arch-specific directories

[mdf at FreeBSD.org]

This is as much as request for information as a suggestion.

I am wondering of the current layout of sys/<arch> make sense given
that in several cases the only difference between two "arch" is the
bitness, e.g. powerpc and powerpc64.  The 64-bit version supports a
few new instructions, but in many cases is the same.  The same issue
exists with i386/amd64 but because both have been supported for a long
time the have full arch separation.  However, there has been some
movement of files that are common between i386 and amd64 into a common
x86 directory.

So what I'm wondering is it it makes more sense to have files broken
up more like:

sys/<arch>      for common file between bitness
sys/<arch>/32
sys/<arch>/64  for files that are specific to the bitness

This would presumably serve at least powerpc and i386/amd64 well, and
though I don't know for sure I assume at the moment that it works for
sun/sparc as well.

So... is this reasonable?  Or does the existence of ia64 throw a
monkey wrench into this layout?  Is it not worth the shuffle (though
I'd argue that, if we're moving some files to x86 and creating a new
powerpc64 that it's better to consider now than later).

I realize there was a discussion earlier along similar lines (the
bi-yearly architecture source tree layout discussion) but I don't
think it was specifically considering the 32/64 bit differences, which
seem to be more common now.

Thanks,
matthew