Reduce hash collisions for reference and pointer types

[v.g.vassilev]

Summary

While investigating the work done in D41416 I found out that the hash values for pointer and reference types are the same.

[rsmith]

Looks reasonable, can you add a testcase that shows the ODR checker now distinguishes pointers/references to distinct types?

lib/AST/ODRHash.cpp

581

This looks redundant, the above Visit(const Type*) function seems to already do this.

[rtrieu]

lib/AST/ODRHash.cpp

581

That's correct, VisitType is intended to be empty. The TypeClass enum value is added in Visit so that it is the first value added to the data stream.

590

Use T->getPointeeTypeAsWritten() here.

[v.g.vassilev]

lib/AST/ODRHash.cpp

581

Ok, then I am a little confused. If VisitType is supposed to be nop why we call it in all VisitXXX functions.

[rtrieu]

lib/AST/ODRHash.cpp

581

Each Type calls its parent Type, all the way up to Type. It's just a manual traversal of the Type hierarchy. Right now, there's nothing in VisitType, but there might be in the future.

[rtrieu]

r328404 has been committed to support references and pointers.

[v.g.vassilev]

Ok, that's great! Sorry for the delay and thanks for landing a similar patch. Btw, we should probably find a more terse way to test the ODRHash, eg. with unittests.

lib/AST/ODRHash.cpp

void VisitQualifiers(Qualifiers Quals) {
     ID.AddInteger(Quals.getAsOpaqueValue());
   }
 
   void Visit(const Type *T) {
     ID.AddInteger(T->getTypeClass());
     Inherited::Visit(T);
   }
 
-  void VisitType(const Type *T) {}
+  void VisitType(const Type *T) {
+    ID.AddInteger(T->getTypeClass());
+  }
+
+  void VisitPointerType(const PointerType *T) {
+    AddQualType(T->getPointeeType());
+    VisitType(T);
+  }
+
+  void VisitReferenceType(const ReferenceType *T) {
+    AddQualType(T->getPointeeType());
+    VisitType(T);
+  }
 
   void VisitAdjustedType(const AdjustedType *T) {
     AddQualType(T->getOriginalType());
     AddQualType(T->getAdjustedType());
     VisitType(T);
   }
 
   void VisitDecayedType(const DecayedType *T) {