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Re: [PATCH] Define HAS_CPUID/HAS_I586/HAS_I686 from -march=

On Tue, 18 Aug 2015, H.J. Lu wrote:

> My change is based on sysdeps/x86/bits/string.h and
> sysdeps/x86/bits/byteswap.h.  None of them check
> __i586__ nor __i686__.


(a) there should be a new (installed) bits/ header for x86, say 
bits/x86-arch.h, that defines __x86_arch to 4, 5 or 6 depending on such 
macros, so the logic doesn't need duplicating;

(b) the header should test for the probably much smaller number of 486 / 
586 processors supported by GCC, with the default being i686, to avoid 
keeping needing updating it for future processors;

(c) GCC should add such a predefined macro, with bits/x86-arch.h only 
defining it itself if not already defined, as further future-proofing 
against anyone adding new support for an i486-class or i586-class 
processor with new predefined macros?

(Cf. sysdeps/arm/memcpy.S working based on a list of ARM architectures 
without preload support, instead of a list with it; and the __ARM_ARCH 
macro from ACLE in newer versions of GCC.)

Joseph S. Myers

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