In HLFIR, the address of a Fortran entity in lowering must be defined
by an operation that has the FortranVariableOpInterface (it is a sanity
requirement to ensure that the mlir::Value propagated in certain places
of lowering can be reasoned about).
fir.zero_bits does not have this interface and it makes little sense to
add it since it can "zero initialize" more types than just addresses.
Creating an hlfir.declare for null addresses is a bit too much (what
would be the name), and it would be noisy in the IR.
Instead add a small hlfir.null operation whose codegen is simply a
replacement by fir.zero_bits.
It may also later help dealing with the NULL(MOLD) cases in a nicer
way (the current lowering of this uses special handling it).
Differential Revision: https://reviews.llvm.org/D141040
Hlfir.designate was made to support substrings but so far substrings
were not yet lowered to it. Implement support for them.
Differential Revision: https://reviews.llvm.org/D140310
Add the default unoptimized implementation implementation
of hlfir.assign. It relies on the runtime for array assignment
and always makes a temp of the right hand side for arrays.
Assignment optimization will be done when all HLFIR pieces are in place
and aliasing analysis is available.
Differential Revision: https://reviews.llvm.org/D139426
hlfir.declare codegen generates a fir.declare, and may generate a
fir.embox/fir.rebox/fir.emboxchar if the base value does not convey
all the variable bounds and length parameter information.
Leave OPTIONAL as a TODO to keep this patch simple. It will require
making the embox/rebox optional to preserve the optionality aspects.
Differential Revision: https://reviews.llvm.org/D137789
