On Fri, 29 Sep 2017, Joseph Myers wrote: > On Fri, 29 Sep 2017, Segher Boessenkool wrote: > > > How do other ports deal with this? Insns with a specific rounding mode? > > Have a separate unspec for every operation? Not very nice either :-( > > Well, ideally you'd have a machine-independent representation of constant > rounding modes that could be used with the TS 18661-1 FENV_ROUND pragma, > respectively FENV_DEC_ROUND for decimal floating point (as the standard > machine-independent way of accessing such a facility at the C language > level - you'd then need to extend it to handle round-to-odd, but given the > basic facility, accepting additional rounding mode names with it should be > easy). But I don't know what that would look like in either GIMPLE or > RTL, and I'd certainly expect it to be a large project (quite likely > depending on other large projects to handle dynamic rounding modes > properly through optimizers). So you probably can't do much better than > lots of unspecs and machine-specific built-in functions at present.
(But the answer to your question seems to be that AVX512 uses something involving UNSPEC_EMBEDDED_ROUNDING.) -- Joseph S. Myers jos...@codesourcery.com