From: Adrian Prantl <adrian@qbert.apple.com>
Date:   Wed Feb 20 13:22:06 2013 -0800

    Emit the DIType for ObjC 'id<protocol>' as 'id' rather than objc_object*
        Fix for rdar://problem/12601916.
    
        The frontend treats 'id' as a typedef to an ObjCObjectType,
        whereas 'id<protocol>' is treated as an ObjCPointerType. For the
        debug info, we want to emit 'id' in both cases.

diff --git a/lib/CodeGen/CGDebugInfo.cpp b/lib/CodeGen/CGDebugInfo.cpp
index a4153d3..349e71a 100644
--- a/lib/CodeGen/CGDebugInfo.cpp
+++ b/lib/CodeGen/CGDebugInfo.cpp
@@ -530,9 +530,19 @@ llvm::DIType CGDebugInfo::CreateQualifiedType(QualType Ty, llvm::DIFile Unit) {
 
 llvm::DIType CGDebugInfo::CreateType(const ObjCObjectPointerType *Ty,
                                      llvm::DIFile Unit) {
+
+  // The frontend treats 'id' as a typedef to an ObjCObjectType,
+  // whereas 'id<protocol>' is treated as an ObjCPointerType. For the
+  // debug info, we want to emit 'id' in both cases.
+  QualType PointeeType = Ty->getPointeeType();
+  if (const ObjCObjectType *Obj = dyn_cast<ObjCObjectType>(PointeeType))
+    if (Obj->isObjCId() && (Obj->getNumProtocols() > 0)) {
+      return getOrCreateType(CGM.getContext().getObjCIdType(), Unit);
+    }
+
   llvm::DIType DbgTy =
     CreatePointerLikeType(llvm::dwarf::DW_TAG_pointer_type, Ty, 
-                          Ty->getPointeeType(), Unit);
+                          PointeeType, Unit);
   return DbgTy;
 }
 
@@ -618,7 +628,6 @@ llvm::DIType CGDebugInfo::CreatePointeeType(QualType PointeeTy,
     return RetTy;
   }
   return getOrCreateType(PointeeTy, Unit);
-
 }
 
 llvm::DIType CGDebugInfo::CreatePointerLikeType(unsigned Tag,
@@ -629,7 +638,7 @@ llvm::DIType CGDebugInfo::CreatePointerLikeType(unsigned Tag,
       Tag == llvm::dwarf::DW_TAG_rvalue_reference_type)
     return DBuilder.createReferenceType(Tag,
                                         CreatePointeeType(PointeeTy, Unit));
-                                    
+
   // Bit size, align and offset of the type.
   // Size is always the size of a pointer. We can't use getTypeSize here
   // because that does not return the correct value for references.
diff --git a/test/CodeGenObjC/debug-info-id-with-protocol.m b/test/CodeGenObjC/debug-info-id-with-protocol.m
new file mode 100644
index 0000000..db1a3ef
--- /dev/null
+++ b/test/CodeGenObjC/debug-info-id-with-protocol.m
@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -fobjc-default-synthesize-properties -emit-llvm -g %s -o - | FileCheck %s
+__attribute((objc_root_class)) @interface NSObject {
+	id isa;
+}
++ (id)alloc;
+- (id)init;
+- (id)retain;
+@end
+
+void NSLog(id, ...);
+
+@protocol MyProtocol
+
+-(const char *)hello;
+
+@end
+
+@interface MyClass : NSObject {
+}
+
+@property (nonatomic, assign) id <MyProtocol> bad_carrier;
+@property (nonatomic, assign) id good_carrier;
+
+@end
+
+@implementation MyClass
+@end
+
+int main()
+{
+    @autoreleasepool
+    {
+        MyClass *my_class = [MyClass alloc];
+        NSLog(@"%p\n", my_class.bad_carrier);
+        NSLog(@"%p\n", my_class.good_carrier);
+    }
+}
+// Verify that the debug type for both variables is 'id'.
+// CHECK: metadata !{i32 {{[0-9]+}}, metadata !{{[0-9]+}}, metadata !"bad_carrier", metadata !{{[0-9]+}}, i32 {{[0-9]+}}, metadata ![[IDTYPE:[0-9]+]], i32 0, i32 0} ; [ DW_TAG_arg_variable ] [bad_carrier] [line 21]
+// CHECK: metadata !{i32 {{[0-9]+}}, metadata !{{[0-9]+}}, metadata !"good_carrier", metadata !{{[0-9]+}}, i32 {{[0-9]+}}, metadata !{{.*}}[[IDTYPE]], i32 0, i32 0} ; [ DW_TAG_arg_variable ] [good_carrier] [line 22]
+// CHECK !{{.*}}[[IDTYPE]] = metadata !{i32 {{[0-9]+}}, null, metadata !"id", metadata !{{[0-9]+}}, i32 !{{[0-9]+}}, i64 0, i64 0, i64 0, i32 0, metadata !{{[0-9]+}}} ; [ DW_TAG_typedef ] [id]