Creation of LTS branch "lts_2018_12_18"20181200

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GitOrigin-RevId: 44b0fafc62d9b8f192e8180cbe9c4b806b339d57
Change-Id: I2c427b5b41b2d34101922048b00f3d9dafcb498d

39 files changed, 907 insertions, 356 deletions

diff --git a/absl/base/internal/atomic_hook.h b/absl/base/internal/atomic_hook.h
index 7d0ee2fa..58ddf272 100644
--- a/absl/base/internal/atomic_hook.h
+++ b/absl/base/internal/atomic_hook.h
@@ -28,7 +28,7 @@
 #endif
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 template <typename T>
@@ -161,7 +161,7 @@ class AtomicHook<ReturnType (*)(Args...)> {
 #undef ABSL_HAVE_WORKING_ATOMIC_POINTER
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_
diff --git a/absl/base/internal/bits.h b/absl/base/internal/bits.h
new file mode 100644
index 00000000..29657426
--- /dev/null
+++ b/absl/base/internal/bits.h
@@ -0,0 +1,195 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_BITS_H_
+#define ABSL_BASE_INTERNAL_BITS_H_
+
+// This file contains bitwise ops which are implementation details of various
+// absl libraries.
+
+#include <cstdint>
+
+// Clang on Windows has __builtin_clzll; otherwise we need to use the
+// windows intrinsic functions.
+#if defined(_MSC_VER)
+#include <intrin.h>
+#if defined(_M_X64)
+#pragma intrinsic(_BitScanReverse64)
+#pragma intrinsic(_BitScanForward64)
+#endif
+#pragma intrinsic(_BitScanReverse)
+#pragma intrinsic(_BitScanForward)
+#endif
+
+#include "absl/base/attributes.h"
+
+#if defined(_MSC_VER)
+// We can achieve something similar to attribute((always_inline)) with MSVC by
+// using the __forceinline keyword, however this is not perfect. MSVC is
+// much less aggressive about inlining, and even with the __forceinline keyword.
+#define ABSL_BASE_INTERNAL_FORCEINLINE __forceinline
+#else
+// Use default attribute inline.
+#define ABSL_BASE_INTERNAL_FORCEINLINE inline ABSL_ATTRIBUTE_ALWAYS_INLINE
+#endif
+
+
+namespace absl {
+inline namespace lts_2018_12_18 {
+namespace base_internal {
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64Slow(uint64_t n) {
+  int zeroes = 60;
+  if (n >> 32) zeroes -= 32, n >>= 32;
+  if (n >> 16) zeroes -= 16, n >>= 16;
+  if (n >> 8) zeroes -= 8, n >>= 8;
+  if (n >> 4) zeroes -= 4, n >>= 4;
+  return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[n] + zeroes;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64(uint64_t n) {
+#if defined(_MSC_VER) && defined(_M_X64)
+  // MSVC does not have __buitin_clzll. Use _BitScanReverse64.
+  unsigned long result = 0;  // NOLINT(runtime/int)
+  if (_BitScanReverse64(&result, n)) {
+    return 63 - result;
+  }
+  return 64;
+#elif defined(_MSC_VER)
+  // MSVC does not have __buitin_clzll. Compose two calls to _BitScanReverse
+  unsigned long result = 0;  // NOLINT(runtime/int)
+  if ((n >> 32) && _BitScanReverse(&result, n >> 32)) {
+    return 31 - result;
+  }
+  if (_BitScanReverse(&result, n)) {
+    return 63 - result;
+  }
+  return 64;
+#elif defined(__GNUC__)
+  // Use __builtin_clzll, which uses the following instructions:
+  //  x86: bsr
+  //  ARM64: clz
+  //  PPC: cntlzd
+  static_assert(sizeof(unsigned long long) == sizeof(n),  // NOLINT(runtime/int)
+                "__builtin_clzll does not take 64-bit arg");
+
+  // Handle 0 as a special case because __builtin_clzll(0) is undefined.
+  if (n == 0) {
+    return 64;
+  }
+  return __builtin_clzll(n);
+#else
+  return CountLeadingZeros64Slow(n);
+#endif
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32Slow(uint64_t n) {
+  int zeroes = 28;
+  if (n >> 16) zeroes -= 16, n >>= 16;
+  if (n >> 8) zeroes -= 8, n >>= 8;
+  if (n >> 4) zeroes -= 4, n >>= 4;
+  return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[n] + zeroes;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32(uint32_t n) {
+#if defined(_MSC_VER)
+  unsigned long result = 0;  // NOLINT(runtime/int)
+  if (_BitScanReverse(&result, n)) {
+    return 31 - result;
+  }
+  return 32;
+#elif defined(__GNUC__)
+  // Use __builtin_clz, which uses the following instructions:
+  //  x86: bsr
+  //  ARM64: clz
+  //  PPC: cntlzd
+  static_assert(sizeof(int) == sizeof(n),
+                "__builtin_clz does not take 32-bit arg");
+
+  // Handle 0 as a special case because __builtin_clz(0) is undefined.
+  if (n == 0) {
+    return 32;
+  }
+  return __builtin_clz(n);
+#else
+  return CountLeadingZeros32Slow(n);
+#endif
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64Slow(uint64_t n) {
+  int c = 63;
+  n &= ~n + 1;
+  if (n & 0x00000000FFFFFFFF) c -= 32;
+  if (n & 0x0000FFFF0000FFFF) c -= 16;
+  if (n & 0x00FF00FF00FF00FF) c -= 8;
+  if (n & 0x0F0F0F0F0F0F0F0F) c -= 4;
+  if (n & 0x3333333333333333) c -= 2;
+  if (n & 0x5555555555555555) c -= 1;
+  return c;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64(uint64_t n) {
+#if defined(_MSC_VER) && defined(_M_X64)
+  unsigned long result = 0;  // NOLINT(runtime/int)
+  _BitScanForward64(&result, n);
+  return result;
+#elif defined(_MSC_VER)
+  unsigned long result = 0;  // NOLINT(runtime/int)
+  if (static_cast<uint32_t>(n) == 0) {
+    _BitScanForward(&result, n >> 32);
+    return result + 32;
+  }
+  _BitScanForward(&result, n);
+  return result;
+#elif defined(__GNUC__)
+  static_assert(sizeof(unsigned long long) == sizeof(n),  // NOLINT(runtime/int)
+                "__builtin_ctzll does not take 64-bit arg");
+  return __builtin_ctzll(n);
+#else
+  return CountTrailingZerosNonZero64Slow(n);
+#endif
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32Slow(uint32_t n) {
+  int c = 31;
+  n &= ~n + 1;
+  if (n & 0x0000FFFF) c -= 16;
+  if (n & 0x00FF00FF) c -= 8;
+  if (n & 0x0F0F0F0F) c -= 4;
+  if (n & 0x33333333) c -= 2;
+  if (n & 0x55555555) c -= 1;
+  return c;
+}
+
+ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
+#if defined(_MSC_VER)
+  unsigned long result = 0;  // NOLINT(runtime/int)
+  _BitScanForward(&result, n);
+  return result;
+#elif defined(__GNUC__)
+  static_assert(sizeof(int) == sizeof(n),
+                "__builtin_ctz does not take 32-bit arg");
+  return __builtin_ctz(n);
+#else
+  return CountTrailingZerosNonZero32Slow(n);
+#endif
+}
+
+#undef ABSL_BASE_INTERNAL_FORCEINLINE
+
+}  // namespace base_internal
+}  // inline namespace lts_2018_12_18
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_BITS_H_
diff --git a/absl/base/internal/bits_test.cc b/absl/base/internal/bits_test.cc
new file mode 100644
index 00000000..e5d991d6
--- /dev/null
+++ b/absl/base/internal/bits_test.cc
@@ -0,0 +1,97 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/base/internal/bits.h"
+
+#include "gtest/gtest.h"
+
+namespace {
+
+int CLZ64(uint64_t n) {
+  int fast = absl::base_internal::CountLeadingZeros64(n);
+  int slow = absl::base_internal::CountLeadingZeros64Slow(n);
+  EXPECT_EQ(fast, slow) << n;
+  return fast;
+}
+
+TEST(BitsTest, CountLeadingZeros64) {
+  EXPECT_EQ(64, CLZ64(uint64_t{}));
+  EXPECT_EQ(0, CLZ64(~uint64_t{}));
+
+  for (int index = 0; index < 64; index++) {
+    uint64_t x = static_cast<uint64_t>(1) << index;
+    const auto cnt = 63 - index;
+    ASSERT_EQ(cnt, CLZ64(x)) << index;
+    ASSERT_EQ(cnt, CLZ64(x + x - 1)) << index;
+  }
+}
+
+int CLZ32(uint32_t n) {
+  int fast = absl::base_internal::CountLeadingZeros32(n);
+  int slow = absl::base_internal::CountLeadingZeros32Slow(n);
+  EXPECT_EQ(fast, slow) << n;
+  return fast;
+}
+
+TEST(BitsTest, CountLeadingZeros32) {
+  EXPECT_EQ(32, CLZ32(uint32_t{}));
+  EXPECT_EQ(0, CLZ32(~uint32_t{}));
+
+  for (int index = 0; index < 32; index++) {
+    uint32_t x = static_cast<uint32_t>(1) << index;
+    const auto cnt = 31 - index;
+    ASSERT_EQ(cnt, CLZ32(x)) << index;
+    ASSERT_EQ(cnt, CLZ32(x + x - 1)) << index;
+    ASSERT_EQ(CLZ64(x), CLZ32(x) + 32);
+  }
+}
+
+int CTZ64(uint64_t n) {
+  int fast = absl::base_internal::CountTrailingZerosNonZero64(n);
+  int slow = absl::base_internal::CountTrailingZerosNonZero64Slow(n);
+  EXPECT_EQ(fast, slow) << n;
+  return fast;
+}
+
+TEST(BitsTest, CountTrailingZerosNonZero64) {
+  EXPECT_EQ(0, CTZ64(~uint64_t{}));
+
+  for (int index = 0; index < 64; index++) {
+    uint64_t x = static_cast<uint64_t>(1) << index;
+    const auto cnt = index;
+    ASSERT_EQ(cnt, CTZ64(x)) << index;
+    ASSERT_EQ(cnt, CTZ64(~(x - 1))) << index;
+  }
+}
+
+int CTZ32(uint32_t n) {
+  int fast = absl::base_internal::CountTrailingZerosNonZero32(n);
+  int slow = absl::base_internal::CountTrailingZerosNonZero32Slow(n);
+  EXPECT_EQ(fast, slow) << n;
+  return fast;
+}
+
+TEST(BitsTest, CountTrailingZerosNonZero32) {
+  EXPECT_EQ(0, CTZ32(~uint32_t{}));
+
+  for (int index = 0; index < 32; index++) {
+    uint32_t x = static_cast<uint32_t>(1) << index;
+    const auto cnt = index;
+    ASSERT_EQ(cnt, CTZ32(x)) << index;
+    ASSERT_EQ(cnt, CTZ32(~(x - 1))) << index;
+  }
+}
+
+
+}  // namespace
diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc
index a4f1fc21..d99b63d3 100644
--- a/absl/base/internal/cycleclock.cc
+++ b/absl/base/internal/cycleclock.cc
@@ -27,7 +27,7 @@
 #include "absl/base/internal/unscaledcycleclock.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 #if ABSL_USE_UNSCALED_CYCLECLOCK
@@ -79,5 +79,5 @@ double CycleClock::Frequency() {
 #endif
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/cycleclock.h b/absl/base/internal/cycleclock.h
index 5fd8b348..ae5ede3e 100644
--- a/absl/base/internal/cycleclock.h
+++ b/absl/base/internal/cycleclock.h
@@ -46,7 +46,7 @@
 #include <cstdint>
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // -----------------------------------------------------------------------------
@@ -73,7 +73,7 @@ class CycleClock {
 };
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_CYCLECLOCK_H_
diff --git a/absl/base/internal/direct_mmap.h b/absl/base/internal/direct_mmap.h
index e98c9960..f064e363 100644
--- a/absl/base/internal/direct_mmap.h
+++ b/absl/base/internal/direct_mmap.h
@@ -62,7 +62,7 @@ extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
 #endif  // __BIONIC__
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // Platform specific logic extracted from
@@ -76,7 +76,11 @@ inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
   // On these architectures, implement mmap with mmap2.
   static int pagesize = 0;
   if (pagesize == 0) {
+#if defined(__wasm__) || defined(__asmjs__)
     pagesize = getpagesize();
+#else
+    pagesize = sysconf(_SC_PAGESIZE);
+#endif
   }
   if (offset < 0 || offset % pagesize != 0) {
     errno = EINVAL;
@@ -93,11 +97,13 @@ inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
 #endif
 #elif defined(__s390x__)
   // On s390x, mmap() arguments are passed in memory.
-  uint32_t buf[6] = {
-      reinterpret_cast<uint32_t>(start), static_cast<uint32_t>(length),
-      static_cast<uint32_t>(prot),       static_cast<uint32_t>(flags),
-      static_cast<uint32_t>(fd),         static_cast<uint32_t>(offset)};
-  return reintrepret_cast<void*>(syscall(SYS_mmap, buf));
+  unsigned long buf[6] = {reinterpret_cast<unsigned long>(start),  // NOLINT
+                          static_cast<unsigned long>(length),      // NOLINT
+                          static_cast<unsigned long>(prot),        // NOLINT
+                          static_cast<unsigned long>(flags),       // NOLINT
+                          static_cast<unsigned long>(fd),          // NOLINT
+                          static_cast<unsigned long>(offset)};     // NOLINT
+  return reinterpret_cast<void*>(syscall(SYS_mmap, buf));
 #elif defined(__x86_64__)
 // The x32 ABI has 32 bit longs, but the syscall interface is 64 bit.
 // We need to explicitly cast to an unsigned 64 bit type to avoid implicit
@@ -123,7 +129,7 @@ inline int DirectMunmap(void* start, size_t length) {
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #else  // !__linux__
@@ -132,7 +138,7 @@ inline int DirectMunmap(void* start, size_t length) {
 // actual mmap()/munmap() methods.
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
@@ -145,7 +151,7 @@ inline int DirectMunmap(void* start, size_t length) {
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // __linux__
diff --git a/absl/base/internal/endian.h b/absl/base/internal/endian.h
index 00447110..52c09c5b 100644
--- a/absl/base/internal/endian.h
+++ b/absl/base/internal/endian.h
@@ -34,7 +34,7 @@
 #include "absl/base/port.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 // Use compiler byte-swapping intrinsics if they are available.  32-bit
 // and 64-bit versions are available in Clang and GCC as of GCC 4.3.0.
@@ -83,14 +83,14 @@ inline uint64_t gbswap_64(uint64_t host_int) {
 #elif defined(__GLIBC__)
   return bswap_64(host_int);
 #else
-  return (((x & uint64_t{(0xFF}) << 56) |
-          ((x & uint64_t{(0xFF00}) << 40) |
-          ((x & uint64_t{(0xFF0000}) << 24) |
-          ((x & uint64_t{(0xFF000000}) << 8) |
-          ((x & uint64_t{(0xFF00000000}) >> 8) |
-          ((x & uint64_t{(0xFF0000000000}) >> 24) |
-          ((x & uint64_t{(0xFF000000000000}) >> 40) |
-          ((x & uint64_t{(0xFF00000000000000}) >> 56));
+  return (((host_int & uint64_t{0xFF}) << 56) |
+          ((host_int & uint64_t{0xFF00}) << 40) |
+          ((host_int & uint64_t{0xFF0000}) << 24) |
+          ((host_int & uint64_t{0xFF000000}) << 8) |
+          ((host_int & uint64_t{0xFF00000000}) >> 8) |
+          ((host_int & uint64_t{0xFF0000000000}) >> 24) |
+          ((host_int & uint64_t{0xFF000000000000}) >> 40) |
+          ((host_int & uint64_t{0xFF00000000000000}) >> 56));
 #endif  // bswap_64
 }
 
@@ -98,8 +98,10 @@ inline uint32_t gbswap_32(uint32_t host_int) {
 #if defined(__GLIBC__)
   return bswap_32(host_int);
 #else
-  return (((x & 0xFF) << 24) | ((x & 0xFF00) << 8) | ((x & 0xFF0000) >> 8) |
-          ((x & 0xFF000000) >> 24));
+  return (((host_int & uint32_t{0xFF}) << 24) |
+          ((host_int & uint32_t{0xFF00}) << 8) |
+          ((host_int & uint32_t{0xFF0000}) >> 8) |
+          ((host_int & uint32_t{0xFF000000}) >> 24));
 #endif
 }
 
@@ -107,7 +109,8 @@ inline uint16_t gbswap_16(uint16_t host_int) {
 #if defined(__GLIBC__)
   return bswap_16(host_int);
 #else
-  return uint16_t{((x & 0xFF) << 8) | ((x & 0xFF00) >> 8)};
+  return (((host_int & uint16_t{0xFF}) << 8) |
+          ((host_int & uint16_t{0xFF00}) >> 8));
 #endif
 }
 
@@ -265,7 +268,7 @@ inline void Store64(void *p, uint64_t v) {
 
 }  // namespace big_endian
 
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_ENDIAN_H_
diff --git a/absl/base/internal/endian_test.cc b/absl/base/internal/endian_test.cc
index 66ccd45a..14ac4765 100644
--- a/absl/base/internal/endian_test.cc
+++ b/absl/base/internal/endian_test.cc
@@ -24,7 +24,7 @@
 #include "absl/base/config.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace {
 
 const uint64_t kInitialNumber{0x0123456789abcdef};
@@ -34,32 +34,16 @@ const uint16_t k16Value{0x0123};
 const int kNumValuesToTest = 1000000;
 const int kRandomSeed = 12345;
 
-#ifdef ABSL_IS_BIG_ENDIAN
+#if defined(ABSL_IS_BIG_ENDIAN)
 const uint64_t kInitialInNetworkOrder{kInitialNumber};
 const uint64_t k64ValueLE{0xefcdab8967452301};
 const uint32_t k32ValueLE{0x67452301};
 const uint16_t k16ValueLE{0x2301};
-const uint8_t k8ValueLE{k8Value};
-const uint64_t k64IValueLE{0xefcdab89674523a1};
-const uint32_t k32IValueLE{0x67452391};
-const uint16_t k16IValueLE{0x85ff};
-const uint8_t k8IValueLE{0xff};
-const uint64_t kDoubleValueLE{0x6e861bf0f9210940};
-const uint32_t kFloatValueLE{0xd00f4940};
-const uint8_t kBoolValueLE{0x1};
 
 const uint64_t k64ValueBE{kInitialNumber};
 const uint32_t k32ValueBE{k32Value};
 const uint16_t k16ValueBE{k16Value};
-const uint8_t k8ValueBE{k8Value};
-const uint64_t k64IValueBE{0xa123456789abcdef};
-const uint32_t k32IValueBE{0x91234567};
-const uint16_t k16IValueBE{0xff85};
-const uint8_t k8IValueBE{0xff};
-const uint64_t kDoubleValueBE{0x400921f9f01b866e};
-const uint32_t kFloatValueBE{0x40490fd0};
-const uint8_t kBoolValueBE{0x1};
-#elif defined ABSL_IS_LITTLE_ENDIAN
+#elif defined(ABSL_IS_LITTLE_ENDIAN)
 const uint64_t kInitialInNetworkOrder{0xefcdab8967452301};
 const uint64_t k64ValueLE{kInitialNumber};
 const uint32_t k32ValueLE{k32Value};
@@ -277,5 +261,5 @@ TEST(EndianessTest, big_endian) {
 }
 
 }  // namespace
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/exception_safety_testing.cc b/absl/base/internal/exception_safety_testing.cc
index f1d081f7..8207b7d7 100644
--- a/absl/base/internal/exception_safety_testing.cc
+++ b/absl/base/internal/exception_safety_testing.cc
@@ -23,6 +23,10 @@ exceptions_internal::NoThrowTag nothrow_ctor;
 
 exceptions_internal::StrongGuaranteeTagType strong_guarantee;
 
+exceptions_internal::ExceptionSafetyTestBuilder<> MakeExceptionSafetyTester() {
+  return {};
+}
+
 namespace exceptions_internal {
 
 int countdown = -1;
diff --git a/absl/base/internal/exception_safety_testing.h b/absl/base/internal/exception_safety_testing.h
index 8c2f5093..d4d41a8a 100644
--- a/absl/base/internal/exception_safety_testing.h
+++ b/absl/base/internal/exception_safety_testing.h
@@ -33,7 +33,7 @@
 #include "absl/meta/type_traits.h"
 #include "absl/strings/string_view.h"
 #include "absl/strings/substitute.h"
-#include "absl/types/optional.h"
+#include "absl/utility/utility.h"
 
 namespace testing {
 
@@ -127,10 +127,8 @@ class ConstructorTracker {
       void* address = it.first;
       TrackedAddress& tracked_address = it.second;
       if (tracked_address.is_alive) {
-        ADD_FAILURE() << "Object at address " << address
-                      << " with countdown of " << countdown_
-                      << " was not destroyed [" << tracked_address.description
-                      << "]";
+        ADD_FAILURE() << ErrorMessage(address, tracked_address.description,
+                                      countdown_, "Object was not destroyed.");
       }
     }
   }
@@ -141,11 +139,11 @@ class ConstructorTracker {
     TrackedAddress& tracked_address =
         current_tracker_instance_->address_map_[address];
     if (tracked_address.is_alive) {
-      ADD_FAILURE() << "Object at address " << address << " with countdown of "
-                    << current_tracker_instance_->countdown_
-                    << " was re-constructed. Previously: ["
-                    << tracked_address.description << "] Now: [" << description
-                    << "]";
+      ADD_FAILURE() << ErrorMessage(
+          address, tracked_address.description,
+          current_tracker_instance_->countdown_,
+          "Object was re-constructed. Current object was constructed by " +
+              description);
     }
     tracked_address = {true, std::move(description)};
   }
@@ -159,10 +157,9 @@ class ConstructorTracker {
 
     TrackedAddress& tracked_address = it->second;
     if (!tracked_address.is_alive) {
-      ADD_FAILURE() << "Object at address " << address << " with countdown of "
-                    << current_tracker_instance_->countdown_
-                    << " was re-destroyed or created prior to construction "
-                    << "tracking [" << tracked_address.description << "]";
+      ADD_FAILURE() << ErrorMessage(address, tracked_address.description,
+                                    current_tracker_instance_->countdown_,
+                                    "Object was re-destroyed.");
     }
     tracked_address.is_alive = false;
   }
@@ -172,6 +169,16 @@ class ConstructorTracker {
     return current_tracker_instance_ != nullptr;
   }
 
+  static std::string ErrorMessage(void* address, const std::string& address_description,
+                             int countdown, const std::string& error_description) {
+    return absl::Substitute(
+        "With coundtown at $0:\n"
+        "  $1\n"
+        "  Object originally constructed by $2\n"
+        "  Object address: $3\n",
+        countdown, error_description, address_description, address);
+  }
+
   std::unordered_map<void*, TrackedAddress> address_map_;
   int countdown_;
 
@@ -190,70 +197,6 @@ class TrackedObject {
 
   ~TrackedObject() noexcept { ConstructorTracker::ObjectDestructed(this); }
 };
-
-template <typename Factory, typename Operation, typename Invariant>
-absl::optional<testing::AssertionResult> TestSingleInvariantAtCountdownImpl(
-    const Factory& factory, const Operation& operation, int count,
-    const Invariant& invariant) {
-  auto t_ptr = factory();
-  absl::optional<testing::AssertionResult> current_res;
-  SetCountdown(count);
-  try {
-    operation(t_ptr.get());
-  } catch (const exceptions_internal::TestException& e) {
-    current_res.emplace(invariant(t_ptr.get()));
-    if (!current_res.value()) {
-      *current_res << e.what() << " failed invariant check";
-    }
-  }
-  UnsetCountdown();
-  return current_res;
-}
-
-template <typename Factory, typename Operation>
-absl::optional<testing::AssertionResult> TestSingleInvariantAtCountdownImpl(
-    const Factory& factory, const Operation& operation, int count,
-    StrongGuaranteeTagType) {
-  using TPtr = typename decltype(factory())::pointer;
-  auto t_is_strong = [&](TPtr t) { return *t == *factory(); };
-  return TestSingleInvariantAtCountdownImpl(factory, operation, count,
-                                            t_is_strong);
-}
-
-template <typename Factory, typename Operation, typename Invariant>
-int TestSingleInvariantAtCountdown(
-    const Factory& factory, const Operation& operation, int count,
-    const Invariant& invariant,
-    absl::optional<testing::AssertionResult>* reduced_res) {
-  // If reduced_res is empty, it means the current call to
-  // TestSingleInvariantAtCountdown(...) is the first test being run so we do
-  // want to run it. Alternatively, if it's not empty (meaning a previous test
-  // has run) we want to check if it passed. If the previous test did pass, we
-  // want to contine running tests so we do want to run the current one. If it
-  // failed, we want to short circuit so as not to overwrite the AssertionResult
-  // output. If that's the case, we do not run the current test and instead we
-  // simply return.
-  if (!reduced_res->has_value() || reduced_res->value()) {
-    *reduced_res = TestSingleInvariantAtCountdownImpl(factory, operation, count,
-                                                      invariant);
-  }
-  return 0;
-}
-
-template <typename Factory, typename Operation, typename... Invariants>
-inline absl::optional<testing::AssertionResult> TestAllInvariantsAtCountdown(
-    const Factory& factory, const Operation& operation, int count,
-    const Invariants&... invariants) {
-  absl::optional<testing::AssertionResult> reduced_res;
-
-  // Run each checker, short circuiting after the first failure
-  int dummy[] = {
-      0, (TestSingleInvariantAtCountdown(factory, operation, count, invariants,
-                                         &reduced_res))...};
-  static_cast<void>(dummy);
-  return reduced_res;
-}
-
 }  // namespace exceptions_internal
 
 extern exceptions_internal::NoThrowTag nothrow_ctor;
@@ -773,7 +716,7 @@ class ThrowingAllocator : private exceptions_internal::TrackedObject {
   }
 
   size_type max_size() const noexcept {
-    return std::numeric_limits<difference_type>::max() / sizeof(value_type);
+    return (std::numeric_limits<difference_type>::max)() / sizeof(value_type);
   }
 
   ThrowingAllocator select_on_container_copy_construction() noexcept(
@@ -858,7 +801,7 @@ testing::AssertionResult TestNothrowOp(const Operation& operation) {
   try {
     operation();
     return testing::AssertionSuccess();
-  } catch (exceptions_internal::TestException) {
+  } catch (const exceptions_internal::TestException&) {
     return testing::AssertionFailure()
            << "TestException thrown during call to operation() when nothrow "
               "guarantee was expected.";
@@ -871,7 +814,7 @@ testing::AssertionResult TestNothrowOp(const Operation& operation) {
 
 namespace exceptions_internal {
 
-// Dummy struct for ExceptionSafetyTester<> partial state.
+// Dummy struct for ExceptionSafetyTestBuilder<> partial state.
 struct UninitializedT {};
 
 template <typename T>
@@ -884,29 +827,106 @@ class DefaultFactory {
   T t_;
 };
 
-template <size_t LazyInvariantsCount, typename LazyFactory,
+template <size_t LazyContractsCount, typename LazyFactory,
           typename LazyOperation>
 using EnableIfTestable = typename absl::enable_if_t<
-    LazyInvariantsCount != 0 &&
+    LazyContractsCount != 0 &&
     !std::is_same<LazyFactory, UninitializedT>::value &&
     !std::is_same<LazyOperation, UninitializedT>::value>;
 
 template <typename Factory = UninitializedT,
-          typename Operation = UninitializedT, typename... Invariants>
-class ExceptionSafetyTester;
+          typename Operation = UninitializedT, typename... Contracts>
+class ExceptionSafetyTestBuilder;
 
 }  // namespace exceptions_internal
 
-exceptions_internal::ExceptionSafetyTester<> MakeExceptionSafetyTester();
+/*
+ * Constructs an empty ExceptionSafetyTestBuilder. All
+ * ExceptionSafetyTestBuilder objects are immutable and all With[thing] mutation
+ * methods return new instances of ExceptionSafetyTestBuilder.
+ *
+ * In order to test a T for exception safety, a factory for that T, a testable
+ * operation, and at least one contract callback returning an assertion
+ * result must be applied using the respective methods.
+ */
+exceptions_internal::ExceptionSafetyTestBuilder<> MakeExceptionSafetyTester();
 
 namespace exceptions_internal {
+template <typename T>
+struct IsUniquePtr : std::false_type {};
+
+template <typename T, typename D>
+struct IsUniquePtr<std::unique_ptr<T, D>> : std::true_type {};
+
+template <typename Factory>
+struct FactoryPtrTypeHelper {
+  using type = decltype(std::declval<const Factory&>()());
+
+  static_assert(IsUniquePtr<type>::value, "Factories must return a unique_ptr");
+};
+
+template <typename Factory>
+using FactoryPtrType = typename FactoryPtrTypeHelper<Factory>::type;
+
+template <typename Factory>
+using FactoryElementType = typename FactoryPtrType<Factory>::element_type;
+
+template <typename T>
+class ExceptionSafetyTest {
+  using Factory = std::function<std::unique_ptr<T>()>;
+  using Operation = std::function<void(T*)>;
+  using Contract = std::function<AssertionResult(T*)>;
+
+ public:
+  template <typename... Contracts>
+  explicit ExceptionSafetyTest(const Factory& f, const Operation& op,
+                               const Contracts&... contracts)
+      : factory_(f), operation_(op), contracts_{WrapContract(contracts)...} {}
+
+  AssertionResult Test() const {
+    for (int count = 0;; ++count) {
+      exceptions_internal::ConstructorTracker ct(count);
+
+      for (const auto& contract : contracts_) {
+        auto t_ptr = factory_();
+        try {
+          SetCountdown(count);
+          operation_(t_ptr.get());
+          // Unset for the case that the operation throws no exceptions, which
+          // would leave the countdown set and break the *next* exception safety
+          // test after this one.
+          UnsetCountdown();
+          return AssertionSuccess();
+        } catch (const exceptions_internal::TestException& e) {
+          if (!contract(t_ptr.get())) {
+            return AssertionFailure() << e.what() << " failed contract check";
+          }
+        }
+      }
+    }
+  }
+
+ private:
+  template <typename ContractFn>
+  Contract WrapContract(const ContractFn& contract) {
+    return [contract](T* t_ptr) { return AssertionResult(contract(t_ptr)); };
+  }
+
+  Contract WrapContract(StrongGuaranteeTagType) {
+    return [this](T* t_ptr) { return AssertionResult(*factory_() == *t_ptr); };
+  }
+
+  Factory factory_;
+  Operation operation_;
+  std::vector<Contract> contracts_;
+};
 
 /*
  * Builds a tester object that tests if performing a operation on a T follows
- * exception safety guarantees. Verification is done via invariant assertion
+ * exception safety guarantees. Verification is done via contract assertion
  * callbacks applied to T instances post-throw.
  *
- * Template parameters for ExceptionSafetyTester:
+ * Template parameters for ExceptionSafetyTestBuilder:
  *
  * - Factory: The factory object (passed in via tester.WithFactory(...) or
  *   tester.WithInitialValue(...)) must be invocable with the signature
@@ -921,25 +941,25 @@ namespace exceptions_internal {
  *   fresh T instance so it's free to modify and destroy the T instances as it
  *   pleases.
  *
- * - Invariants...: The invariant assertion callback objects (passed in via
- *   tester.WithInvariants(...)) must be invocable with the signature
+ * - Contracts...: The contract assertion callback objects (passed in via
+ *   tester.WithContracts(...)) must be invocable with the signature
  *   `testing::AssertionResult operator()(T*) const` where T is the type being
- *   tested. Invariant assertion callbacks are provided T instances post-throw.
- *   They must return testing::AssertionSuccess when the type invariants of the
- *   provided T instance hold. If the type invariants of the T instance do not
+ *   tested. Contract assertion callbacks are provided T instances post-throw.
+ *   They must return testing::AssertionSuccess when the type contracts of the
+ *   provided T instance hold. If the type contracts of the T instance do not
  *   hold, they must return testing::AssertionFailure. Execution order of
- *   Invariants... is unspecified. They will each individually get a fresh T
+ *   Contracts... is unspecified. They will each individually get a fresh T
  *   instance so they are free to modify and destroy the T instances as they
  *   please.
  */
-template <typename Factory, typename Operation, typename... Invariants>
-class ExceptionSafetyTester {
+template <typename Factory, typename Operation, typename... Contracts>
+class ExceptionSafetyTestBuilder {
  public:
   /*
-   * Returns a new ExceptionSafetyTester with an included T factory based on the
-   * provided T instance. The existing factory will not be included in the newly
-   * created tester instance. The created factory returns a new T instance by
-   * copy-constructing the provided const T& t.
+   * Returns a new ExceptionSafetyTestBuilder with an included T factory based
+   * on the provided T instance. The existing factory will not be included in
+   * the newly created tester instance. The created factory returns a new T
+   * instance by copy-constructing the provided const T& t.
    *
    * Preconditions for tester.WithInitialValue(const T& t):
    *
@@ -948,63 +968,63 @@ class ExceptionSafetyTester {
    *   tester.WithFactory(...).
    */
   template <typename T>
-  ExceptionSafetyTester<DefaultFactory<T>, Operation, Invariants...>
+  ExceptionSafetyTestBuilder<DefaultFactory<T>, Operation, Contracts...>
   WithInitialValue(const T& t) const {
     return WithFactory(DefaultFactory<T>(t));
   }
 
   /*
-   * Returns a new ExceptionSafetyTester with the provided T factory included.
-   * The existing factory will not be included in the newly-created tester
-   * instance. This method is intended for use with types lacking a copy
+   * Returns a new ExceptionSafetyTestBuilder with the provided T factory
+   * included. The existing factory will not be included in the newly-created
+   * tester instance. This method is intended for use with types lacking a copy
    * constructor. Types that can be copy-constructed should instead use the
    * method tester.WithInitialValue(...).
    */
   template <typename NewFactory>
-  ExceptionSafetyTester<absl::decay_t<NewFactory>, Operation, Invariants...>
+  ExceptionSafetyTestBuilder<absl::decay_t<NewFactory>, Operation, Contracts...>
   WithFactory(const NewFactory& new_factory) const {
-    return {new_factory, operation_, invariants_};
+    return {new_factory, operation_, contracts_};
   }
 
   /*
-   * Returns a new ExceptionSafetyTester with the provided testable operation
-   * included. The existing operation will not be included in the newly created
-   * tester.
+   * Returns a new ExceptionSafetyTestBuilder with the provided testable
+   * operation included. The existing operation will not be included in the
+   * newly created tester.
    */
   template <typename NewOperation>
-  ExceptionSafetyTester<Factory, absl::decay_t<NewOperation>, Invariants...>
+  ExceptionSafetyTestBuilder<Factory, absl::decay_t<NewOperation>, Contracts...>
   WithOperation(const NewOperation& new_operation) const {
-    return {factory_, new_operation, invariants_};
+    return {factory_, new_operation, contracts_};
   }
 
   /*
-   * Returns a new ExceptionSafetyTester with the provided MoreInvariants...
-   * combined with the Invariants... that were already included in the instance
-   * on which the method was called. Invariants... cannot be removed or replaced
-   * once added to an ExceptionSafetyTester instance. A fresh object must be
-   * created in order to get an empty Invariants... list.
+   * Returns a new ExceptionSafetyTestBuilder with the provided MoreContracts...
+   * combined with the Contracts... that were already included in the instance
+   * on which the method was called. Contracts... cannot be removed or replaced
+   * once added to an ExceptionSafetyTestBuilder instance. A fresh object must
+   * be created in order to get an empty Contracts... list.
    *
-   * In addition to passing in custom invariant assertion callbacks, this method
+   * In addition to passing in custom contract assertion callbacks, this method
    * accepts `testing::strong_guarantee` as an argument which checks T instances
    * post-throw against freshly created T instances via operator== to verify
    * that any state changes made during the execution of the operation were
    * properly rolled back.
    */
-  template <typename... MoreInvariants>
-  ExceptionSafetyTester<Factory, Operation, Invariants...,
-                        absl::decay_t<MoreInvariants>...>
-  WithInvariants(const MoreInvariants&... more_invariants) const {
-    return {factory_, operation_,
-            std::tuple_cat(invariants_,
-                           std::tuple<absl::decay_t<MoreInvariants>...>(
-                               more_invariants...))};
+  template <typename... MoreContracts>
+  ExceptionSafetyTestBuilder<Factory, Operation, Contracts...,
+                             absl::decay_t<MoreContracts>...>
+  WithContracts(const MoreContracts&... more_contracts) const {
+    return {
+        factory_, operation_,
+        std::tuple_cat(contracts_, std::tuple<absl::decay_t<MoreContracts>...>(
+                                       more_contracts...))};
   }
 
   /*
    * Returns a testing::AssertionResult that is the reduced result of the
    * exception safety algorithm. The algorithm short circuits and returns
-   * AssertionFailure after the first invariant callback returns an
-   * AssertionFailure. Otherwise, if all invariant callbacks return an
+   * AssertionFailure after the first contract callback returns an
+   * AssertionFailure. Otherwise, if all contract callbacks return an
    * AssertionSuccess, the reduced result is AssertionSuccess.
    *
    * The passed-in testable operation will not be saved in a new tester instance
@@ -1013,97 +1033,62 @@ class ExceptionSafetyTester {
    *
    * Preconditions for tester.Test(const NewOperation& new_operation):
    *
-   * - May only be called after at least one invariant assertion callback and a
+   * - May only be called after at least one contract assertion callback and a
    *   factory or initial value have been provided.
    */
   template <
       typename NewOperation,
-      typename = EnableIfTestable<sizeof...(Invariants), Factory, NewOperation>>
+      typename = EnableIfTestable<sizeof...(Contracts), Factory, NewOperation>>
   testing::AssertionResult Test(const NewOperation& new_operation) const {
-    return TestImpl(new_operation, absl::index_sequence_for<Invariants...>());
+    return TestImpl(new_operation, absl::index_sequence_for<Contracts...>());
   }
 
   /*
    * Returns a testing::AssertionResult that is the reduced result of the
    * exception safety algorithm. The algorithm short circuits and returns
-   * AssertionFailure after the first invariant callback returns an
-   * AssertionFailure. Otherwise, if all invariant callbacks return an
+   * AssertionFailure after the first contract callback returns an
+   * AssertionFailure. Otherwise, if all contract callbacks return an
    * AssertionSuccess, the reduced result is AssertionSuccess.
    *
    * Preconditions for tester.Test():
    *
-   * - May only be called after at least one invariant assertion callback, a
+   * - May only be called after at least one contract assertion callback, a
    *   factory or initial value and a testable operation have been provided.
    */
-  template <typename LazyOperation = Operation,
-            typename =
-                EnableIfTestable<sizeof...(Invariants), Factory, LazyOperation>>
+  template <
+      typename LazyOperation = Operation,
+      typename = EnableIfTestable<sizeof...(Contracts), Factory, LazyOperation>>
   testing::AssertionResult Test() const {
-    return TestImpl(operation_, absl::index_sequence_for<Invariants...>());
+    return Test(operation_);
   }
 
  private:
   template <typename, typename, typename...>
-  friend class ExceptionSafetyTester;
+  friend class ExceptionSafetyTestBuilder;
 
-  friend ExceptionSafetyTester<> testing::MakeExceptionSafetyTester();
+  friend ExceptionSafetyTestBuilder<> testing::MakeExceptionSafetyTester();
 
-  ExceptionSafetyTester() {}
+  ExceptionSafetyTestBuilder() {}
 
-  ExceptionSafetyTester(const Factory& f, const Operation& o,
-                        const std::tuple<Invariants...>& i)
-      : factory_(f), operation_(o), invariants_(i) {}
+  ExceptionSafetyTestBuilder(const Factory& f, const Operation& o,
+                             const std::tuple<Contracts...>& i)
+      : factory_(f), operation_(o), contracts_(i) {}
 
   template <typename SelectedOperation, size_t... Indices>
-  testing::AssertionResult TestImpl(const SelectedOperation& selected_operation,
+  testing::AssertionResult TestImpl(SelectedOperation selected_operation,
                                     absl::index_sequence<Indices...>) const {
-    // Starting from 0 and counting upwards until one of the exit conditions is
-    // hit...
-    for (int count = 0;; ++count) {
-      exceptions_internal::ConstructorTracker ct(count);
-
-      // Run the full exception safety test algorithm for the current countdown
-      auto reduced_res =
-          TestAllInvariantsAtCountdown(factory_, selected_operation, count,
-                                       std::get<Indices>(invariants_)...);
-      // If there is no value in the optional, no invariants were run because no
-      // exception was thrown. This means that the test is complete and the loop
-      // can exit successfully.
-      if (!reduced_res.has_value()) {
-        return testing::AssertionSuccess();
-      }
-      // If the optional is not empty and the value is falsy, an invariant check
-      // failed so the test must exit to propegate the failure.
-      if (!reduced_res.value()) {
-        return reduced_res.value();
-      }
-      // If the optional is not empty and the value is not falsy, it means
-      // exceptions were thrown but the invariants passed so the test must
-      // continue to run.
-    }
+    return ExceptionSafetyTest<FactoryElementType<Factory>>(
+               factory_, selected_operation, std::get<Indices>(contracts_)...)
+        .Test();
   }
 
   Factory factory_;
   Operation operation_;
-  std::tuple<Invariants...> invariants_;
+  std::tuple<Contracts...> contracts_;
 };
 
 }  // namespace exceptions_internal
 
-/*
- * Constructs an empty ExceptionSafetyTester. All ExceptionSafetyTester
- * objects are immutable and all With[thing] mutation methods return new
- * instances of ExceptionSafetyTester.
- *
- * In order to test a T for exception safety, a factory for that T, a testable
- * operation, and at least one invariant callback returning an assertion
- * result must be applied using the respective methods.
- */
-inline exceptions_internal::ExceptionSafetyTester<>
-MakeExceptionSafetyTester() {
-  return {};
-}
-
 }  // namespace testing
 
 #endif  // ABSL_BASE_INTERNAL_EXCEPTION_SAFETY_TESTING_H_
diff --git a/absl/base/internal/exception_testing.h b/absl/base/internal/exception_testing.h
index fd89a3f6..0cf7918e 100644
--- a/absl/base/internal/exception_testing.h
+++ b/absl/base/internal/exception_testing.h
@@ -35,7 +35,7 @@
   EXPECT_DEATH(expr, ".*")
 #else
 #define ABSL_BASE_INTERNAL_EXPECT_FAIL(expr, exception_t, text) \
-  EXPECT_DEATH(expr, text)
+  EXPECT_DEATH_IF_SUPPORTED(expr, text)
 
 #endif
 
diff --git a/absl/base/internal/hide_ptr.h b/absl/base/internal/hide_ptr.h
index a2694508..ce390dc4 100644
--- a/absl/base/internal/hide_ptr.h
+++ b/absl/base/internal/hide_ptr.h
@@ -18,7 +18,7 @@
 #include <cstdint>
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // Arbitrary value with high bits set. Xor'ing with it is unlikely
@@ -43,7 +43,7 @@ inline T* UnhidePtr(uintptr_t hidden) {
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_HIDE_PTR_H_
diff --git a/absl/base/internal/identity.h b/absl/base/internal/identity.h
index 2eaab453..d57c83f4 100644
--- a/absl/base/internal/identity.h
+++ b/absl/base/internal/identity.h
@@ -17,7 +17,7 @@
 #define ABSL_BASE_INTERNAL_IDENTITY_H_
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace internal {
 
 template <typename T>
@@ -29,7 +29,7 @@ template <typename T>
 using identity_t = typename identity<T>::type;
 
 }  // namespace internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_IDENTITY_H_
diff --git a/absl/base/internal/inline_variable_testing.h b/absl/base/internal/inline_variable_testing.h
index 49fa4ade..be0b0b96 100644
--- a/absl/base/internal/inline_variable_testing.h
+++ b/absl/base/internal/inline_variable_testing.h
@@ -18,7 +18,7 @@
 #include "absl/base/internal/inline_variable.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace inline_variable_testing_internal {
 
 struct Foo {
@@ -40,7 +40,7 @@ const int& get_int_a();
 const int& get_int_b();
 
 }  // namespace inline_variable_testing_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INLINE_VARIABLE_TESTING_H_
diff --git a/absl/base/internal/invoke.h b/absl/base/internal/invoke.h
index bc05a0a3..1372ef50 100644
--- a/absl/base/internal/invoke.h
+++ b/absl/base/internal/invoke.h
@@ -43,7 +43,7 @@
 // top of this file for the API documentation.
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // The five classes below each implement one of the clauses from the definition
@@ -184,7 +184,7 @@ InvokeT<F, Args...> Invoke(F&& f, Args&&... args) {
                                            std::forward<Args>(args)...);
 }
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_INVOKE_H_
diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc
index ca6239ad..10d805cc 100644
--- a/absl/base/internal/low_level_alloc.cc
+++ b/absl/base/internal/low_level_alloc.cc
@@ -63,7 +63,7 @@
 #endif  // __APPLE__
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // A first-fit allocator with amortized logarithmic free() time.
@@ -209,7 +209,7 @@ struct LowLevelAlloc::Arena {
   int32_t allocation_count GUARDED_BY(mu);
   // flags passed to NewArena
   const uint32_t flags;
-  // Result of getpagesize()
+  // Result of sysconf(_SC_PAGESIZE)
   const size_t pagesize;
   // Lowest power of two >= max(16, sizeof(AllocList))
   const size_t roundup;
@@ -325,8 +325,10 @@ size_t GetPageSize() {
   SYSTEM_INFO system_info;
   GetSystemInfo(&system_info);
   return std::max(system_info.dwPageSize, system_info.dwAllocationGranularity);
-#else
+#elif defined(__wasm__) || defined(__asmjs__)
   return getpagesize();
+#else
+  return sysconf(_SC_PAGESIZE);
 #endif
 }
 
@@ -402,16 +404,20 @@ bool LowLevelAlloc::DeleteArena(Arena *arena) {
     ABSL_RAW_CHECK(munmap_result != 0,
                    "LowLevelAlloc::DeleteArena: VitualFree failed");
 #else
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
     if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
       munmap_result = munmap(region, size);
     } else {
       munmap_result = base_internal::DirectMunmap(region, size);
     }
+#else
+    munmap_result = munmap(region, size);
+#endif  // ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
     if (munmap_result != 0) {
       ABSL_RAW_LOG(FATAL, "LowLevelAlloc::DeleteArena: munmap failed: %d",
                    errno);
     }
-#endif
+#endif  // _WIN32
   }
   section.Leave();
   arena->~Arena();
@@ -546,6 +552,7 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
                                MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
       ABSL_RAW_CHECK(new_pages != nullptr, "VirtualAlloc failed");
 #else
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
       if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
         new_pages = base_internal::DirectMmap(nullptr, new_pages_size,
             PROT_WRITE|PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
@@ -553,10 +560,15 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
         new_pages = mmap(nullptr, new_pages_size, PROT_WRITE | PROT_READ,
                          MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
       }
+#else
+      new_pages = mmap(nullptr, new_pages_size, PROT_WRITE | PROT_READ,
+                       MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+#endif  // ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
       if (new_pages == MAP_FAILED) {
         ABSL_RAW_LOG(FATAL, "mmap error: %d", errno);
       }
-#endif
+
+#endif  // _WIN32
       arena->mu.Lock();
       s = reinterpret_cast<AllocList *>(new_pages);
       s->header.size = new_pages_size;
@@ -600,7 +612,7 @@ void *LowLevelAlloc::AllocWithArena(size_t request, Arena *arena) {
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_LOW_LEVEL_ALLOC_MISSING
diff --git a/absl/base/internal/low_level_alloc.h b/absl/base/internal/low_level_alloc.h
index 3f289571..87cfc934 100644
--- a/absl/base/internal/low_level_alloc.h
+++ b/absl/base/internal/low_level_alloc.h
@@ -39,10 +39,13 @@
 #define ABSL_LOW_LEVEL_ALLOC_MISSING 1
 #endif
 
-// Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows.
+// Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows or
+// asm.js / WebAssembly.
+// See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
+// for more information.
 #ifdef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
 #error ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING cannot be directly set
-#elif defined(_WIN32)
+#elif defined(_WIN32) || defined(__asmjs__) || defined(__wasm__)
 #define ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING 1
 #endif
 
@@ -51,7 +54,7 @@
 #include "absl/base/port.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 class LowLevelAlloc {
@@ -116,6 +119,6 @@ class LowLevelAlloc {
 };
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
diff --git a/absl/base/internal/low_level_alloc_test.cc b/absl/base/internal/low_level_alloc_test.cc
index 15ffe298..65bb519d 100644
--- a/absl/base/internal/low_level_alloc_test.cc
+++ b/absl/base/internal/low_level_alloc_test.cc
@@ -22,7 +22,7 @@
 #include <utility>
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 namespace {
 
@@ -149,7 +149,7 @@ static struct BeforeMain {
 
 }  // namespace
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 int main(int argc, char *argv[]) {
diff --git a/absl/base/internal/low_level_scheduling.h b/absl/base/internal/low_level_scheduling.h
index 2ae464b4..7cb6117e 100644
--- a/absl/base/internal/low_level_scheduling.h
+++ b/absl/base/internal/low_level_scheduling.h
@@ -28,7 +28,7 @@ extern "C" bool __google_disable_rescheduling(void);
 extern "C" void __google_enable_rescheduling(bool disable_result);
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 class SchedulingHelper;  // To allow use of SchedulingGuard.
@@ -101,6 +101,6 @@ inline void SchedulingGuard::EnableRescheduling(bool /* disable_result */) {
 
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
diff --git a/absl/base/internal/raw_logging.cc b/absl/base/internal/raw_logging.cc
index cd1bbc09..ed8b8d7c 100644
--- a/absl/base/internal/raw_logging.cc
+++ b/absl/base/internal/raw_logging.cc
@@ -139,7 +139,7 @@ void RawLogVA(absl::LogSeverity severity, const char* file, int line,
 #endif
 
 #ifdef ABSL_MIN_LOG_LEVEL
-  if (static_cast<int>(severity) < ABSL_MIN_LOG_LEVEL &&
+  if (severity < static_cast<absl::LogSeverity>(ABSL_MIN_LOG_LEVEL) &&
       severity < absl::LogSeverity::kFatal) {
     enabled = false;
   }
@@ -181,7 +181,7 @@ void RawLogVA(absl::LogSeverity severity, const char* file, int line,
 }  // namespace
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace raw_logging_internal {
 void SafeWriteToStderr(const char *s, size_t len) {
 #if defined(ABSL_HAVE_SYSCALL_WRITE)
@@ -207,6 +207,15 @@ void RawLog(absl::LogSeverity severity, const char* file, int line,
   va_end(ap);
 }
 
+// Non-formatting version of RawLog().
+//
+// TODO(gfalcon): When string_view no longer depends on base, change this
+// interface to take its message as a string_view instead.
+static void DefaultInternalLog(absl::LogSeverity severity, const char* file,
+                               int line, const std::string& message) {
+  RawLog(severity, file, line, "%s", message.c_str());
+}
+
 bool RawLoggingFullySupported() {
 #ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
   return true;
@@ -215,6 +224,13 @@ bool RawLoggingFullySupported() {
 #endif  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
 }
 
+ABSL_CONST_INIT absl::base_internal::AtomicHook<InternalLogFunction>
+    internal_log_function(DefaultInternalLog);
+
+void RegisterInternalLogFunction(InternalLogFunction func) {
+  internal_log_function.Store(func);
+}
+
 }  // namespace raw_logging_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/raw_logging.h b/absl/base/internal/raw_logging.h
index 04ff0607..2786a3de 100644
--- a/absl/base/internal/raw_logging.h
+++ b/absl/base/internal/raw_logging.h
@@ -19,7 +19,10 @@
 #ifndef ABSL_BASE_INTERNAL_RAW_LOGGING_H_
 #define ABSL_BASE_INTERNAL_RAW_LOGGING_H_
 
+#include <string>
+
 #include "absl/base/attributes.h"
+#include "absl/base/internal/atomic_hook.h"
 #include "absl/base/log_severity.h"
 #include "absl/base/macros.h"
 #include "absl/base/port.h"
@@ -57,6 +60,34 @@
     }                                                                  \
   } while (0)
 
+// ABSL_INTERNAL_LOG and ABSL_INTERNAL_CHECK work like the RAW variants above,
+// except that if the richer log library is linked into the binary, we dispatch
+// to that instead.  This is potentially useful for internal logging and
+// assertions, where we are using RAW_LOG neither for its async-signal-safety
+// nor for its non-allocating nature, but rather because raw logging has very
+// few other dependencies.
+//
+// The API is a subset of the above: each macro only takes two arguments.  Use
+// StrCat if you need to build a richer message.
+#define ABSL_INTERNAL_LOG(severity, message)                          \
+  do {                                                                \
+    constexpr const char* absl_raw_logging_internal_basename =        \
+        ::absl::raw_logging_internal::Basename(__FILE__,              \
+                                               sizeof(__FILE__) - 1); \
+    ::absl::raw_logging_internal::internal_log_function(              \
+        ABSL_RAW_LOGGING_INTERNAL_##severity,                         \
+        absl_raw_logging_internal_basename, __LINE__, message);       \
+  } while (0)
+
+#define ABSL_INTERNAL_CHECK(condition, message)               \
+  do {                                                        \
+    if (ABSL_PREDICT_FALSE(!(condition))) {                   \
+      std::string death_message = "Check " #condition " failed: "; \
+      death_message += std::string(message);                       \
+      ABSL_INTERNAL_LOG(FATAL, death_message);                \
+    }                                                         \
+  } while (0)
+
 #define ABSL_RAW_LOGGING_INTERNAL_INFO ::absl::LogSeverity::kInfo
 #define ABSL_RAW_LOGGING_INTERNAL_WARNING ::absl::LogSeverity::kWarning
 #define ABSL_RAW_LOGGING_INTERNAL_ERROR ::absl::LogSeverity::kError
@@ -65,7 +96,7 @@
   ::absl::NormalizeLogSeverity(severity)
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace raw_logging_internal {
 
 // Helper function to implement ABSL_RAW_LOG
@@ -84,7 +115,7 @@ void SafeWriteToStderr(const char *s, size_t len);
 
 // compile-time function to get the "base" filename, that is, the part of
 // a filename after the last "/" or "\" path separator.  The search starts at
-// the end of the std::string; the second parameter is the length of the std::string.
+// the end of the string; the second parameter is the length of the string.
 constexpr const char* Basename(const char* fname, int offset) {
   return offset == 0 || fname[offset - 1] == '/' || fname[offset - 1] == '\\'
              ? fname + offset
@@ -132,8 +163,20 @@ using LogPrefixHook = bool (*)(absl::LogSeverity severity, const char* file,
 using AbortHook = void (*)(const char* file, int line, const char* buf_start,
                            const char* prefix_end, const char* buf_end);
 
+// Internal logging function for ABSL_INTERNAL_LOG to dispatch to.
+//
+// TODO(gfalcon): When string_view no longer depends on base, change this
+// interface to take its message as a string_view instead.
+using InternalLogFunction = void (*)(absl::LogSeverity severity,
+                                     const char* file, int line,
+                                     const std::string& message);
+
+extern base_internal::AtomicHook<InternalLogFunction> internal_log_function;
+
+void RegisterInternalLogFunction(InternalLogFunction func);
+
 }  // namespace raw_logging_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_RAW_LOGGING_H_
diff --git a/absl/base/internal/scheduling_mode.h b/absl/base/internal/scheduling_mode.h
index dd7df6bb..19a7514c 100644
--- a/absl/base/internal/scheduling_mode.h
+++ b/absl/base/internal/scheduling_mode.h
@@ -19,7 +19,7 @@
 #define ABSL_BASE_INTERNAL_SCHEDULING_MODE_H_
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // Used to describe how a thread may be scheduled.  Typically associated with
@@ -50,7 +50,7 @@ enum SchedulingMode {
 };
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_SCHEDULING_MODE_H_
diff --git a/absl/base/internal/spinlock.cc b/absl/base/internal/spinlock.cc
index 9d90b3cb..8f8eef82 100644
--- a/absl/base/internal/spinlock.cc
+++ b/absl/base/internal/spinlock.cc
@@ -54,7 +54,7 @@
 //          holder to acquire the lock.  There may be outstanding waiter(s).
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 ABSL_CONST_INIT static base_internal::AtomicHook<void (*)(const void *lock,
@@ -96,13 +96,9 @@ void SpinLock::InitLinkerInitializedAndCooperative() {
 }
 
 // Monitor the lock to see if its value changes within some time period
-// (adaptive_spin_count loop iterations).  A timestamp indicating
-// when the thread initially started waiting for the lock is passed in via
-// the initial_wait_timestamp value.  The total wait time in cycles for the
-// lock is returned in the wait_cycles parameter.  The last value read
-// from the lock is returned from the method.
-uint32_t SpinLock::SpinLoop(int64_t initial_wait_timestamp,
-                            uint32_t *wait_cycles) {
+// (adaptive_spin_count loop iterations). The last value read from the lock
+// is returned from the method.
+uint32_t SpinLock::SpinLoop() {
   // We are already in the slow path of SpinLock, initialize the
   // adaptive_spin_count here.
   ABSL_CONST_INIT static absl::once_flag init_adaptive_spin_count;
@@ -116,22 +112,21 @@ uint32_t SpinLock::SpinLoop(int64_t initial_wait_timestamp,
   do {
     lock_value = lockword_.load(std::memory_order_relaxed);
   } while ((lock_value & kSpinLockHeld) != 0 && --c > 0);
-  uint32_t spin_loop_wait_cycles =
-      EncodeWaitCycles(initial_wait_timestamp, CycleClock::Now());
-  *wait_cycles = spin_loop_wait_cycles;
-
-  return TryLockInternal(lock_value, spin_loop_wait_cycles);
+  return lock_value;
 }
 
 void SpinLock::SlowLock() {
+  uint32_t lock_value = SpinLoop();
+  lock_value = TryLockInternal(lock_value, 0);
+  if ((lock_value & kSpinLockHeld) == 0) {
+    return;
+  }
   // The lock was not obtained initially, so this thread needs to wait for
   // it.  Record the current timestamp in the local variable wait_start_time
   // so the total wait time can be stored in the lockword once this thread
   // obtains the lock.
   int64_t wait_start_time = CycleClock::Now();
-  uint32_t wait_cycles;
-  uint32_t lock_value = SpinLoop(wait_start_time, &wait_cycles);
-
+  uint32_t wait_cycles = 0;
   int lock_wait_call_count = 0;
   while ((lock_value & kSpinLockHeld) != 0) {
     // If the lock is currently held, but not marked as having a sleeper, mark
@@ -142,7 +137,7 @@ void SpinLock::SlowLock() {
       // owner to think it experienced contention.
       if (lockword_.compare_exchange_strong(
               lock_value, lock_value | kSpinLockSleeper,
-              std::memory_order_acquire, std::memory_order_relaxed)) {
+              std::memory_order_relaxed, std::memory_order_relaxed)) {
         // Successfully transitioned to kSpinLockSleeper.  Pass
         // kSpinLockSleeper to the SpinLockWait routine to properly indicate
         // the last lock_value observed.
@@ -171,7 +166,9 @@ void SpinLock::SlowLock() {
     ABSL_TSAN_MUTEX_POST_DIVERT(this, 0);
     // Spin again after returning from the wait routine to give this thread
     // some chance of obtaining the lock.
-    lock_value = SpinLoop(wait_start_time, &wait_cycles);
+    lock_value = SpinLoop();
+    wait_cycles = EncodeWaitCycles(wait_start_time, CycleClock::Now());
+    lock_value = TryLockInternal(lock_value, wait_cycles);
   }
 }
 
@@ -207,14 +204,20 @@ uint32_t SpinLock::EncodeWaitCycles(int64_t wait_start_time,
       (wait_end_time - wait_start_time) >> PROFILE_TIMESTAMP_SHIFT;
 
   // Return a representation of the time spent waiting that can be stored in
-  // the lock word's upper bits.  bit_cast is required as Atomic32 is signed.
-  const uint32_t clamped = static_cast<uint32_t>(
+  // the lock word's upper bits.
+  uint32_t clamped = static_cast<uint32_t>(
       std::min(scaled_wait_time, kMaxWaitTime) << LOCKWORD_RESERVED_SHIFT);
 
-  // bump up value if necessary to avoid returning kSpinLockSleeper.
-  const uint32_t after_spinlock_sleeper =
-     kSpinLockSleeper + (1 << LOCKWORD_RESERVED_SHIFT);
-  return clamped == kSpinLockSleeper ? after_spinlock_sleeper : clamped;
+  if (clamped == 0) {
+    return kSpinLockSleeper;  // Just wake waiters, but don't record contention.
+  }
+  // Bump up value if necessary to avoid returning kSpinLockSleeper.
+  const uint32_t kMinWaitTime =
+      kSpinLockSleeper + (1 << LOCKWORD_RESERVED_SHIFT);
+  if (clamped == kSpinLockSleeper) {
+    return kMinWaitTime;
+  }
+  return clamped;
 }
 
 uint64_t SpinLock::DecodeWaitCycles(uint32_t lock_value) {
@@ -226,5 +229,5 @@ uint64_t SpinLock::DecodeWaitCycles(uint32_t lock_value) {
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/spinlock.h b/absl/base/internal/spinlock.h
index 7b59fe26..d53878b2 100644
--- a/absl/base/internal/spinlock.h
+++ b/absl/base/internal/spinlock.h
@@ -45,7 +45,7 @@
 #include "absl/base/thread_annotations.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 class LOCKABLE SpinLock {
@@ -102,8 +102,8 @@ class LOCKABLE SpinLock {
   inline void Unlock() UNLOCK_FUNCTION() {
     ABSL_TSAN_MUTEX_PRE_UNLOCK(this, 0);
     uint32_t lock_value = lockword_.load(std::memory_order_relaxed);
-    lockword_.store(lock_value & kSpinLockCooperative,
-                    std::memory_order_release);
+    lock_value = lockword_.exchange(lock_value & kSpinLockCooperative,
+                                    std::memory_order_release);
 
     if ((lock_value & kSpinLockDisabledScheduling) != 0) {
       base_internal::SchedulingGuard::EnableRescheduling(true);
@@ -162,7 +162,7 @@ class LOCKABLE SpinLock {
   void InitLinkerInitializedAndCooperative();
   void SlowLock() ABSL_ATTRIBUTE_COLD;
   void SlowUnlock(uint32_t lock_value) ABSL_ATTRIBUTE_COLD;
-  uint32_t SpinLoop(int64_t initial_wait_timestamp, uint32_t* wait_cycles);
+  uint32_t SpinLoop();
 
   inline bool TryLockImpl() {
     uint32_t lock_value = lockword_.load(std::memory_order_relaxed);
@@ -235,7 +235,7 @@ inline uint32_t SpinLock::TryLockInternal(uint32_t lock_value,
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_SPINLOCK_H_
diff --git a/absl/base/internal/spinlock_benchmark.cc b/absl/base/internal/spinlock_benchmark.cc
new file mode 100644
index 00000000..907d3e27
--- /dev/null
+++ b/absl/base/internal/spinlock_benchmark.cc
@@ -0,0 +1,52 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// See also //absl/synchronization:mutex_benchmark for a comparison of SpinLock
+// and Mutex performance under varying levels of contention.
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/internal/spinlock.h"
+#include "absl/synchronization/internal/create_thread_identity.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+
+template <absl::base_internal::SchedulingMode scheduling_mode>
+static void BM_SpinLock(benchmark::State& state) {
+  // Ensure a ThreadIdentity is installed.
+  ABSL_INTERNAL_CHECK(
+      absl::synchronization_internal::GetOrCreateCurrentThreadIdentity() !=
+          nullptr,
+      "GetOrCreateCurrentThreadIdentity() failed");
+
+  static auto* spinlock = new absl::base_internal::SpinLock(scheduling_mode);
+  for (auto _ : state) {
+    absl::base_internal::SpinLockHolder holder(spinlock);
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_SpinLock,
+                   absl::base_internal::SCHEDULE_KERNEL_ONLY)
+    ->UseRealTime()
+    ->Threads(1)
+    ->ThreadPerCpu();
+
+BENCHMARK_TEMPLATE(BM_SpinLock,
+                   absl::base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL)
+    ->UseRealTime()
+    ->Threads(1)
+    ->ThreadPerCpu();
+
+}  // namespace
diff --git a/absl/base/internal/spinlock_linux.inc b/absl/base/internal/spinlock_linux.inc
new file mode 100644
index 00000000..94c861dc
--- /dev/null
+++ b/absl/base/internal/spinlock_linux.inc
@@ -0,0 +1,72 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file is a Linux-specific part of spinlock_wait.cc
+
+#include <linux/futex.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include <atomic>
+#include <cerrno>
+#include <climits>
+#include <cstdint>
+#include <ctime>
+
+#include "absl/base/attributes.h"
+
+// The SpinLock lockword is `std::atomic<uint32_t>`. Here we assert that
+// `std::atomic<uint32_t>` is bitwise equivalent of the `int` expected
+// by SYS_futex. We also assume that reads/writes done to the lockword
+// by SYS_futex have rational semantics with regard to the
+// std::atomic<> API. C++ provides no guarantees of these assumptions,
+// but they are believed to hold in practice.
+static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),
+              "SpinLock lockword has the wrong size for a futex");
+
+// Some Android headers are missing these definitions even though they
+// support these futex operations.
+#ifdef __BIONIC__
+#ifndef SYS_futex
+#define SYS_futex __NR_futex
+#endif
+#ifndef FUTEX_PRIVATE_FLAG
+#define FUTEX_PRIVATE_FLAG 128
+#endif
+#endif
+
+extern "C" {
+
+ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay(
+    std::atomic<uint32_t> *w, uint32_t value, int loop,
+    absl::base_internal::SchedulingMode) {
+  if (loop != 0) {
+    int save_errno = errno;
+    struct timespec tm;
+    tm.tv_sec = 0;
+    // Increase the delay; we expect (but do not rely on) explicit wakeups.
+    // We don't rely on explicit wakeups because we intentionally allow for
+    // a race on the kSpinLockSleeper bit.
+    tm.tv_nsec = 16 * absl::base_internal::SpinLockSuggestedDelayNS(loop);
+    syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm);
+    errno = save_errno;
+  }
+}
+
+ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockWake(std::atomic<uint32_t> *w,
+                                                  bool all) {
+  syscall(SYS_futex, w, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, all ? INT_MAX : 1, 0);
+}
+
+}  // extern "C"
diff --git a/absl/base/internal/spinlock_wait.cc b/absl/base/internal/spinlock_wait.cc
index 6709d01e..3f8e43f0 100644
--- a/absl/base/internal/spinlock_wait.cc
+++ b/absl/base/internal/spinlock_wait.cc
@@ -13,7 +13,7 @@
 // limitations under the License.
 
 // The OS-specific header included below must provide two calls:
-// base::subtle::SpinLockDelay() and base::subtle::SpinLockWake().
+// AbslInternalSpinLockDelay() and AbslInternalSpinLockWake().
 // See spinlock_wait.h for the specs.
 
 #include <atomic>
@@ -23,6 +23,8 @@
 
 #if defined(_WIN32)
 #include "absl/base/internal/spinlock_win32.inc"
+#elif defined(__linux__)
+#include "absl/base/internal/spinlock_linux.inc"
 #elif defined(__akaros__)
 #include "absl/base/internal/spinlock_akaros.inc"
 #else
@@ -30,21 +32,22 @@
 #endif
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // See spinlock_wait.h for spec.
 uint32_t SpinLockWait(std::atomic<uint32_t> *w, int n,
                       const SpinLockWaitTransition trans[],
                       base_internal::SchedulingMode scheduling_mode) {
-  for (int loop = 0; ; loop++) {
+  int loop = 0;
+  for (;;) {
     uint32_t v = w->load(std::memory_order_acquire);
     int i;
     for (i = 0; i != n && v != trans[i].from; i++) {
     }
     if (i == n) {
-      SpinLockDelay(w, v, loop, scheduling_mode);  // no matching transition
-    } else if (trans[i].to == v ||                 // null transition
+      SpinLockDelay(w, v, ++loop, scheduling_mode);  // no matching transition
+    } else if (trans[i].to == v ||                   // null transition
                w->compare_exchange_strong(v, trans[i].to,
                                           std::memory_order_acquire,
                                           std::memory_order_relaxed)) {
@@ -77,5 +80,5 @@ int SpinLockSuggestedDelayNS(int loop) {
 }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/spinlock_wait.h b/absl/base/internal/spinlock_wait.h
index 31aaa8c6..5eb727f1 100644
--- a/absl/base/internal/spinlock_wait.h
+++ b/absl/base/internal/spinlock_wait.h
@@ -24,7 +24,7 @@
 #include "absl/base/internal/scheduling_mode.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // SpinLockWait() waits until it can perform one of several transitions from
@@ -63,7 +63,7 @@ void SpinLockDelay(std::atomic<uint32_t> *w, uint32_t value, int loop,
 int SpinLockSuggestedDelayNS(int loop);
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 // In some build configurations we pass --detect-odr-violations to the
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 7db2e001..ce14fc0f 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -56,7 +56,7 @@
 #include "absl/base/internal/unscaledcycleclock.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 static once_flag init_system_info_once;
@@ -402,5 +402,5 @@ pid_t GetTID() {
 #endif
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/sysinfo.h b/absl/base/internal/sysinfo.h
index 18aa2e29..79100f61 100644
--- a/absl/base/internal/sysinfo.h
+++ b/absl/base/internal/sysinfo.h
@@ -33,7 +33,7 @@
 #include "absl/base/port.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // Nominal core processor cycles per second of each processor.   This is _not_
@@ -59,7 +59,7 @@ using pid_t = DWORD;
 pid_t GetTID();
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_SYSINFO_H_
diff --git a/absl/base/internal/sysinfo_test.cc b/absl/base/internal/sysinfo_test.cc
index fdbbdf88..c072ebc2 100644
--- a/absl/base/internal/sysinfo_test.cc
+++ b/absl/base/internal/sysinfo_test.cc
@@ -28,7 +28,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 namespace {
 
@@ -96,5 +96,5 @@ TEST(SysinfoTest, LinuxGetTID) {
 
 }  // namespace
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/thread_identity.cc b/absl/base/internal/thread_identity.cc
index aa1add8b..b35bee34 100644
--- a/absl/base/internal/thread_identity.cc
+++ b/absl/base/internal/thread_identity.cc
@@ -28,7 +28,7 @@
 #include "absl/base/internal/spinlock.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 #if ABSL_THREAD_IDENTITY_MODE != ABSL_THREAD_IDENTITY_MODE_USE_CPP11
@@ -69,6 +69,14 @@ void SetCurrentThreadIdentity(
   // NOTE: Not async-safe.  But can be open-coded.
   absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
                   reclaimer);
+
+#ifdef __EMSCRIPTEN__
+  // Emscripten PThread implementation does not support signals.
+  // See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
+  // for more information.
+  pthread_setspecific(thread_identity_pthread_key,
+                      reinterpret_cast<void*>(identity));
+#else
   // We must mask signals around the call to setspecific as with current glibc,
   // a concurrent getspecific (needed for GetCurrentThreadIdentityIfPresent())
   // may zero our value.
@@ -82,6 +90,8 @@ void SetCurrentThreadIdentity(
   pthread_setspecific(thread_identity_pthread_key,
                       reinterpret_cast<void*>(identity));
   pthread_sigmask(SIG_SETMASK, &curr_signals, nullptr);
+#endif  // !__EMSCRIPTEN__
+
 #elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS
   // NOTE: Not async-safe.  But can be open-coded.
   absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
@@ -121,5 +131,5 @@ ThreadIdentity* CurrentThreadIdentityIfPresent() {
 #endif
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/thread_identity.h b/absl/base/internal/thread_identity.h
index 18a5a750..17ac2a7c 100644
--- a/absl/base/internal/thread_identity.h
+++ b/absl/base/internal/thread_identity.h
@@ -33,7 +33,7 @@
 #include "absl/base/internal/per_thread_tls.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 
 struct SynchLocksHeld;
 struct SynchWaitParams;
@@ -237,6 +237,6 @@ inline ThreadIdentity* CurrentThreadIdentityIfPresent() {
 #endif
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
diff --git a/absl/base/internal/thread_identity_test.cc b/absl/base/internal/thread_identity_test.cc
index f39f11d2..ec93fc27 100644
--- a/absl/base/internal/thread_identity_test.cc
+++ b/absl/base/internal/thread_identity_test.cc
@@ -25,7 +25,7 @@
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 namespace {
 
@@ -124,5 +124,5 @@ TEST(ThreadIdentityTest, ReusedThreadIdentityMutexTest) {
 
 }  // namespace
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/throw_delegate.cc b/absl/base/internal/throw_delegate.cc
index 5466e0f3..0f73c3eb 100644
--- a/absl/base/internal/throw_delegate.cc
+++ b/absl/base/internal/throw_delegate.cc
@@ -22,7 +22,7 @@
 #include "absl/base/internal/raw_logging.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 namespace {
@@ -31,8 +31,8 @@ template <typename T>
 #ifdef ABSL_HAVE_EXCEPTIONS
   throw error;
 #else
-  ABSL_RAW_LOG(ERROR, "%s", error.what());
-  abort();
+  ABSL_RAW_LOG(FATAL, "%s", error.what());
+  std::abort();
 #endif
 }
 }  // namespace
@@ -104,5 +104,5 @@ void ThrowStdBadFunctionCall() { Throw(std::bad_function_call()); }
 void ThrowStdBadAlloc() { Throw(std::bad_alloc()); }
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
diff --git a/absl/base/internal/throw_delegate.h b/absl/base/internal/throw_delegate.h
index d34ff79c..7e5510c0 100644
--- a/absl/base/internal/throw_delegate.h
+++ b/absl/base/internal/throw_delegate.h
@@ -20,7 +20,7 @@
 #include <string>
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 // Helper functions that allow throwing exceptions consistently from anywhere.
@@ -67,7 +67,7 @@ namespace base_internal {
 // [[noreturn]] void ThrowStdBadArrayNewLength();
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_BASE_INTERNAL_THROW_DELEGATE_H_
diff --git a/absl/base/internal/unaligned_access.h b/absl/base/internal/unaligned_access.h
index f20a8694..07a64bba 100644
--- a/absl/base/internal/unaligned_access.h
+++ b/absl/base/internal/unaligned_access.h
@@ -65,7 +65,8 @@ void __sanitizer_unaligned_store64(void *p, uint64_t v);
 }  // extern "C"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
+namespace base_internal {
 
 inline uint16_t UnalignedLoad16(const void *p) {
   return __sanitizer_unaligned_load16(p);
@@ -91,19 +92,71 @@ inline void UnalignedStore64(void *p, uint64_t v) {
   __sanitizer_unaligned_store64(p, v);
 }
 
-}  // inline namespace lts_2018_06_20
+}  // namespace base_internal
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
-#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) (absl::UnalignedLoad16(_p))
-#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) (absl::UnalignedLoad32(_p))
-#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
+  (absl::base_internal::UnalignedLoad16(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
+  (absl::base_internal::UnalignedLoad32(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
+  (absl::base_internal::UnalignedLoad64(_p))
+
+#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
+  (absl::base_internal::UnalignedStore16(_p, _val))
+#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
+  (absl::base_internal::UnalignedStore32(_p, _val))
+#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
+  (absl::base_internal::UnalignedStore64(_p, _val))
+
+#elif defined(UNDEFINED_BEHAVIOR_SANITIZER)
+
+namespace absl {
+inline namespace lts_2018_12_18 {
+namespace base_internal {
+
+inline uint16_t UnalignedLoad16(const void *p) {
+  uint16_t t;
+  memcpy(&t, p, sizeof t);
+  return t;
+}
+
+inline uint32_t UnalignedLoad32(const void *p) {
+  uint32_t t;
+  memcpy(&t, p, sizeof t);
+  return t;
+}
+
+inline uint64_t UnalignedLoad64(const void *p) {
+  uint64_t t;
+  memcpy(&t, p, sizeof t);
+  return t;
+}
+
+inline void UnalignedStore16(void *p, uint16_t v) { memcpy(p, &v, sizeof v); }
+
+inline void UnalignedStore32(void *p, uint32_t v) { memcpy(p, &v, sizeof v); }
+
+inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }
+
+}  // namespace base_internal
+}  // inline namespace lts_2018_12_18
+}  // namespace absl
+
+#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
+  (absl::base_internal::UnalignedLoad16(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
+  (absl::base_internal::UnalignedLoad32(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
+  (absl::base_internal::UnalignedLoad64(_p))
 
 #define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
-  (absl::UnalignedStore16(_p, _val))
+  (absl::base_internal::UnalignedStore16(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
-  (absl::UnalignedStore32(_p, _val))
+  (absl::base_internal::UnalignedStore32(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
-  (absl::UnalignedStore64(_p, _val))
+  (absl::base_internal::UnalignedStore64(_p, _val))
 
 #elif defined(__x86_64__) || defined(_M_X64) || defined(__i386) || \
     defined(_M_IX86) || defined(__ppc__) || defined(__PPC__) ||    \
@@ -160,8 +213,8 @@ inline void UnalignedStore64(void *p, uint64_t v) {
 // so we do that.
 
 namespace absl {
-inline namespace lts_2018_06_20 {
-namespace internal {
+inline namespace lts_2018_12_18 {
+namespace base_internal {
 
 struct Unaligned16Struct {
   uint16_t value;
@@ -173,24 +226,27 @@ struct Unaligned32Struct {
   uint8_t dummy;  // To make the size non-power-of-two.
 } ABSL_ATTRIBUTE_PACKED;
 
-}  // namespace internal
-}  // inline namespace lts_2018_06_20
+}  // namespace base_internal
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
-#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
-  ((reinterpret_cast<const ::absl::internal::Unaligned16Struct *>(_p))->value)
-#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
-  ((reinterpret_cast<const ::absl::internal::Unaligned32Struct *>(_p))->value)
+#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p)                                  \
+  ((reinterpret_cast<const ::absl::base_internal::Unaligned16Struct *>(_p)) \
+       ->value)
+#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p)                                  \
+  ((reinterpret_cast<const ::absl::base_internal::Unaligned32Struct *>(_p)) \
+       ->value)
 
-#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val)                          \
-  ((reinterpret_cast< ::absl::internal::Unaligned16Struct *>(_p))->value = \
-       (_val))
-#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val)                          \
-  ((reinterpret_cast< ::absl::internal::Unaligned32Struct *>(_p))->value = \
-       (_val))
+#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val)                      \
+  ((reinterpret_cast< ::absl::base_internal::Unaligned16Struct *>(_p)) \
+       ->value = (_val))
+#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val)                      \
+  ((reinterpret_cast< ::absl::base_internal::Unaligned32Struct *>(_p)) \
+       ->value = (_val))
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
+namespace base_internal {
 
 inline uint64_t UnalignedLoad64(const void *p) {
   uint64_t t;
@@ -200,12 +256,14 @@ inline uint64_t UnalignedLoad64(const void *p) {
 
 inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }
 
-}  // inline namespace lts_2018_06_20
+}  // namespace base_internal
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
-#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
+  (absl::base_internal::UnalignedLoad64(_p))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
-  (absl::UnalignedStore64(_p, _val))
+  (absl::base_internal::UnalignedStore64(_p, _val))
 
 #else
 
@@ -217,7 +275,8 @@ inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }
 // unaligned loads and stores.
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
+namespace base_internal {
 
 inline uint16_t UnalignedLoad16(const void *p) {
   uint16_t t;
@@ -243,19 +302,23 @@ inline void UnalignedStore32(void *p, uint32_t v) { memcpy(p, &v, sizeof v); }
 
 inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }
 
-}  // inline namespace lts_2018_06_20
+}  // namespace base_internal
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
-#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) (absl::UnalignedLoad16(_p))
-#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) (absl::UnalignedLoad32(_p))
-#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
+  (absl::base_internal::UnalignedLoad16(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
+  (absl::base_internal::UnalignedLoad32(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
+  (absl::base_internal::UnalignedLoad64(_p))
 
 #define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
-  (absl::UnalignedStore16(_p, _val))
+  (absl::base_internal::UnalignedStore16(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
-  (absl::UnalignedStore32(_p, _val))
+  (absl::base_internal::UnalignedStore32(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
-  (absl::UnalignedStore64(_p, _val))
+  (absl::base_internal::UnalignedStore64(_p, _val))
 
 #endif
 
diff --git a/absl/base/internal/unscaledcycleclock.cc b/absl/base/internal/unscaledcycleclock.cc
index e0798eb9..888caf1e 100644
--- a/absl/base/internal/unscaledcycleclock.cc
+++ b/absl/base/internal/unscaledcycleclock.cc
@@ -27,7 +27,7 @@
 #include "absl/base/internal/sysinfo.h"
 
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace base_internal {
 
 #if defined(__i386__)
@@ -97,7 +97,7 @@ double UnscaledCycleClock::Frequency() {
 #endif
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 
 #endif  // ABSL_USE_UNSCALED_CYCLECLOCK
diff --git a/absl/base/internal/unscaledcycleclock.h b/absl/base/internal/unscaledcycleclock.h
index 9da14d0b..c71674f3 100644
--- a/absl/base/internal/unscaledcycleclock.h
+++ b/absl/base/internal/unscaledcycleclock.h
@@ -84,7 +84,7 @@
 #define ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
 #endif
 namespace absl {
-inline namespace lts_2018_06_20 {
+inline namespace lts_2018_12_18 {
 namespace time_internal {
 class UnscaledCycleClockWrapperForGetCurrentTime;
 }  // namespace time_internal
@@ -114,7 +114,7 @@ class UnscaledCycleClock {
 };
 
 }  // namespace base_internal
-}  // inline namespace lts_2018_06_20
+}  // inline namespace lts_2018_12_18
 }  // namespace absl
 #endif  // ABSL_USE_UNSCALED_CYCLECLOCK