https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114347
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Richard Biener from comment #7) > (In reply to Jakub Jelinek from comment #6) > > You can use -fexcess-precision=16 if you don't want treating _Float16 and > > __bf16 as having excess precision. With excess precision, I think the above > > behavior is correct. > > You'd need (int) (__bf16) 257.0bf16 to get 256 even with excess precision. > > Ah, -fexcess-precision=16 doesn't seem to be documented though I've noticed that too. > (how does > this influence long double handling then?) ix86_get_excess_precision has all the details. x86 has 4 different ways of excess precision, one is not to use excess precision for anything, another only for __bf16/_Float16 (promote to float), another one is promote everything to long double and last is unpredictable. With -fexcess-precision=fast, with -mavx512fp16 we don't promote anything, without that to float. With -fexcess-precision=16 we don't promote anything. With -fexcess-precision=standard and the implicit case, it depends on -mavx512fp16, -mfpmath=sse, -mfpmath=387, -mfpmath=both etc.
