5 files changed, 33 insertions, 7 deletions
diff --git a/absl/base/BUILD.bazel b/absl/base/BUILD.bazel
index 5f886359..23439a09 100644
--- a/absl/base/BUILD.bazel
+++ b/absl/base/BUILD.bazel
@@ -286,6 +286,7 @@ cc_test(
     copts = ABSL_TEST_COPTS,
     deps = [
         ":config",
+        "//absl/synchronization:thread_pool",
         "@com_google_googletest//:gtest_main",
     ],
 )
diff --git a/absl/base/casts.h b/absl/base/casts.h
index 2a0adc29..266c4a0a 100644
--- a/absl/base/casts.h
+++ b/absl/base/casts.h
@@ -50,7 +50,7 @@ namespace absl {
 //
 // An `implicit_cast()` may also be used to annotate numeric type conversions
 // that, although safe, may produce compiler warnings (such as `long` to `int`).
-// Additionally, an `implict_cast()` is also useful within return statements to
+// Additionally, an `implicit_cast()` is also useful within return statements to
 // indicate a specific implicit conversion is being undertaken.
 //
 // Example:
diff --git a/absl/base/config.h b/absl/base/config.h
index cf47f84c..c768e722 100644
--- a/absl/base/config.h
+++ b/absl/base/config.h
@@ -56,6 +56,13 @@
 #include <cstddef>
 #endif  // __cplusplus
 
+#if defined(__APPLE__)
+// Included for TARGET_OS_IPHONE, __IPHONE_OS_VERSION_MIN_REQUIRED,
+// __IPHONE_8_0.
+#include <Availability.h>
+#include <TargetConditionals.h>
+#endif
+
 #include "absl/base/policy_checks.h"
 
 // -----------------------------------------------------------------------------
@@ -151,12 +158,13 @@
 //
 // Checks whether C++11's `thread_local` storage duration specifier is
 // supported.
-//
-// Notes: Clang implements the `thread_local` keyword but Xcode did not support
-// the implementation until Xcode 8.
 #ifdef ABSL_HAVE_THREAD_LOCAL
 #error ABSL_HAVE_THREAD_LOCAL cannot be directly set
-#elif !defined(__apple_build_version__) || __apple_build_version__ >= 8000042
+#elif !defined(__apple_build_version__) ||   \
+    ((__apple_build_version__ >= 8000042) && \
+     !(TARGET_OS_IPHONE && __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_8_0))
+// Notes: Xcode's clang did not support `thread_local` until version
+// 8, and even then not for iOS < 8.0.
 #define ABSL_HAVE_THREAD_LOCAL 1
 #endif
 
diff --git a/absl/base/config_test.cc b/absl/base/config_test.cc
index ab04b447..c839712a 100644
--- a/absl/base/config_test.cc
+++ b/absl/base/config_test.cc
@@ -17,12 +17,12 @@
 #include <cstdint>
 
 #include "gtest/gtest.h"
+#include "absl/synchronization/internal/thread_pool.h"
 
 namespace {
 
 TEST(ConfigTest, Endianness) {
-  union
-  {
+  union {
     uint32_t value;
     uint8_t data[sizeof(uint32_t)];
   } number;
@@ -41,4 +41,20 @@ TEST(ConfigTest, Endianness) {
 #endif
 }
 
+#if defined(ABSL_HAVE_THREAD_LOCAL)
+TEST(ConfigTest, ThreadLocal) {
+  static thread_local int mine_mine_mine = 16;
+  EXPECT_EQ(16, mine_mine_mine);
+  {
+    absl::synchronization_internal::ThreadPool pool(1);
+    pool.Schedule([&] {
+      EXPECT_EQ(16, mine_mine_mine);
+      mine_mine_mine = 32;
+      EXPECT_EQ(32, mine_mine_mine);
+    });
+  }
+  EXPECT_EQ(16, mine_mine_mine);
+}
+#endif
+
 }  // namespace
diff --git a/absl/base/optimization.h b/absl/base/optimization.h
index db8beafa..aaaffa49 100644
--- a/absl/base/optimization.h
+++ b/absl/base/optimization.h
@@ -46,6 +46,7 @@
 // GCC will not tail call given inline volatile assembly.
 #define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() __asm__ __volatile__("")
 #elif defined(_MSC_VER)
+#include <intrin.h>
 // The __nop() intrinsic blocks the optimisation.
 #define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() __nop()
 #else