[flang][OpenMP] Implement HAS_DEVICE_ADDR clause #252
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The HAS_DEVICE_ADDR indicates that the object(s) listed exists at an address that is a valid device address. Specifically, `has_device_addr(x)` means that (in C/C++ terms) `&x` is a device address. When entering a target region, `x` does not need to be allocated on the device, or have its contents copied over (in the absence of additional mapping clauses). Passing its address verbatim to the region for use is sufficient, and is the intended goal of the clause. Some Fortran objects use descriptors in their in-memory representation. If `x` had a descriptor, both the descriptor and the contents of `x` would be located in the device memory. However, the descriptors are managed by the compiler, and can be regenerated at various points as needed. The address of the effective descriptor may change, hence it's not safe to pass the address of the descriptor to the target region. Instead, the descriptor itself is always copied, but for objects like `x`, no further mapping takes place (as this keeps the storage pointer in the descriptor unchanged). To accommodate this, descriptor mappings will be marked with the OMP_MAP_DESCRIPTOR flag.
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The HAS_DEVICE_ADDR indicates that the object(s) listed exists at an address that is a valid device address. Specifically,
has_device_addr(x)means that (in C/C++ terms)&xis a device address.When entering a target region,
xdoes not need to be allocated on the device, or have its contents copied over (in the absence of additional mapping clauses). Passing its address verbatim to the region for use is sufficient, and is the intended goal of the clause.Some Fortran objects use descriptors in their in-memory representation. If
xhad a descriptor, both the descriptor and the contents ofxwould be located in the device memory. However, the descriptors are managed by the compiler, and can be regenerated at various points as needed. The address of the effective descriptor may change, hence it's not safe to pass the address of the descriptor to the target region. Instead, the descriptor itself is always copied, but for objects likex, no further mapping takes place (as this keeps the storage pointer in the descriptor unchanged).To accommodate this, descriptor mappings will be marked with the OMP_MAP_DESCRIPTOR flag.
This fixes #207