Index: clang/include/clang/Sema/Lookup.h
===================================================================
--- clang/include/clang/Sema/Lookup.h
+++ clang/include/clang/Sema/Lookup.h
@@ -814,6 +814,8 @@
     Decls.erase(cast<NamedDecl>(D->getCanonicalDecl()));
   }

+  bool empty(void) { return Decls.empty(); }
+
   using iterator =
       llvm::mapped_iterator<decltype(Decls)::iterator, select_second>;

Index: clang/lib/Sema/SemaOverload.cpp
===================================================================
--- clang/lib/Sema/SemaOverload.cpp
+++ clang/lib/Sema/SemaOverload.cpp
@@ -9389,6 +9389,9 @@
   // FIXME: Pass in the explicit template arguments?
   ArgumentDependentLookup(Name, Loc, Args, Fns);

+  if (Fns.empty())
+    return;
+
   // Erase all of the candidates we already knew about.
   for (OverloadCandidateSet::iterator Cand = CandidateSet.begin(),
                                    CandEnd = CandidateSet.end();