[LLVMdev] Proposal: Move host CPU auto-detection out of the TargetMachine

[Jim Grosbach]

On Apr 10, 2014, at 1:48 AM, Richard Sandiford <rsandifo at linux.vnet.ibm.com> wrote:

> Eric Christopher <echristo at gmail.com> writes:
>> I'm not a huge fan of this because then you get to decide on a default
>> for all the ports, but I can understand if people want to move this
>> way to reduce uncertainty.
> 
> FWIW, since it's one of the three targets Jim mentioned, -march=z10 is
> the obvious default for SystemZ.

Makes sense.

> 
> On the other hand, I think it's good to run the tests on both z10 and z196,
> since there were significant additions to the architecture in z196.
> Until now we've been getting that by implicitly using -mcpu=z10 for
> cross testing on the usual x86_64 buildbots and implicitly using
> -mcpu=native (-mcpu=z196) on the z buildbot.
> 
> We could do it instead by having two llcs and FileChecks per
> CodeGen/SystemZ test, which would give better cross-toolchain
> coverage, but would almost double the test time.  Would that
> still be OK?

If you really want to run both variations of the tests, yes, absolutely, and that’s the right way to do it. Having the tests run differently in a cross-compile vs. a host-compile situation is exactly the sort of thing I’m hoping to move away from.

-Jim