diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -743,18 +743,6 @@
   }
 }
 
-/// Add extensions to the function declaration.
-/// \param S (in/out) The Sema instance.
-/// \param BIDecl (in) Description of the builtin.
-/// \param FDecl (in/out) FunctionDecl instance.
-static void AddOpenCLExtensions(Sema &S, const OpenCLBuiltinStruct &BIDecl,
-                                FunctionDecl *FDecl) {
-  // Fetch extension associated with a function prototype.
-  StringRef E = FunctionExtensionTable[BIDecl.Extension];
-  if (E != "")
-    S.setOpenCLExtensionForDecl(FDecl, E);
-}
-
 /// When trying to resolve a function name, if isOpenCLBuiltin() returns a
 /// non-null <Index, Len> pair, then the name is referencing an OpenCL
 /// builtin function.  Add all candidate signatures to the LookUpResult.
@@ -790,6 +778,13 @@
         (OpenCLVersion >= OpenCLBuiltin.MaxVersion))
       continue;
 
+    // Ignore this builtin function if it carries an extension macro that is
+    // not defined. This indicates that the extension is not supported by the
+    // target, so the builtin function should not be available.
+    StringRef Ext = FunctionExtensionTable[OpenCLBuiltin.Extension];
+    if (!Ext.empty() && !S.getPreprocessor().isMacroDefined(Ext))
+      continue;
+
     SmallVector<QualType, 1> RetTypes;
     SmallVector<SmallVector<QualType, 1>, 5> ArgTypes;
 
@@ -843,8 +838,6 @@
       if (!S.getLangOpts().OpenCLCPlusPlus)
         NewOpenCLBuiltin->addAttr(OverloadableAttr::CreateImplicit(Context));
 
-      AddOpenCLExtensions(S, OpenCLBuiltin, NewOpenCLBuiltin);
-
       LR.addDecl(NewOpenCLBuiltin);
     }
   }
diff --git a/clang/test/SemaOpenCL/fdeclare-opencl-builtins.cl b/clang/test/SemaOpenCL/fdeclare-opencl-builtins.cl
--- a/clang/test/SemaOpenCL/fdeclare-opencl-builtins.cl
+++ b/clang/test/SemaOpenCL/fdeclare-opencl-builtins.cl
@@ -38,26 +38,6 @@
 
   prefetch(a, 2);
 
-  atom_add((volatile __global int *)global_p, i);
-#if !defined(__OPENCL_CPP_VERSION__) && __OPENCL_C_VERSION__ < CL_VERSION_1_1
-// expected-error@-2{{no matching function for call to 'atom_add'}}
-
-// There are two potential definitions of the function "atom_add", both are
-// currently disabled because the associated extension is disabled.
-// expected-note@-6{{candidate function not viable: cannot pass pointer to address space '__global' as a pointer to address space '__local' in 1st argument}}
-// expected-note@-7{{candidate function not viable: no known conversion}}
-// expected-note@-8{{candidate function not viable: no known conversion}}
-// expected-note@-9{{candidate function not viable: no known conversion}}
-// expected-note@-10{{candidate unavailable as it requires OpenCL extension 'cl_khr_global_int32_base_atomics' to be enabled}}
-// expected-note@-11{{candidate unavailable as it requires OpenCL extension 'cl_khr_global_int32_base_atomics' to be enabled}}
-// expected-note@-12{{candidate unavailable as it requires OpenCL extension 'cl_khr_int64_base_atomics' to be enabled}}
-// expected-note@-13{{candidate unavailable as it requires OpenCL extension 'cl_khr_int64_base_atomics' to be enabled}}
-#endif
-
-#if __OPENCL_C_VERSION__ < CL_VERSION_1_1
-#pragma OPENCL EXTENSION cl_khr_global_int32_base_atomics : enable
-#endif
-
   atom_add((volatile __global int *)global_p, i);
   atom_cmpxchg((volatile __global unsigned int *)global_p, ui, ui);
 }
@@ -146,11 +126,9 @@
 
 kernel void basic_subgroup(global uint *out) {
   out[0] = get_sub_group_size();
-#if defined(__OPENCL_CPP_VERSION__)
-  // expected-error@-2{{no matching function for call to 'get_sub_group_size'}}
-  // expected-note@-3{{candidate unavailable as it requires OpenCL extension 'cl_khr_subgroups' to be enabled}}
-#else
-  // expected-error@-5{{use of declaration 'get_sub_group_size' requires cl_khr_subgroups extension to be enabled}}
+#if __OPENCL_C_VERSION__ <= CL_VERSION_1_2 && !defined(__OPENCL_CPP_VERSION__)
+  // expected-error@-2{{implicit declaration of function 'get_sub_group_size' is invalid in OpenCL}}
+  // expected-error@-3{{implicit conversion changes signedness}}
 #endif
 }