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[Flang][OpenMP] Derived type explicit allocatable member mapping (#113557)
This PR is one of 3 in a PR stack, this is the primary change set which
seeks to extend the current derived type explicit member mapping support
to handle descriptor member mapping at arbitrary levels of nesting. The
PR stack seems to do this reasonably (from testing so far) but as you
can create quite complex mappings with derived types (in particular when
adding allocatable derived types or arrays of allocatable derived types)
I imagine there will be hiccups, which I am more than happy to address.
There will also be further extensions to this work to handle the
implicit auto-magical mapping of descriptor members in derived types and
a few other changes planned for the future (with some ideas on
optimizing things).
The changes in this PR primarily occur in the OpenMP lowering and the
OMPMapInfoFinalization pass.
In the OpenMP lowering several utility functions were added or extended
to support the generation of appropriate intermediate member mappings
which are currently required when the parent (or multiple parents) of a
mapped member are descriptor types. We need to map the entirety of these
types or do a "deep copy" for lack of a better term, where we map both
the base address and the descriptor as without the copying of both of
these we lack the information in the case of the descriptor to access
the member or attach the pointers data to the pointer and in the latter
case we require the base address to map the chunk of data. Currently we
do not segment descriptor based derived types as we do with regular
non-descriptor derived types, we effectively map their entirety in all
cases at the moment, I hope to address this at some point in the future
as it adds a fair bit of a performance penalty to having nestings of
allocatable derived types as an example. The process of mapping all
intermediate descriptor members in a members path only occurs if a
member has an allocatable or object parent in its symbol path or the
member itself is a member or allocatable. This occurs in the
createParentSymAndGenIntermediateMaps function, which will also generate
the appropriate address for the allocatable member within the derived
type to use as a the varPtr field of the map (for intermediate
allocatable maps and final allocatable mappings). In this case it's
necessary as we can't utilise the usual Fortran::lower functionality
such as gatherDataOperandAddrAndBounds without causing issues later in
the lowering due to extra allocas being spawned which seem to affect the
pointer attachment (at least this is my current assumption, it results
in memory access errors on the device due to incorrect map information
generation). This is similar to why we do not use the MLIR value
generated for this and utilise the original symbol provided when mapping
descriptor types external to derived types. Hopefully this can be
rectified in the future so this function can be simplified and more
closely aligned to the other type mappings. We also make use of
fir::CoordinateOp as opposed to the HLFIR version as the HLFIR version
doesn't support the appropriate lowering to FIR necessary at the moment,
we also cannot use a single CoordinateOp (similarly to a single GEP) as
when we index through a descriptor operation (BoxType) we encounter
issues later in the lowering, however in either case we need access to
intermediate descriptors so individual CoordinateOp's aid this
(although, being able to compress them into a smaller amount of
CoordinateOp's may simplify the IR and perhaps result in a better end
product, something to consider for the future).
The other large change area was in the OMPMapInfoFinalization pass,
where the pass had to be extended to support the expansion of box types
(or multiple nestings of box types) within derived types, or box type
derived types. This requires expanding each BoxType mapping from one
into two maps and then modifying all of the existing member indices of
the overarching parent mapping to account for the addition of these new
members alongside adjusting the existing member indices to support the
addition of these new maps which extend the original member indices (as
a base address of a box type is currently considered a member of the box
type at a position of 0 as when lowered to LLVM-IR it's a pointer
contained at this position in the descriptor type, however, this means
extending mapped children of this expanded descriptor type to
additionally incorporate the new member index in the correct location in
its own index list). I believe there is a reasonable amount of comments
that should aid in understanding this better, alongside the test
alterations for the pass.
A subset of the changes were also aimed at making some of the utilities
for packing and unpacking the DenseIntElementsAttr containing the member
indices shareable across the lowering and OMPMapInfoFinalization, this
required moving some functions to the Lower/Support/Utils.h header, and
transforming the lowering structure containing the member index data
into something more similar to the version used in
OMPMapInfoFinalization. There we also some other attempts at tidying
things up in relation to the member index data generation in the
lowering, some of which required creating a logical operator for the
OpenMP ID class so it can be utilised as a map key (it simply utilises
the symbol address for the moment as ordering isn't particularly
important).
Otherwise I have added a set of new tests encompassing some of the
mappings currently supported by this PR (unfortunately as you can have
arbitrary nestings of all shapes and types it's not very feasible to
cover them all).
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