[llvm-dev] NVPTX codegen for llvm.sin (and friends)

[Artem Belevich via llvm-dev]

On Wed, Mar 10, 2021 at 11:41 AM Johannes Doerfert <
johannesdoerfert at gmail.com> wrote:

> Artem, Justin,
>
> I am running into a problem and I'm curious if I'm missing something or
> if the support is simply missing.
> Am I correct to assume the NVPTX backend does not deal with `llvm.sin`
> and friends?
>

Correct. It can't deal with anything that may need to lower to a standard
library call.

>
> This is what I see, with some variations: https://godbolt.org/z/PxsEWs
>
> If this is missing in the backend, is there a plan to get this working,
> I'd really like to have the
> intrinsics in the middle end rather than __nv_cos, not to mention that
> -ffast-math does emit intrinsics
> and crashes.
>

It all boils down to the fact that PTX does not have the standard libc/libm
which LLVM could lower the calls to, nor does it have a 'linking' phase
where we could link such a library in, if we had it.

Libdevice bitcode does provide the implementations for some of the
functions (though with a __nv_ prefix) and clang links it in in order to
avoid generating IR that LLVM can't handle, but that's a workaround that
does not help LLVM itself.

--Artem



>
> ~ Johannes
>
>
> --
> ───────────────────
> ∽ Johannes (he/his)
>
>

-- 
--Artem Belevich
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