Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -7524,7 +7524,7 @@
   RecordKernelParam
 };
 
-static OpenCLParamType getOpenCLKernelParameterType(QualType PT) {
+static OpenCLParamType getOpenCLKernelParameterType(Sema &S, QualType PT) {
   if (PT->isPointerType()) {
     QualType PointeeType = PT->getPointeeType();
     if (PointeeType->isPointerType())
@@ -7545,7 +7545,10 @@
   if (PT->isEventT())
     return InvalidKernelParam;
 
-  if (PT->isHalfType())
+  // OpenCL extension spec v1.2 s9.5:
+  // This extension adds support for half scalar and vector types as built-in
+  // types that can be used for arithmetic operations, conversions etc.
+  if (!S.getOpenCLOptions().cl_khr_fp16 && PT->isHalfType())
     return InvalidKernelParam;
 
   if (PT->isRecordType())
@@ -7566,7 +7569,7 @@
   if (ValidTypes.count(PT.getTypePtr()))
     return;
 
-  switch (getOpenCLKernelParameterType(PT)) {
+  switch (getOpenCLKernelParameterType(S, PT)) {
   case PtrPtrKernelParam:
     // OpenCL v1.2 s6.9.a:
     // A kernel function argument cannot be declared as a
@@ -7593,7 +7596,10 @@
     // OpenCL v1.2 s6.8 n:
     // A kernel function argument cannot be declared
     // of event_t type.
-    S.Diag(Param->getLocation(), diag::err_bad_kernel_param_type) << PT;
+    // Do not diagnose half type since it is diagnosed as invalid argument
+    // type for any function eleswhere.
+    if (!PT->isHalfType())
+      S.Diag(Param->getLocation(), diag::err_bad_kernel_param_type) << PT;
     D.setInvalidType();
     return;
 
@@ -7649,7 +7655,7 @@
       if (ValidTypes.count(QT.getTypePtr()))
         continue;
 
-      OpenCLParamType ParamType = getOpenCLKernelParameterType(QT);
+      OpenCLParamType ParamType = getOpenCLKernelParameterType(S, QT);
       if (ParamType == ValidKernelParam)
         continue;
 
Index: test/SemaOpenCL/half.cl
===================================================================
--- test/SemaOpenCL/half.cl
+++ test/SemaOpenCL/half.cl
@@ -25,6 +25,9 @@
   return h;
 }
 
+kernel void half_disabled_kernel(global half *p,
+                                 half h);  // expected-error{{declaring function parameter of type 'half' is not allowed; did you forget * ?}}
+
 // Exactly the same as above but with the cl_khr_fp16 extension enabled.
 #pragma OPENCL EXTENSION cl_khr_fp16 : enable
 constant half a = 1.0h;
@@ -48,3 +51,7 @@
 
   return h;
 }
+
+kernel void half_enabled_kernel(global half *p,
+                                half h);
+
Index: test/SemaOpenCL/invalid-kernel-parameters.cl
===================================================================
--- test/SemaOpenCL/invalid-kernel-parameters.cl
+++ test/SemaOpenCL/invalid-kernel-parameters.cl
@@ -1,5 +1,7 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple spir-unknown-unknown
 
+kernel void half_arg(half x) { } // expected-error{{declaring function parameter of type 'half' is not allowed; did you forget * ?}}
+
 #pragma OPENCL EXTENSION cl_khr_fp16 : enable
 
 
@@ -11,7 +13,8 @@
 
 kernel void bool_arg(bool x) { } // expected-error{{'bool' cannot be used as the type of a kernel parameter}}
 
-kernel void half_arg(half x) { } // expected-error{{'half' cannot be used as the type of a kernel parameter}}
+// half kernel argument is allowed when cl_khr_fp16 is enabled.
+kernel void half_arg(half x) { }
 
 typedef struct ContainsBool // expected-note{{within field of type 'ContainsBool' declared here}}
 {