Richard Biener <richard.guent...@gmail.com> writes: > On Wed, Jul 1, 2015 at 11:39 AM, Trevor Saunders <tbsau...@tbsaunde.org> > wrote: >> On Tue, Jun 23, 2015 at 07:41:42PM +0100, Richard Sandiford wrote: >>> [A fair bit later than promised, sorry...] >>> >>> Mikhail posted a patch to make genflags generate the default HAVE_foo >>> and gen_foo definitions that have recently been added to defaults.h: >>> >>> https://gcc.gnu.org/ml/gcc-patches/2015-06/msg00723.html >>> >>> I agree it'd be a good idea to generate this kind of thing automatically, >>> but I think we should take the opportunity to move the interface to the >>> target structure. I.e.: >>> >>> HAVE_foo -> targetm.have_foo () >>> gen_foo -> targetm.gen_foo () >>> >>> This should move us closer to the pipedream goal of supporting multiple >>> targets at once. It should also mean that only the target code depends >>> on insn-flags.h. >> >> using targetm. certainly seems like an improvement. I wonder if it >> would be faster to stick this data on a per function object. I think >> that would mean you could compute what insns are available once when the >> function is created and afterwards all checks would only needed to be >> reading computed values. > > I think the memory cost of this is prohibitive.
Yeah. I did wonder about having optabs-like caching in some target_globals structure, but I don't think it's really worth it. In practice we only tend to call the have_*() functions when we're trying to generate something (unlike optabs), and so any saving would be dwarfed by the cost of generating whatever rtx we go on to create. Thanks, Richard
