+/// \brief API for tracking metadata references through RAUW and deletion.
+///
+/// Shared API for updating \a Metadata pointers in subclasses that support
+/// RAUW.
+///
+/// This API is not meant to be used directly. See \a TrackingMDRef for a
+/// user-friendly tracking reference.
+class MetadataTracking {
+public:
+ /// \brief Track the reference to metadata.
+ ///
+ /// Register \c MD with \c *MD, if the subclass supports tracking. If \c *MD
+ /// gets RAUW'ed, \c MD will be updated to the new address. If \c *MD gets
+ /// deleted, \c MD will be set to \c nullptr.
+ ///
+ /// If tracking isn't supported, \c *MD will not change.
+ ///
+ /// \return true iff tracking is supported by \c MD.
+ static bool track(Metadata *&MD) {
+ return track(&MD, *MD, static_cast<Metadata *>(nullptr));
+ }
+
+ /// \brief Track the reference to metadata for \a Metadata.
+ ///
+ /// As \a track(Metadata*&), but with support for calling back to \c Owner to
+ /// tell it that its operand changed. This could trigger \c Owner being
+ /// re-uniqued.
+ static bool track(void *Ref, Metadata &MD, Metadata &Owner) {
+ return track(Ref, MD, &Owner);
+ }
+
+ /// \brief Track the reference to metadata for \a MetadataAsValue.
+ ///
+ /// As \a track(Metadata*&), but with support for calling back to \c Owner to
+ /// tell it that its operand changed. This could trigger \c Owner being
+ /// re-uniqued.
+ static bool track(void *Ref, Metadata &MD, MetadataAsValue &Owner) {
+ return track(Ref, MD, &Owner);
+ }
+
+ /// \brief Stop tracking a reference to metadata.
+ ///
+ /// Stops \c *MD from tracking \c MD.
+ static void untrack(Metadata *&MD) { untrack(&MD, *MD); }
+ static void untrack(void *Ref, Metadata &MD);
+
+ /// \brief Move tracking from one reference to another.
+ ///
+ /// Semantically equivalent to \c untrack(MD) followed by \c track(New),
+ /// except that ownership callbacks are maintained.
+ ///
+ /// Note: it is an error if \c *MD does not equal \c New.
+ ///
+ /// \return true iff tracking is supported by \c MD.
+ static bool retrack(Metadata *&MD, Metadata *&New) {
+ return retrack(&MD, *MD, &New);
+ }
+ static bool retrack(void *Ref, Metadata &MD, void *New);
+
+ /// \brief Check whether metadata is replaceable.
+ static bool isReplaceable(const Metadata &MD);
+
+ typedef PointerUnion<MetadataAsValue *, Metadata *> OwnerTy;
+
+private:
+ /// \brief Track a reference to metadata for an owner.
+ ///
+ /// Generalized version of tracking.
+ static bool track(void *Ref, Metadata &MD, OwnerTy Owner);
+};
+