On Thu, 26 Aug 2010 08:50:37 -0500, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> Well the PGI compiler has
>
> enum _mm_hint
> {
> _MM_HINT_T0 = 3,
> _MM_HINT_T1 = 2,
> _MM_HINT_T2 = 1,
> _MM_HINT_NTA = 0
> };
> extern void _mm_prefetch (const void *__P, enum _mm_hint __I);
>
> Intel on my Mac has
>
> /* constants for use with _mm_prefetch */
> #define _MM_HINT_T0 1
> #define _MM_HINT_T1 2
> #define _MM_HINT_T2 3
> #define _MM_HINT_NTA 0
> extern void __cdecl _mm_prefetch(char const*a, int sel);
>
> clang on my mac has
>
> #define _MM_HINT_T0 1
> #define _MM_HINT_T1 2
> #define _MM_HINT_T2 3
> #define _MM_HINT_NTA 0
>
> /* FIXME: We have to #define this because "sel" must be a constant integer,
> and
> Sema doesn't do any form of constant propagation yet. */
>
> #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)a, 0, sel))
>
> Some GNU headers I found on the web have
>
> /* Constants for use with _mm_prefetch. */
> enum _mm_hint
> {
> _MM_HINT_T0 = 3,
> _MM_HINT_T1 = 2,
> _MM_HINT_T2 = 1,
> _MM_HINT_NTA = 0
> };
> static __inline void
> _mm_prefetch (void *__P, enum _mm_hint __I)
Urgh, I hadn't noticed that T0,T1,T2 were defined to different values by
different hardware. We usually only use NTA (and the others hints are
sometimes all equivalent), but it's not ideal.
> Though it may be non-conforming I think it still needs to be
> supported. It seems _MM_HINT* etc and friends always exist, what about
> just not using 1, 2 3 etc but consistently using the macros would work
> and not require adding to configure.
The problem is that PetscPrefetch is also for non-Intel architectures,
in which case it calls __builtin_prefetch or something else. Kinda
looks like we're obliged to have configure define
PETSC_PREFETCH_HINT_{T0,T1,T2,NTA} so that it can work correctly in all
cases. Note that T0,T1,T2 are sometimes equivalent and could all be
defined to the same thing if necessary.
Jed
