In #173438 I added a FIR specific loop invariant code motion pass.
During the review, Tom pointed out certain limitations about OpenMP
dialect operations that should be taken into consideration during
transformations such as LICM:
https://github.com/llvm/llvm-project/pull/173438#discussion_r2657612148
I also found issues with hoisting operations out of `acc.loop`
operations in certain conditions (see the added test in `licm.fir`).
I am proposing a new operation interface that will allow to control
movement of operations during MLIR transformations. In particular, I
propose two methods (there might be more):
* op.canMoveOutOf(cand) - returns true, if it is allowed to move 'cand'
operation out of 'op'.
* op.canMoveFromDescendant(descendant, cand) - return true, if it is
allowed to move 'cand' out of 'descendant' and into 'op'.
I used the new interface to get rid of explicit OpenMP interfaces checks
in Flang's LICM, and I also used it for `acc.loop` operation (though, I
provided conservative initial implementation).
The new interface is part of FIR dialect, but I think it would better
fit into the core MLIR set of interfaces so that the checks that I make
in Flang's LICM are actually done in
`mlir::moveLoopInvariantCode`. Moreover, other code movement
transformations that may appear in MLIR may also need to use such an
interface.
I would like to get some feedback on whether it is reasonable to move
the interface to core MLIR.
09ae1bf8b7