On Thu, Aug 27, 2020 at 10:00 AM Uros Bizjak <ubiz...@gmail.com> wrote:
>
> On Thu, Aug 27, 2020 at 4:45 PM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> > > > > > > How about target("baseline-isas-only")? All CPUID functions are
> > > > > > > inlined.
> > > > > >
> > > > > > No, I don't think this is a good idea. Now consider the situation
> > > > > > that
> > > > > > caller functions are compiled with e.g. -mgeneral-regs-only. Due to
> > > > > > #pragmas, CPUID functions are compiled with a superset ISAs, so they
> > > > > > again won't be inlined. ISAs of caller functions and CPUID should
> > > > > > match, the best way is to include <cpuid.h> after the #pragma. And
> > > > > > IMO, general-regs-only target #pragma is an excellent setting for
> > > > > > both: cpuid.h and caller bit testing functions.
> > > > > >
> > > > > > So, if we care about inlining, decorating cpuid.h with target
> > > > > > pragmas
> > > > > > is a bad idea.
> > > > >
> > > > > This can be done with #pragma in <cpuid.h>.
> > > > >
> > > >
> > > > We just need to update ix86_can_inline_p to allow inline functions
> > > > with baseline-isas-only and general-regs-only attributes if caller
> > > > supports the same set of ISAs.
> > > >
> > > > Here is the updated patch.
> > >
> > > I'm not against it, but I don't plan to approve the attached patch.
> > >
> >
> > How about this one?
>
> I really don't see any benefit in introducing baseline-isas-only
> #pragma, when we have general-regs-only #pragma. We may want (for
> whatever reason) to avoid SSE2 movd/movq instructions also for 64bit
> targets in functions that test bits, returned by cpuid. And since
> cpuid.h functions are extremely simple (because we want them to be
> inlined!), we can simply #include them after mentioned #pragma,
> together with bit testing functions. This way, all problems involving
> inlining are avoided.
>
Baseline ISAs are related to -march=x86-64. The differences are
1. Baseline ISAs apply to both 32-bit and 64-bit.
2. Baseline ISAs doesn't change -mtune.
It is guaranteed to work for both 32-bit and 64-bit as well as any
-mXXX options at command-line.
--
H.J.
