From 42d495539ab024c194343fa3c32bd021aa3215a0 Mon Sep 17 00:00:00 2001
From: Fariborz Jahanian <fjahanian@apple.com>
Date: Thu, 24 Oct 2013 17:40:28 +0000
Subject: [PATCH] ObjectiveC IRGen. Replace _objc_empty_vtable pointer in
 Objective-C class metadata for certain deployment targets. // rdar://14802916

llvm-svn: 193359
---
 clang/lib/CodeGen/CGObjCMac.cpp               | 26 +++++++++++++------
 .../test/CodeGenObjC/null-objc-empty-vtable.m | 10 +++++++
 2 files changed, 28 insertions(+), 8 deletions(-)
 create mode 100644 clang/test/CodeGenObjC/null-objc-empty-vtable.m

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index f76182213a4d..b7209692e5e8 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -5757,6 +5757,9 @@ llvm::GlobalVariable * CGObjCNonFragileABIMac::BuildClassMetaData(
   };
   if (!Values[1])
     Values[1] = llvm::Constant::getNullValue(ObjCTypes.ClassnfABIPtrTy);
+  if (!Values[3])
+    Values[3] = llvm::Constant::getNullValue(
+                  llvm::PointerType::getUnqual(ObjCTypes.ImpnfABITy));
   llvm::Constant *Init = llvm::ConstantStruct::get(ObjCTypes.ClassnfABITy,
                                                    Values);
   llvm::GlobalVariable *GV = GetClassGlobal(ClassName);
@@ -5800,14 +5803,21 @@ void CGObjCNonFragileABIMac::GenerateClass(const ObjCImplementationDecl *ID) {
       llvm::GlobalValue::ExternalLinkage,
       0,
       "_objc_empty_cache");
-
-    ObjCEmptyVtableVar = new llvm::GlobalVariable(
-      CGM.getModule(),
-      ObjCTypes.ImpnfABITy,
-      false,
-      llvm::GlobalValue::ExternalLinkage,
-      0,
-      "_objc_empty_vtable");
+    
+    // Make this entry NULL for any iOS device target, any iOS simulator target,
+    // OS X with deployment target 10.9 or later.
+    const llvm::Triple &Triple = CGM.getTarget().getTriple();
+    if (Triple.isiOS() || (Triple.isMacOSX() && !Triple.isMacOSXVersionLT(10, 9)))
+      // This entry will be null.
+      ObjCEmptyVtableVar = 0;
+    else
+      ObjCEmptyVtableVar = new llvm::GlobalVariable(
+                                                    CGM.getModule(),
+                                                    ObjCTypes.ImpnfABITy,
+                                                    false,
+                                                    llvm::GlobalValue::ExternalLinkage,
+                                                    0,
+                                                    "_objc_empty_vtable");
   }
   assert(ID->getClassInterface() &&
          "CGObjCNonFragileABIMac::GenerateClass - class is 0");
diff --git a/clang/test/CodeGenObjC/null-objc-empty-vtable.m b/clang/test/CodeGenObjC/null-objc-empty-vtable.m
new file mode 100644
index 000000000000..fe69ce1f69c1
--- /dev/null
+++ b/clang/test/CodeGenObjC/null-objc-empty-vtable.m
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.9 -emit-llvm -o - %s | FileCheck -check-prefix CHECK-OSX %s
+// RUN: %clang_cc1 -triple thumbv7-apple-ios3.0.0  -emit-llvm -o - %s | FileCheck -check-prefix CHECK-IOS %s
+// rdar://14802916
+
+@interface I
+@end
+
+@implementation I @end
+// CHECK-OSX: %struct._class_t* null, %struct._objc_cache* @_objc_empty_cache, i8* (i8*, i8*)** null
+// CHECK-IOS: %struct._class_t* null, %struct._objc_cache* @_objc_empty_cache, i8* (i8*, i8*)** null