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

clang/lib/Sema/SemaInit.cpp

@@ -5231,7 +5231,7 @@ static OverloadingResult TryRefInitWithConversionFunction(
 
   // Add the final conversion sequence, if necessary.
   if (NewRefRelationship == Sema::Ref_Incompatible) {
-    assert(!isa<CXXConstructorDecl>(Function) &&
+    assert(Best->HasFinalConversion && !isa<CXXConstructorDecl>(Function) &&
            "should not have conversion after constructor");
 
     ImplicitConversionSequence ICS;
@@ -6200,6 +6200,7 @@ static void TryUserDefinedConversion(Sema &S,
 
   // If the conversion following the call to the conversion function
   // is interesting, add it as a separate step.
+  assert(Best->HasFinalConversion);
   if (Best->FinalConversion.First || Best->FinalConversion.Second ||
       Best->FinalConversion.Third) {
     ImplicitConversionSequence ICS;

clang/lib/Sema/SemaOverload.cpp

@@ -4079,6 +4079,9 @@ IsUserDefinedConversion(Sema &S, Expr *From, QualType ToType,
     }
     if (CXXConversionDecl *Conversion
                  = dyn_cast<CXXConversionDecl>(Best->Function)) {
+
+      assert(Best->HasFinalConversion);
+
       // C++ [over.ics.user]p1:
       //
       //   [...] If the user-defined conversion is specified by a
@@ -5175,6 +5178,7 @@ FindConversionForRefInit(Sema &S, ImplicitConversionSequence &ICS,
     if (!Best->FinalConversion.DirectBinding)
       return false;
 
+    assert(Best->HasFinalConversion);
     ICS.setUserDefined();
     ICS.UserDefined.Before = Best->Conversions[0].Standard;
     ICS.UserDefined.After = Best->FinalConversion;
@@ -10758,6 +10762,8 @@ bool clang::isBetterOverloadCandidate(
       Cand1.Function && Cand2.Function &&
       isa<CXXConversionDecl>(Cand1.Function) &&
       isa<CXXConversionDecl>(Cand2.Function)) {
+
+    assert(Cand1.HasFinalConversion && Cand2.HasFinalConversion);
     // First check whether we prefer one of the conversion functions over the
     // other. This only distinguishes the results in non-standard, extension
     // cases such as the conversion from a lambda closure type to a function