[llvm] r193742 - [SystemZ] Automatically detect zEC12 and z196 hosts

[Richard Sandiford]

Ulrich Weigand <Ulrich.Weigand at de.ibm.com> writes:
> Richard Sandiford <rsandifo at linux.vnet.ibm.com> wrote on 31.10.2013
> 14:15:01:
>
>> Yeah, I thought about doing that, but I don't think it's necessary.
>> If IBM uses sensible numbering for future architectures -- and (looks at
>> pay cheque) I'm sure they will -- then matching ranges means we get the
>> benefit of zEC12 features automatically.  If for some reason the machine
>> numbers go down, the worst that will happen is that we'll unnecessarily
>> pick an older architecture instead.  Whereas if we only match the numbers
>> we know about, we'll _always_ get the oldest architecture (z10 in our
> case)
>> for new machines.
>
> So what I would have suggested is:
> - If the number matches a machine we support (z10, z196, zEC12),
>   set the architecture accordingly.
> - Otherwise, if the number matches a known old machine (pre-z10,
>   S/390, ...), either set architecture to z10, or maybe better,
>   error out with "unsupported machine type"
> - Otherwise, assume we have a future machine and default to the
>   latest model we support (i.e. zEC12)

OK, I think we'll have to agree to disagree on this one.  I think
if a new machine came out with a number 2819, say, it'd be safer to
assume that it's a z196-compatible rather than a zEC12-compatible.

Thanks,
Richard