Index: include/clang/Basic/OpenCLOptions.h
===================================================================
--- include/clang/Basic/OpenCLOptions.h
+++ include/clang/Basic/OpenCLOptions.h
@@ -15,6 +15,8 @@
 #ifndef LLVM_CLANG_BASIC_OPENCLOPTIONS_H
 #define LLVM_CLANG_BASIC_OPENCLOPTIONS_H
 
+#include "llvm/ADT/StringRef.h"
+
 namespace clang {
 
 /// \brief OpenCL supported extensions and optional core features
@@ -29,8 +31,33 @@
   }
 
   // Enable all options.
-  void setAll() {
-#define OPENCLEXT(nm)   nm = 1;
+  void setAll(bool Enable = true) {
+#define OPENCLEXT(nm)   nm = Enable ? 1 : 0;
+#include "clang/Basic/OpenCLExtensions.def"
+  }
+
+  void set(llvm::StringRef Ext, bool Enable = true) {
+    assert(!Ext.empty() && "Extension is empty.");
+
+    switch (Ext[0]) {
+    case '+':
+      Enable = true;
+      Ext = Ext.drop_front();
+      break;
+    case '-':
+      Enable = false;
+      Ext = Ext.drop_front();
+      break;
+    }
+
+    if (Ext.equals("all")) {
+      setAll(Enable);
+    }
+
+#define OPENCLEXT(nm)       \
+    if (Ext.equals(#nm)) {  \
+      nm = Enable ? 1 : 0;  \
+    }
 #include "clang/Basic/OpenCLExtensions.def"
   }
 
Index: include/clang/Basic/TargetInfo.h
===================================================================
--- include/clang/Basic/TargetInfo.h
+++ include/clang/Basic/TargetInfo.h
@@ -981,6 +981,13 @@
   /// \brief Set supported OpenCL extensions and optional core features.
   virtual void setSupportedOpenCLOpts() {}
 
+  /// \brief Set supported OpenCL extensions as written on command line
+  virtual void setOpenCLExtensionOpts() {
+    for (const auto &Ext:getTargetOpts().OpenCLExtensionsAsWritten) {
+      getTargetOpts().SupportedOpenCLOptions.set(Ext);
+    }
+  }
+
   /// \brief Get supported OpenCL extensions and optional core features.
   OpenCLOptions &getSupportedOpenCLOpts() {
     return getTargetOpts().SupportedOpenCLOptions;
Index: include/clang/Basic/TargetOptions.h
===================================================================
--- include/clang/Basic/TargetOptions.h
+++ include/clang/Basic/TargetOptions.h
@@ -58,6 +58,10 @@
 
   /// Supported OpenCL extensions and optional core features.
   OpenCLOptions SupportedOpenCLOptions;
+
+  /// \brief The list of OpenCL extensions to enable or disable, as written on
+  /// the command line.
+  std::vector<std::string> OpenCLExtensionsAsWritten;
 };
 
 }  // end namespace clang
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -391,6 +391,8 @@
   HelpText<"OpenCL only. Allow denormals to be flushed to zero.">;
 def cl_fp32_correctly_rounded_divide_sqrt : Flag<["-"], "cl-fp32-correctly-rounded-divide-sqrt">, Group<opencl_Group>, Flags<[CC1Option]>,
   HelpText<"OpenCL only. Specify that single precision floating-point divide and sqrt used in the program source are correctly rounded.">;
+def cl_ext_EQ : CommaJoined<["-"], "cl-ext=">, Group<opencl_Group>, Flags<[CC1Option]>,
+  HelpText<"OpenCL only. Enable or disable specific OpenCL extensions.">;
 def client__name : JoinedOrSeparate<["-"], "client_name">;
 def combine : Flag<["-", "--"], "combine">, Flags<[DriverOption, Unsupported]>;
 def compatibility__version : JoinedOrSeparate<["-"], "compatibility_version">;
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -1874,6 +1874,8 @@
     Opts.cl_khr_global_int32_extended_atomics = 1;
     Opts.cl_khr_local_int32_base_atomics = 1;
     Opts.cl_khr_local_int32_extended_atomics = 1;
+
+    setOpenCLExtensionOpts();
   }
 };
 
@@ -2157,6 +2159,7 @@
       Opts.cl_amd_media_ops = 1;
       Opts.cl_amd_media_ops2 = 1;
     }
+    setOpenCLExtensionOpts();
   }
 
   LangAS::ID getOpenCLImageAddrSpace() const override {
@@ -2848,6 +2851,7 @@
 
   void setSupportedOpenCLOpts() override {
     getSupportedOpenCLOpts().setAll();
+    setOpenCLExtensionOpts();
   }
 };
 
@@ -8007,6 +8011,7 @@
     // Assume all OpenCL extensions and optional core features are supported
     // for SPIR since it is a generic target.
     getSupportedOpenCLOpts().setAll();
+    setOpenCLExtensionOpts();
   }
 };
 
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -2316,6 +2316,7 @@
   // Use the default target triple if unspecified.
   if (Opts.Triple.empty())
     Opts.Triple = llvm::sys::getDefaultTargetTriple();
+  Opts.OpenCLExtensionsAsWritten = Args.getAllArgValues(OPT_cl_ext_EQ);
 }
 
 bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
Index: test/SemaOpenCL/extensions.cl
===================================================================
--- test/SemaOpenCL/extensions.cl
+++ test/SemaOpenCL/extensions.cl
@@ -2,7 +2,20 @@
 // RUN: %clang_cc1 %s -triple spir-unknown-unknown -verify -pedantic -fsyntax-only -cl-std=CL1.1
 
 // Test with a target not supporting fp64.
-// RUN: %clang_cc1 %s -triple r600-unknown-unknown -target-cpu r600 -verify -pedantic -fsyntax-only -DNOFP64
+// RUN: %clang_cc1 %s -triple r600-unknown-unknown -target-cpu r600 -verify -pedantic -fsyntax-only -DNOFP64 -DNOFP16
+
+// Test with some extensions enabled or disabled by cmd-line args
+//
+// Target does not support fp64 and fp16 - override it
+// RUN: %clang_cc1 %s -triple r600-unknown-unknown -target-cpu r600 -verify -pedantic -fsyntax-only -cl-ext=+cl_khr_fp64,+cl_khr_fp16
+//
+// Disable or enable all extensions
+// RUN: %clang_cc1 %s -triple spir-unknown-unknown -verify -pedantic -fsyntax-only -cl-ext=-all -DNOFP64 -DNOFP16
+// RUN: %clang_cc1 %s -triple r600-unknown-unknown -target-cpu r600 -verify -pedantic -fsyntax-only -cl-ext=+all
+// RUN: %clang_cc1 %s -triple r600-unknown-unknown -target-cpu r600 -verify -pedantic -fsyntax-only -cl-ext=+all,-cl_khr_fp64 -DNOFP64
+// RUN: %clang_cc1 %s -triple r600-unknown-unknown -target-cpu r600 -verify -pedantic -fsyntax-only -cl-ext=-all,+cl_khr_fp64 -DNOFP16
+
+
 
 void f1(double da) { // expected-error {{type 'double' requires cl_khr_fp64 extension}}
   double d; // expected-error {{type 'double' requires cl_khr_fp64 extension}}
@@ -14,6 +27,11 @@
 // expected-warning@-2{{unsupported OpenCL extension 'cl_khr_fp64' - ignoring}}
 #endif
 
+#pragma OPENCL EXTENSION cl_khr_fp16 : enable
+#ifdef NOFP16
+// expected-warning@-2{{unsupported OpenCL extension 'cl_khr_fp16' - ignoring}}
+#endif
+
 void f2(void) {
   double d;
 #ifdef NOFP64
@@ -34,3 +52,13 @@
 void f3(void) {
   double d; // expected-error {{type 'double' requires cl_khr_fp64 extension}}
 }
+
+#ifdef CL_EXT_OPT
+#pragma OPENCL EXTENSION cl_khr_fp64 : enable // expected-warning{{unsupported OpenCL extension 'cl_khr_fp64' - ignoring}}
+#pragma OPENCL EXTENSION cl_khr_fp16 : enable
+
+#pragma OPENCL EXTENSION cl_khr_fp16 : disable
+void f4(__global half* h) {
+  *h = 4.h; // expected-error{{half precision constant requires cl_khr_fp16}}
+}
+#endif