Abseil LTS 2020092320200923

What's New:
* `absl::StatusOr<T>` has been released. See our [blog
  post](https://abseil.io/blog/2020-091021-status) for more
  information.
* Abseil Flags reflection interfaces have been released.
* Abseil Flags memory usage has been significantly optimized.
* Abseil now supports a "hardened" build mode. This build mode enables
  runtime checks that guard against programming errors that may lead
  to security vulnerabilities.

Notable Fixes:
* Sanitizer dynamic annotations like `AnnotateRWLockCreate` that are
  also defined by the compiler sanitizer implementation are no longer
  also defined by Abseil.
* Sanitizer macros are now prefixed with `ABSL_` to avoid naming collisions.
* Sanitizer usage is now automatically detected and no longer requires
  macros like `ADDRESS_SANITIZER` to be defined on the command line.

Breaking Changes:
* Abseil no longer contains a `dynamic_annotations` library. Users
  using a supported build system (Bazel or CMake) are unaffected by
  this, but users manually specifying link libraries may get an error
  about a missing linker input.

Baseline: 7680a5f8efe32de4753baadbd63e74e59d95bac1
Cherry picks: None

27 files changed, 1071 insertions, 123 deletions

diff --git a/absl/base/internal/bits.h b/absl/base/internal/bits.h
index 8b03453c..81648e2c 100644
--- a/absl/base/internal/bits.h
+++ b/absl/base/internal/bits.h
@@ -24,7 +24,7 @@
 
 // Clang on Windows has __builtin_clzll; otherwise we need to use the
 // windows intrinsic functions.
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && !defined(__clang__)
 #include <intrin.h>
 #if defined(_M_X64)
 #pragma intrinsic(_BitScanReverse64)
@@ -36,7 +36,7 @@
 
 #include "absl/base/attributes.h"
 
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && !defined(__clang__)
 // 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.
@@ -73,24 +73,25 @@ ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64Slow(uint64_t n) {
 }
 
 ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64(uint64_t n) {
-#if defined(_MSC_VER) && defined(_M_X64)
+#if defined(_MSC_VER) && !defined(__clang__) && 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)
+#elif defined(_MSC_VER) && !defined(__clang__)
   // 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)) {
+  if ((n >> 32) &&
+      _BitScanReverse(&result, static_cast<unsigned long>(n >> 32))) {
     return 31 - result;
   }
-  if (_BitScanReverse(&result, n)) {
+  if (_BitScanReverse(&result, static_cast<unsigned long>(n))) {
     return 63 - result;
   }
   return 64;
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) || defined(__clang__)
   // Use __builtin_clzll, which uses the following instructions:
   //  x86: bsr
   //  ARM64: clz
@@ -126,13 +127,13 @@ ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32Slow(uint64_t n) {
 }
 
 ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32(uint32_t n) {
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && !defined(__clang__)
   unsigned long result = 0;  // NOLINT(runtime/int)
   if (_BitScanReverse(&result, n)) {
     return 31 - result;
   }
   return 32;
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) || defined(__clang__)
   // Use __builtin_clz, which uses the following instructions:
   //  x86: bsr
   //  ARM64: clz
@@ -163,19 +164,19 @@ ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64Slow(uint64_t n) {
 }
 
 ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64(uint64_t n) {
-#if defined(_MSC_VER) && defined(_M_X64)
+#if defined(_MSC_VER) && !defined(__clang__) && defined(_M_X64)
   unsigned long result = 0;  // NOLINT(runtime/int)
   _BitScanForward64(&result, n);
   return result;
-#elif defined(_MSC_VER)
+#elif defined(_MSC_VER) && !defined(__clang__)
   unsigned long result = 0;  // NOLINT(runtime/int)
   if (static_cast<uint32_t>(n) == 0) {
-    _BitScanForward(&result, n >> 32);
+    _BitScanForward(&result, static_cast<unsigned long>(n >> 32));
     return result + 32;
   }
-  _BitScanForward(&result, n);
+  _BitScanForward(&result, static_cast<unsigned long>(n));
   return result;
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) || defined(__clang__)
   static_assert(sizeof(unsigned long long) == sizeof(n),  // NOLINT(runtime/int)
                 "__builtin_ctzll does not take 64-bit arg");
   return __builtin_ctzll(n);
@@ -196,11 +197,11 @@ ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32Slow(uint32_t n) {
 }
 
 ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && !defined(__clang__)
   unsigned long result = 0;  // NOLINT(runtime/int)
   _BitScanForward(&result, n);
   return result;
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) || defined(__clang__)
   static_assert(sizeof(int) == sizeof(n),
                 "__builtin_ctz does not take 32-bit arg");
   return __builtin_ctz(n);
diff --git a/absl/base/internal/direct_mmap.h b/absl/base/internal/direct_mmap.h
index 5618867b..16accf09 100644
--- a/absl/base/internal/direct_mmap.h
+++ b/absl/base/internal/direct_mmap.h
@@ -61,6 +61,10 @@ extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
 #endif
 #endif  // __BIONIC__
 
+#if defined(__NR_mmap2) && !defined(SYS_mmap2)
+#define SYS_mmap2 __NR_mmap2
+#endif
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
@@ -72,6 +76,7 @@ inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
 #if defined(__i386__) || defined(__ARM_ARCH_3__) || defined(__ARM_EABI__) || \
     (defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI32) ||                   \
     (defined(__PPC__) && !defined(__PPC64__)) ||                             \
+    (defined(__riscv) && __riscv_xlen == 32) ||                              \
     (defined(__s390__) && !defined(__s390x__))
   // On these architectures, implement mmap with mmap2.
   static int pagesize = 0;
diff --git a/absl/base/internal/dynamic_annotations.h b/absl/base/internal/dynamic_annotations.h
new file mode 100644
index 00000000..b23c5ec1
--- /dev/null
+++ b/absl/base/internal/dynamic_annotations.h
@@ -0,0 +1,398 @@
+// Copyright 2017 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
+//
+//      https://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 defines dynamic annotations for use with dynamic analysis tool
+// such as valgrind, PIN, etc.
+//
+// Dynamic annotation is a source code annotation that affects the generated
+// code (that is, the annotation is not a comment). Each such annotation is
+// attached to a particular instruction and/or to a particular object (address)
+// in the program.
+//
+// The annotations that should be used by users are macros in all upper-case
+// (e.g., ANNOTATE_THREAD_NAME).
+//
+// Actual implementation of these macros may differ depending on the dynamic
+// analysis tool being used.
+//
+// This file supports the following configurations:
+// - Dynamic Annotations enabled (with static thread-safety warnings disabled).
+//   In this case, macros expand to functions implemented by Thread Sanitizer,
+//   when building with TSan. When not provided an external implementation,
+//   dynamic_annotations.cc provides no-op implementations.
+//
+// - Static Clang thread-safety warnings enabled.
+//   When building with a Clang compiler that supports thread-safety warnings,
+//   a subset of annotations can be statically-checked at compile-time. We
+//   expand these macros to static-inline functions that can be analyzed for
+//   thread-safety, but afterwards elided when building the final binary.
+//
+// - All annotations are disabled.
+//   If neither Dynamic Annotations nor Clang thread-safety warnings are
+//   enabled, then all annotation-macros expand to empty.
+
+#ifndef ABSL_BASE_INTERNAL_DYNAMIC_ANNOTATIONS_H_
+#define ABSL_BASE_INTERNAL_DYNAMIC_ANNOTATIONS_H_
+
+#include <stddef.h>
+
+#include "absl/base/config.h"
+
+// -------------------------------------------------------------------------
+// Decide which features are enabled
+
+#ifndef DYNAMIC_ANNOTATIONS_ENABLED
+#define DYNAMIC_ANNOTATIONS_ENABLED 0
+#endif
+
+#if defined(__clang__) && !defined(SWIG)
+#define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 1
+#endif
+
+#if DYNAMIC_ANNOTATIONS_ENABLED != 0
+
+#define ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 0
+#define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED 1
+
+#else
+
+#define ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED 0
+#define ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED 0
+#define ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED 0
+
+// Clang provides limited support for static thread-safety analysis through a
+// feature called Annotalysis. We configure macro-definitions according to
+// whether Annotalysis support is available. When running in opt-mode, GCC
+// will issue a warning, if these attributes are compiled. Only include them
+// when compiling using Clang.
+
+// ANNOTALYSIS_ENABLED == 1 when IGNORE_READ_ATTRIBUTE_ENABLED == 1
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED \
+  defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+// Read/write annotations are enabled in Annotalysis mode; disabled otherwise.
+#define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED \
+  ABSL_INTERNAL_ANNOTALYSIS_ENABLED
+#endif
+
+// Memory annotations are also made available to LLVM's Memory Sanitizer
+#if defined(ABSL_HAVE_MEMORY_SANITIZER) && !defined(__native_client__)
+#define ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED 1
+#endif
+
+#ifndef ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED
+#define ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED 0
+#endif
+
+#ifdef __cplusplus
+#define ABSL_INTERNAL_BEGIN_EXTERN_C extern "C" {
+#define ABSL_INTERNAL_END_EXTERN_C }  // extern "C"
+#define ABSL_INTERNAL_GLOBAL_SCOPED(F) ::F
+#define ABSL_INTERNAL_STATIC_INLINE inline
+#else
+#define ABSL_INTERNAL_BEGIN_EXTERN_C  // empty
+#define ABSL_INTERNAL_END_EXTERN_C    // empty
+#define ABSL_INTERNAL_GLOBAL_SCOPED(F) F
+#define ABSL_INTERNAL_STATIC_INLINE static inline
+#endif
+
+// -------------------------------------------------------------------------
+// Define race annotations.
+
+#if ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 1
+
+// -------------------------------------------------------------
+// Annotations that suppress errors. It is usually better to express the
+// program's synchronization using the other annotations, but these can be used
+// when all else fails.
+
+// Report that we may have a benign race at `pointer`, with size
+// "sizeof(*(pointer))". `pointer` must be a non-void* pointer. Insert at the
+// point where `pointer` has been allocated, preferably close to the point
+// where the race happens. See also ANNOTATE_BENIGN_RACE_STATIC.
+#define ANNOTATE_BENIGN_RACE(pointer, description)     \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateBenignRaceSized) \
+  (__FILE__, __LINE__, pointer, sizeof(*(pointer)), description)
+
+// Same as ANNOTATE_BENIGN_RACE(`address`, `description`), but applies to
+// the memory range [`address`, `address`+`size`).
+#define ANNOTATE_BENIGN_RACE_SIZED(address, size, description) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateBenignRaceSized)         \
+  (__FILE__, __LINE__, address, size, description)
+
+// Enable (`enable`!=0) or disable (`enable`==0) race detection for all threads.
+// This annotation could be useful if you want to skip expensive race analysis
+// during some period of program execution, e.g. during initialization.
+#define ANNOTATE_ENABLE_RACE_DETECTION(enable)             \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateEnableRaceDetection) \
+  (__FILE__, __LINE__, enable)
+
+// -------------------------------------------------------------
+// Annotations useful for debugging.
+
+// Report the current thread `name` to a race detector.
+#define ANNOTATE_THREAD_NAME(name) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateThreadName)(__FILE__, __LINE__, name)
+
+// -------------------------------------------------------------
+// Annotations useful when implementing locks. They are not normally needed by
+// modules that merely use locks. The `lock` argument is a pointer to the lock
+// object.
+
+// Report that a lock has been created at address `lock`.
+#define ANNOTATE_RWLOCK_CREATE(lock) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockCreate)(__FILE__, __LINE__, lock)
+
+// Report that a linker initialized lock has been created at address `lock`.
+#ifdef ABSL_HAVE_THREAD_SANITIZER
+#define ANNOTATE_RWLOCK_CREATE_STATIC(lock)               \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockCreateStatic) \
+  (__FILE__, __LINE__, lock)
+#else
+#define ANNOTATE_RWLOCK_CREATE_STATIC(lock) ANNOTATE_RWLOCK_CREATE(lock)
+#endif
+
+// Report that the lock at address `lock` is about to be destroyed.
+#define ANNOTATE_RWLOCK_DESTROY(lock) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockDestroy)(__FILE__, __LINE__, lock)
+
+// Report that the lock at address `lock` has been acquired.
+// `is_w`=1 for writer lock, `is_w`=0 for reader lock.
+#define ANNOTATE_RWLOCK_ACQUIRED(lock, is_w)          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockAcquired) \
+  (__FILE__, __LINE__, lock, is_w)
+
+// Report that the lock at address `lock` is about to be released.
+// `is_w`=1 for writer lock, `is_w`=0 for reader lock.
+#define ANNOTATE_RWLOCK_RELEASED(lock, is_w)          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockReleased) \
+  (__FILE__, __LINE__, lock, is_w)
+
+// Apply ANNOTATE_BENIGN_RACE_SIZED to a static variable `static_var`.
+#define ANNOTATE_BENIGN_RACE_STATIC(static_var, description)      \
+  namespace {                                                     \
+  class static_var##_annotator {                                  \
+   public:                                                        \
+    static_var##_annotator() {                                    \
+      ANNOTATE_BENIGN_RACE_SIZED(&static_var, sizeof(static_var), \
+                                 #static_var ": " description);   \
+    }                                                             \
+  };                                                              \
+  static static_var##_annotator the##static_var##_annotator;      \
+  }  // namespace
+
+#else  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 0
+
+#define ANNOTATE_RWLOCK_CREATE(lock)                            // empty
+#define ANNOTATE_RWLOCK_CREATE_STATIC(lock)                     // empty
+#define ANNOTATE_RWLOCK_DESTROY(lock)                           // empty
+#define ANNOTATE_RWLOCK_ACQUIRED(lock, is_w)                    // empty
+#define ANNOTATE_RWLOCK_RELEASED(lock, is_w)                    // empty
+#define ANNOTATE_BENIGN_RACE(address, description)              // empty
+#define ANNOTATE_BENIGN_RACE_SIZED(address, size, description)  // empty
+#define ANNOTATE_THREAD_NAME(name)                              // empty
+#define ANNOTATE_ENABLE_RACE_DETECTION(enable)                  // empty
+#define ANNOTATE_BENIGN_RACE_STATIC(static_var, description)    // empty
+
+#endif  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED
+
+// -------------------------------------------------------------------------
+// Define memory annotations.
+
+#if ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED == 1
+
+#include <sanitizer/msan_interface.h>
+
+#define ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+  __msan_unpoison(address, size)
+
+#define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+  __msan_allocated_memory(address, size)
+
+#else  // ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED == 0
+
+#if DYNAMIC_ANNOTATIONS_ENABLED == 1
+#define ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+  do {                                                \
+    (void)(address);                                  \
+    (void)(size);                                     \
+  } while (0)
+#define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+  do {                                                  \
+    (void)(address);                                    \
+    (void)(size);                                       \
+  } while (0)
+#else
+#define ANNOTATE_MEMORY_IS_INITIALIZED(address, size)    // empty
+#define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size)  // empty
+#endif
+
+#endif  // ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED
+
+// -------------------------------------------------------------------------
+// Define IGNORE_READS_BEGIN/_END attributes.
+
+#if defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+#define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE \
+  __attribute((exclusive_lock_function("*")))
+#define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE \
+  __attribute((unlock_function("*")))
+
+#else  // !defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+#define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE  // empty
+#define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE    // empty
+
+#endif  // defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+// -------------------------------------------------------------------------
+// Define IGNORE_READS_BEGIN/_END annotations.
+
+#if ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED == 1
+
+// Request the analysis tool to ignore all reads in the current thread until
+// ANNOTATE_IGNORE_READS_END is called. Useful to ignore intentional racey
+// reads, while still checking other reads and all writes.
+// See also ANNOTATE_UNPROTECTED_READ.
+#define ANNOTATE_IGNORE_READS_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreReadsBegin)(__FILE__, __LINE__)
+
+// Stop ignoring reads.
+#define ANNOTATE_IGNORE_READS_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreReadsEnd)(__FILE__, __LINE__)
+
+#elif defined(ABSL_INTERNAL_ANNOTALYSIS_ENABLED)
+
+// When Annotalysis is enabled without Dynamic Annotations, the use of
+// static-inline functions allows the annotations to be read at compile-time,
+// while still letting the compiler elide the functions from the final build.
+//
+// TODO(delesley) -- The exclusive lock here ignores writes as well, but
+// allows IGNORE_READS_AND_WRITES to work properly.
+
+#define ANNOTATE_IGNORE_READS_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AbslInternalAnnotateIgnoreReadsBegin)()
+
+#define ANNOTATE_IGNORE_READS_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AbslInternalAnnotateIgnoreReadsEnd)()
+
+#else
+
+#define ANNOTATE_IGNORE_READS_BEGIN()  // empty
+#define ANNOTATE_IGNORE_READS_END()    // empty
+
+#endif
+
+// -------------------------------------------------------------------------
+// Define IGNORE_WRITES_BEGIN/_END annotations.
+
+#if ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED == 1
+
+// Similar to ANNOTATE_IGNORE_READS_BEGIN, but ignore writes instead.
+#define ANNOTATE_IGNORE_WRITES_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreWritesBegin)(__FILE__, __LINE__)
+
+// Stop ignoring writes.
+#define ANNOTATE_IGNORE_WRITES_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreWritesEnd)(__FILE__, __LINE__)
+
+#else
+
+#define ANNOTATE_IGNORE_WRITES_BEGIN()  // empty
+#define ANNOTATE_IGNORE_WRITES_END()    // empty
+
+#endif
+
+// -------------------------------------------------------------------------
+// Define the ANNOTATE_IGNORE_READS_AND_WRITES_* annotations using the more
+// primitive annotations defined above.
+//
+//     Instead of doing
+//        ANNOTATE_IGNORE_READS_BEGIN();
+//        ... = x;
+//        ANNOTATE_IGNORE_READS_END();
+//     one can use
+//        ... = ANNOTATE_UNPROTECTED_READ(x);
+
+#if defined(ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED)
+
+// Start ignoring all memory accesses (both reads and writes).
+#define ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN() \
+  do {                                           \
+    ANNOTATE_IGNORE_READS_BEGIN();               \
+    ANNOTATE_IGNORE_WRITES_BEGIN();              \
+  } while (0)
+
+// Stop ignoring both reads and writes.
+#define ANNOTATE_IGNORE_READS_AND_WRITES_END() \
+  do {                                         \
+    ANNOTATE_IGNORE_WRITES_END();              \
+    ANNOTATE_IGNORE_READS_END();               \
+  } while (0)
+
+#ifdef __cplusplus
+// ANNOTATE_UNPROTECTED_READ is the preferred way to annotate racey reads.
+#define ANNOTATE_UNPROTECTED_READ(x) \
+  absl::base_internal::AnnotateUnprotectedRead(x)
+
+#endif
+
+#else
+
+#define ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN()  // empty
+#define ANNOTATE_IGNORE_READS_AND_WRITES_END()    // empty
+#define ANNOTATE_UNPROTECTED_READ(x) (x)
+
+#endif
+
+// -------------------------------------------------------------------------
+// Address sanitizer annotations
+
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+// Describe the current state of a contiguous container such as e.g.
+// std::vector or std::string. For more details see
+// sanitizer/common_interface_defs.h, which is provided by the compiler.
+#include <sanitizer/common_interface_defs.h>
+
+#define ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid) \
+  __sanitizer_annotate_contiguous_container(beg, end, old_mid, new_mid)
+#define ADDRESS_SANITIZER_REDZONE(name)    \
+  struct {                                 \
+    char x[8] __attribute__((aligned(8))); \
+  } name
+
+#else
+
+#define ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid)
+#define ADDRESS_SANITIZER_REDZONE(name) static_assert(true, "")
+
+#endif  // ABSL_HAVE_ADDRESS_SANITIZER
+
+// -------------------------------------------------------------------------
+// Undefine the macros intended only for this file.
+
+#undef ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_ANNOTALYSIS_ENABLED
+#undef ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_BEGIN_EXTERN_C
+#undef ABSL_INTERNAL_END_EXTERN_C
+#undef ABSL_INTERNAL_STATIC_INLINE
+
+#endif  // ABSL_BASE_INTERNAL_DYNAMIC_ANNOTATIONS_H_
diff --git a/absl/base/internal/endian_test.cc b/absl/base/internal/endian_test.cc
index aa6b8496..a1691b1f 100644
--- a/absl/base/internal/endian_test.cc
+++ b/absl/base/internal/endian_test.cc
@@ -54,24 +54,22 @@ const uint32_t k32ValueBE{0x67452301};
 const uint16_t k16ValueBE{0x2301};
 #endif
 
-template<typename T>
-std::vector<T> GenerateAllValuesForType() {
-  std::vector<T> result;
-  T next = std::numeric_limits<T>::min();
-  while (true) {
-    result.push_back(next);
-    if (next == std::numeric_limits<T>::max()) {
-      return result;
-    }
-    ++next;
+std::vector<uint16_t> GenerateAllUint16Values() {
+  std::vector<uint16_t> result;
+  result.reserve(size_t{1} << (sizeof(uint16_t) * 8));
+  for (uint32_t i = std::numeric_limits<uint16_t>::min();
+       i <= std::numeric_limits<uint16_t>::max(); ++i) {
+    result.push_back(static_cast<uint16_t>(i));
   }
+  return result;
 }
 
 template<typename T>
-std::vector<T> GenerateRandomIntegers(size_t numValuesToTest) {
+std::vector<T> GenerateRandomIntegers(size_t num_values_to_test) {
   std::vector<T> result;
+  result.reserve(num_values_to_test);
   std::mt19937_64 rng(kRandomSeed);
-  for (size_t i = 0; i < numValuesToTest; ++i) {
+  for (size_t i = 0; i < num_values_to_test; ++i) {
     result.push_back(rng());
   }
   return result;
@@ -148,7 +146,7 @@ void Swap64(char* bytes) {
 }
 
 TEST(EndianessTest, Uint16) {
-  GBSwapHelper(GenerateAllValuesForType<uint16_t>(), &Swap16);
+  GBSwapHelper(GenerateAllUint16Values(), &Swap16);
 }
 
 TEST(EndianessTest, Uint32) {
diff --git a/absl/base/internal/errno_saver_test.cc b/absl/base/internal/errno_saver_test.cc
index b845e2dd..e9b742c5 100644
--- a/absl/base/internal/errno_saver_test.cc
+++ b/absl/base/internal/errno_saver_test.cc
@@ -18,6 +18,7 @@
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
+#include "absl/base/internal/strerror.h"
 
 namespace {
 using ::testing::Eq;
@@ -26,7 +27,7 @@ struct ErrnoPrinter {
   int no;
 };
 std::ostream &operator<<(std::ostream &os, ErrnoPrinter ep) {
-  return os << strerror(ep.no) << " [" << ep.no << "]";
+  return os << absl::base_internal::StrError(ep.no) << " [" << ep.no << "]";
 }
 bool operator==(ErrnoPrinter one, ErrnoPrinter two) { return one.no == two.no; }
 
diff --git a/absl/base/internal/fast_type_id.h b/absl/base/internal/fast_type_id.h
new file mode 100644
index 00000000..3db59e83
--- /dev/null
+++ b/absl/base/internal/fast_type_id.h
@@ -0,0 +1,48 @@
+//
+// Copyright 2020 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
+//
+//      https://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_FAST_TYPE_ID_H_
+#define ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+template <typename Type>
+struct FastTypeTag {
+  constexpr static char dummy_var = 0;
+};
+
+template <typename Type>
+constexpr char FastTypeTag<Type>::dummy_var;
+
+// FastTypeId<Type>() evaluates at compile/link-time to a unique pointer for the
+// passed-in type. These are meant to be good match for keys into maps or
+// straight up comparisons.
+using FastTypeIdType = const void*;
+
+template <typename Type>
+constexpr inline FastTypeIdType FastTypeId() {
+  return &FastTypeTag<Type>::dummy_var;
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_
diff --git a/absl/base/internal/fast_type_id_test.cc b/absl/base/internal/fast_type_id_test.cc
new file mode 100644
index 00000000..16f3c145
--- /dev/null
+++ b/absl/base/internal/fast_type_id_test.cc
@@ -0,0 +1,123 @@
+// Copyright 2020 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
+//
+//     https://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/fast_type_id.h"
+
+#include <cstdint>
+#include <map>
+#include <vector>
+
+#include "gtest/gtest.h"
+
+namespace {
+namespace bi = absl::base_internal;
+
+// NOLINTNEXTLINE
+#define PRIM_TYPES(A)   \
+  A(bool)               \
+  A(short)              \
+  A(unsigned short)     \
+  A(int)                \
+  A(unsigned int)       \
+  A(long)               \
+  A(unsigned long)      \
+  A(long long)          \
+  A(unsigned long long) \
+  A(float)              \
+  A(double)             \
+  A(long double)
+
+TEST(FastTypeIdTest, PrimitiveTypes) {
+  bi::FastTypeIdType type_ids[] = {
+#define A(T) bi::FastTypeId<T>(),
+    PRIM_TYPES(A)
+#undef A
+#define A(T) bi::FastTypeId<const T>(),
+    PRIM_TYPES(A)
+#undef A
+#define A(T) bi::FastTypeId<volatile T>(),
+    PRIM_TYPES(A)
+#undef A
+#define A(T) bi::FastTypeId<const volatile T>(),
+    PRIM_TYPES(A)
+#undef A
+  };
+  size_t total_type_ids = sizeof(type_ids) / sizeof(bi::FastTypeIdType);
+
+  for (int i = 0; i < total_type_ids; ++i) {
+    EXPECT_EQ(type_ids[i], type_ids[i]);
+    for (int j = 0; j < i; ++j) {
+      EXPECT_NE(type_ids[i], type_ids[j]);
+    }
+  }
+}
+
+#define FIXED_WIDTH_TYPES(A) \
+  A(int8_t)                  \
+  A(uint8_t)                 \
+  A(int16_t)                 \
+  A(uint16_t)                \
+  A(int32_t)                 \
+  A(uint32_t)                \
+  A(int64_t)                 \
+  A(uint64_t)
+
+TEST(FastTypeIdTest, FixedWidthTypes) {
+  bi::FastTypeIdType type_ids[] = {
+#define A(T) bi::FastTypeId<T>(),
+    FIXED_WIDTH_TYPES(A)
+#undef A
+#define A(T) bi::FastTypeId<const T>(),
+    FIXED_WIDTH_TYPES(A)
+#undef A
+#define A(T) bi::FastTypeId<volatile T>(),
+    FIXED_WIDTH_TYPES(A)
+#undef A
+#define A(T) bi::FastTypeId<const volatile T>(),
+    FIXED_WIDTH_TYPES(A)
+#undef A
+  };
+  size_t total_type_ids = sizeof(type_ids) / sizeof(bi::FastTypeIdType);
+
+  for (int i = 0; i < total_type_ids; ++i) {
+    EXPECT_EQ(type_ids[i], type_ids[i]);
+    for (int j = 0; j < i; ++j) {
+      EXPECT_NE(type_ids[i], type_ids[j]);
+    }
+  }
+}
+
+TEST(FastTypeIdTest, AliasTypes) {
+  using int_alias = int;
+  EXPECT_EQ(bi::FastTypeId<int_alias>(), bi::FastTypeId<int>());
+}
+
+TEST(FastTypeIdTest, TemplateSpecializations) {
+  EXPECT_NE(bi::FastTypeId<std::vector<int>>(),
+            bi::FastTypeId<std::vector<long>>());
+
+  EXPECT_NE((bi::FastTypeId<std::map<int, float>>()),
+            (bi::FastTypeId<std::map<int, double>>()));
+}
+
+struct Base {};
+struct Derived : Base {};
+struct PDerived : private Base {};
+
+TEST(FastTypeIdTest, Inheritance) {
+  EXPECT_NE(bi::FastTypeId<Base>(), bi::FastTypeId<Derived>());
+  EXPECT_NE(bi::FastTypeId<Base>(), bi::FastTypeId<PDerived>());
+}
+
+}  // namespace
diff --git a/absl/base/internal/invoke.h b/absl/base/internal/invoke.h
index c4eceebd..5c71f328 100644
--- a/absl/base/internal/invoke.h
+++ b/absl/base/internal/invoke.h
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
-// absl::base_internal::Invoke(f, args...) is an implementation of
+// absl::base_internal::invoke(f, args...) is an implementation of
 // INVOKE(f, args...) from section [func.require] of the C++ standard.
 //
 // [func.require]
@@ -29,7 +29,7 @@
 //    is not one of the types described in the previous item;
 // 5. f(t1, t2, ..., tN) in all other cases.
 //
-// The implementation is SFINAE-friendly: substitution failure within Invoke()
+// The implementation is SFINAE-friendly: substitution failure within invoke()
 // isn't an error.
 
 #ifndef ABSL_BASE_INTERNAL_INVOKE_H_
@@ -170,13 +170,13 @@ struct Invoker {
 
 // The result type of Invoke<F, Args...>.
 template <typename F, typename... Args>
-using InvokeT = decltype(Invoker<F, Args...>::type::Invoke(
+using invoke_result_t = decltype(Invoker<F, Args...>::type::Invoke(
     std::declval<F>(), std::declval<Args>()...));
 
 // Invoke(f, args...) is an implementation of INVOKE(f, args...) from section
 // [func.require] of the C++ standard.
 template <typename F, typename... Args>
-InvokeT<F, Args...> Invoke(F&& f, Args&&... args) {
+invoke_result_t<F, Args...> invoke(F&& f, Args&&... args) {
   return Invoker<F, Args...>::type::Invoke(std::forward<F>(f),
                                            std::forward<Args>(args)...);
 }
diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc
index 1bf94438..229ab916 100644
--- a/absl/base/internal/low_level_alloc.cc
+++ b/absl/base/internal/low_level_alloc.cc
@@ -598,7 +598,7 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
     section.Leave();
     result = &s->levels;
   }
-  ANNOTATE_MEMORY_IS_UNINITIALIZED(result, request);
+  ABSL_ANNOTATE_MEMORY_IS_UNINITIALIZED(result, request);
   return result;
 }
 
diff --git a/absl/base/internal/low_level_alloc_test.cc b/absl/base/internal/low_level_alloc_test.cc
index 7abbbf9c..2f2eaffa 100644
--- a/absl/base/internal/low_level_alloc_test.cc
+++ b/absl/base/internal/low_level_alloc_test.cc
@@ -21,6 +21,8 @@
 #include <unordered_map>
 #include <utility>
 
+#include "absl/container/node_hash_map.h"
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
@@ -75,7 +77,7 @@ static bool using_low_level_alloc = false;
 // allocations and deallocations are reported via the MallocHook
 // interface.
 static void Test(bool use_new_arena, bool call_malloc_hook, int n) {
-  typedef std::unordered_map<int, BlockDesc> AllocMap;
+  typedef absl::node_hash_map<int, BlockDesc> AllocMap;
   AllocMap allocated;
   AllocMap::iterator it;
   BlockDesc block_desc;
diff --git a/absl/base/internal/low_level_scheduling.h b/absl/base/internal/low_level_scheduling.h
index 961cc981..6ef79fbf 100644
--- a/absl/base/internal/low_level_scheduling.h
+++ b/absl/base/internal/low_level_scheduling.h
@@ -18,6 +18,7 @@
 #ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
 #define ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
 
+#include "absl/base/internal/raw_logging.h"
 #include "absl/base/internal/scheduling_mode.h"
 #include "absl/base/macros.h"
 
@@ -29,6 +30,13 @@ extern "C" void __google_enable_rescheduling(bool disable_result);
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
+class CondVar;
+class Mutex;
+
+namespace synchronization_internal {
+int MutexDelay(int32_t c, int mode);
+}  // namespace synchronization_internal
+
 namespace base_internal {
 
 class SchedulingHelper;  // To allow use of SchedulingGuard.
@@ -76,9 +84,23 @@ class SchedulingGuard {
     bool disabled;
   };
 
-  // Access to SchedulingGuard is explicitly white-listed.
+  // A scoped helper to enable rescheduling temporarily.
+  // REQUIRES: destructor must run in same thread as constructor.
+  class ScopedEnable {
+   public:
+    ScopedEnable();
+    ~ScopedEnable();
+
+   private:
+    int scheduling_disabled_depth_;
+  };
+
+  // Access to SchedulingGuard is explicitly permitted.
+  friend class absl::CondVar;
+  friend class absl::Mutex;
   friend class SchedulingHelper;
   friend class SpinLock;
+  friend int absl::synchronization_internal::MutexDelay(int32_t c, int mode);
 
   SchedulingGuard(const SchedulingGuard&) = delete;
   SchedulingGuard& operator=(const SchedulingGuard&) = delete;
@@ -100,6 +122,12 @@ inline void SchedulingGuard::EnableRescheduling(bool /* disable_result */) {
   return;
 }
 
+inline SchedulingGuard::ScopedEnable::ScopedEnable()
+    : scheduling_disabled_depth_(0) {}
+inline SchedulingGuard::ScopedEnable::~ScopedEnable() {
+  ABSL_RAW_CHECK(scheduling_disabled_depth_ == 0, "disable unused warning");
+}
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/base/internal/raw_logging.cc b/absl/base/internal/raw_logging.cc
index 40cea550..ae8754c6 100644
--- a/absl/base/internal/raw_logging.cc
+++ b/absl/base/internal/raw_logging.cc
@@ -69,7 +69,7 @@
 
 // TODO(gfalcon): We want raw-logging to work on as many platforms as possible.
 // Explicitly #error out when not ABSL_LOW_LEVEL_WRITE_SUPPORTED, except for a
-// whitelisted set of platforms for which we expect not to be able to raw log.
+// selected set of platforms for which we expect not to be able to raw log.
 
 ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES static absl::base_internal::AtomicHook<
     absl::raw_logging_internal::LogPrefixHook>
@@ -227,7 +227,7 @@ bool RawLoggingFullySupported() {
 #endif  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
 }
 
-ABSL_DLL ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
+ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_DLL
     absl::base_internal::AtomicHook<InternalLogFunction>
         internal_log_function(DefaultInternalLog);
 
diff --git a/absl/base/internal/raw_logging.h b/absl/base/internal/raw_logging.h
index 418d6c85..2508f3cf 100644
--- a/absl/base/internal/raw_logging.h
+++ b/absl/base/internal/raw_logging.h
@@ -72,10 +72,12 @@
 //
 // 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 {                                                                      \
-    ::absl::raw_logging_internal::internal_log_function(                    \
-        ABSL_RAW_LOGGING_INTERNAL_##severity, __FILE__, __LINE__, message); \
+#define ABSL_INTERNAL_LOG(severity, message)                             \
+  do {                                                                   \
+    constexpr const char* absl_raw_logging_internal_filename = __FILE__; \
+    ::absl::raw_logging_internal::internal_log_function(                 \
+        ABSL_RAW_LOGGING_INTERNAL_##severity,                            \
+        absl_raw_logging_internal_filename, __LINE__, message);          \
   } while (0)
 
 #define ABSL_INTERNAL_CHECK(condition, message)                    \
@@ -170,7 +172,7 @@ using InternalLogFunction = void (*)(absl::LogSeverity severity,
                                      const char* file, int line,
                                      const std::string& message);
 
-ABSL_DLL ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES extern base_internal::AtomicHook<
+ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_DLL extern base_internal::AtomicHook<
     InternalLogFunction>
     internal_log_function;
 
diff --git a/absl/base/internal/spinlock.cc b/absl/base/internal/spinlock.cc
index 830d4729..a7d44f3e 100644
--- a/absl/base/internal/spinlock.cc
+++ b/absl/base/internal/spinlock.cc
@@ -66,35 +66,19 @@ void RegisterSpinLockProfiler(void (*fn)(const void *contendedlock,
   submit_profile_data.Store(fn);
 }
 
+// Static member variable definitions.
+constexpr uint32_t SpinLock::kSpinLockHeld;
+constexpr uint32_t SpinLock::kSpinLockCooperative;
+constexpr uint32_t SpinLock::kSpinLockDisabledScheduling;
+constexpr uint32_t SpinLock::kSpinLockSleeper;
+constexpr uint32_t SpinLock::kWaitTimeMask;
+
 // Uncommon constructors.
 SpinLock::SpinLock(base_internal::SchedulingMode mode)
     : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) {
   ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static);
 }
 
-SpinLock::SpinLock(base_internal::LinkerInitialized,
-                   base_internal::SchedulingMode mode) {
-  ABSL_TSAN_MUTEX_CREATE(this, 0);
-  if (IsCooperative(mode)) {
-    InitLinkerInitializedAndCooperative();
-  }
-  // Otherwise, lockword_ is already initialized.
-}
-
-// Static (linker initialized) spinlocks always start life as functional
-// non-cooperative locks.  When their static constructor does run, it will call
-// this initializer to augment the lockword with the cooperative bit.  By
-// actually taking the lock when we do this we avoid the need for an atomic
-// operation in the regular unlock path.
-//
-// SlowLock() must be careful to re-test for this bit so that any outstanding
-// waiters may be upgraded to cooperative status.
-void SpinLock::InitLinkerInitializedAndCooperative() {
-  Lock();
-  lockword_.fetch_or(kSpinLockCooperative, std::memory_order_relaxed);
-  Unlock();
-}
-
 // Monitor the lock to see if its value changes within some time period
 // (adaptive_spin_count loop iterations). The last value read from the lock
 // is returned from the method.
@@ -121,6 +105,14 @@ void SpinLock::SlowLock() {
   if ((lock_value & kSpinLockHeld) == 0) {
     return;
   }
+
+  base_internal::SchedulingMode scheduling_mode;
+  if ((lock_value & kSpinLockCooperative) != 0) {
+    scheduling_mode = base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL;
+  } else {
+    scheduling_mode = base_internal::SCHEDULE_KERNEL_ONLY;
+  }
+
   // 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
@@ -151,12 +143,6 @@ void SpinLock::SlowLock() {
       }
     }
 
-    base_internal::SchedulingMode scheduling_mode;
-    if ((lock_value & kSpinLockCooperative) != 0) {
-      scheduling_mode = base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL;
-    } else {
-      scheduling_mode = base_internal::SCHEDULE_KERNEL_ONLY;
-    }
     // SpinLockDelay() calls into fiber scheduler, we need to see
     // synchronization there to avoid false positives.
     ABSL_TSAN_MUTEX_PRE_DIVERT(this, 0);
@@ -190,30 +176,32 @@ void SpinLock::SlowUnlock(uint32_t lock_value) {
 // We use the upper 29 bits of the lock word to store the time spent waiting to
 // acquire this lock.  This is reported by contentionz profiling.  Since the
 // lower bits of the cycle counter wrap very quickly on high-frequency
-// processors we divide to reduce the granularity to 2^PROFILE_TIMESTAMP_SHIFT
+// processors we divide to reduce the granularity to 2^kProfileTimestampShift
 // sized units.  On a 4Ghz machine this will lose track of wait times greater
 // than (2^29/4 Ghz)*128 =~ 17.2 seconds.  Such waits should be extremely rare.
-enum { PROFILE_TIMESTAMP_SHIFT = 7 };
-enum { LOCKWORD_RESERVED_SHIFT = 3 };  // We currently reserve the lower 3 bits.
+static constexpr int kProfileTimestampShift = 7;
+
+// We currently reserve the lower 3 bits.
+static constexpr int kLockwordReservedShift = 3;
 
 uint32_t SpinLock::EncodeWaitCycles(int64_t wait_start_time,
                                     int64_t wait_end_time) {
   static const int64_t kMaxWaitTime =
-      std::numeric_limits<uint32_t>::max() >> LOCKWORD_RESERVED_SHIFT;
+      std::numeric_limits<uint32_t>::max() >> kLockwordReservedShift;
   int64_t scaled_wait_time =
-      (wait_end_time - wait_start_time) >> PROFILE_TIMESTAMP_SHIFT;
+      (wait_end_time - wait_start_time) >> kProfileTimestampShift;
 
   // Return a representation of the time spent waiting that can be stored in
   // the lock word's upper bits.
   uint32_t clamped = static_cast<uint32_t>(
-      std::min(scaled_wait_time, kMaxWaitTime) << LOCKWORD_RESERVED_SHIFT);
+      std::min(scaled_wait_time, kMaxWaitTime) << kLockwordReservedShift);
 
   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);
+      kSpinLockSleeper + (1 << kLockwordReservedShift);
   if (clamped == kSpinLockSleeper) {
     return kMinWaitTime;
   }
@@ -224,8 +212,7 @@ uint64_t SpinLock::DecodeWaitCycles(uint32_t lock_value) {
   // Cast to uint32_t first to ensure bits [63:32] are cleared.
   const uint64_t scaled_wait_time =
       static_cast<uint32_t>(lock_value & kWaitTimeMask);
-  return scaled_wait_time
-      << (PROFILE_TIMESTAMP_SHIFT - LOCKWORD_RESERVED_SHIFT);
+  return scaled_wait_time << (kProfileTimestampShift - kLockwordReservedShift);
 }
 
 }  // namespace base_internal
diff --git a/absl/base/internal/spinlock.h b/absl/base/internal/spinlock.h
index 24e2e9a6..e6ac9e64 100644
--- a/absl/base/internal/spinlock.h
+++ b/absl/base/internal/spinlock.h
@@ -36,6 +36,7 @@
 #include <atomic>
 
 #include "absl/base/attributes.h"
+#include "absl/base/const_init.h"
 #include "absl/base/dynamic_annotations.h"
 #include "absl/base/internal/low_level_scheduling.h"
 #include "absl/base/internal/raw_logging.h"
@@ -55,29 +56,22 @@ class ABSL_LOCKABLE SpinLock {
     ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static);
   }
 
-  // Special constructor for use with static SpinLock objects.  E.g.,
-  //
-  //    static SpinLock lock(base_internal::kLinkerInitialized);
-  //
-  // When initialized using this constructor, we depend on the fact
-  // that the linker has already initialized the memory appropriately. The lock
-  // is initialized in non-cooperative mode.
-  //
-  // A SpinLock constructed like this can be freely used from global
-  // initializers without worrying about the order in which global
-  // initializers run.
-  explicit SpinLock(base_internal::LinkerInitialized) {
-    // Does nothing; lockword_ is already initialized
-    ABSL_TSAN_MUTEX_CREATE(this, 0);
-  }
-
   // Constructors that allow non-cooperative spinlocks to be created for use
   // inside thread schedulers.  Normal clients should not use these.
   explicit SpinLock(base_internal::SchedulingMode mode);
-  SpinLock(base_internal::LinkerInitialized,
-           base_internal::SchedulingMode mode);
 
+  // Constructor for global SpinLock instances.  See absl/base/const_init.h.
+  constexpr SpinLock(absl::ConstInitType, base_internal::SchedulingMode mode)
+      : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) {}
+
+  // For global SpinLock instances prefer trivial destructor when possible.
+  // Default but non-trivial destructor in some build configurations causes an
+  // extra static initializer.
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
   ~SpinLock() { ABSL_TSAN_MUTEX_DESTROY(this, __tsan_mutex_not_static); }
+#else
+  ~SpinLock() = default;
+#endif
 
   // Acquire this SpinLock.
   inline void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() {
@@ -148,12 +142,13 @@ class ABSL_LOCKABLE SpinLock {
   // bit[1] encodes whether a lock uses cooperative scheduling.
   // bit[2] encodes whether a lock disables scheduling.
   // bit[3:31] encodes time a lock spent on waiting as a 29-bit unsigned int.
-  enum { kSpinLockHeld = 1 };
-  enum { kSpinLockCooperative = 2 };
-  enum { kSpinLockDisabledScheduling = 4 };
-  enum { kSpinLockSleeper = 8 };
-  enum { kWaitTimeMask =                      // Includes kSpinLockSleeper.
-    ~(kSpinLockHeld | kSpinLockCooperative | kSpinLockDisabledScheduling) };
+  static constexpr uint32_t kSpinLockHeld = 1;
+  static constexpr uint32_t kSpinLockCooperative = 2;
+  static constexpr uint32_t kSpinLockDisabledScheduling = 4;
+  static constexpr uint32_t kSpinLockSleeper = 8;
+  // Includes kSpinLockSleeper.
+  static constexpr uint32_t kWaitTimeMask =
+      ~(kSpinLockHeld | kSpinLockCooperative | kSpinLockDisabledScheduling);
 
   // Returns true if the provided scheduling mode is cooperative.
   static constexpr bool IsCooperative(
@@ -162,7 +157,6 @@ class ABSL_LOCKABLE SpinLock {
   }
 
   uint32_t TryLockInternal(uint32_t lock_value, uint32_t wait_cycles);
-  void InitLinkerInitializedAndCooperative();
   void SlowLock() ABSL_ATTRIBUTE_COLD;
   void SlowUnlock(uint32_t lock_value) ABSL_ATTRIBUTE_COLD;
   uint32_t SpinLoop();
diff --git a/absl/base/internal/spinlock_linux.inc b/absl/base/internal/spinlock_linux.inc
index 323edd62..e31c6ed4 100644
--- a/absl/base/internal/spinlock_linux.inc
+++ b/absl/base/internal/spinlock_linux.inc
@@ -46,6 +46,14 @@ static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),
 #endif
 #endif
 
+#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)
+#define SYS_futex_time64 __NR_futex_time64
+#endif
+
+#if defined(SYS_futex_time64) && !defined(SYS_futex)
+#define SYS_futex SYS_futex_time64
+#endif
+
 extern "C" {
 
 ABSL_ATTRIBUTE_WEAK void AbslInternalSpinLockDelay(
diff --git a/absl/base/internal/strerror.cc b/absl/base/internal/strerror.cc
new file mode 100644
index 00000000..d66ba120
--- /dev/null
+++ b/absl/base/internal/strerror.cc
@@ -0,0 +1,88 @@
+// Copyright 2020 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
+//
+//      https://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/strerror.h"
+
+#include <array>
+#include <cerrno>
+#include <cstddef>
+#include <cstdio>
+#include <cstring>
+#include <string>
+#include <type_traits>
+
+#include "absl/base/internal/errno_saver.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+namespace {
+
+const char* StrErrorAdaptor(int errnum, char* buf, size_t buflen) {
+#if defined(_WIN32)
+  int rc = strerror_s(buf, buflen, errnum);
+  buf[buflen - 1] = '\0';  // guarantee NUL termination
+  if (rc == 0 && strncmp(buf, "Unknown error", buflen) == 0) *buf = '\0';
+  return buf;
+#else
+  // The type of `ret` is platform-specific; both of these branches must compile
+  // either way but only one will execute on any given platform:
+  auto ret = strerror_r(errnum, buf, buflen);
+  if (std::is_same<decltype(ret), int>::value) {
+    // XSI `strerror_r`; `ret` is `int`:
+    if (ret) *buf = '\0';
+    return buf;
+  } else {
+    // GNU `strerror_r`; `ret` is `char *`:
+    return reinterpret_cast<const char*>(ret);
+  }
+#endif
+}
+
+std::string StrErrorInternal(int errnum) {
+  absl::base_internal::ErrnoSaver errno_saver;
+  char buf[100];
+  const char* str = StrErrorAdaptor(errnum, buf, sizeof buf);
+  if (*str == '\0') {
+    snprintf(buf, sizeof buf, "Unknown error %d", errnum);
+    str = buf;
+  }
+  return str;
+}
+
+// kSysNerr is the number of errors from a recent glibc. `StrError()` falls back
+// to `StrErrorAdaptor()` if the value is larger than this.
+constexpr int kSysNerr = 135;
+
+std::array<std::string, kSysNerr>* NewStrErrorTable() {
+  auto* table = new std::array<std::string, kSysNerr>;
+  for (int i = 0; i < static_cast<int>(table->size()); ++i) {
+    (*table)[i] = StrErrorInternal(i);
+  }
+  return table;
+}
+
+}  // namespace
+
+std::string StrError(int errnum) {
+  static const auto* table = NewStrErrorTable();
+  if (errnum >= 0 && errnum < static_cast<int>(table->size())) {
+    return (*table)[errnum];
+  }
+  return StrErrorInternal(errnum);
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/absl/base/internal/strerror.h b/absl/base/internal/strerror.h
new file mode 100644
index 00000000..35009736
--- /dev/null
+++ b/absl/base/internal/strerror.h
@@ -0,0 +1,39 @@
+// Copyright 2020 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
+//
+//      https://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_STRERROR_H_
+#define ABSL_BASE_INTERNAL_STRERROR_H_
+
+#include <string>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// A portable and thread-safe alternative to C89's `strerror`.
+//
+// The C89 specification of `strerror` is not suitable for use in a
+// multi-threaded application as the returned string may be changed by calls to
+// `strerror` from another thread.  The many non-stdlib alternatives differ
+// enough in their names, availability, and semantics to justify this wrapper
+// around them.  `errno` will not be modified by a call to `absl::StrError`.
+std::string StrError(int errnum);
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_STRERROR_H_
diff --git a/absl/base/internal/strerror_benchmark.cc b/absl/base/internal/strerror_benchmark.cc
new file mode 100644
index 00000000..c9ab14a8
--- /dev/null
+++ b/absl/base/internal/strerror_benchmark.cc
@@ -0,0 +1,29 @@
+// Copyright 2020 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
+//
+//      https://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 <cerrno>
+#include <cstdio>
+#include <string>
+
+#include "absl/base/internal/strerror.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+void BM_AbslStrError(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(absl::base_internal::StrError(ERANGE));
+  }
+}
+BENCHMARK(BM_AbslStrError);
+}  // namespace
diff --git a/absl/base/internal/strerror_test.cc b/absl/base/internal/strerror_test.cc
new file mode 100644
index 00000000..a53da97f
--- /dev/null
+++ b/absl/base/internal/strerror_test.cc
@@ -0,0 +1,86 @@
+// Copyright 2020 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
+//
+//      https://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/strerror.h"
+
+#include <atomic>
+#include <cerrno>
+#include <cstdio>
+#include <cstring>
+#include <string>
+#include <thread>  // NOLINT(build/c++11)
+#include <vector>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/strings/match.h"
+
+namespace {
+using ::testing::AnyOf;
+using ::testing::Eq;
+
+TEST(StrErrorTest, ValidErrorCode) {
+  errno = ERANGE;
+  EXPECT_THAT(absl::base_internal::StrError(EDOM), Eq(strerror(EDOM)));
+  EXPECT_THAT(errno, Eq(ERANGE));
+}
+
+TEST(StrErrorTest, InvalidErrorCode) {
+  errno = ERANGE;
+  EXPECT_THAT(absl::base_internal::StrError(-1),
+              AnyOf(Eq("No error information"), Eq("Unknown error -1")));
+  EXPECT_THAT(errno, Eq(ERANGE));
+}
+
+TEST(StrErrorTest, MultipleThreads) {
+  // In this test, we will start up 2 threads and have each one call
+  // StrError 1000 times, each time with a different errnum.  We
+  // expect that StrError(errnum) will return a string equal to the
+  // one returned by strerror(errnum), if the code is known.  Since
+  // strerror is known to be thread-hostile, collect all the expected
+  // strings up front.
+  const int kNumCodes = 1000;
+  std::vector<std::string> expected_strings(kNumCodes);
+  for (int i = 0; i < kNumCodes; ++i) {
+    expected_strings[i] = strerror(i);
+  }
+
+  std::atomic_int counter(0);
+  auto thread_fun = [&]() {
+    for (int i = 0; i < kNumCodes; ++i) {
+      ++counter;
+      errno = ERANGE;
+      const std::string value = absl::base_internal::StrError(i);
+      // Only the GNU implementation is guaranteed to provide the
+      // string "Unknown error nnn". POSIX doesn't say anything.
+      if (!absl::StartsWith(value, "Unknown error ")) {
+        EXPECT_THAT(absl::base_internal::StrError(i), Eq(expected_strings[i]));
+      }
+      EXPECT_THAT(errno, Eq(ERANGE));
+    }
+  };
+
+  const int kNumThreads = 100;
+  std::vector<std::thread> threads;
+  for (int i = 0; i < kNumThreads; ++i) {
+    threads.push_back(std::thread(thread_fun));
+  }
+  for (auto& thread : threads) {
+    thread.join();
+  }
+
+  EXPECT_THAT(counter, Eq(kNumThreads * kNumCodes));
+}
+
+}  // namespace
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index a0930e97..349d9268 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -39,6 +39,7 @@
 #endif
 
 #include <string.h>
+
 #include <cassert>
 #include <cstdint>
 #include <cstdio>
@@ -50,9 +51,11 @@
 #include <vector>
 
 #include "absl/base/call_once.h"
+#include "absl/base/config.h"
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/internal/spinlock.h"
 #include "absl/base/internal/unscaledcycleclock.h"
+#include "absl/base/thread_annotations.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
@@ -72,6 +75,12 @@ static int GetNumCPUs() {
 #if defined(_WIN32)
 
 static double GetNominalCPUFrequency() {
+#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP) && \
+    !WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+  // UWP apps don't have access to the registry and currently don't provide an
+  // API informing about CPU nominal frequency.
+  return 1.0;
+#else
 #pragma comment(lib, "advapi32.lib")  // For Reg* functions.
   HKEY key;
   // Use the Reg* functions rather than the SH functions because shlwapi.dll
@@ -91,6 +100,7 @@ static double GetNominalCPUFrequency() {
     }
   }
   return 1.0;
+#endif  // WINAPI_PARTITION_APP && !WINAPI_PARTITION_DESKTOP
 }
 
 #elif defined(CTL_HW) && defined(HW_CPU_FREQ)
@@ -336,15 +346,16 @@ pid_t GetTID() {
 #else
 
 // Fallback implementation of GetTID using pthread_getspecific.
-static once_flag tid_once;
-static pthread_key_t tid_key;
-static absl::base_internal::SpinLock tid_lock(
-    absl::base_internal::kLinkerInitialized);
+ABSL_CONST_INIT static once_flag tid_once;
+ABSL_CONST_INIT static pthread_key_t tid_key;
+ABSL_CONST_INIT static absl::base_internal::SpinLock tid_lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
 
 // We set a bit per thread in this array to indicate that an ID is in
 // use. ID 0 is unused because it is the default value returned by
 // pthread_getspecific().
-static std::vector<uint32_t>* tid_array GUARDED_BY(tid_lock) = nullptr;
+ABSL_CONST_INIT static std::vector<uint32_t> *tid_array
+    ABSL_GUARDED_BY(tid_lock) = nullptr;
 static constexpr int kBitsPerWord = 32;  // tid_array is uint32_t.
 
 // Returns the TID to tid_array.
@@ -411,6 +422,18 @@ pid_t GetTID() {
 
 #endif
 
+// GetCachedTID() caches the thread ID in thread-local storage (which is a
+// userspace construct) to avoid unnecessary system calls. Without this caching,
+// it can take roughly 98ns, while it takes roughly 1ns with this caching.
+pid_t GetCachedTID() {
+#if ABSL_HAVE_THREAD_LOCAL
+  static thread_local pid_t thread_id = GetTID();
+  return thread_id;
+#else
+  return GetTID();
+#endif  // ABSL_HAVE_THREAD_LOCAL
+}
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/base/internal/sysinfo.h b/absl/base/internal/sysinfo.h
index 7246d5dd..119cf1f0 100644
--- a/absl/base/internal/sysinfo.h
+++ b/absl/base/internal/sysinfo.h
@@ -30,6 +30,7 @@
 
 #include <cstdint>
 
+#include "absl/base/config.h"
 #include "absl/base/port.h"
 
 namespace absl {
@@ -59,6 +60,13 @@ using pid_t = uint32_t;
 #endif
 pid_t GetTID();
 
+// Like GetTID(), but caches the result in thread-local storage in order
+// to avoid unnecessary system calls. Note that there are some cases where
+// one must call through to GetTID directly, which is why this exists as a
+// separate function. For example, GetCachedTID() is not safe to call in
+// an asynchronous signal-handling context nor right after a call to fork().
+pid_t GetCachedTID();
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/base/internal/thread_identity_test.cc b/absl/base/internal/thread_identity_test.cc
index 3685779c..46a6f743 100644
--- a/absl/base/internal/thread_identity_test.cc
+++ b/absl/base/internal/thread_identity_test.cc
@@ -21,6 +21,7 @@
 #include "absl/base/attributes.h"
 #include "absl/base/internal/spinlock.h"
 #include "absl/base/macros.h"
+#include "absl/base/thread_annotations.h"
 #include "absl/synchronization/internal/per_thread_sem.h"
 #include "absl/synchronization/mutex.h"
 
@@ -29,10 +30,9 @@ ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 namespace {
 
-// protects num_identities_reused
-static absl::base_internal::SpinLock map_lock(
-    absl::base_internal::kLinkerInitialized);
-static int num_identities_reused;
+ABSL_CONST_INIT static absl::base_internal::SpinLock map_lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
+ABSL_CONST_INIT static int num_identities_reused ABSL_GUARDED_BY(map_lock);
 
 static const void* const kCheckNoIdentity = reinterpret_cast<void*>(1);
 
@@ -75,7 +75,7 @@ TEST(ThreadIdentityTest, BasicIdentityWorksThreaded) {
   // - If a thread implementation chooses to recycle threads, that
   //   correct re-initialization occurs.
   static const int kNumLoops = 3;
-  static const int kNumThreads = 400;
+  static const int kNumThreads = 32;
   for (int iter = 0; iter < kNumLoops; iter++) {
     std::vector<std::thread> threads;
     for (int i = 0; i < kNumThreads; ++i) {
@@ -90,6 +90,7 @@ TEST(ThreadIdentityTest, BasicIdentityWorksThreaded) {
   // We should have recycled ThreadIdentity objects above; while (external)
   // library threads allocating their own identities may preclude some
   // reuse, we should have sufficient repetitions to exclude this.
+  absl::base_internal::SpinLockHolder l(&map_lock);
   EXPECT_LT(kNumThreads, num_identities_reused);
 }
 
diff --git a/absl/base/internal/tsan_mutex_interface.h b/absl/base/internal/tsan_mutex_interface.h
index 2a510603..39207d8a 100644
--- a/absl/base/internal/tsan_mutex_interface.h
+++ b/absl/base/internal/tsan_mutex_interface.h
@@ -19,6 +19,8 @@
 #ifndef ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
 #define ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
 
+#include "absl/base/config.h"
+
 // ABSL_INTERNAL_HAVE_TSAN_INTERFACE
 // Macro intended only for internal use.
 //
@@ -28,7 +30,7 @@
 #error "ABSL_INTERNAL_HAVE_TSAN_INTERFACE cannot be directly set."
 #endif
 
-#if defined(THREAD_SANITIZER) && defined(__has_include)
+#if defined(ABSL_HAVE_THREAD_SANITIZER) && defined(__has_include)
 #if __has_include(<sanitizer/tsan_interface.h>)
 #define ABSL_INTERNAL_HAVE_TSAN_INTERFACE 1
 #endif
diff --git a/absl/base/internal/unaligned_access.h b/absl/base/internal/unaligned_access.h
index 6be56c86..dd5250de 100644
--- a/absl/base/internal/unaligned_access.h
+++ b/absl/base/internal/unaligned_access.h
@@ -32,8 +32,8 @@
 // (namespaces, inline) which are absent or incompatible in C.
 #if defined(__cplusplus)
 
-#if defined(ADDRESS_SANITIZER) || defined(THREAD_SANITIZER) ||\
-    defined(MEMORY_SANITIZER)
+#if defined(ABSL_HAVE_ADDRESS_SANITIZER) || \
+    defined(ABSL_HAVE_THREAD_SANITIZER) || defined(ABSL_HAVE_MEMORY_SANITIZER)
 // Consider we have an unaligned load/store of 4 bytes from address 0x...05.
 // AddressSanitizer will treat it as a 3-byte access to the range 05:07 and
 // will miss a bug if 08 is the first unaddressable byte.
diff --git a/absl/base/internal/unique_small_name_test.cc b/absl/base/internal/unique_small_name_test.cc
new file mode 100644
index 00000000..ff8c2b3f
--- /dev/null
+++ b/absl/base/internal/unique_small_name_test.cc
@@ -0,0 +1,77 @@
+// Copyright 2020 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
+//
+//      https://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 "gtest/gtest.h"
+#include "absl/base/optimization.h"
+#include "absl/strings/string_view.h"
+
+// This test by itself does not do anything fancy, but it serves as binary I can
+// query in shell test.
+
+namespace {
+
+template <class T>
+void DoNotOptimize(const T& var) {
+#ifdef __GNUC__
+  asm volatile("" : "+m"(const_cast<T&>(var)));
+#else
+  std::cout << (void*)&var;
+#endif
+}
+
+int very_long_int_variable_name ABSL_INTERNAL_UNIQUE_SMALL_NAME() = 0;
+char very_long_str_variable_name[] ABSL_INTERNAL_UNIQUE_SMALL_NAME() = "abc";
+
+TEST(UniqueSmallName, NonAutomaticVar) {
+  EXPECT_EQ(very_long_int_variable_name, 0);
+  EXPECT_EQ(absl::string_view(very_long_str_variable_name), "abc");
+}
+
+int VeryLongFreeFunctionName() ABSL_INTERNAL_UNIQUE_SMALL_NAME();
+
+TEST(UniqueSmallName, FreeFunction) {
+  DoNotOptimize(&VeryLongFreeFunctionName);
+
+  EXPECT_EQ(VeryLongFreeFunctionName(), 456);
+}
+
+int VeryLongFreeFunctionName() { return 456; }
+
+struct VeryLongStructName {
+  explicit VeryLongStructName(int i);
+
+  int VeryLongMethodName() ABSL_INTERNAL_UNIQUE_SMALL_NAME();
+
+  static int VeryLongStaticMethodName() ABSL_INTERNAL_UNIQUE_SMALL_NAME();
+
+ private:
+  int fld;
+};
+
+TEST(UniqueSmallName, Struct) {
+  VeryLongStructName var(10);
+
+  DoNotOptimize(var);
+  DoNotOptimize(&VeryLongStructName::VeryLongMethodName);
+  DoNotOptimize(&VeryLongStructName::VeryLongStaticMethodName);
+
+  EXPECT_EQ(var.VeryLongMethodName(), 10);
+  EXPECT_EQ(VeryLongStructName::VeryLongStaticMethodName(), 123);
+}
+
+VeryLongStructName::VeryLongStructName(int i) : fld(i) {}
+int VeryLongStructName::VeryLongMethodName() { return fld; }
+int VeryLongStructName::VeryLongStaticMethodName() { return 123; }
+
+}  // namespace
diff --git a/absl/base/internal/unscaledcycleclock.h b/absl/base/internal/unscaledcycleclock.h
index cdce9bf8..82f2c87a 100644
--- a/absl/base/internal/unscaledcycleclock.h
+++ b/absl/base/internal/unscaledcycleclock.h
@@ -15,8 +15,8 @@
 // UnscaledCycleClock
 //    An UnscaledCycleClock yields the value and frequency of a cycle counter
 //    that increments at a rate that is approximately constant.
-//    This class is for internal / whitelisted use only, you should consider
-//    using CycleClock instead.
+//    This class is for internal use only, you should consider using CycleClock
+//    instead.
 //
 // Notes:
 // The cycle counter frequency is not necessarily the core clock frequency.
@@ -109,7 +109,7 @@ class UnscaledCycleClock {
   // value.
   static double Frequency();
 
-  // Whitelisted friends.
+  // Allowed users
   friend class base_internal::CycleClock;
   friend class time_internal::UnscaledCycleClockWrapperForGetCurrentTime;
   friend class base_internal::UnscaledCycleClockWrapperForInitializeFrequency;