The runtime Assign function is not meant to initialize an array from a
scalar. For that we need to use DoAssignFromSource. Update the data
transfer from scalar to descriptor to use a new entry point that use
this function underneath.
Data transfer from a variable with a descriptor to a pointer. We create
a descriptor for the pointer so we can use the flang runtime to perform
the transfer. The Assign function handles all corner cases. We add a new
entry points `CUFDataTransferDescDescNoRealloc` to avoid reallocation
since the variable on the LHS is not an allocatable.
When source is a pointer to an array or a scalar, embox it and use the
`CUFDataTransferDescDesc` or `CUFDataTransferGlobalDescDesc` entry
points. The runtime is already able to deal with all the corner cases
like non contiguous arrays and so on so we exploit this.
Memset might still be used for simple case where we want to initialize
to 0 for example. This will come in a follow up patch.
When the destination of the data transfer is a global we might need to
sync the descriptor after the data transfer is done. This is the case
when the data transfer is from host/device to device as reallocation
might have happened and the descriptor on the device needs to take the
new values written on the host.
A new entry point is added `CUFDataTransferGlobalDescDesc` with the sync
when needed.
Passing a descriptor as a `const Descriptor &` or a `const Descriptor *`
generates a FIR signature where the box is passed by value.
This is an issue, as it requires a load of the box to be passed. But
since, ultimately, all boxes are passed by reference a temporary is
generated in LLVM and the reference to the temporary is passed.
The boxes addresses are registered with the CUDA runtime but the
temporaries are not, thus preventing the runtime to properly map a host
side address to its device side counterpart.
To address this issue, this PR changes the signatures to the transfer
functions to pass a descriptor as a `Descriptor *`, which will in turn
generate a FIR signature with that takes a box reference as an argument.
Add new entry points for more complex data transfer involving
descriptors. These functions will be called when converting
`cuf.data_transfer` operations.
