[acc][flang] Define hasUnknownDimensions in MappableType (#165794)

The MappableType interface currently defines a `generateAccBounds`
method which examines a variable and generates `acc.bounds` operations
that encode its dimensions. The implementation can extract bounds
information in various ways: either from the MLIR type itself or by
analyzing the IR to find dimension information from defining operations.

However, we need to distinguish between cases where dimensional
information is not directly available from the type itself. This new
`hasUnknownDimensions` API returns true when the MLIR type does not
encode dimensional information and there is no associated descriptor or
metadata that would make this information extractable from the visible
ssa value the represents the variable. The expected use case is calling
`generateAccBounds` only when this returns true, as it indicates that
bounds must be extracted from the IR (by walking back from current
variable to its defining spots or its descriptor).

This supports cases such as raw references to arrays with non-constant
bounds (e.g., explicit-shape arrays in Fortran where bounds are passed
as arguments). This functionality could also be leveraged for CIR VLA
support in the future.

For FIR types:
- Box types return false (descriptor encodes dimensions)
- Reference types check if the pointee has dynamic size using
fir::hasDynamicSize()

0 files changed, 0 insertions, 0 deletions