Add a virtual method on Action to indicate if they can be skipped safely

[mehdi_amini]

Summary

This can be useful to drive something like debug counters for example.

[mehdi_amini]

reviewers

[mehdi_amini]

reviewers

[mehdi_amini]

reviewers

[mehdi_amini]

rebase

[rriddle]

This patch feels kind of weird here, why not delay this until when it can actually be used?

[rriddle]

After looking at the followup, I'd honestly just fold this into the followup.

[mehdi_amini]

rebase

mlir/include/mlir/IR/Action.h

public:
 
   virtual void print(raw_ostream &os) const {
     os << "Action \"" << getTag() << "\"";
   }
 
   /// Return the set of IR units that are associated with this action.
   virtual ArrayRef<IRUnit> getContextIRUnits() const { return irUnits; }
 
+  /// Return whether this action can be skipped by the action manager without
+  /// breaking the compiler. We assume that the majority of actions are in
+  /// this category, for the others (like lowering passes), the derived classes
+  /// can override.
+  virtual bool canBeSkipped() const { return true; }
+
 protected:
   Action(TypeID actionID, ArrayRef<IRUnit> irUnits)
       : actionID(actionID), irUnits(irUnits) {}
 
   /// The type of the derived action class, used for `isa`/`dyn_cast`.
   TypeID actionID;
 
   /// Set of IR units (operations, regions, blocks, values) that are associated
   /// with this action.
   ArrayRef<IRUnit> irUnits;
 };
 
 /// CRTP Implementation of an action. This class provides a base class for
 /// implementing specific actions.
+///
 ///  Derived classes are expected to provide the following:
 ///   * static constexpr StringLiteral tag = "...";
 ///     - This method returns a unique string identifier, similar to a command
 ///       line flag or DEBUG_TYPE.
 template <typename Derived>
 class ActionImpl : public Action {
 public:
   ActionImpl(ArrayRef<IRUnit> irUnits = {})