[Openmp-dev] Sharing enums between llvm and openmp

[Doerfert, Johannes via Openmp-dev]

We should do something here, I have a very strong preference what but so
far not the time.

On 12/30, Jon Chesterfield via Openmp-dev wrote:
> This email motivated by D71948, but the question has come up before
> without resolution.
> 
> The compiler and runtime need to agree on various things. Values of enums,
> other constants, typedefs, prototype of functions. Currently we achieve
> that through careful programming and review which is slow and a bit fragile.
> 
> I don't think building the compiler should depend on the openmp runtime
> source (so the compiler can build without openmp).
> 
> Someone in a previous review didn't want building the runtime to depend on
> the compiler source (so that the runtime can be easily built with other
> compilers).

I don't see this problem. If you download the runtime you have the llvm
source.


> Options seem to be:
> 1/ Status quo - copy/paste/hope. This is working for us but I don't like
> the hope part
> 2/ Put header files somewhere outside of the llvm / openmp / clang projects
> and include
> 3/ Put header file in the compiler and include it from openmp
> 4/ Put header file in openmp and include it from the compiler
> 5/ Other?
> 
> I think we should create llvm/CodeGen/OpenMPConstants.h under the llvm tree
> and use that. This will fractionally inconvenience downstream people using
> llvm's bundled openmp library without llvm in that they'll have to copy the
> file out of the llvm tree. That seems fine.

3/ is the right way, except that it is not "a header" per se. The
"source of truth" is `llvm/lib/Frontend/OpenMP/OMPKinds.def`. Not all
constants are defined in their yet but we are getting there. I tried to
make sure "numerical values" in their already match the runtime
definitions. The last step that is missing is to use things like
`OMP_PROC_BIND_KIND` in the definition of `omp_proc_bind_t` (omp.h.var)
and `kmp_proc_bind_t` (kmp.h). That would look like the `ProcBindKind`
definition in `llvm/include/llvm/Frontend/OpenMP/OMPConstants.h`. Thus,

typedef enum omp_proc_bind_t {
#define OMP_PROC_BIND_KIND(Enum, Str, Value) Enum = Value;
#include "llvm/Frontend/OpenMP/OMPKinds.def"
} omp_proc_bind_t;


Cheers,
  Johannes
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