[Clang] Bypass TAD during overload resolution if a perfect match exists

clang/include/clang/Sema/Overload.h

@@ -1005,14 +1005,14 @@ class Sema;
 
     // An overload is a perfect match if the conversion
     // sequences for each argument are perfect.
-    bool isPerfectMatch(const ASTContext &Ctx) const {
+    bool isPerfectMatch(const ASTContext &Ctx, bool ForConversion) const {
       if (!Viable)
         return false;
       for (const auto &C : Conversions) {
         if (!C.isInitialized() || !C.isPerfect(Ctx))
           return false;
       }
-      if (isa_and_nonnull<CXXConversionDecl>(Function))
+      if (ForConversion && isa_and_nonnull<CXXConversionDecl>(Function))
         return FinalConversion.isPerfect(Ctx);
       return true;
     }

clang/lib/Sema/SemaOverload.cpp

@@ -11229,7 +11229,8 @@ void OverloadCandidateSet::PerfectViableFunction(
   Best = end();
   for (auto It = begin(); It != end(); ++It) {
 
-    if (!It->isPerfectMatch(S.getASTContext()))
+    if (!It->isPerfectMatch(S.getASTContext(),
+                            Kind == CSK_InitByUserDefinedConversion))
       continue;
 
     // We found a suitable conversion function

clang/test/SemaCXX/overload-resolution-deferred-templates.cpp

@@ -183,3 +183,18 @@ void h(short n) { f(n); }
 }
 
 #endif
+
+template<typename ...Ts>
+struct t1 {
+};
+struct t6 {
+  template<typename T = int>
+  operator t1<float>() {
+    return {};
+  }
+};
+
+int main() {
+  t6 v6;
+  v6.operator t1<float>();
+}