[Openmp-dev] [RFC] Clarify the absence of API stability for the *device runtime* (aka. libomptarget-nvptx-sm_XX.bc)

[Johannes Doerfert via Openmp-dev]

As part of a patch to remove dead arguments [0] a discussion started 
which asked for an RFC [1].


--


I want to clarify that there is no guarantee the *device runtime* (aka. 
libomptarget-nvptx-sm_XX.bc) has a stable API.


Quick summary of the discussion:

- The library in question is *not* part of libomp (which has a stable 
API) or even libomptarget.

- We are not aware of any non-clang user of this library.

- The only usage model we (properly) support is static linking of the 
runtime as LLVM-IR. This inherently ties the runtime to the compiler 
(version):

   - Combining a new compiler with an old (LLVM-IR) runtime cannot be 
expected to work as we might have new entry points.

- Combining an old compiler with a new (LLVM-IR) runtime cannot be 
expected to work as we cannot guarantee the old toolchain can handle the 
new IR .


Please provide feedback asap, this is a requirement for the GPU state 
machine patch [2] which fixes an important register usage bug [3].


Thanks,

   Johannes



[0] https://reviews.llvm.org/D83268

[1] https://reviews.llvm.org/D83268#2136060

[2] https://reviews.llvm.org/D83271

[3] http://llvm.org/PR46450

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