IRGen: Fix type conversion of protocol compositions containing a generic superclass constraint

Do the same thing we do for nominal types, where if the type
contains an archetype, just mangle the unbound generic form,
since the name is just for documentation purposes in LLVM IR
dumps and does not have to be unique.

This is tested as part of an upcoming patch.

Author: slavapestov

lib/IRGen/GenType.cpp

@@ -1531,8 +1531,9 @@ llvm::StructType *IRGenModule::createNominalType(CanType type) {
   assert(type.getNominalOrBoundGenericNominal());
 
   // We share type infos for different instantiations of a generic type
-  // when the archetypes have the same exemplars.  Mangling the archetypes
-  // in this case can be very misleading, so we just mangle the base name.
+  // when the archetypes have the same exemplars.  We cannot mangle
+  // archetypes, and the mangling does not have to be unique, so we just
+  // mangle the unbound generic form of the type.
   if (type->hasArchetype())
     type = type.getNominalOrBoundGenericNominal()->getDeclaredType()
                                                  ->getCanonicalType();

lib/IRGen/IRGenMangler.cpp

@@ -94,7 +94,18 @@ mangleProtocolForLLVMTypeName(ProtocolCompositionType *type) {
         appendOperator("_");
     }
     if (layout.superclass) {
-      appendType(layout.superclass);
+      auto superclassTy = layout.superclass;
+
+      // We share type infos for different instantiations of a generic type
+      // when the archetypes have the same exemplars.  We cannot mangle
+      // archetypes, and the mangling does not have to be unique, so we just
+      // mangle the unbound generic form of the type.
+      if (superclassTy->hasArchetype()) {
+        superclassTy = superclassTy->getClassOrBoundGenericClass()
+          ->getDeclaredType();
+      }
+
+      appendType(CanType(superclassTy));
       appendOperator("Xc");
     } else if (layout.getLayoutConstraint()) {
       appendOperator("Xl");