Index: cfe/trunk/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/CGBuiltin.cpp
+++ cfe/trunk/lib/CodeGen/CGBuiltin.cpp
@@ -1982,6 +1982,12 @@
       return RValue::get(ConstantInt::get(ResultType, 0));
 
     Value *ArgValue = EmitScalarExpr(Arg);
+    if (ArgType->isObjCObjectPointerType()) {
+      // Convert Objective-C objects to id because we cannot distinguish between
+      // LLVM types for Obj-C classes as they are opaque.
+      ArgType = CGM.getContext().getObjCIdType();
+      ArgValue = Builder.CreateBitCast(ArgValue, ConvertType(ArgType));
+    }
     Function *F =
         CGM.getIntrinsic(Intrinsic::is_constant, ConvertType(ArgType));
     Value *Result = Builder.CreateCall(F, ArgValue);
Index: cfe/trunk/test/CodeGenObjC/builtin-constant-p.m
===================================================================
--- cfe/trunk/test/CodeGenObjC/builtin-constant-p.m
+++ cfe/trunk/test/CodeGenObjC/builtin-constant-p.m
@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -emit-llvm -O3 -disable-llvm-passes -o - %s | FileCheck %s
+
+// Test that can call `__builtin_constant_p` with instances of different
+// Objective-C classes.
+// rdar://problem/47499250
+@class Foo;
+@class Bar;
+
+extern void callee(void);
+
+// CHECK-LABEL: define void @test(%0* %foo, %1* %bar)
+void test(Foo *foo, Bar *bar) {
+  // CHECK: [[ADDR_FOO:%.*]] = bitcast %0* %{{.*}} to i8*
+  // CHECK-NEXT: call i1 @llvm.is.constant.p0i8(i8* [[ADDR_FOO]])
+  // CHECK: [[ADDR_BAR:%.*]] = bitcast %1* %{{.*}} to i8*
+  // CHECK-NEXT: call i1 @llvm.is.constant.p0i8(i8* [[ADDR_BAR]])
+  if (__builtin_constant_p(foo) && __builtin_constant_p(bar))
+    callee();
+}
+
+// Test other Objective-C types.
+// CHECK-LABEL: define void @test_more(i8* %object, i8* %klass)
+void test_more(id object, Class klass) {
+  // CHECK: call i1 @llvm.is.constant.p0i8(i8* %{{.*}})
+  // CHECK: call i1 @llvm.is.constant.p0i8(i8* %{{.*}})
+  if (__builtin_constant_p(object) && __builtin_constant_p(klass))
+    callee();
+}