[LLVMdev] [PATCH] Detect Haswell subarchitecture (i.e. using -march=native)

[Craig Topper]

I agree with Tim, you need to implement a GetCpuIDAndInfoEx function in
Host.cpp and pass the correct value to ecx. Also you need to verify that 7
is a valid leaf because an invalid leaf is defined to return the highest
supported leaf on that processor. So if a processor supports say leaf 6 and
not leaf 7, then an access leaf 7 will return the data from leaf 6 causing
unrelated bits to be interpretted as feature flags for AVX etc.


On Fri, Nov 22, 2013 at 7:34 AM, Tim Northover <t.p.northover at gmail.com>wrote:

> > I don’t remember really, but presuming the conclusions of the
> discussion, seems it is fixed now. It was something about registers when
> using inline assembly. Anyway this works just fine on all my Haswell
> machines.
>
> I think that's more coincidence than anything else (something
> perturbed in your host compiler's backend). If you look at
> lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp there's a
> GetCpuIDAndInfoEx function which specifically sets %ecx to a valid
> value before executing "cpuid".
>
> The code in Host.cpp needs to do something similar.
>
> Cheers.
>
> Tim.
>
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-- 
~Craig
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