Dealing with target variance

[Joseph Myers]

On Wed, 2 Oct 2019, Florian Weimer wrote:

> The only concern I would have is something like generic → m68k →
> coldfire, where coldfire goes back to the generic default.  At that

In that particular case you'd put it in sysdeps/m68k/m680x0/.

> point, it's no longer obvious in which direction the override works, you
> need to look at the file contents, and there is risk that we end up with
> the existing multitude of override mechanisms.

In quite a few of these cases you need to look at the file contents 
anyway, because the override is conditional within the file in some 
architecture-specific way that might not correspond to sysdeps 
directories.  For example, sysdeps/mips/nan-high-order-bit.h tests 
__mips_nan2008.

> Can we make the default definition the one for future targets?  Even if

I think that's the right way to go.

(In some cases there may not be a clear default that most future 
architectures are definitely going to choose.  E.g. tininess.h is an 
architecture property; the default is more or less arbitrarily "before 
rounding" but new architectures might choose either "before rounding" or 
"after rounding".)

-- 
Joseph S. Myers
joseph@codesourcery.com