ldc nvvm GPU intrinsics good news

[Bruce Carneal]

On Sunday, 25 April 2021 at 22:26:06 UTC, Johan Engelen wrote:
> On Friday, 5 March 2021 at 00:03:26 UTC, Bruce Carneal wrote:
>> After updating the first line to 
>> '@compute(CompileFor.hostAndDevice) module ...' and adding an 
>> 'import ldc.dcompute;' line, the 
>> runtime/import/ldc/gccbuiltins_nvvm.di file from a current LDC 
>> build apparently gives access to all manner of GPU intrinsics.
>
> Hi Bruce,
>   Why not submit a PR that modifies `gen_gccbuiltins.cpp` such 
> that it adds the `@compute` attribute for the relevant 
> intrinsics files?
> I think it's OK if `gen_gccbuiltins` contains some hacks like 
> that . Please add a small compile test case, so we verify that 
> it won't bitrot in the future.
>
> Wouldn't `@compute(CompileFor.deviceOnly)` make more sense, 
> because the intrinsics will not be available on normal CPUs 
> anyway?
>
> I hope all your work will land in either LDC or dcompute's 
> repositories, such that others can easily benefit from it.
>
> cheers,
>   Johan

Yes, I'll help when the current push is over here, but I think I 
dont understand enough quite yet.  I'm still bumping in to 
limitations/awkwardness in dcompute that should admit simple 
solutions. At least it feels that way.

One idea from my experience to date is that we can and probably 
should create a simpler (from a programmer perspective) and finer 
granularity way to handle multiple targets.  Intrinsic selection 
is part of that as is library selection.

Also on my mind is how we should handle deployment.  For the 
ultimate in speed we can do AOT per-target specialized compiles 
and "fat" binaries but using SPIR-V + Vulkan compute could 
significantly improve penetration and reduce bloat.

I read a relatively recent thread in an LLVM forum indicating 
that the Intel guys are pushing a "real" SPIR-V IR effort now so 
maybe we can help out there.

Also, I dont know how MLIR should fit in to our plans.

I'll be in touch when I get my head above water here.  Thanks to 
you and the rest of the LDC crew for the help so far.  Looking 
forward to advancing dlang on GPUs in the future.  It really can 
be much much better than C++ in that arena.

Bruce