Add support for non-allocatable module-level CUDA managed variables
using pointer indirection through a companion global in
__nv_managed_data__. The CUDA runtime populates this pointer with the
unified memory address via __cudaRegisterManagedVar and
__cudaInitModule.
- Create a .managed.ptr companion global in the __nv_managed_data__
section and register it with _FortranACUFRegisterManagedVariable
- Call __cudaInitModule once after all variables are registered, only
when non-allocatable managed globals are present, to populate managed
pointers
- Annotate managed globals in gpu.module with nvvm.managed for PTX
.attribute(.managed) generation
- Suppress cuf.data_transfer for assignments to/from non-allocatable
module managed variables, since cudaMemcpy would target the shadow
address rather than the actual unified memory
- Preserve cuf.data_transfer for device_var = managed_var assignments
where explicit transfer is still required
Note: This PR depends on
[#189751](https://github.com/llvm/llvm-project/pull/189751) (MLIR:
nvvm.managed attribute).
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