AST: Use source location instead of memory address to tie break associated types

If two associated types in an (invalid) protocol have the same name, use their
source location to order them instead of their memory address. This fixes a
non-deterministic test failure with the requirement machine enabled.

Author: slavapestov

lib/AST/GenericSignature.cpp

@@ -23,6 +23,7 @@
 #include "swift/AST/Module.h"
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/Types.h"
+#include "swift/Basic/SourceManager.h"
 #include "swift/Basic/STLExtras.h"
 #include "RequirementMachine/RequirementMachine.h"
 #include <functional>
@@ -1492,9 +1493,12 @@ int swift::compareAssociatedTypes(AssociatedTypeDecl *assocType1,
     return compareProtocols;
 
   // Error case: if we have two associated types with the same name in the
-  // same protocol, just tie-break based on address.
-  if (assocType1 != assocType2)
-    return assocType1 < assocType2 ? -1 : +1;
+  // same protocol, just tie-break based on source location.
+  if (assocType1 != assocType2) {
+    auto &ctx = assocType1->getASTContext();
+    return ctx.SourceMgr.isBeforeInBuffer(assocType1->getLoc(),
+                                          assocType2->getLoc()) ? -1 : +1;
+  }
 
   return 0;
 }