On Fri, Sep 29, 2017 at 08:42:45PM +0000, Joseph Myers wrote: > 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.)
Thanks. So this seems to be the same as Mike's patch does. I was hoping for a nifty trick, not another huge project :-) Oh well. Segher
