[Openmp-dev] Preferred alternative to a C++ dialect for device library functions

[Jon Chesterfield via Openmp-dev]

Hi Hal,

In this case (atomicInc) it's a target specific IR intrinsic but there are
other cases where there is target-independent IR support but not clang.
OpenCL memory fences for one.

So the general question is what do do about functions with IR/asm support
but no clang builtins.

Thanks!

Jon


On Tue, Jan 14, 2020 at 5:15 PM Finkel, Hal J. <hfinkel at anl.gov> wrote:

>
> On 1/14/20 10:37 AM, Jon Chesterfield via Openmp-dev wrote:
>
> Hello OpenMP dev,
>
> A motivating example is atomicInc for amdgcn. There is ISA support for
> this so a good implementation folds to a single instruction. There is no
> corresponding clang intrinsic, though there is an llvm intrinsic.
>
>
> Do you mean a target-specific intrinsic, or a target-independent intrinsic?
>
>  -Hal
>
>
>
> I see the following options:
> - Implement it in IR, linked into deviceRTL
> - Inline assembly
> - Delay implementation until the intrinsic can be added to clang
> - Implement in terms of CAS
> - Your suggestion here
>
> Adding atomicInc.ll to the source tree is the easy short term fix. It has
> drawbacks in terms of future ABI change, build complexity and limited
> precedent - libclc does this, but nowhere else.
>
> Inline assembly works (modulo getting the syntax right) and hits the right
> instruction.
>
> Implementing in terms of CAS means one can stay in HIP or OpenCL, but
> performance suffers.
>
> What would the you prefer out of these options?
>
> Thanks,
>
> Jon
>
> _______________________________________________
> Openmp-dev mailing listOpenmp-dev at lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>
>
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