[Bug target/110748] RISC-V: optimize store of DF 0.0

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110748

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
aarch64 has the following function to check for +0.0:
```
/* Return TRUE if rtx X is immediate constant 0.0 (but not in Decimal
   Floating Point).  */
bool
aarch64_float_const_zero_rtx_p (rtx x)
{
  /* 0.0 in Decimal Floating Point cannot be represented by #0 or
     zr as our callers expect, so no need to check the actual
     value if X is of Decimal Floating Point type.  */
  if (GET_MODE_CLASS (GET_MODE (x)) == MODE_DECIMAL_FLOAT)
    return false;

  if (REAL_VALUE_MINUS_ZERO (*CONST_DOUBLE_REAL_VALUE (x)))
    return !HONOR_SIGNED_ZEROS (GET_MODE (x));
  return real_equal (CONST_DOUBLE_REAL_VALUE (x), &dconst0);
}
```
Which most likely needed for the new predicate ...