+/// Discriminated union of Pass ID types.
+///
+/// The PassConfig API prefers dealing with IDs because they are safer and more
+/// efficient. IDs decouple configuration from instantiation. This way, when a
+/// pass is overriden, it isn't unnecessarily instantiated. It is also unsafe to
+/// refer to a Pass pointer after adding it to a pass manager, which deletes
+/// redundant pass instances.
+///
+/// However, it is convient to directly instantiate target passes with
+/// non-default ctors. These often don't have a registered PassInfo. Rather than
+/// force all target passes to implement the pass registry boilerplate, allow
+/// the PassConfig API to handle either type.
+///
+/// AnalysisID is sadly char*, so PointerIntPair won't work.
+class IdentifyingPassPtr {
+ union {
+ AnalysisID ID;
+ Pass *P;
+ };
+ bool IsInstance;
+public:
+ IdentifyingPassPtr() : P(nullptr), IsInstance(false) {}
+ IdentifyingPassPtr(AnalysisID IDPtr) : ID(IDPtr), IsInstance(false) {}
+ IdentifyingPassPtr(Pass *InstancePtr) : P(InstancePtr), IsInstance(true) {}