[PATCH v2 3/3] powerpc64le: Add glibc-hwcaps support

[Florian Weimer]

* Segher Boessenkool:

> Not going to happen.  A new powerpc64le-linux-novec triple (or whatever
> naming, this is just an example) can be made of course, but the existing
> name will keep standing for the existing ABI!

Fine with me.

>> >> ISA features that cannot automatically and pervasively used by compilers
>> >> can be excluded as well.  MMA could be in that category, and I think
>> >> cryptography-related instructions generally are.
>> >
>> > MMA is indeed optional for Linux.
>> > AFAICS, cryptography-related instructions are part of SIMD and should be
>> > required for Linux.
>> 
>> Then I think we should change GCC not to enable MMA with -mcpu=power10.
>
> No.
>
> -mcpu=power10 enables MMA.  If you do not want all Power10 features, you
> should not use -mcpu=power10.  It is that simple.

Then we need a different name, or require MMA for the "power10"
glibc-hwcaps subdirectory.

> Since powerpc64le-linux requires Power8 or later, you always have VMX
> and VSX enabled there.  In exactly that same way.
>
> GCC never generates anything MMA that the user did not explicitly ask
> for in the source code (with builtins, say), so this is not an issue.
> Compare this with hardware DFP.

GCC defines __MMA__ for -mcpu=power10, and source code will evenually be
sensitive to that macro.

I think it is important that -mcpu=power10 and the "power10"
subdirectory mean the same thing.

Thanks,
Florian
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