Product: gcc
           Version: 14.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tydeman at tybor dot com
  Target Milestone: ---

The following code raises FE_INVALID and FE_INEXACT, but not the other three.

#define __STDC_WANT_DEC_FP__ 1
#define __STDC_WANT_IEC_60559_DFP_EXT__ 1

#include <assert.h>
#include <stdio.h>
#include <limits.h>
#include <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>

static _Decimal32 fpdiv( const _Decimal32 x, const _Decimal32 y ) { return x /
y; }

int main(void){

  if(1){
    _Decimal32 dfp26;
    int flags = 0;
    feclearexcept(FE_ALL_EXCEPT);

    dfp26 = fpdiv( 1e0DF, 3e0DF );      /* inexact */
    assert( 0.3333333DF == dfp26 );
    flags |= fetestexcept(FE_ALL_EXCEPT);

    dfp26 = fpdiv( DEC32_MIN, DEC32_MAX );/* underflow */
    assert( 0e0DF == dfp26 );
    flags |= fetestexcept(FE_ALL_EXCEPT);

    dfp26 = fpdiv( DEC32_MAX, DEC32_MIN );/* overflow */
    assert( DEC_INFINITY == dfp26 );
    flags |= fetestexcept(FE_ALL_EXCEPT);

    dfp26 = fpdiv( 1e0DF, 0e0DF );      /* div-by-0 */
    assert( DEC_INFINITY == dfp26 );
    flags |= fetestexcept(FE_ALL_EXCEPT);

    dfp26 = fpdiv( 0e0DF, 0e0DF );      /* invalid */
    assert( isnan(dfp26) );
    flags |= fetestexcept(FE_ALL_EXCEPT);

    (void)printf("%#x=flags\n", flags);
    (void)printf("%#x=FE_INEXACT\n", FE_INEXACT );
    (void)printf("%#x=FE_UNDERFLOW\n", FE_UNDERFLOW );
    (void)printf("%#x=FE_OVERFLOW\n", FE_OVERFLOW );
    (void)printf("%#x=FE_DIVBYZERO\n", FE_DIVBYZERO );
    (void)printf("%#x=FE_INVALID\n", FE_INVALID );
    (void)fflush(NULL);
    assert( 0 != flags );
    assert( FE_INEXACT & flags );
    assert( FE_INVALID & flags );
    assert( FE_UNDERFLOW & flags );     /* fails here */
    assert( FE_OVERFLOW & flags );
    assert( FE_DIVBYZERO & flags );
  }
  return 0;
}

Here are the flags being passed to gcc:
export CFLAGS="-H -std=gnu23 -O0 -march=native -mhard-float -mfpmath=387
-mieee-fp \
 -enable-decimal-float=yes \
 -fexcess-precision=standard \
 -ffloat-store \
 -ffp-contract=off \
 -fmath-errno \
 -fno-associative-math \
 -fno-builtin \
 -fno-cx-limited-range \
 -fno-fast-math \
 -fno-finite-math-only \
 -fno-reciprocal-math \
 -fno-unsafe-math-optimizations \
 -frounding-math \
 -fsignaling-nans \
 -fsigned-zeros \
 -ftrapping-math \
 ${INCS} \
 -I/usr/include/dfp"

This is being run on Fedora Linux 41 on Intel Core i5 vPRO.