[mlir][sparse] Misc cleanup in Merger.h

[wrengr]

Summary

• Moving the Children class to be nested under TensorExp.
• Marking TensorExp, TensorExp::Children, and LatPoint as final.

Depends On D146083

[aartbik]

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

82–83

is it, an MLIR expression?

[wrengr]

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

82–83

I didn't actually change anything there (the diff is misaligned for some reason), but yes it should be "an" :)

[wrengr]

rebase

[wrengr]

rebase, and removing D146561 as a dependency

[wrengr]

rebase

mlir/include/mlir/Dialect/SparseTensor/Utils/Merger.h

 /// `LatSet` identifiers.  These are allocated by `Merger::addSet` (and
 /// by other methods calling that one), and serve as unique identifiers
 /// for the corresponding `SmallVector<LatPointId>` object.
 using LatSetId = unsigned;
 
 /// A constant serving as the canonically invalid identifier, regardless
 /// of the identifier type.
 static constexpr unsigned kInvalidId = -1u;
 
-/// Children subexpressions of tensor operations.
-struct Children {
+/// Tensor expression. Represents an MLIR expression in tensor index notation.
+struct TensorExp final {
+  enum class Kind;
+
+  /// Child subexpressions for non-leaf expressions.
+  struct Children final {
     ExprId e0;
     ExprId e1;
   };
 
-/// Tensor expression. Represents a MLIR expression in tensor index notation.
-struct TensorExp {
-  enum class Kind;
-
   // The `x` parameter has different types depending on the value of the
   // `k` parameter.  The correspondences are:
   // * `kTensor`    -> `TensorId`
   // * `kInvariant` -> `kInvalidId`
   // * `kLoopVar`   -> `LoopId`
   // * else         -> `ExprId`
   //
   // The `y`, `v`, and `op` parameters either must or must not be
enum class TensorExp::Kind {
   kBinary, // semiring binary op
   kReduce, // semiring reduction op
 };
 
 /// Lattice point.  Each lattice point consists of a formal conjunction
 /// of `TensorLoopId`s, together with the identifier of the corresponding
 /// tensor expression.  The formal conjunction is represented as a set of
 /// `TensorLoopId`, where that set is implemented as a `BitVector`.
-struct LatPoint {
+struct LatPoint final {
   /// Construct the lattice point from a given set of `TensorLoopId`s.
   LatPoint(const BitVector &bits, ExprId e);
 
   /// Construct a lattice point with `(t,i)` as the only `TensorLoopId`,
   /// where `(t,i) < (numTensors,numLoops)`.
   LatPoint(unsigned numTensors, unsigned numLoops, TensorId t, LoopId i,
            ExprId e);