Call VisitRedeclarable before VisitDeclContext to avoid any recursion that might occur.

This should have been included in the prior commit, but as it affects [ordering in] other DeclUnloader functions;
the ability to back it out separately is better.

Also exposes a bug/change necessary in clang when building in Debug mode to avoid an infinite loop.

lib/Interpreter/DeclUnloader.cpp

@@ -557,8 +557,8 @@ bool DeclUnloader::VisitRedeclarable(clang::Redeclarable<T>* R, DeclContext* DC)
     // We start with the decl context first, because parameters are part of the
     // DeclContext and when trying to remove them we need the full redecl chain
     // still in place.
-    bool Successful = VisitDeclContext(FD);
-    Successful &= VisitRedeclarable(FD, FD->getDeclContext());
+    bool Successful = VisitRedeclarable(FD, FD->getDeclContext());
+    Successful &= VisitDeclContext(FD);
     Successful &= VisitDeclaratorDecl(FD);
 
     // Template instantiation of templated function first creates a canonical
@@ -711,8 +711,8 @@ bool DeclUnloader::VisitRedeclarable(clang::Redeclarable<T>* R, DeclContext* DC)
 
   bool DeclUnloader::VisitNamespaceDecl(NamespaceDecl* NSD) {
     // NamespaceDecl: NamedDecl, DeclContext, Redeclarable
-    bool Successful = VisitDeclContext(NSD);
-    Successful &= VisitRedeclarable(NSD, NSD->getDeclContext());
+    bool Successful = VisitRedeclarable(NSD, NSD->getDeclContext());
+    Successful &= VisitDeclContext(NSD);
     Successful &= VisitNamedDecl(NSD);
 
     return Successful;
@@ -809,8 +809,8 @@ bool DeclUnloader::VisitRedeclarable(clang::Redeclarable<T>* R, DeclContext* DC)
 
   bool DeclUnloader::VisitTagDecl(TagDecl* TD) {
     // TagDecl: TypeDecl, DeclContext, Redeclarable
-    bool Successful = VisitDeclContext(TD);
-    Successful &= VisitRedeclarable(TD, TD->getDeclContext());
+    bool Successful = VisitRedeclarable(TD, TD->getDeclContext());
+    Successful &= VisitDeclContext(TD);
     Successful &= VisitTypeDecl(TD);
     return Successful;
   }

test/CodeUnloading/Friend.C

@@ -22,6 +22,12 @@ void bestFriend();
 .compareState "NF"
 //CHECK-NOT: Differences
 
+#include "FriendRecursive.h"
+.undo
+.compareState "NF"
+//CHECK-NOT: Differences
+
+
 // STL has many of these in memory & stdexcept
 //#include <memory>
 //.undo

test/CodeUnloading/FriendRecursive.h

@@ -0,0 +1,9 @@
+class TestA {
+  friend class TestB;
+  void empty() {}
+};
+
+class TestB {
+  friend class TestA;
+  void empty() {}
+};