Docs: DPC++ Compiler

[ax3l]

Document on how to set up the dpcpp compiler with spack.

cc @becker33 @jeffhammond @rscohn2

[becker33]

I don't think this belongs in the "getting started" section.

Maybe it could go in the longer section on intel tools?

[becker33]

https://spack.readthedocs.io/en/latest/build_systems/intelpackage.html?highlight=intel#intel-packages-in-spack

[ax3l]

Wasn't sure, that section reads:

Vendor-Specific Compiler Configuration

With Spack, things usually “just work” with GCC. Not so for other compilers. This section provides details on how to get specific compilers working.

It sets up ICC, PGI and NAG compilers in detail and lacks so far details on how to set environment vars for them. I think its activation details are unique enough to add value for the section.

[roblatham00]

I struggled with DPCPP just last week so this is well timed.

[rscohn2]

@frankwillmore Can you look at the compilers.yaml?

[frankwillmore]

@rscohn2 That stanza looks pretty involved for an example. I've never had to add that much stuff, by ymmv.
I stopped naming the compiler as 'clang' a while back, in favor of 'oneapi', because I think it's important to distinguish the intel version, as with the cray version of it. All of the environment stuff may well be necessary and valid for that particular installation, and I don't see anything fundamentally wrong, but imho it looks a bit cluttered.

In my work, I've used icpx instead of dpcpp. afaik it will compile dpcpp code, just needs a few extra include paths. And I would set up the environment in a module, but this may just be a matter of taste.

[rscohn2]

I also stopped using dpcpp driver and instead add -fsycl to compile and link. All the cmake docs discourage changing the driver.
Unfortunately, you may also need -fscyl-unnamed-lambda for compile, but I hope they make that unnecessary.

[jeffhammond]

I don't use Spack much but my primary use for it in this case would be to get the PTX back-end without having to build it myself. Is that working (in Spack)?

[ax3l]

Here I am just trying to use the pre-built, distributed dpcpp to build a spack software stack.

For building advanced binary variants of dpcpp that do not come with that release, one would need to add to the llvm package in Spack (or create/derive a new package). I have not yet seen someone working on that.

[tldahlgren]

Closing and re-opening this PR to see if the two required build and clingo will finally have their status reported (after re-running).

[tldahlgren]

Closing and re-opening again to see if we can get past the unreported results from required tests.

[ax3l]

I currently have no capacity to update this PR further and I think something similar was merged recently :)
Feel free to scavenge as needed, this was more of a proof-of-concept.