[Openmp-dev] Declare variant + Nvidia Device Offload

[Jonas Hahnfeld via Openmp-dev]

Am Mittwoch, den 20.05.2020, 11:40 -0500 schrieb Johannes Doerfert:
> On 5/20/20 11:19 AM, Jonas Hahnfeld wrote:
> > Am Dienstag, den 19.05.2020, 17:50 +0200 schrieb Lukas Sommer via
> > Openmp-dev:
> > > Hi Johannes,
> > > 
> > > > Yes, we need to replace the dot with either of the symbols you
> > > > mentioned. If we can use the same symbols on the host, I'm fine with
> > > > chaining it unconditionally.
> > > 
> > > I've prototyped this change locally, replacing the dot with a
> > > dollar-sign in the places you mentioned. With this change, declaring
> > > variants for offloading to CUDA devices works for my testcase in my
> > > setup (ARM + Nvidia SM 7.2).
> > > 
> > > If you want, I could create a patch for that, but do you (or anyone else
> > > on the list) know whether the other offloading targets (AMDGPU, NEC VE,
> > > ...) are all able to handle the dollar sign in the mangled name, so we
> > > could make this change unconditionally? I do not have a setup for each
> > > of these to test.
> > > 
> > > I was also wondering if legalizing the mangled name shouldn't be handled
> > > by the backend (NVPTX in this case) instead of the OpenMP-specific parts.
> > 
> > For some context on this, see the following set of reviews:
> > https://reviews.llvm.org/D17738
> > https://reviews.llvm.org/D29883
> > https://reviews.llvm.org/D39005
> > https://reviews.llvm.org/D40573
> > 
> > My favorite statement from the last patch: "This is silly. This bug has
> > been open for so long that nvidia could've just fixed their toolchain
> > by now to accept dots in symbol names."
> 
> Thanks for the links!
> 
> I think in those reviews people also concluded you cannot/should not 
> modify visible symbol names late.
> 
> I guess, since we have _$_ in other cases we should do _$_ as separator 
> in Clang too. WDYT?

Probably depending on the target architecture, see for example
CGOpenMPRuntime::getOutlinedHelperName() and the override in
CGOpenMPRuntimeNVPTX for precedence.
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