[Bug c/121988] New: DFP casts are ignored

[tydeman at tybor dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121988

            Bug ID: 121988
           Summary: DFP casts are ignored
           Product: gcc
           Version: 15.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tydeman at tybor dot com
  Target Milestone: ---

This fails:

/* Prereq: dnf install libdfp-devel */
#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>

#pragma STDC FENV_ACCESS ON
#pragma STDC FP_CONTRACT OFF
#pragma STDC FENV_ROUND FE_TONEAREST
#pragma STDC FENV_DEC_ROUND FE_DEC_TONEAREST
#pragma STDC CX_LIMITED_RANGE OFF

int main(void){

  if(1){
    _Decimal128 dfp35_128;
    _Decimal64 dfp35_64;
    dfp35_128 = (_Decimal64) (_Decimal64)(1.DF/3.DF);
    dfp35_64  = (_Decimal64) (_Decimal64)(1.DF/3.DF);
    assert(dfp35_128 == dfp35_64);      /* fails here */
  }
  return 0;
}