[cfe-dev] OpenMP in Flang and Clang
Johannes Doerfert via cfe-dev
cfe-dev at lists.llvm.org
Thu Apr 9 09:46:13 PDT 2020
Since we now merged F18, yay!, we should start reusing OpenMP
"infrastructure" between LLVM/Clang and LLVM/Flang. This will reduce
duplication (coding & maintenance), improve testing, and thereby should
get us to OpenMP 5.X support faster.
I started to look at `parse-tree.h` and `openmp-parsers.cpp` which
contain a lot of code dealing with the OpenMP "grammar". Arguably, we
don't want the duplication with
(and the almost empty "old" clang file `OpenMPKinds.def`).
I think there are multiple steps we should take. Note that I have to
list them in some order, please don't interpret this as the order I
suggest we work on them.
Move and merge the ENUM_CLASS definitions that can be shared into
OMPKinds.def. This might require to extend the macros such that we
have a flag for C/C++ or Fortran only but that should not be too hard.
The existing Clang code (or better OpenMPIRBuilder by now) could
benefit from new enum classes already in Flang, e.g. OmpCancelType,
while things like the kind of an OmpScheduleClause should only be
Determine how we can merge the definitions in `parse-tree.h` with the
ones in `OpenMPClauses.h`. I was hoping to trim down the latter anyway
as it seems there is quite a bit of duplication in there. I was also
hoping we could generate them from the macro file (or a table-gen
file) so we don't have to write all the boilerplate when new
directives and clauses are added. As an example, in the new OpenMP
context selector support for Clang new selector sets, selectors, and
traits can be added via macros in the OMPKinds.def file. Boilerplate
like parsing, pretty printing, error messages, will work right away.
Only if the existing logic to determine if the selector matches a
context is not sufficient you need to modify one more place.
(This is not true for implementation defined extensions that change
the behavior of the entire thing but anyway.)
Rethink the use of `std::tuple` in and `std::variant` in (the OpenMP
parts) of parse-tree.h. The latter is used for OmpLinearClause for
example. As far as I can tell, the two members of the variant have two
common fields and one has a third, an enum. In clang this is usually
solved by having an "unknown" or "none" member in the enum which
allows to remove the duplication and variant completely. I would like
to replace tuples so we can give their constitutes proper names. I
think a similar point was made before when we discussed tooling with
(or extending) Flang.
I hope to get some feedback and thoughts on this.
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