On 2/23/20 1:12 PM, Segher Boessenkool wrote:
On Sun, Feb 23, 2020 at 10:55:53AM -0600, Bill Schmidt wrote:
Though I'm usually uncomfortable with kicking the can down the road on these
sorts of things, I can probably be convinced in this case. Tulio and I were
wondering why the libmvec interface doesn't make use of ifunc capability for
this sort of thing. Something to look into when more advanced
implementations
are added later, I guess, and a valid reason to not lock ourselves into the
'c' ABI today.
I have some questions, too. Why is this called an ABI at all? Why will
it not work with *any* underlying ABI? What *is* this, what is it *for*,
where is the documentation, where is the design documentation? Etc.
So, I can answer a small amount of this, but I will say that overall, design
or implementation documentation seems to be between lacking and nonexistent.
This has to do with "#pragma omp simd" and providing the rules for vectorizing
functions into calls to libmvec. I tend to agree that it is a bit more like
API than ABI, but we are just fitting into existing frameworks and using the
same nomenclature.
The ABI that Bert has produced for us is available at
https://sourceware.org/glibc/wiki/HomePage?action=AttachFile&do=view&target=powerarchvectfuncabi.html.
It is based on a similar document for x86. I believe this is the most up-to-
date version:
https://software.intel.com/sites/default/files/managed/b4/c8/Intel-Vector-Function-ABI.pdf
There's been ongoing work in the same area for AArch64, with the most recent
version available here, I believe:
https://developer.arm.com/docs/101129/latest
I am not certain of the completion status of the AArch64 implementation.
The libmvec implementation for Intel has been around for a long time.
Hope that at least starts to help,
Bill
Segher
