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 PR contains 2 commits:
1. A commit to reapply changes introduced #91116 (was reverted earlier
due to test suite failures)
2. A commit containing a possible solution for the issue causing the
test suite failures. In particular, it introduces a simple symbol
visitor class to keep track of the current active OMP construct and
marking this active construct as the scope defining the symbol being
visisted.
Fixes#88935
Toggling reduction by-ref broke when multiple reduction clauses were
used. Decisions made for the by-ref status for later clauses could then
invalidate decisions for earlier clauses. For example,
```
reduction(+:scalar,scalar2) reduction(+:array)
```
The first clause would choose by value reduction and generate by-value
reduction regions, but then after this the second clause would force
by-ref to support the array argument. But by the time the second clause
is processed, the first clause has already had the wrong kind of
reduction regions generated.
This is solved by toggling whether a variable should be reduced by
reference per variable. In the above example, this allows only `array`
to be reduced by ref.
This patch updates lowering from PFT to MLIR of workshare loops to
follow the loop wrapper approach. Unit tests impacted by this change are
also updated.
As the last patch of the stack, this should compile and pass unit tests.
It turned out that `hlfir::genVariableBox` didn't add lower bounds to
the boxes it created. Using a shapeshift instead of only a shape adds
the lower bounds information to the thread-local copy of the box.
Fixes#89259
Both arrays and trivial scalars are supported. Both cases must use
by-ref reductions because both are boxed.
My understanding of the standards are that OpenMP says that this should
follow the rules of the intrinsic reduction operators in fortran, and
fortran says that unallocated allocatable variables can only be
referenced to allocate them or test if they are already allocated.
Therefore we do not need a null pointer check in the combiner region.
