[mlir][NFC] Provide accessor for TableGen record

[math-fehr]

Summary

Constraint and Predicate classes did not expose their underlying
tablegen records. This means that for Constraints, it is not possible
to get the underlying base constraint of a variadic constraint.
For Predicate, it is not possible to get the predicates forming an
Or predicate for instance.

[math-fehr]

By the way, I do not have commit access, so would it be possible to land it for me if this is accepted?

[Mogball]

mlir/include/mlir/TableGen/Constraint.h

74

mlir/include/mlir/TableGen/Predicate.h

70

[Mogball]

Yes

[math-fehr]

Use documentation comments

[math-fehr]

Addressed comments

mlir/include/mlir/TableGen/Constraint.h

public:
   /// Returns a unique name for the TablGen def of this constraint. This is
   /// generally just the name of the def, but in some cases where the current
   /// def is anonymous, the name of the base def is attached (to provide more
   /// context on the def).
   std::string getUniqueDefName() const;
 
   Kind getKind() const { return kind; }
 
+  /// Return the underlying def.
+  const llvm::Record &getDef() const { return *def; }
+
 protected:
   // The TableGen definition of this constraint.
   const llvm::Record *def;
 
 private:
   /// Return the name of the base def if there is one, or None otherwise.
   Optional<StringRef> getBaseDefName() const;
 

mlir/include/mlir/TableGen/Predicate.h

public:
   // Return true if the predicate is not null.
   operator bool() const { return def; }
 
   // Hash a predicate by its pointer value.
   friend llvm::hash_code hash_value(Pred pred) {
     return llvm::hash_value(pred.def);
   }
 
+  /// Return the underlying def.
+  const llvm::Record &getDef() const { return *def; }
+
 protected:
   // The TableGen definition of this predicate.
   const llvm::Record *def{nullptr};
 };
 
 // A logical predicate wrapping a C expression.  This class must closely follow
 // the definition of TableGen class 'CPred'.
 class CPred : public Pred {