Minimum GCC version for building glibc

[Joseph Myers]

On Tue, 4 Nov 2014, Mike Frysinger wrote:

> > * Should 4.6 or 4.7 be the minimum?
> 
> i tend to prefer to maintain older compatibility when possible.  gcc-4.7 was 
> released in Mar 2012.  when we drop support for older versions, i think a 
> prerequisite should be: what does dropping the older version gain us ?  when i 
> look at the body of code using __GNUC_PREREQ, i see very few hits for <4.7.
> 
> you mentioned that we might want to use __atomic_* for some arches.  so if we 
> aren't requiring 4.7, what's the diff between 4.4 and 4.6 ?

If nothing else, 4.6 provides the _Static_assert keyword (and I think 
there's been some desire to use static assertions).  I'd definitely like 
to get glibc using -Werror for default builds, and not having to allow for 
lots of different GCC versions helps reduce the number of cases where you 
need version-specific warning workarounds / use of -Wno-error= / 
equivalent pragmas.  It also seems quite plausible some vector libm 
functions or associated tests could require GCC versions more recent than 
4.4 (e.g. -mavx2 was added in 4.7, but maybe some were added in 4.6 - if 
you require a relevant version then that saves on configure tests).

-- 
Joseph S. Myers
joseph@codesourcery.com