Update list of i686-class processors in sysdeps/x86/cpu-features.h

  On Wed, 19 Sep 2018, Florian Weimer wrote:

> > We have a general principle that it's best for compile-time selection of 
> > subarchitecture variants of functions to be based on how the compiler 
> > behaves rather than configuring for a variant host triplet or using 
> > --with-cpu.  We could e.g. select SSE functions by default based on 
> > __SSE2__ (even if we don't do so at present).  But testing whether the 
> > compiler produces a CMOV instruction for particular code seems more 
> > fragile than testing #if conditions for processors without CMOV.
> 
> I agree about CMOV because it is extremely unlikely that we will see
> another useful x86 CPU that doesn't have CMOV.

So how about this patch that makes sysdeps/x86/cpu-features.h use short 
lists of processors without certain features instead of long lists of 
those with them?


Invert sense of list of i686-class processors in sysdeps/x86/cpu-features.h.

I noticed that sysdeps/x86/cpu-features.h had conditionals on whether
to define HAS_CPUID, HAS_I586 and HAS_I686 with a long list of
preprocessor macros for i686-and-later processors which however was
out of date.  This patch avoids the problem of the list getting out of
date by instead having conditionals on all the (few, old) pre-i686
processors for which GCC has preprocessor macros, rather than the
(many, expanding list) i686-and-later processors.  It seems HAS_I586
and HAS_I686 are unused so the only effect of these macros being
missing is that 32-bit glibc built for one of these processors would
end up doing runtime detection of CPUID availability.

i386 builds are prevented by a configure test so there is no need to
allow for them here.  __geode__ (no long nops?) and __k6__ (no CMOV,
at least according to GCC) are conservatively handled as i586, not
i686, here (as noted above, this is a theoretical distinction at
present in that only HAS_CPUID appears to be used).

Tested for x86.

2018-09-19  Joseph Myers  <joseph@codesourcery.com>

	* sysdeps/x86/cpu-features.h [__geode__ || __k6__]: Handle like
	[__i586__ || __pentium__].
	[__i486__]: Handle explicitly.
	(HAS_CPUID): Define to 1 if above macros are undefined.
	(HAS_I586): Likewise.
	(HAS_I686): Likewise.
  

* Joseph Myers:

> 2018-09-19  Joseph Myers  <joseph@codesourcery.com>
>
> 	* sysdeps/x86/cpu-features.h [__geode__ || __k6__]: Handle like
> 	[__i586__ || __pentium__].
> 	[__i486__]: Handle explicitly.
> 	(HAS_CPUID): Define to 1 if above macros are undefined.
> 	(HAS_I586): Likewise.
> 	(HAS_I686): Likewise.

Looks okay to me, thanks.

Florian