[Bug c/119014] Extending _Float16 constant at compile and run time differs

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119014

--- Comment #16 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
2 is of course the right value for -fexcess-precision=standard -m32 on x86 (for
-fexcess-precision=fast arguably it should be IMHO -1).

Anyway, if you don't believe -fexcess-precision= affects the FLT_EVAL_METHOD
values, just look at the source:
/* Return the value that should be set for FLT_EVAL_METHOD in the
   context of ISO/IEC TS 18861-3.

   This relates to the effective excess precision seen by the user,
   which is the join point of the precision the target requests for
   -fexcess-precision={standard,fast,16} and the implicit excess precision
   the target uses.  */

static enum flt_eval_method
c_ts18661_flt_eval_method (void)
{
  enum flt_eval_method implicit
    = targetm.c.excess_precision (EXCESS_PRECISION_TYPE_IMPLICIT);

  enum excess_precision_type flag_type
    = (flag_excess_precision == EXCESS_PRECISION_STANDARD
       ? EXCESS_PRECISION_TYPE_STANDARD
       : (flag_excess_precision == EXCESS_PRECISION_FLOAT16
          ? EXCESS_PRECISION_TYPE_FLOAT16
          : EXCESS_PRECISION_TYPE_FAST));

  enum flt_eval_method requested
    = targetm.c.excess_precision (flag_type);

  return excess_precision_mode_join (implicit, requested);
}

/* As c_cpp_ts18661_flt_eval_method, but clamps the expected values to
   those that were permitted by C11.  That is to say, eliminates
   FLT_EVAL_METHOD_PROMOTE_TO_FLOAT16.  */

static enum flt_eval_method
c_c11_flt_eval_method (void)
{
  return excess_precision_mode_join (c_ts18661_flt_eval_method (),
                                     FLT_EVAL_METHOD_PROMOTE_TO_FLOAT);
}

/* Return the value that should be set for FLT_EVAL_METHOD.
   MAYBE_C11_ONLY_P is TRUE if we should check
   FLAG_PERMITTED_EVAL_METHODS as to whether we should limit the possible
   values we can return to those from C99/C11, and FALSE otherwise.
   See the comments on c_ts18661_flt_eval_method for what value we choose
   to set here.  */

int
c_flt_eval_method (bool maybe_c11_only_p)
{
  if (maybe_c11_only_p
      && flag_permitted_flt_eval_methods
          == PERMITTED_FLT_EVAL_METHODS_C11)
    return c_c11_flt_eval_method ();
  else
    return c_ts18661_flt_eval_method ();
}

..
  builtin_define_with_int_value ("__FLT_EVAL_METHOD__",
                                 c_flt_eval_method (true));
  builtin_define_with_int_value ("__FLT_EVAL_METHOD_TS_18661_3__",
                                 c_flt_eval_method (false));