adjust infinite type substitution workaround

resolves rdar://124697829

Co-authored-by: Slava Pestov <spestov@apple.com>

Author: kavon

lib/AST/ProtocolConformanceRef.cpp

@@ -118,13 +118,6 @@ ProtocolConformanceRef::subst(Type origType, InFlightSubstitution &IFS) const {
     return ProtocolConformanceRef::forInvalid();
   }
 
-  // If the type has been fully substituted and the requirement is for
-  // an invertible protocol, just do a module lookup. This avoids an infinite
-  // substitution issue by recognizing that these protocols are very simple
-  // (see rdar://119950540 for the general issue).
-  if (!substType->hasTypeParameter() && proto->getInvertibleProtocolKind())
-    return proto->getModuleContext()->lookupConformance(substType, proto);
-
   // Check the conformance map.
   // FIXME: Pack element level?
   return IFS.lookupConformance(origType->getCanonicalType(), substType, proto,

lib/AST/SubstitutionMap.cpp

@@ -355,6 +355,16 @@ SubstitutionMap::lookupConformance(CanType type, ProtocolDecl *proto) const {
   if (!type->isTypeParameter())
     return ProtocolConformanceRef::forInvalid();
 
+  // If the protocol is invertible, just do a global lookup. This avoids an
+  // infinite substitution issue by recognizing that these protocols are
+  // very simple (see rdar://119950540 for the general issue).
+  if (proto->getInvertibleProtocolKind()) {
+    auto substType = type.subst(*this);
+    if (!substType->isTypeParameter())
+      return proto->getModuleContext()->lookupConformance(substType, proto);
+    return ProtocolConformanceRef(proto);
+  }
+
   auto genericSig = getGenericSignature();
 
   auto getSignatureConformance =