Index: lib/Parse/ParsePragma.cpp
===================================================================
--- lib/Parse/ParsePragma.cpp
+++ lib/Parse/ParsePragma.cpp
@@ -506,10 +506,12 @@
   // overriding all previously issued extension directives, but only if the
   // behavior is set to disable."
   if (Name == "all") {
-    if (State == Disable)
+    if (State == Disable) {
       Opt.disableAll();
-    else
+      Opt.enableSupportedCore(getLangOpts().OpenCLVersion);
+    } else {
       PP.Diag(NameLoc, diag::warn_pragma_expected_predicate) << 1;
+    }
   } else if (State == Begin) {
     if (!Opt.isKnown(Name) ||
         !Opt.isSupported(Name, getLangOpts().OpenCLVersion)) {
Index: test/SemaOpenCL/extensions.cl
===================================================================
--- test/SemaOpenCL/extensions.cl
+++ test/SemaOpenCL/extensions.cl
@@ -22,6 +22,17 @@
 // RUN: %clang_cc1 %s -triple spir-unknown-unknown -verify -pedantic -fsyntax-only -cl-ext=-all -cl-ext=+cl_khr_fp64 -cl-ext=+cl_khr_fp16 -cl-ext=-cl_khr_fp64 -DNOFP64
 // RUN: %clang_cc1 %s -triple spir-unknown-unknown -verify -pedantic -fsyntax-only -cl-ext=-all -cl-ext=+cl_khr_fp64,-cl_khr_fp64,+cl_khr_fp16 -DNOFP64
 
+// Test with -finclude-default-header, which includes opencl-c.h. opencl-c.h
+// disables all extensions by default, but supported core extensions for a
+// particular OpenCL version must be re-enabled (for example, cl_khr_fp64 is
+// enabled by default with -cl-std=CL2.0).
+//
+// RUN: %clang_cc1 %s -triple amdgcn-unknown-unknown -verify -pedantic -fsyntax-only -cl-std=CL2.0 -finclude-default-header
+
+#ifdef _OPENCL_H_
+// expected-no-diagnostics
+#endif
+
 #ifdef FP64
 // expected-no-diagnostics
 #endif
@@ -33,6 +44,7 @@
 }
 #endif
 
+#ifndef _OPENCL_H_
 int isnan(float x) {
     return __builtin_isnan(x);
 }
@@ -40,6 +52,7 @@
 int isfinite(float x) {
     return __builtin_isfinite(x);
 }
+#endif
 
 #pragma OPENCL EXTENSION cl_khr_fp64 : enable
 #ifdef NOFP64