This patch simplifies the representation of OpenMP loop wrapper
operations by introducing the `NoTerminator` trait and updating
accordingly the verifier for the `LoopWrapperInterface`.
Since loop wrappers are already limited to having exactly one region
containing exactly one block, and this block can only hold a single
`omp.loop_nest` or loop wrapper and an `omp.terminator` that does not
return any values, it makes sense to simplify the representation of loop
wrappers by removing the terminator.
There is an extensive list of Lit tests that needed updating to remove
the `omp.terminator`s adding some noise to this patch, but actual
changes are limited to the definition of the `omp.wsloop`, `omp.simd`,
`omp.distribute` and `omp.taskloop` loop wrapper ops, Flang lowering for
those, `LoopWrapperInterface::verifyImpl()`, SCF to OpenMP conversion
and OpenMP dialect documentation.
This patch adds general information on the proposed approach to unify
the handling and representation of clauses that define entry block
arguments attached to operations that accept them.
This patch updates the OpenMP dialect top-level documentation to
describe the operand structures, when they can be used and how they are
automatically generated.
This patch describes the loop wrapper approach to represent
loop-associated constructs in the OpenMP MLIR dialect and documents
current limitations and ongoing efforts.
This patch creates a handwritten main documentation page for the OpenMP
dialect linking to the ODS-generated one as a sub-section.
This new page can be extended to better describe overall design
decisions of the dialect rather than relying exclusively on
documentation generated automatically from ODS descriptions. After some
investigation, there seem to be a few main ways we could structure
dialect documentation to allow the introduction of possibly extensive
handwritten text.
- Create a top-level OpenMPDialect.td file that includes the
auto-generated one. This is what the `acc` dialect currently does, but
it results in the addition of two equal TOCs. It would be possible to
move the `include` before all handwritten sections so that the page
would have a single TOC, but I believe moving general descriptions to
the end of the document would hurt readability. Also keeping the section
order without introducing a second TOC would mean the TOC would be
inserted somewhere halfway through the page, which isn't useful.
- Create an OpenMPDialect directory with an _index.md including the
auto-generated documentation. This is a different way of reproducing the
same issues described above, which is what is currently done for the
`linalg` dialect. The multiple TOC issue there is avoided by only
including automatically-generated documentation for operations (i.e.
`mlir-tblgen -gen-op-doc`) rather than for dialects (i.e. `mlir-tblgen
-gen-dialect-doc`). That approach would make it impossible to generate
all of the documentation without adding new tablegen backends for
`DialectAttr`, `DialectType` and `EnumAttrInfo` definitions or making
the TOC optional through a command line option.
- Create an OpenMPDialect directory with an _index.md that does not
include the auto-generated documentation. Instead, link to another
document in that directory that includes it. This is the approach taken
here, and it circumvents all these issues without having to make any
changes to tablegen backends.
