**Scope of the PR:**
1. Lowering global and local procedure pointer declaration statement
with explicit or implicit interface. The explicit interface can be from
an interface block, a module procedure or an internal procedure.
2. Lowering procedure pointer assignment, where the target procedure
could be external, module or internal procedures.
3. Lowering reference to procedure pointers so that it works end to end.
**PR notes:**
1. The first commit of the PR does not include testing. I would like to
collect some comments first, which may alter the output. Once I confirm
the implementation, I will add some testing as a follow up commit to
this PR.
2. No special handling of the host-associated entities when an internal
procedure is the target of a procedure pointer assignment in this PR.
**Implementation notes:**
1. The implementation is using the HLFIR path.
2. Flang currently uses `getUntypedBoxProcType` to get the
`fir::BoxProcType` for `ProcedureDesignator` when getting the address of
a procedure in order to pass it as an actual argument. This PR inherits
the same design decision for procedure pointer as the `fir::StoreOp`
requires the same memory type.
Currently, if the first usage of a procedure not defined in the file was
inside a procedure designator reference (not a call to it), the lowered
func.func lacked the argument attributes if any.
Fix this by using `CallInterface<T>::declare` too in SignatureBuilder to
create a new func.func instead of using custom code.
Note: this problem was made worse by the fact that module variables
fir.global are currently lowered before the module procedures func.func
are created. I will try to fix that in a later patch (the debug location
may still be wrong in certain cases) because there is quite some test
fallout when changing the order of globals/funcop in the output.
- Add a convertProcedureDesignatorToHLFIR that converts the
fir::ExtendedValue from the current lowering to a
fir.boxproc/tuple<fir.boxproc, len> mlir::Value.
- Allow fir.boxproc/tuple<fir.boxproc, len> as hlfir::Entity values
(a function is an address, but from a Fortran entity point of view,
procedure that are not procedure pointers cannot be assigned to, so
it makes a lot more sense to consider those as values).
- Modify symbol association to not generate an hlfir.declare for dummy
procedures. They are not needed and allowing hlfir.declare to declare
function values would make its verifier and handling overly complex
for little benefits (maybe an hlfir.declare_proc could be added if it
turnout out useful later for debug info and attributes storing
purposes).
- Allow translation from hlfir::Entity to fir::ExtendedValue.
convertToBox return type had to be relaxed because some intrinsics
handles both object and procedure arguments and need to lower their
object arguments "asBox". fir::BoxValue is not intended to carry
dummy procedures (all its member functions would make little sense
and its verifier does not accept such type).
Note that AsAddr, AsValue and AsBox will always return the same MLIR
value for procedure designators because they are always handled the
same way in FIR.
Differential Revision: https://reviews.llvm.org/D143585
Code move without any change, the goal is to re-use this piece of
code for procedure designator lowering in HLFIR since there is no
significant changes in the way procedure designators will be
lowered.
Differential Revision: https://reviews.llvm.org/D143563
