[Bug c/121666] __builtin_expect_with_probability accepts non constant expression

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121666

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2025-08-25
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |accepts-invalid

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fexpect_005fwith_005fprobability

"The probability argument must be a constant floating-point expression."

GCC does it reject it some of the time:
```
double rand_impl();
void h();

void foo (int i){
    if (__builtin_expect_with_probability (i, 0, rand_impl()))
      return;
   h();
}
```
At -O1+ .