[IRGen] Stop using "extended" type encodings where not supported

These are only used in two places in the Apple Objective-C runtime:

- A protocol's "extended method types" list
- Block type descriptors

We were using them when dynamically registering a protocol with the
Objective-C runtime, but that's just expecting "normal" types; the
"extended method types" list is never present in such a protocol.

Author: jrose-apple

lib/IRGen/GenClass.cpp

@@ -1650,7 +1650,7 @@ namespace {
     }
 
     llvm::Constant *buildOptExtendedMethodTypes() {
-      if (!isBuildingProtocol()) return null();
+      assert(isBuildingProtocol());
 
       ConstantInitBuilder builder(IGM);
       auto array = builder.beginArray();
@@ -1670,6 +1670,8 @@ namespace {
 
     void buildExtMethodTypes(ConstantArrayBuilder &array,
                              ArrayRef<MethodDescriptor> methods) {
+      assert(isBuildingProtocol());
+
       for (auto descriptor : methods) {
         assert(descriptor.getKind() == MethodDescriptor::Kind::Method &&
                "cannot emit descriptor for non-method");

lib/IRGen/GenDecl.cpp

@@ -189,9 +189,7 @@ class CategoryInitializerVisitor
       return;
 
     llvm::Constant *name, *imp, *types;
-    emitObjCMethodDescriptorParts(IGM, method,
-                                  /*extended*/false,
-                                  /*concrete*/true,
+    emitObjCMethodDescriptorParts(IGM, method, /*concrete*/true,
                                   name, types, imp);
 
     // When generating JIT'd code, we need to call sel_registerName() to force
@@ -215,8 +213,7 @@ class CategoryInitializerVisitor
   void visitConstructorDecl(ConstructorDecl *constructor) {
     if (!requiresObjCMethodDescriptor(constructor)) return;
     llvm::Constant *name, *imp, *types;
-    emitObjCMethodDescriptorParts(IGM, constructor, /*extended*/false,
-                                  /*concrete*/true,
+    emitObjCMethodDescriptorParts(IGM, constructor, /*concrete*/true,
                                   name, types, imp);
 
     // When generating JIT'd code, we need to call sel_registerName() to force
@@ -392,8 +389,7 @@ class ObjCProtocolInitializerVisitor
 
   void visitAbstractFunctionDecl(AbstractFunctionDecl *method) {
     llvm::Constant *name, *imp, *types;
-    emitObjCMethodDescriptorParts(IGM, method, /*extended*/true,
-                                  /*concrete*/false,
+    emitObjCMethodDescriptorParts(IGM, method, /*concrete*/false,
                                   name, types, imp);
 
     // When generating JIT'd code, we need to call sel_registerName() to force

lib/IRGen/GenObjC.cpp

@@ -1124,7 +1124,6 @@ static llvm::Constant *getObjCEncodingForMethodType(IRGenModule &IGM,
 /// type encoding, and IMP pointer.
 SILFunction *irgen::emitObjCMethodDescriptorParts(IRGenModule &IGM,
                                                   AbstractFunctionDecl *method,
-                                                  bool extendedEncoding,
                                                   bool concrete,
                                                   llvm::Constant *&selectorRef,
                                                   llvm::Constant *&atEncoding,
@@ -1138,7 +1137,7 @@ SILFunction *irgen::emitObjCMethodDescriptorParts(IRGenModule &IGM,
   /// the return type @encoding and every parameter type @encoding, glued with
   /// numbers that used to represent stack offsets for each of these elements.
   CanSILFunctionType methodType = getObjCMethodType(IGM, method);
-  atEncoding = getObjCEncodingForMethodType(IGM, methodType, extendedEncoding);
+  atEncoding = getObjCEncodingForMethodType(IGM, methodType, /*extended*/false);
 
   /// The third element is the method implementation pointer.
   if (!concrete) {
@@ -1315,10 +1314,8 @@ void irgen::emitObjCMethodDescriptor(IRGenModule &IGM,
                                      ConstantArrayBuilder &descriptors,
                                      AbstractFunctionDecl *method) {
   llvm::Constant *selectorRef, *atEncoding, *impl;
-  auto silFn = emitObjCMethodDescriptorParts(IGM, method,
-                                /*extended*/ false,
-                                /*concrete*/ true,
-                                selectorRef, atEncoding, impl);
+  auto silFn = emitObjCMethodDescriptorParts(IGM, method, /*concrete*/ true,
+                                             selectorRef, atEncoding, impl);
   buildMethodDescriptor(descriptors, selectorRef, atEncoding, impl);
 
   if (silFn && silFn->hasObjCReplacement()) {

lib/IRGen/GenObjC.h

@@ -109,7 +109,6 @@ namespace irgen {
   /// method or constructor implementation.
   SILFunction *emitObjCMethodDescriptorParts(IRGenModule &IGM,
                                              AbstractFunctionDecl *method,
-                                             bool extendedEncoding,
                                              bool concrete,
                                              llvm::Constant *&selectorRef,
                                              llvm::Constant *&atEncoding,