[IRGen] Functions with the ObjCMethod convention are not polymorphic.

...even if the 'self' type is generic. Additionally, Objective-C generic
types cannot be used as a source of type metadata, because Objective-C
generics are erased at runtime by default. (This may need to change.)

With these two changes, we now pass type metadata explicitly when we need
to, and /don't/ try to pass it to Objective-C methods that would have
needed it if they were Swift methods.

Author: jrose-apple

lib/IRGen/Fulfillment.cpp

@@ -230,6 +230,9 @@ bool FulfillmentMap::searchBoundGenericTypeMetadata(ModuleDecl &M,
                                                     unsigned source,
                                                     MetadataPath &&path,
                                          const InterestingKeysCallback &keys) {
+  if (type->getDecl()->hasClangNode())
+    return false;
+
   auto params = type->getDecl()->getGenericParams()->getAllArchetypes();
   auto substitutions = type->getSubstitutions(&M, nullptr);
   assert(params.size() >= substitutions.size() &&

lib/IRGen/GenProto.cpp

@@ -1283,9 +1283,13 @@ bool irgen::hasPolymorphicParameters(CanSILFunctionType ty) {
   case SILFunctionTypeRepresentation::Thick:
   case SILFunctionTypeRepresentation::Thin:
   case SILFunctionTypeRepresentation::Method:
-  case SILFunctionTypeRepresentation::ObjCMethod:
     return ty->isPolymorphic();
 
+  case SILFunctionTypeRepresentation::ObjCMethod:
+    // May be polymorphic at the SIL level, but no type metadata is actually
+    // passed.
+    return false;
+
   case SILFunctionTypeRepresentation::WitnessMethod:
     // Always carries polymorphic parameters for the Self type.
     return true;
@@ -1482,8 +1486,6 @@ namespace {
 
   private:
     void initGenerics() {
-      assert(hasPolymorphicParameters(FnType));
-
       // The canonical mangling signature removes dependent types that are
       // equal to concrete types, but isn't necessarily parallel with
       // substitutions.

lib/IRGen/IRGenSIL.cpp

@@ -1290,16 +1290,14 @@ static void emitEntryPointArgumentsCOrObjC(IRGenSILFunction &IGF,
 
   assert(params.empty() && "didn't claim all parameters!");
 
-  // Bind polymorphic arguments.  This can only be done after binding
-  // all the value parameters.
-  if (hasPolymorphicParameters(funcTy)) {
-    emitPolymorphicParameters(IGF, *IGF.CurSILFn, params,
-                              nullptr,
-      [&](unsigned paramIndex) -> llvm::Value* {
-        SILValue parameter = entry->getBBArgs()[paramIndex];
-        return IGF.getLoweredSingletonExplosion(parameter);
-      });
-  }
+  // Bind polymorphic arguments. This can only be done after binding
+  // all the value parameters, and must be done even for non-polymorphic
+  // functions because of imported Objective-C generics.
+  emitPolymorphicParameters(IGF, *IGF.CurSILFn, params, nullptr,
+                            [&](unsigned paramIndex) -> llvm::Value* {
+    SILValue parameter = entry->getBBArgs()[paramIndex];
+    return IGF.getLoweredSingletonExplosion(parameter);
+  });
 }
 
 /// Get metadata for the dynamic Self type if we have it.

test/Interpreter/imported_objc_generics.swift

@@ -102,8 +102,7 @@ ImportedObjCGenerics.test("ProtocolConstraints") {
   }
 
   let cs = CopyingContainer<NSString>(object: "Happy 2012")
-  // TODO: Fixed in next commit.
-  // expectEqual("Happy 2012", copyContainerContents(cs))
+  expectEqual("Happy 2012", copyContainerContents(cs))
 }
 
 ImportedObjCGenerics.test("ClassConstraints") {