Currently, the kernel type (i.e. `generic`, `spmd`, `spmd-no-loop` and
`bare`) of an `omp.target` operation is not an explicit attribute of the
operation. Rather, this is inferred based on the contents of its region
and clauses.
The problems with this approach are that it can be a potentially
resource intensive check for large kernels, and misidentifications are
prone to happen based on the presence of arbitrary operations from other
dialects.
Since the AST already contains the information needed to identify the
kernel type in a more reliable manner, this patch moves that
responsiblity to the Flang frontend. Other MLIR passes that create
`omp.target` operations are updated as well.
One known limitation of this approach is that the MLIR op verifier for
`omp.target` can't completely check that the contents of its region are
compatible with the declared kernel type without being exposed to the
same pattern-matching limitations that this patch is removing. Also, the
`TargetOp::getInnermostCapturedOmpOp()` function is maintained but,
ideally, a better solution should be implemented to remove its expensive
and potentially flaky checks from MLIR.
Sergio Afonso
8cd49c6f64