[Libre-soc-dev] [PATCH] D57504: RFC: Prototype & Roadmap for vector predication in LLVM

[Luke Kenneth Casson Leighton]

On Friday, August 28, 2020, Jacob Lifshay <programmerjake at gmail.com> wrote:

> On Fri, Aug 28, 2020, 06:00 lkcl <luke.leighton at gmail.com> wrote:
>
> > jacob are you following these,
>
>
> not anymore, I was getting too much email from LLVM to keep up


lol sounds about right



>
> do you happen to know what
> > get.active.lane.mask is about and how it works?
> >
>
> yeah, it's pretty simple:
> https://github.com/llvm/llvm-project/blob/248a67f1445d716cd18a588db35328
> d1f5b501c8/llvm/docs/LangRef.rst#L16899
>
> the code:
> %m = @llvm.get.active.lane.mask(%base, %n)
> is basically the equivalent of the following python:
> m = [base + i < n for i in range(...)]
> where base is an unsigned integer; n must be > 0 and is a hint to the
> backend of how many times the loop that was vectorized executes


i tracked this down


https://reviews.llvm.org/file/data/a7hg6qsyebhfa74ky2b4/PHID-FILE-ntwgfk7dalich5gljlho/llvm_docs_LangRef.rst

it looks very much like data-dependent fail-on-first.

l.



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