[Bug middle-end/94111] New: Wrong optimization: decimal floating-point infinity casted to double -> zero

[ch3root at openwall dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94111

            Bug ID: 94111
           Summary: Wrong optimization: decimal floating-point infinity
                    casted to double -> zero
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ch3root at openwall dot com
  Target Milestone: ---

Cast to double of a decimal floating-point infinity gives zero:

----------------------------------------------------------------------
#include <math.h>
#include <string.h>
#include <stdio.h>

int main()
{
    _Decimal32 d = (_Decimal32)INFINITY;

    unsigned u;
    memcpy(&u, &d, sizeof u);
    printf("repr: %08x\n", u);

    printf("cast: %g\n", (double)d);
}
----------------------------------------------------------------------
$ gcc -std=c2x -pedantic -Wall -Wextra test.c && ./a.out
repr: 78000000
cast: inf
$ gcc -std=c2x -pedantic -Wall -Wextra -O3 test.c && ./a.out
repr: 78000000
cast: 0
----------------------------------------------------------------------
gcc x86-64 version: gcc (GCC) 10.0.1 20200305 (experimental)
----------------------------------------------------------------------

The representation is right for infinity in _Decimal32.