Allow protocols to be just declared.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217704 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CGObjCMac.cpp

@@ -6236,7 +6236,7 @@ llvm::Constant *CGObjCNonFragileABIMac::GetOrEmitProtocolRef(
     // contents for protocols which were referenced but never defined.
     Entry =
         new llvm::GlobalVariable(CGM.getModule(), ObjCTypes.ProtocolnfABITy,
-                                 false, llvm::GlobalValue::WeakAnyLinkage,
+                                 false, llvm::GlobalValue::ExternalLinkage,
                                  nullptr,
                                  "\01l_OBJC_PROTOCOL_$_" + PD->getObjCRuntimeNameAsString());
     Entry->setSection("__DATA,__datacoal_nt,coalesced");
@@ -6347,8 +6347,8 @@ llvm::Constant *CGObjCNonFragileABIMac::GetOrEmitProtocol(
                                                    Values);
 
   if (Entry) {
-    // Already created, update the initializer.
-    assert(Entry->hasWeakAnyLinkage());
+    // Already created, fix the linkage and update the initializer.
+    Entry->setLinkage(llvm::GlobalValue::WeakAnyLinkage);
     Entry->setInitializer(Init);
   } else {
     Entry =

test/CodeGenObjC/undefined-protocol2.m

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -emit-llvm %s -o - | FileCheck %s
+
+// Test that we produce a declaration for the protocol. It must be matched
+// by a definition in another TU, so external is the correct linkage
+// (not extern_weak).
+// CHECK: @"\01l_OBJC_PROTOCOL_$_p1" = external global
+
+@interface NSObject
+@end
+
+@protocol p1;
+
+@interface I1 : NSObject <p1>
+@end
+
+@implementation I1
+@end