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:
   /// Return a string "tag" which intends to uniquely identify this type of
   /// action. For example "pass-application" or "pattern-rewrite".
   virtual StringRef getTag() const = 0;
 
   virtual void print(raw_ostream &os) const {
     os << "Action \"" << getTag() << "\"";
   }
 
+  /// 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) : actionID(actionID) {}
 
   /// The type of the derived action class, used for `isa`/`dyn_cast`.
   TypeID actionID;
 };
 
 //===----------------------------------------------------------------------===//
private:
   }
 
   /// The set of action handlers that have been registered with the manager.
   SmallVector<std::unique_ptr<HandlerBase>> actionHandlers;
 };
 
 /// 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, typename... ParameterTs>
 class ActionImpl : public Action {
 public:
+
   ActionImpl() : Action(TypeID::get<Derived>()) {}
 
   /// Provide classof to allow casting between action types.
   static bool classof(const Action *action) {
     return action->getActionID() == TypeID::get<Derived>();
   }
 
   /// Forward tag access to the derived class.
private:
   /// Allow access to `canHandleWith`.
   friend class ActionManager;
 };
 
 } // namespace tracing
 } // namespace mlir
 
 #endif // MLIR_IR_ACTION_H
 No newline at end of file