Export of internal Abseil changes

--
8bdb2020150ed0fd4a4e520e454dc5f54e33f776 by Eric Fiselier <ericwf@google.com>:

Workaround bug in GCC 9.2 and after.

PiperOrigin-RevId: 291982551

--
47ff4820e595f96c082a90d733725f6882d83e3b by Abseil Team <absl-team@google.com>:

Improve ABSL_ATTRIBUTE_PACKED documentation

Recommend to apply ABSL_ATTRIBUTE_PACKED to structure members instead of to an entire structure because applying this attribute to an entire structure may cause the compiler to generate suboptimal code. It reduces the alignment of the data structure from a value larger than one to one. When applied to a structure, ABSL_ATTRIBUTE_PACKED reduces the alignment of a structure (alignof()) to 1. As a result, the compiler can no longer assume that e.g. uint32 members are aligned on a four byte boundary and hence is forced to use single-byte load and store instructions on CPU architectures that do not support non-aligned loads or stores.

PiperOrigin-RevId: 291977920

--
902b7a86f860da699d3a2e5c738be5ef73ede3b4 by Mark Barolak <mbar@google.com>:

Internal change

PiperOrigin-RevId: 291963048

--
bb3bd3247e376d53a3080b105f13ec7566d3ae50 by Abseil Team <absl-team@google.com>:

Support the C++17 insert_or_assign() API in btree_map.

PiperOrigin-RevId: 291945474

--
ff3b3cfcbbc64f086f95501f48d49426bcde356f by Gennadiy Rozental <rogeeff@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 291861110

--
fd465cd9cbbacd3962f67a7346d6462edaddd809 by Derek Mauro <dmauro@google.com>:

Add flaky=1 to beta_distribution_test.

PiperOrigin-RevId: 291757364

--
3603adfb59c4128c542b670952cce250d59e1f67 by Derek Mauro <dmauro@google.com>:

Separate the initialization of NumCPUs() and NominalCPUFrequency()

The OSS version of Abseil never needs to call NominalCPUFrequency().
In some configurations, initializing NominalCPUFrequency() requires
spending at least 3ms measuring the CPU frequency. By separating the
initialization from NumCPUs(), which is called in most configurations,
we can save at least 3ms of program startup time.

PiperOrigin-RevId: 291737273

--
bea9e4a6bff5a0351d340deab966641867e08c4d by Abseil Team <absl-team@google.com>:

Change the cmake library names not to have a redundant `absl_` prefix.

PiperOrigin-RevId: 291640501

--
501b602ef260cd7c8c527342581ceffb3c5b6d4c by Gennadiy Rozental <rogeeff@google.com>:

Introducing benchmark for absl::GetFlag.

PiperOrigin-RevId: 291433394

--
4eeaddc788da4b91c272a8adca77ca6dbbbc1d44 by Xiaoyi Zhang <zhangxy@google.com>:

fix: Add support for more ARM processors detection

Import of https://github.com/abseil/abseil-cpp/pull/608

PiperOrigin-RevId: 291420397

--
a3087a8e883c5d71de7d9bd4ec8f4db5142dfcf5 by Derek Mauro <dmauro@google.com>:

Removes the flaky raw_hash_set prefetch test

PiperOrigin-RevId: 291197079

--
aad6c2121c102ac36216e771c83227cf3e3bfd66 by Andy Soffer <asoffer@google.com>:

Enable building Abseil as a DLL.
This is currently experimental and unsupported.

This CL does a few things:
1. Adds the ABSL_DLL macro to any class holding a static data member, or to global constants in headers.
2. Adds a whitelist of all files in the DLL and all the build targets that are conglomerated into the DLL.
3. When BUILD_SHARED_LIBS is specified, any build target that would be in the DLL still exists, but we swap out all of it's dependencies so it just depends on abseil_dll

PiperOrigin-RevId: 291192055

--
5e888cd6f2a7722805d41f872108a03a84e421c7 by Mark Barolak <mbar@google.com>:

Move absl/strings/internal/escaping.{cc,h} into internal build targets.

This puts absl/strings/internal/escaping.h behind a whitelist and it also resolves https://github.com/abseil/abseil-cpp/issues/604.

PiperOrigin-RevId: 291173320

--
166836d24970da87587c1728036f53f05a28f0af by Eric Fiselier <ericwf@google.com>:

Internal Change.

PiperOrigin-RevId: 291012718

--
996ddb3dffda02440fa93f30ca5d71b14b688875 by Abseil Team <absl-team@google.com>:

Fix shared libraries log spam for built-in types in absl::GetFlag

PiperOrigin-RevId: 290772743
GitOrigin-RevId: 8bdb2020150ed0fd4a4e520e454dc5f54e33f776
Change-Id: I8bf2265dd14ebbace220a1b6b982bb5040ad2a26

45 files changed, 527 insertions, 225 deletions

diff --git a/absl/CMakeLists.txt b/absl/CMakeLists.txt
index 3e78397c..a1b1f8d8 100644
--- a/absl/CMakeLists.txt
+++ b/absl/CMakeLists.txt
@@ -14,8 +14,6 @@
 # limitations under the License.
 #
 
-
-
 add_subdirectory(base)
 add_subdirectory(algorithm)
 add_subdirectory(container)
@@ -31,3 +29,7 @@ add_subdirectory(synchronization)
 add_subdirectory(time)
 add_subdirectory(types)
 add_subdirectory(utility)
+
+if (${ABSL_BUILD_DLL})
+  absl_make_dll()
+endif()
diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index acd1c526..8f77db77 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -563,7 +563,19 @@
 
 // ABSL_ATTRIBUTE_PACKED
 //
-// Prevents the compiler from padding a structure to natural alignment
+// Instructs the compiler not to use natural alignment for a tagged data
+// structure, but instead to reduce its alignment to 1. This attribute can
+// either be applied to members of a structure or to a structure in its
+// entirety. Applying this attribute (judiciously) to a structure in its
+// entirety to optimize the memory footprint of very commonly-used structs is
+// fine. Do not apply this attribute to a structure in its entirety if the
+// purpose is to control the offsets of the members in the structure. Instead,
+// apply this attribute only to structure members that need it.
+//
+// When applying ABSL_ATTRIBUTE_PACKED only to specific structure members the
+// natural alignment of structure members not annotated is preserved. Aligned
+// member accesses are faster than non-aligned member accesses even if the
+// targeted microprosessor supports non-aligned accesses.
 #if ABSL_HAVE_ATTRIBUTE(packed) || (defined(__GNUC__) && !defined(__clang__))
 #define ABSL_ATTRIBUTE_PACKED __attribute__((__packed__))
 #else
diff --git a/absl/base/config.h b/absl/base/config.h
index c4e8dce4..eac5d268 100644
--- a/absl/base/config.h
+++ b/absl/base/config.h
@@ -643,4 +643,23 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 
 #undef ABSL_INTERNAL_HAS_KEYWORD
 
+// ABSL_DLL
+//
+// When building Abseil as a DLL, this macro expands to `__declspec(dllexport)`
+// so we can annotate symbols appropriately as being exported. When used in
+// headers consuming a DLL, this macro expands to `__declspec(dllimport)` so
+// that consumers know the symbol is defined inside the DLL. In all other cases,
+// the macro expands to nothing.
+#if defined(_MSC_VER)
+#if defined(ABSL_BUILD_DLL)
+#define ABSL_DLL __declspec(dllexport)
+#elif defined(ABSL_CONSUME_DLL)
+#define ABSL_DLL __declspec(dllimport)
+#else
+#define ABSL_DLL
+#endif
+#else
+#define ABSL_DLL
+#endif  // defined(_MSC_VER)
+
 #endif  // ABSL_BASE_CONFIG_H_
diff --git a/absl/base/internal/raw_logging.cc b/absl/base/internal/raw_logging.cc
index d79c5486..e36eb29a 100644
--- a/absl/base/internal/raw_logging.cc
+++ b/absl/base/internal/raw_logging.cc
@@ -225,8 +225,9 @@ bool RawLoggingFullySupported() {
 #endif  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
 }
 
-ABSL_CONST_INIT absl::base_internal::AtomicHook<InternalLogFunction>
-    internal_log_function(DefaultInternalLog);
+ABSL_CONST_INIT ABSL_DLL
+    absl::base_internal::AtomicHook<InternalLogFunction>
+        internal_log_function(DefaultInternalLog);
 
 void RegisterInternalLogFunction(InternalLogFunction func) {
   internal_log_function.Store(func);
diff --git a/absl/base/internal/raw_logging.h b/absl/base/internal/raw_logging.h
index cff45058..ac74f97d 100644
--- a/absl/base/internal/raw_logging.h
+++ b/absl/base/internal/raw_logging.h
@@ -22,9 +22,11 @@
 #include <string>
 
 #include "absl/base/attributes.h"
+#include "absl/base/config.h"
 #include "absl/base/internal/atomic_hook.h"
 #include "absl/base/log_severity.h"
 #include "absl/base/macros.h"
+#include "absl/base/optimization.h"
 #include "absl/base/port.h"
 
 // This is similar to LOG(severity) << format..., but
@@ -168,7 +170,8 @@ using InternalLogFunction = void (*)(absl::LogSeverity severity,
                                      const char* file, int line,
                                      const std::string& message);
 
-extern base_internal::AtomicHook<InternalLogFunction> internal_log_function;
+ABSL_DLL extern base_internal::AtomicHook<InternalLogFunction>
+    internal_log_function;
 
 void RegisterInternalLogFunction(InternalLogFunction func);
 
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 7945322f..a0930e97 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -58,10 +58,6 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 
-static once_flag init_system_info_once;
-static int num_cpus = 0;
-static double nominal_cpu_frequency = 1.0;  // 0.0 might be dangerous.
-
 static int GetNumCPUs() {
 #if defined(__myriad2__)
   return 1;
@@ -265,21 +261,27 @@ static double GetNominalCPUFrequency() {
 
 #endif
 
-// InitializeSystemInfo() may be called before main() and before
-// malloc is properly initialized, therefore this must not allocate
-// memory.
-static void InitializeSystemInfo() {
-  num_cpus = GetNumCPUs();
-  nominal_cpu_frequency = GetNominalCPUFrequency();
-}
+ABSL_CONST_INIT static once_flag init_num_cpus_once;
+ABSL_CONST_INIT static int num_cpus = 0;
 
+// NumCPUs() may be called before main() and before malloc is properly
+// initialized, therefore this must not allocate memory.
 int NumCPUs() {
-  base_internal::LowLevelCallOnce(&init_system_info_once, InitializeSystemInfo);
+  base_internal::LowLevelCallOnce(
+      &init_num_cpus_once, []() { num_cpus = GetNumCPUs(); });
   return num_cpus;
 }
 
+// A default frequency of 0.0 might be dangerous if it is used in division.
+ABSL_CONST_INIT static once_flag init_nominal_cpu_frequency_once;
+ABSL_CONST_INIT static double nominal_cpu_frequency = 1.0;
+
+// NominalCPUFrequency() may be called before main() and before malloc is
+// properly initialized, therefore this must not allocate memory.
 double NominalCPUFrequency() {
-  base_internal::LowLevelCallOnce(&init_system_info_once, InitializeSystemInfo);
+  base_internal::LowLevelCallOnce(
+      &init_nominal_cpu_frequency_once,
+      []() { nominal_cpu_frequency = GetNominalCPUFrequency(); });
   return nominal_cpu_frequency;
 }
 
diff --git a/absl/base/internal/thread_identity.cc b/absl/base/internal/thread_identity.cc
index 6a28f246..d63a04ae 100644
--- a/absl/base/internal/thread_identity.cc
+++ b/absl/base/internal/thread_identity.cc
@@ -113,6 +113,18 @@ void SetCurrentThreadIdentity(
 #endif
 }
 
+#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
+    ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+
+// Please see the comment on `CurrentThreadIdentityIfPresent` in
+// thread_identity.h. Because DLLs cannot expose thread_local variables in
+// headers, we opt for the correct-but-slower option of placing the definition
+// of this function only in a translation unit inside DLL.
+#if defined(ABSL_BUILD_DLL) || defined(ABSL_CONSUME_DLL)
+ThreadIdentity* CurrentThreadIdentityIfPresent() { return thread_identity_ptr; }
+#endif
+#endif
+
 void ClearCurrentThreadIdentity() {
 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
     ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
diff --git a/absl/base/internal/thread_identity.h b/absl/base/internal/thread_identity.h
index 5dfd0715..ceb109b4 100644
--- a/absl/base/internal/thread_identity.h
+++ b/absl/base/internal/thread_identity.h
@@ -30,6 +30,7 @@
 #include <atomic>
 #include <cstdint>
 
+#include "absl/base/config.h"
 #include "absl/base/internal/per_thread_tls.h"
 
 namespace absl {
@@ -234,9 +235,17 @@ ABSL_CONST_INIT extern thread_local ThreadIdentity* thread_identity_ptr;
 #error Thread-local storage not detected on this platform
 #endif
 
+// thread_local variables cannot be in headers exposed by DLLs. However, it is
+// important for performance reasons in general that
+// `CurrentThreadIdentityIfPresent` be inlined. This is not possible across a
+// DLL boundary so, with DLLs, we opt to have the function not be inlined. Note
+// that `CurrentThreadIdentityIfPresent` is declared above so we can exclude
+// this entire inline definition when compiling as a DLL.
+#if !defined(ABSL_BUILD_DLL) && !defined(ABSL_CONSUME_DLL)
 inline ThreadIdentity* CurrentThreadIdentityIfPresent() {
   return thread_identity_ptr;
 }
+#endif
 
 #elif ABSL_THREAD_IDENTITY_MODE != \
     ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
diff --git a/absl/base/options.h b/absl/base/options.h
index 592b33b7..6868c77b 100644
--- a/absl/base/options.h
+++ b/absl/base/options.h
@@ -66,7 +66,13 @@
 // NOTE: the defaults within this file all assume that Abseil can select the
 // proper Abseil implementation at compile-time, which will not be sufficient
 // to guarantee ABI stability to package managers.
-//
+
+// Include a standard library header to allow configuration based on the
+// standard library in use.
+#ifdef __cplusplus
+#include <ciso646>
+#endif
+
 // -----------------------------------------------------------------------------
 // Type Compatibility Options
 // -----------------------------------------------------------------------------
@@ -158,7 +164,6 @@
 
 #define ABSL_OPTION_USE_STD_STRING_VIEW 2
 
-
 // ABSL_OPTION_USE_STD_VARIANT
 //
 // This option controls whether absl::variant is implemented as an alias to
diff --git a/absl/container/btree_map.h b/absl/container/btree_map.h
index cbfcb58c..d23f4ee5 100644
--- a/absl/container/btree_map.h
+++ b/absl/container/btree_map.h
@@ -226,6 +226,30 @@ class btree_map
   //   Inserts the elements within the initializer list `ilist`.
   using Base::insert;
 
+  // btree_map::insert_or_assign()
+  //
+  // Inserts an element of the specified value into the `btree_map` provided
+  // that a value with the given key does not already exist, or replaces the
+  // corresponding mapped type with the forwarded `obj` argument if a key for
+  // that value already exists, returning an iterator pointing to the newly
+  // inserted element. Overloads are listed below.
+  //
+  // pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj):
+  // pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj):
+  //
+  //   Inserts/Assigns (or moves) the element of the specified key into the
+  //   `btree_map`. If the returned bool is true, insertion took place, and if
+  //   it's false, assignment took place.
+  //
+  // iterator insert_or_assign(const_iterator hint,
+  //                           const key_type& k, M&& obj):
+  // iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj):
+  //
+  //   Inserts/Assigns (or moves) the element of the specified key into the
+  //   `btree_map` using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search.
+  using Base::insert_or_assign;
+
   // btree_map::emplace()
   //
   // Inserts an element of the specified value by constructing it in-place
diff --git a/absl/container/btree_test.cc b/absl/container/btree_test.cc
index 8692b9c2..af8ee00b 100644
--- a/absl/container/btree_test.cc
+++ b/absl/container/btree_test.cc
@@ -2345,6 +2345,65 @@ TEST(Btree, EraseIf) {
   }
 }
 
+TEST(Btree, InsertOrAssign) {
+  absl::btree_map<int, int> m = {{1, 1}, {3, 3}};
+  using value_type = typename decltype(m)::value_type;
+
+  auto ret = m.insert_or_assign(4, 4);
+  EXPECT_EQ(*ret.first, value_type(4, 4));
+  EXPECT_TRUE(ret.second);
+  ret = m.insert_or_assign(3, 100);
+  EXPECT_EQ(*ret.first, value_type(3, 100));
+  EXPECT_FALSE(ret.second);
+
+  auto hint_ret = m.insert_or_assign(ret.first, 3, 200);
+  EXPECT_EQ(*hint_ret, value_type(3, 200));
+  hint_ret = m.insert_or_assign(m.find(1), 0, 1);
+  EXPECT_EQ(*hint_ret, value_type(0, 1));
+  // Test with bad hint.
+  hint_ret = m.insert_or_assign(m.end(), -1, 1);
+  EXPECT_EQ(*hint_ret, value_type(-1, 1));
+
+  EXPECT_THAT(m, ElementsAre(Pair(-1, 1), Pair(0, 1), Pair(1, 1), Pair(3, 200),
+                             Pair(4, 4)));
+}
+
+TEST(Btree, InsertOrAssignMovableOnly) {
+  absl::btree_map<int, MovableOnlyInstance> m;
+  using value_type = typename decltype(m)::value_type;
+
+  auto ret = m.insert_or_assign(4, MovableOnlyInstance(4));
+  EXPECT_EQ(*ret.first, value_type(4, MovableOnlyInstance(4)));
+  EXPECT_TRUE(ret.second);
+  ret = m.insert_or_assign(4, MovableOnlyInstance(100));
+  EXPECT_EQ(*ret.first, value_type(4, MovableOnlyInstance(100)));
+  EXPECT_FALSE(ret.second);
+
+  auto hint_ret = m.insert_or_assign(ret.first, 3, MovableOnlyInstance(200));
+  EXPECT_EQ(*hint_ret, value_type(3, MovableOnlyInstance(200)));
+
+  EXPECT_EQ(m.size(), 2);
+}
+
+TEST(Btree, BitfieldArgument) {
+  union {
+    int n : 1;
+  };
+  n = 0;
+  absl::btree_map<int, int> m;
+  m.erase(n);
+  m.count(n);
+  m.find(n);
+  m.contains(n);
+  m.equal_range(n);
+  m.insert_or_assign(n, n);
+  m.insert_or_assign(m.end(), n, n);
+  m.try_emplace(n);
+  m.try_emplace(m.end(), n);
+  m.at(n);
+  m[n];
+}
+
 }  // namespace
 }  // namespace container_internal
 ABSL_NAMESPACE_END
diff --git a/absl/container/internal/btree_container.h b/absl/container/internal/btree_container.h
index 04795c2e..3e6ff4b8 100644
--- a/absl/container/internal/btree_container.h
+++ b/absl/container/internal/btree_container.h
@@ -372,7 +372,7 @@ class btree_map_container : public btree_set_container<Tree> {
   using super_type = btree_set_container<Tree>;
   using params_type = typename Tree::params_type;
 
- protected:
+ private:
   template <class K>
   using key_arg = typename super_type::template key_arg<K>;
 
@@ -390,6 +390,69 @@ class btree_map_container : public btree_set_container<Tree> {
   btree_map_container() {}
 
   // Insertion routines.
+  // Note: the nullptr template arguments and extra `const M&` overloads allow
+  // for supporting bitfield arguments.
+  // Note: when we call `std::forward<M>(obj)` twice, it's safe because
+  // insert_unique/insert_hint_unique are guaranteed to not consume `obj` when
+  // `ret.second` is false.
+  template <class M>
+  std::pair<iterator, bool> insert_or_assign(const key_type &k, const M &obj) {
+    const std::pair<iterator, bool> ret = this->tree_.insert_unique(k, k, obj);
+    if (!ret.second) ret.first->second = obj;
+    return ret;
+  }
+  template <class M, key_type * = nullptr>
+  std::pair<iterator, bool> insert_or_assign(key_type &&k, const M &obj) {
+    const std::pair<iterator, bool> ret =
+        this->tree_.insert_unique(k, std::move(k), obj);
+    if (!ret.second) ret.first->second = obj;
+    return ret;
+  }
+  template <class M, M * = nullptr>
+  std::pair<iterator, bool> insert_or_assign(const key_type &k, M &&obj) {
+    const std::pair<iterator, bool> ret =
+        this->tree_.insert_unique(k, k, std::forward<M>(obj));
+    if (!ret.second) ret.first->second = std::forward<M>(obj);
+    return ret;
+  }
+  template <class M, key_type * = nullptr, M * = nullptr>
+  std::pair<iterator, bool> insert_or_assign(key_type &&k, M &&obj) {
+    const std::pair<iterator, bool> ret =
+        this->tree_.insert_unique(k, std::move(k), std::forward<M>(obj));
+    if (!ret.second) ret.first->second = std::forward<M>(obj);
+    return ret;
+  }
+  template <class M>
+  iterator insert_or_assign(const_iterator position, const key_type &k,
+                            const M &obj) {
+    const std::pair<iterator, bool> ret =
+        this->tree_.insert_hint_unique(iterator(position), k, k, obj);
+    if (!ret.second) ret.first->second = obj;
+    return ret.first;
+  }
+  template <class M, key_type * = nullptr>
+  iterator insert_or_assign(const_iterator position, key_type &&k,
+                            const M &obj) {
+    const std::pair<iterator, bool> ret = this->tree_.insert_hint_unique(
+        iterator(position), k, std::move(k), obj);
+    if (!ret.second) ret.first->second = obj;
+    return ret.first;
+  }
+  template <class M, M * = nullptr>
+  iterator insert_or_assign(const_iterator position, const key_type &k,
+                            M &&obj) {
+    const std::pair<iterator, bool> ret = this->tree_.insert_hint_unique(
+        iterator(position), k, k, std::forward<M>(obj));
+    if (!ret.second) ret.first->second = std::forward<M>(obj);
+    return ret.first;
+  }
+  template <class M, key_type * = nullptr, M * = nullptr>
+  iterator insert_or_assign(const_iterator position, key_type &&k, M &&obj) {
+    const std::pair<iterator, bool> ret = this->tree_.insert_hint_unique(
+        iterator(position), k, std::move(k), std::forward<M>(obj));
+    if (!ret.second) ret.first->second = std::forward<M>(obj);
+    return ret.first;
+  }
   template <typename... Args>
   std::pair<iterator, bool> try_emplace(const key_type &k, Args &&... args) {
     return this->tree_.insert_unique(
diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc
index e15f4444..56447251 100644
--- a/absl/container/internal/hashtablez_sampler.cc
+++ b/absl/container/internal/hashtablez_sampler.cc
@@ -39,17 +39,16 @@ ABSL_CONST_INIT std::atomic<bool> g_hashtablez_enabled{
 ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_sample_parameter{1 << 10};
 ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_max_samples{1 << 20};
 
-#if ABSL_PER_THREAD_TLS == 1
+#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 ABSL_PER_THREAD_TLS_KEYWORD absl::base_internal::ExponentialBiased
     g_exponential_biased_generator;
 #endif
 
 }  // namespace
 
-#if ABSL_PER_THREAD_TLS == 1
+#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample = 0;
-#endif  // ABSL_PER_THREAD_TLS == 1
-
+#endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 HashtablezSampler& HashtablezSampler::Global() {
   static auto* sampler = new HashtablezSampler();
@@ -192,7 +191,7 @@ HashtablezInfo* SampleSlow(int64_t* next_sample) {
     return HashtablezSampler::Global().Register();
   }
 
-#if ABSL_PER_THREAD_TLS == 0
+#if !defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
   *next_sample = std::numeric_limits<int64_t>::max();
   return nullptr;
 #else
diff --git a/absl/container/internal/hashtablez_sampler.h b/absl/container/internal/hashtablez_sampler.h
index c4f9629f..34d5e572 100644
--- a/absl/container/internal/hashtablez_sampler.h
+++ b/absl/container/internal/hashtablez_sampler.h
@@ -180,14 +180,23 @@ class HashtablezInfoHandle {
   HashtablezInfo* info_;
 };
 
-#if ABSL_PER_THREAD_TLS == 1
+#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
+#error ABSL_INTERNAL_HASHTABLEZ_SAMPLE cannot be directly set
+#endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
+
+#if (ABSL_PER_THREAD_TLS == 1) && !defined(ABSL_BUILD_DLL) && \
+    !defined(ABSL_CONSUME_DLL)
+#define ABSL_INTERNAL_HASHTABLEZ_SAMPLE
+#endif
+
+#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 extern ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample;
 #endif  // ABSL_PER_THREAD_TLS
 
 // Returns an RAII sampling handle that manages registration and unregistation
 // with the global sampler.
 inline HashtablezInfoHandle Sample() {
-#if ABSL_PER_THREAD_TLS == 1
+#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
   if (ABSL_PREDICT_TRUE(--global_next_sample > 0)) {
     return HashtablezInfoHandle(nullptr);
   }
diff --git a/absl/container/internal/hashtablez_sampler_test.cc b/absl/container/internal/hashtablez_sampler_test.cc
index 102b2375..36f5ccdd 100644
--- a/absl/container/internal/hashtablez_sampler_test.cc
+++ b/absl/container/internal/hashtablez_sampler_test.cc
@@ -169,7 +169,7 @@ TEST(HashtablezInfoTest, RecordRehash) {
   EXPECT_EQ(info.num_erases.load(), 0);
 }
 
-#if ABSL_PER_THREAD_TLS == 1
+#if defined(ABSL_HASHTABLEZ_SAMPLE)
 TEST(HashtablezSamplerTest, SmallSampleParameter) {
   SetHashtablezEnabled(true);
   SetHashtablezSampleParameter(100);
diff --git a/absl/container/internal/raw_hash_set_test.cc b/absl/container/internal/raw_hash_set_test.cc
index 38e5e0e8..a96ae68a 100644
--- a/absl/container/internal/raw_hash_set_test.cc
+++ b/absl/container/internal/raw_hash_set_test.cc
@@ -418,53 +418,6 @@ TEST(Table, Empty) {
   EXPECT_TRUE(t.empty());
 }
 
-#ifdef __GNUC__
-template <class T>
-ABSL_ATTRIBUTE_ALWAYS_INLINE inline void DoNotOptimize(const T& v) {
-  asm volatile("" : : "r,m"(v) : "memory");
-}
-#endif
-
-TEST(Table, Prefetch) {
-  IntTable t;
-  t.emplace(1);
-  // Works for both present and absent keys.
-  t.prefetch(1);
-  t.prefetch(2);
-
-  // Do not run in debug mode, when prefetch is not implemented, or when
-  // sanitizers are enabled, or on WebAssembly.
-#if defined(NDEBUG) && defined(__GNUC__) && defined(__x86_64__) &&          \
-    !defined(ADDRESS_SANITIZER) && !defined(MEMORY_SANITIZER) &&            \
-    !defined(THREAD_SANITIZER) && !defined(UNDEFINED_BEHAVIOR_SANITIZER) && \
-    !defined(__EMSCRIPTEN__)
-  const auto now = [] { return absl::base_internal::CycleClock::Now(); };
-
-  // Make size enough to not fit in L2 cache (16.7 Mb)
-  static constexpr int size = 1 << 22;
-  for (int i = 0; i < size; ++i) t.insert(i);
-
-  int64_t no_prefetch = 0, prefetch = 0;
-  for (int iter = 0; iter < 10; ++iter) {
-    int64_t time = now();
-    for (int i = 0; i < size; ++i) {
-      DoNotOptimize(t.find(i));
-    }
-    no_prefetch += now() - time;
-
-    time = now();
-    for (int i = 0; i < size; ++i) {
-      t.prefetch(i + 20);
-      DoNotOptimize(t.find(i));
-    }
-    prefetch += now() - time;
-  }
-
-  // no_prefetch is at least 30% slower.
-  EXPECT_GE(1.0 * no_prefetch / prefetch, 1.3);
-#endif
-}
-
 TEST(Table, LookupEmpty) {
   IntTable t;
   auto it = t.find(0);
@@ -1842,7 +1795,7 @@ TEST(TableDeathTest, EraseOfEndAsserts) {
   EXPECT_DEATH_IF_SUPPORTED(t.erase(t.end()), kDeathMsg);
 }
 
-#if ABSL_PER_THREAD_TLS == 1
+#if defined(ABSL_HASHTABLEZ_SAMPLE)
 TEST(RawHashSamplerTest, Sample) {
   // Enable the feature even if the prod default is off.
   SetHashtablezEnabled(true);
@@ -1863,7 +1816,7 @@ TEST(RawHashSamplerTest, Sample) {
   EXPECT_NEAR((end_size - start_size) / static_cast<double>(tables.size()),
               0.01, 0.005);
 }
-#endif
+#endif  // ABSL_HASHTABLEZ_SAMPLER
 
 TEST(RawHashSamplerTest, DoNotSampleCustomAllocators) {
   // Enable the feature even if the prod default is off.
diff --git a/absl/copts/AbseilConfigureCopts.cmake b/absl/copts/AbseilConfigureCopts.cmake
index 7543928a..77d4ace8 100644
--- a/absl/copts/AbseilConfigureCopts.cmake
+++ b/absl/copts/AbseilConfigureCopts.cmake
@@ -5,6 +5,13 @@ set(ABSL_LSAN_LINKOPTS "")
 set(ABSL_HAVE_LSAN OFF)
 set(ABSL_DEFAULT_LINKOPTS "")
 
+if (BUILD_SHARED_LIBS AND MSVC)
+  set(ABSL_BUILD_DLL TRUE)
+  set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
+else()
+  set(ABSL_BUILD_DLL FALSE)
+endif()
+
 if("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "x86_64" OR "${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "AMD64")
   if (MSVC)
     set(ABSL_RANDOM_RANDEN_COPTS "${ABSL_RANDOM_HWAES_MSVC_X64_FLAGS}")
diff --git a/absl/debugging/symbolize_test.cc b/absl/debugging/symbolize_test.cc
index 0bac60b9..a1d03aab 100644
--- a/absl/debugging/symbolize_test.cc
+++ b/absl/debugging/symbolize_test.cc
@@ -473,6 +473,7 @@ void ABSL_ATTRIBUTE_NOINLINE TestWithReturnAddress() {
 }
 
 #elif defined(_WIN32)
+#if !defined(ABSL_CONSUME_DLL)
 
 TEST(Symbolize, Basics) {
   EXPECT_STREQ("nonstatic_func", TrySymbolize((void *)(&nonstatic_func)));
@@ -511,6 +512,7 @@ TEST(Symbolize, SymbolizeWithDemangling) {
   EXPECT_TRUE(strstr(result, "Foo::func") != nullptr) << result;
 }
 
+#endif  // !defined(ABSL_CONSUME_DLL)
 #else  // Symbolizer unimplemented
 
 TEST(Symbolize, Unimplemented) {
diff --git a/absl/flags/BUILD.bazel b/absl/flags/BUILD.bazel
index 6c7b2b6e..cbdbae52 100644
--- a/absl/flags/BUILD.bazel
+++ b/absl/flags/BUILD.bazel
@@ -324,6 +324,23 @@ cc_test(
     ],
 )
 
+cc_binary(
+    name = "flag_benchmark",
+    testonly = 1,
+    srcs = [
+        "flag_benchmark.cc",
+    ],
+    copts = ABSL_TEST_COPTS,
+    tags = ["benchmark"],
+    visibility = ["//visibility:private"],
+    deps = [
+        ":flag",
+        "//absl/time",
+        "//absl/types:optional",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+)
+
 cc_test(
     name = "marshalling_test",
     size = "small",
diff --git a/absl/flags/flag.cc b/absl/flags/flag.cc
index 9af80079..e67f7304 100644
--- a/absl/flags/flag.cc
+++ b/absl/flags/flag.cc
@@ -22,7 +22,14 @@
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
-// This global nutex protects on-demand construction of flag objects in MSVC
+#ifndef NDEBUG
+#define ABSL_FLAGS_GET(T) \
+  T GetFlag(const absl::Flag<T>& flag) { return flag.Get(); }
+ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(ABSL_FLAGS_GET)
+#undef ABSL_FLAGS_GET
+#endif
+
+// This global mutex protects on-demand construction of flag objects in MSVC
 // builds.
 #if defined(_MSC_VER) && !defined(__clang__)
 
diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index cc22cdb9..bd61668f 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -186,25 +186,29 @@ class Flag {
 //
 //   // FLAGS_firstname is a Flag of type `std::string`
 //   std::string first_name = absl::GetFlag(FLAGS_firstname);
-template <typename T,
-          typename std::enable_if<
-              !flags_internal::IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
-ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
-  return flag.Get();
-}
-
+#ifndef NDEBUG
 // We want to validate the type mismatch between type definition and
 // declaration. The lock-free implementation does not allow us to do it,
 // so in debug builds we always use the slower implementation, which always
 // validates the type.
-#ifndef NDEBUG
+template <typename T>
+ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
+  return flag.Get();
+}
+// We currently need an external linkage for built-in types because shared
+// libraries have different addresses of flags_internal::FlagOps<T> which
+// might cause log spam when checking the same flag type.
+#define ABSL_FLAGS_INTERNAL_BUILT_IN_EXPORT(T) \
+  ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag);
+ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(ABSL_FLAGS_INTERNAL_BUILT_IN_EXPORT)
+#undef ABSL_FLAGS_INTERNAL_BUILT_IN_EXPORT
+#else
 template <typename T,
           typename std::enable_if<
-              flags_internal::IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
+              !flags_internal::IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
 ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
   return flag.Get();
 }
-#else
 // Overload for `GetFlag()` for types that support lock-free reads.
 template <typename T,
           typename std::enable_if<
diff --git a/absl/flags/flag_benchmark.cc b/absl/flags/flag_benchmark.cc
new file mode 100644
index 00000000..87f73170
--- /dev/null
+++ b/absl/flags/flag_benchmark.cc
@@ -0,0 +1,111 @@
+//
+// 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/flags/flag.h"
+#include "absl/time/time.h"
+#include "absl/types/optional.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+using String = std::string;
+using VectorOfStrings = std::vector<std::string>;
+using AbslDuration = absl::Duration;
+
+// We do not want to take over marshalling for the types absl::optional<int>,
+// absl::optional<std::string> which we do not own. Instead we introduce unique
+// "aliases" to these types, which we do.
+using AbslOptionalInt = absl::optional<int>;
+struct OptionalInt : AbslOptionalInt {
+  using AbslOptionalInt::AbslOptionalInt;
+};
+// Next two functions represent Abseil Flags marshalling for OptionalInt.
+bool AbslParseFlag(absl::string_view src, OptionalInt* flag,
+                   std::string* error) {
+  int val;
+  if (src.empty())
+    flag->reset();
+  else if (!absl::ParseFlag(src, &val, error))
+    return false;
+  *flag = val;
+  return true;
+}
+std::string AbslUnparseFlag(const OptionalInt& flag) {
+  return !flag ? "" : absl::UnparseFlag(*flag);
+}
+
+using AbslOptionalString = absl::optional<std::string>;
+struct OptionalString : AbslOptionalString {
+  using AbslOptionalString::AbslOptionalString;
+};
+// Next two functions represent Abseil Flags marshalling for OptionalString.
+bool AbslParseFlag(absl::string_view src, OptionalString* flag,
+                   std::string* error) {
+  std::string val;
+  if (src.empty())
+    flag->reset();
+  else if (!absl::ParseFlag(src, &val, error))
+    return false;
+  *flag = val;
+  return true;
+}
+std::string AbslUnparseFlag(const OptionalString& flag) {
+  return !flag ? "" : absl::UnparseFlag(*flag);
+}
+
+struct UDT {
+  UDT() = default;
+  UDT(const UDT&) {}
+  UDT& operator=(const UDT&) { return *this; }
+};
+// Next two functions represent Abseil Flags marshalling for UDT.
+bool AbslParseFlag(absl::string_view, UDT*, std::string*) { return true; }
+std::string AbslUnparseFlag(const UDT&) { return ""; }
+
+}  // namespace
+
+#define BENCHMARKED_TYPES(A) \
+  A(bool)                    \
+  A(int16_t)                 \
+  A(uint16_t)                \
+  A(int32_t)                 \
+  A(uint32_t)                \
+  A(int64_t)                 \
+  A(uint64_t)                \
+  A(double)                  \
+  A(float)                   \
+  A(String)                  \
+  A(VectorOfStrings)         \
+  A(OptionalInt)             \
+  A(OptionalString)          \
+  A(AbslDuration)            \
+  A(UDT)
+
+#define FLAG_DEF(T) ABSL_FLAG(T, T##_flag, {}, "");
+
+BENCHMARKED_TYPES(FLAG_DEF)
+
+namespace {
+
+#define BM_GetFlag(T)                                            \
+  void BM_GetFlag_##T(benchmark::State& state) {                 \
+    for (auto _ : state) {                                       \
+      benchmark::DoNotOptimize(absl::GetFlag(FLAGS_##T##_flag)); \
+    }                                                            \
+  }                                                              \
+  BENCHMARK(BM_GetFlag_##T);
+
+BENCHMARKED_TYPES(BM_GetFlag)
+
+}  // namespace
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h
index 8639181f..ae7a60cd 100644
--- a/absl/hash/internal/hash.h
+++ b/absl/hash/internal/hash.h
@@ -708,7 +708,8 @@ struct is_hashable
     : std::integral_constant<bool, HashSelect::template Apply<T>::value> {};
 
 // CityHashState
-class CityHashState : public HashStateBase<CityHashState> {
+class ABSL_DLL CityHashState
+    : public HashStateBase<CityHashState> {
   // absl::uint128 is not an alias or a thin wrapper around the intrinsic.
   // We use the intrinsic when available to improve performance.
 #ifdef ABSL_HAVE_INTRINSIC_INT128
diff --git a/absl/numeric/int128.cc b/absl/numeric/int128.cc
index a20a77e7..b605a870 100644
--- a/absl/numeric/int128.cc
+++ b/absl/numeric/int128.cc
@@ -25,8 +25,8 @@
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
-const uint128 kuint128max = MakeUint128(std::numeric_limits<uint64_t>::max(),
-                                        std::numeric_limits<uint64_t>::max());
+ABSL_DLL const uint128 kuint128max = MakeUint128(
+    std::numeric_limits<uint64_t>::max(), std::numeric_limits<uint64_t>::max());
 
 namespace {
 
diff --git a/absl/numeric/int128.h b/absl/numeric/int128.h
index 718f70b1..636e3a5b 100644
--- a/absl/numeric/int128.h
+++ b/absl/numeric/int128.h
@@ -234,7 +234,7 @@ class
 // Prefer to use the constexpr `Uint128Max()`.
 //
 // TODO(absl-team) deprecate kuint128max once migration tool is released.
-extern const uint128 kuint128max;
+ABSL_DLL extern const uint128 kuint128max;
 
 // allow uint128 to be logged
 std::ostream& operator<<(std::ostream& os, uint128 v);
diff --git a/absl/random/BUILD.bazel b/absl/random/BUILD.bazel
index 2585b397..f78fbc7e 100644
--- a/absl/random/BUILD.bazel
+++ b/absl/random/BUILD.bazel
@@ -67,6 +67,7 @@ cc_library(
     linkopts = ABSL_DEFAULT_LINKOPTS,
     deps = [
         "//absl/base:base_internal",
+        "//absl/base:config",
         "//absl/base:core_headers",
         "//absl/meta:type_traits",
         "//absl/random/internal:distributions",
@@ -183,6 +184,7 @@ cc_test(
     timeout = "eternal",  # Android can take a very long time
     srcs = ["beta_distribution_test.cc"],
     copts = ABSL_TEST_COPTS,
+    flaky = 1,
     linkopts = ABSL_DEFAULT_LINKOPTS,
     deps = [
         ":distributions",
diff --git a/absl/random/CMakeLists.txt b/absl/random/CMakeLists.txt
index 46dbc3ef..efa55d8f 100644
--- a/absl/random/CMakeLists.txt
+++ b/absl/random/CMakeLists.txt
@@ -183,6 +183,7 @@ absl_cc_library(
     ${ABSL_DEFAULT_LINKOPTS}
   DEPS
     absl::base_internal
+    absl::config
     absl::core_headers
     absl::random_internal_generate_real
     absl::random_internal_distributions
diff --git a/absl/random/gaussian_distribution.h b/absl/random/gaussian_distribution.h
index c1427b06..4b07a5c0 100644
--- a/absl/random/gaussian_distribution.h
+++ b/absl/random/gaussian_distribution.h
@@ -28,6 +28,7 @@
 #include <limits>
 #include <type_traits>
 
+#include "absl/base/config.h"
 #include "absl/random/internal/fast_uniform_bits.h"
 #include "absl/random/internal/generate_real.h"
 #include "absl/random/internal/iostream_state_saver.h"
@@ -43,7 +44,7 @@ namespace random_internal {
 // The specific algorithm has some of the improvements suggested by the
 // 2005 paper, "An Improved Ziggurat Method to Generate Normal Random Samples",
 // Jurgen A Doornik.  (https://www.doornik.com/research/ziggurat.pdf)
-class gaussian_distribution_base {
+class ABSL_DLL gaussian_distribution_base {
  public:
   template <typename URBG>
   inline double zignor(URBG& g);  // NOLINT(runtime/references)
diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index dc7e1bfd..d5a362d0 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -37,7 +37,6 @@ cc_library(
         "internal/charconv_bigint.h",
         "internal/charconv_parse.cc",
         "internal/charconv_parse.h",
-        "internal/escaping.cc",
         "internal/memutil.cc",
         "internal/memutil.h",
         "internal/stl_type_traits.h",
@@ -55,7 +54,6 @@ cc_library(
         "ascii.h",
         "charconv.h",
         "escaping.h",
-        "internal/escaping.h",
         "match.h",
         "numbers.h",
         "str_cat.h",
@@ -85,11 +83,13 @@ cc_library(
 cc_library(
     name = "internal",
     srcs = [
+        "internal/escaping.cc",
         "internal/ostringstream.cc",
         "internal/utf8.cc",
     ],
     hdrs = [
         "internal/char_map.h",
+        "internal/escaping.h",
         "internal/ostringstream.h",
         "internal/resize_uninitialized.h",
         "internal/utf8.h",
@@ -99,6 +99,7 @@ cc_library(
         "//absl/base:config",
         "//absl/base:core_headers",
         "//absl/base:endian",
+        "//absl/base:raw_logging_internal",
         "//absl/meta:type_traits",
     ],
 )
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index 36702f71..3feb5e94 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -38,8 +38,6 @@ absl_cc_library(
     "internal/charconv_bigint.h"
     "internal/charconv_parse.cc"
     "internal/charconv_parse.h"
-    "internal/escaping.cc"
-    "internal/escaping.h"
     "internal/memutil.cc"
     "internal/memutil.h"
     "internal/stl_type_traits.h"
@@ -74,6 +72,8 @@ absl_cc_library(
     strings_internal
   HDRS
     "internal/char_map.h"
+    "internal/escaping.cc"
+    "internal/escaping.h"
     "internal/ostringstream.h"
     "internal/resize_uninitialized.h"
     "internal/utf8.h"
@@ -86,6 +86,7 @@ absl_cc_library(
     absl::config
     absl::core_headers
     absl::endian
+    absl::raw_logging_internal
     absl::type_traits
 )
 
diff --git a/absl/strings/ascii.cc b/absl/strings/ascii.cc
index abea3e4f..93bb03e9 100644
--- a/absl/strings/ascii.cc
+++ b/absl/strings/ascii.cc
@@ -57,7 +57,7 @@ namespace ascii_internal {
 // of these bits is tightly coupled to this implementation, the individual bits
 // are not named. Note that bitfields for all characters above ASCII 127 are
 // zero-initialized.
-const unsigned char kPropertyBits[256] = {
+ABSL_DLL const unsigned char kPropertyBits[256] = {
     0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x00
     0x40, 0x68, 0x48, 0x48, 0x48, 0x48, 0x40, 0x40,
     0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x10
@@ -79,7 +79,7 @@ const unsigned char kPropertyBits[256] = {
 // Array of characters for the ascii_tolower() function. For values 'A'
 // through 'Z', return the lower-case character; otherwise, return the
 // identity of the passed character.
-const char kToLower[256] = {
+ABSL_DLL const char kToLower[256] = {
   '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07',
   '\x08', '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f',
   '\x10', '\x11', '\x12', '\x13', '\x14', '\x15', '\x16', '\x17',
@@ -117,7 +117,7 @@ const char kToLower[256] = {
 // Array of characters for the ascii_toupper() function. For values 'a'
 // through 'z', return the upper-case character; otherwise, return the
 // identity of the passed character.
-const char kToUpper[256] = {
+ABSL_DLL const char kToUpper[256] = {
   '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07',
   '\x08', '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f',
   '\x10', '\x11', '\x12', '\x13', '\x14', '\x15', '\x16', '\x17',
diff --git a/absl/strings/ascii.h b/absl/strings/ascii.h
index 792aabe5..b46bc71f 100644
--- a/absl/strings/ascii.h
+++ b/absl/strings/ascii.h
@@ -56,6 +56,7 @@
 #include <string>
 
 #include "absl/base/attributes.h"
+#include "absl/base/config.h"
 #include "absl/strings/string_view.h"
 
 namespace absl {
@@ -63,13 +64,13 @@ ABSL_NAMESPACE_BEGIN
 namespace ascii_internal {
 
 // Declaration for an array of bitfields holding character information.
-extern const unsigned char kPropertyBits[256];
+ABSL_DLL extern const unsigned char kPropertyBits[256];
 
 // Declaration for the array of characters to upper-case characters.
-extern const char kToUpper[256];
+ABSL_DLL extern const char kToUpper[256];
 
 // Declaration for the array of characters to lower-case characters.
-extern const char kToLower[256];
+ABSL_DLL extern const char kToLower[256];
 
 }  // namespace ascii_internal
 
diff --git a/absl/strings/internal/charconv_bigint.cc b/absl/strings/internal/charconv_bigint.cc
index 860c27b2..66f33e72 100644
--- a/absl/strings/internal/charconv_bigint.cc
+++ b/absl/strings/internal/charconv_bigint.cc
@@ -158,12 +158,12 @@ const uint32_t* LargePowerOfFiveData(int i) {
 int LargePowerOfFiveSize(int i) { return 2 * i; }
 }  // namespace
 
-const uint32_t kFiveToNth[14] = {
+ABSL_DLL const uint32_t kFiveToNth[14] = {
     1,     5,      25,      125,     625,      3125,      15625,
     78125, 390625, 1953125, 9765625, 48828125, 244140625, 1220703125,
 };
 
-const uint32_t kTenToNth[10] = {
+ABSL_DLL const uint32_t kTenToNth[10] = {
     1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000,
 };
 
diff --git a/absl/strings/internal/charconv_bigint.h b/absl/strings/internal/charconv_bigint.h
index 108e1eb2..999e9ae3 100644
--- a/absl/strings/internal/charconv_bigint.h
+++ b/absl/strings/internal/charconv_bigint.h
@@ -20,6 +20,7 @@
 #include <iostream>
 #include <string>
 
+#include "absl/base/config.h"
 #include "absl/strings/ascii.h"
 #include "absl/strings/internal/charconv_parse.h"
 #include "absl/strings/string_view.h"
@@ -33,8 +34,9 @@ constexpr int kMaxSmallPowerOfFive = 13;
 // The largest power that 10 that can be raised to, and still fit in a uint32_t.
 constexpr int kMaxSmallPowerOfTen = 9;
 
-extern const uint32_t kFiveToNth[kMaxSmallPowerOfFive + 1];
-extern const uint32_t kTenToNth[kMaxSmallPowerOfTen + 1];
+ABSL_DLL extern const uint32_t
+    kFiveToNth[kMaxSmallPowerOfFive + 1];
+ABSL_DLL extern const uint32_t kTenToNth[kMaxSmallPowerOfTen + 1];
 
 // Large, fixed-width unsigned integer.
 //
diff --git a/absl/strings/internal/str_format/bind.h b/absl/strings/internal/str_format/bind.h
index 2bf0c085..cf41b197 100644
--- a/absl/strings/internal/str_format/bind.h
+++ b/absl/strings/internal/str_format/bind.h
@@ -122,8 +122,8 @@ class FormatSpecTemplate
 #endif  // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
   template <Conv... C, typename = typename std::enable_if<
-                           sizeof...(C) == sizeof...(Args) &&
-                           AllOf(Contains(ArgumentToConv<Args>(),
+                           AllOf(sizeof...(C) == sizeof...(Args),
+                             Contains(ArgumentToConv<Args>(),
                                           C)...)>::type>
   FormatSpecTemplate(const ExtendedParsedFormat<C...>& pc)  // NOLINT
       : Base(&pc) {}
diff --git a/absl/strings/internal/str_format/extension.h b/absl/strings/internal/str_format/extension.h
index 51d7dd6f..0a764035 100644
--- a/absl/strings/internal/str_format/extension.h
+++ b/absl/strings/internal/str_format/extension.h
@@ -17,10 +17,12 @@
 #define ABSL_STRINGS_INTERNAL_STR_FORMAT_EXTENSION_H_
 
 #include <limits.h>
+
 #include <cstddef>
 #include <cstring>
 #include <ostream>
 
+#include "absl/base/config.h"
 #include "absl/base/port.h"
 #include "absl/strings/internal/str_format/output.h"
 #include "absl/strings/string_view.h"
@@ -134,7 +136,7 @@ struct Flags {
   }
 };
 
-struct LengthMod {
+struct ABSL_DLL LengthMod {
  public:
   enum Id : uint8_t {
     h, hh, l, ll, L, j, z, t, q, none
@@ -196,7 +198,7 @@ struct LengthMod {
   X_VAL(n) X_SEP X_VAL(p)
 // clang-format on
 
-struct ConversionChar {
+struct ABSL_DLL ConversionChar {
  public:
   enum Id : uint8_t {
     c, C, s, S,              // text
diff --git a/absl/strings/numbers.cc b/absl/strings/numbers.cc
index a0e5a7fd..68c26dd6 100644
--- a/absl/strings/numbers.cc
+++ b/absl/strings/numbers.cc
@@ -900,9 +900,10 @@ inline bool safe_uint_internal(absl::string_view text, IntType* value_p,
 namespace numbers_internal {
 
 // Digit conversion.
-ABSL_CONST_INIT const char kHexChar[] = "0123456789abcdef";
+ABSL_CONST_INIT ABSL_DLL const char kHexChar[] =
+    "0123456789abcdef";
 
-ABSL_CONST_INIT const char kHexTable[513] =
+ABSL_CONST_INIT ABSL_DLL const char kHexTable[513] =
     "000102030405060708090a0b0c0d0e0f"
     "101112131415161718191a1b1c1d1e1f"
     "202122232425262728292a2b2c2d2e2f"
@@ -920,7 +921,7 @@ ABSL_CONST_INIT const char kHexTable[513] =
     "e0e1e2e3e4e5e6e7e8e9eaebecedeeef"
     "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff";
 
-ABSL_CONST_INIT const char two_ASCII_digits[100][2] = {
+ABSL_CONST_INIT ABSL_DLL const char two_ASCII_digits[100][2] = {
     {'0', '0'}, {'0', '1'}, {'0', '2'}, {'0', '3'}, {'0', '4'}, {'0', '5'},
     {'0', '6'}, {'0', '7'}, {'0', '8'}, {'0', '9'}, {'1', '0'}, {'1', '1'},
     {'1', '2'}, {'1', '3'}, {'1', '4'}, {'1', '5'}, {'1', '6'}, {'1', '7'},
diff --git a/absl/strings/numbers.h b/absl/strings/numbers.h
index 61204683..d872cca5 100644
--- a/absl/strings/numbers.h
+++ b/absl/strings/numbers.h
@@ -36,6 +36,7 @@
 #include <string>
 #include <type_traits>
 
+#include "absl/base/config.h"
 #include "absl/base/internal/bits.h"
 #ifdef __SSE4_2__
 // TODO(jorg): Remove this when we figure out the right way
@@ -106,9 +107,11 @@ ABSL_NAMESPACE_BEGIN
 namespace numbers_internal {
 
 // Digit conversion.
-extern const char kHexChar[17];    // 0123456789abcdef
-extern const char kHexTable[513];  // 000102030405060708090a0b0c0d0e0f1011...
-extern const char two_ASCII_digits[100][2];  // 00, 01, 02, 03...
+ABSL_DLL extern const char kHexChar[17];  // 0123456789abcdef
+ABSL_DLL extern const char
+    kHexTable[513];  // 000102030405060708090a0b0c0d0e0f1011...
+ABSL_DLL extern const char
+    two_ASCII_digits[100][2];  // 00, 01, 02, 03...
 
 // Writes a two-character representation of 'i' to 'buf'. 'i' must be in the
 // range 0 <= i < 100, and buf must have space for two characters. Example:
diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
index 4f7dd6b3..01965b0e 100644
--- a/absl/strings/string_view.h
+++ b/absl/strings/string_view.h
@@ -28,7 +28,19 @@
 #define ABSL_STRINGS_STRING_VIEW_H_
 
 #include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstring>
+#include <iosfwd>
+#include <iterator>
+#include <limits>
+#include <string>
+
 #include "absl/base/config.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
 
 #ifdef ABSL_USES_STD_STRING_VIEW
 
@@ -49,19 +61,6 @@ ABSL_NAMESPACE_END
 #define ABSL_INTERNAL_STRING_VIEW_MEMCMP memcmp
 #endif  // ABSL_HAVE_BUILTIN(__builtin_memcmp)
 
-#include <cassert>
-#include <cstddef>
-#include <cstring>
-#include <iosfwd>
-#include <iterator>
-#include <limits>
-#include <string>
-
-#include "absl/base/internal/throw_delegate.h"
-#include "absl/base/macros.h"
-#include "absl/base/optimization.h"
-#include "absl/base/port.h"
-
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
diff --git a/absl/time/format.cc b/absl/time/format.cc
index 5997ef0c..ee088f33 100644
--- a/absl/time/format.cc
+++ b/absl/time/format.cc
@@ -24,11 +24,14 @@ namespace cctz = absl::time_internal::cctz;
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
-extern const char RFC3339_full[] = "%Y-%m-%dT%H:%M:%E*S%Ez";
-extern const char RFC3339_sec[] =  "%Y-%m-%dT%H:%M:%S%Ez";
-
-extern const char RFC1123_full[] = "%a, %d %b %E4Y %H:%M:%S %z";
-extern const char RFC1123_no_wday[] =  "%d %b %E4Y %H:%M:%S %z";
+ABSL_DLL extern const char RFC3339_full[] =
+    "%Y-%m-%dT%H:%M:%E*S%Ez";
+ABSL_DLL extern const char RFC3339_sec[] = "%Y-%m-%dT%H:%M:%S%Ez";
+
+ABSL_DLL extern const char RFC1123_full[] =
+    "%a, %d %b %E4Y %H:%M:%S %z";
+ABSL_DLL extern const char RFC1123_no_wday[] =
+    "%d %b %E4Y %H:%M:%S %z";
 
 namespace {
 
diff --git a/absl/time/internal/cctz/src/time_zone_fixed.cc b/absl/time/internal/cctz/src/time_zone_fixed.cc
index a342e37d..303c0244 100644
--- a/absl/time/internal/cctz/src/time_zone_fixed.cc
+++ b/absl/time/internal/cctz/src/time_zone_fixed.cc
@@ -89,29 +89,29 @@ std::string FixedOffsetToName(const seconds& offset) {
     // offsets and to (somewhat) limit the total number of zones.
     return "UTC";
   }
-  int seconds = static_cast<int>(offset.count());
-  const char sign = (seconds < 0 ? '-' : '+');
-  int minutes = seconds / 60;
-  seconds %= 60;
+  int offset_seconds = static_cast<int>(offset.count());
+  const char sign = (offset_seconds < 0 ? '-' : '+');
+  int offset_minutes = offset_seconds / 60;
+  offset_seconds %= 60;
   if (sign == '-') {
-    if (seconds > 0) {
-      seconds -= 60;
-      minutes += 1;
+    if (offset_seconds > 0) {
+      offset_seconds -= 60;
+      offset_minutes += 1;
     }
-    seconds = -seconds;
-    minutes = -minutes;
+    offset_seconds = -offset_seconds;
+    offset_minutes = -offset_minutes;
   }
-  int hours = minutes / 60;
-  minutes %= 60;
+  int offset_hours = offset_minutes / 60;
+  offset_minutes %= 60;
   const std::size_t prefix_len = sizeof(kFixedZonePrefix) - 1;
   char buf[prefix_len + sizeof("-24:00:00")];
   char* ep = std::copy(kFixedZonePrefix, kFixedZonePrefix + prefix_len, buf);
   *ep++ = sign;
-  ep = Format02d(ep, hours);
+  ep = Format02d(ep, offset_hours);
   *ep++ = ':';
-  ep = Format02d(ep, minutes);
+  ep = Format02d(ep, offset_minutes);
   *ep++ = ':';
-  ep = Format02d(ep, seconds);
+  ep = Format02d(ep, offset_seconds);
   *ep++ = '\0';
   assert(ep == buf + sizeof(buf));
   return buf;
diff --git a/absl/time/internal/cctz/src/time_zone_format_test.cc b/absl/time/internal/cctz/src/time_zone_format_test.cc
index de75629a..caebcc4d 100644
--- a/absl/time/internal/cctz/src/time_zone_format_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_format_test.cc
@@ -1252,9 +1252,9 @@ TEST(Parse, ExtendedSubecondsScan) {
         const auto expected = chrono::system_clock::from_time_t(0) +
                               chrono::nanoseconds(micros * 1000 + ns);
         for (int ps = 0; ps < 1000; ps += 250) {
-          std::ostringstream oss;
+          std::ostringstream ps_oss;
           oss << std::setfill('0') << std::setw(3) << ps;
-          const std::string input = nanos + oss.str() + "999";
+          const std::string input = nanos + ps_oss.str() + "999";
           EXPECT_TRUE(parse("%E*f", input, tz, &tp));
           EXPECT_EQ(expected + chrono::nanoseconds(ps) / 1000, tp) << input;
         }
diff --git a/absl/time/internal/cctz/src/time_zone_info.cc b/absl/time/internal/cctz/src/time_zone_info.cc
index 971542d0..f1697cdf 100644
--- a/absl/time/internal/cctz/src/time_zone_info.cc
+++ b/absl/time/internal/cctz/src/time_zone_info.cc
@@ -641,9 +641,9 @@ std::unique_ptr<ZoneInfoSource> FileZoneInfoSource::Open(
   if (fp == nullptr) return nullptr;
   std::size_t length = 0;
   if (fseek(fp, 0, SEEK_END) == 0) {
-    long pos = ftell(fp);
-    if (pos >= 0) {
-      length = static_cast<std::size_t>(pos);
+    long offset = ftell(fp);
+    if (offset >= 0) {
+      length = static_cast<std::size_t>(offset);
     }
     rewind(fp);
   }
diff --git a/absl/time/internal/cctz/src/time_zone_lookup_test.cc b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
index 227b1278..99137a08 100644
--- a/absl/time/internal/cctz/src/time_zone_lookup_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
@@ -1028,16 +1028,17 @@ TEST(MakeTime, LocalTimeLibC) {
     ASSERT_EQ(0, setenv("TZ", *np, 1));  // change what "localtime" means
     const auto zi = local_time_zone();
     const auto lc = LoadZone("libc:localtime");
-    time_zone::civil_transition trans;
+    time_zone::civil_transition transition;
     for (auto tp = zi.lookup(civil_second()).trans;
-         zi.next_transition(tp, &trans); tp = zi.lookup(trans.to).trans) {
-      const auto fcl = zi.lookup(trans.from);
-      const auto tcl = zi.lookup(trans.to);
+         zi.next_transition(tp, &transition);
+         tp = zi.lookup(transition.to).trans) {
+      const auto fcl = zi.lookup(transition.from);
+      const auto tcl = zi.lookup(transition.to);
       civil_second cs;  // compare cs in zi and lc
       if (fcl.kind == time_zone::civil_lookup::UNIQUE) {
         if (tcl.kind == time_zone::civil_lookup::UNIQUE) {
           // Both unique; must be an is_dst or abbr change.
-          ASSERT_EQ(trans.from, trans.to);
+          ASSERT_EQ(transition.from, transition.to);
           const auto trans = fcl.trans;
           const auto tal = zi.lookup(trans);
           const auto tprev = trans - absl::time_internal::cctz::seconds(1);
@@ -1048,11 +1049,11 @@ TEST(MakeTime, LocalTimeLibC) {
           continue;
         }
         ASSERT_EQ(time_zone::civil_lookup::REPEATED, tcl.kind);
-        cs = trans.to;
+        cs = transition.to;
       } else {
         ASSERT_EQ(time_zone::civil_lookup::UNIQUE, tcl.kind);
         ASSERT_EQ(time_zone::civil_lookup::SKIPPED, fcl.kind);
-        cs = trans.from;
+        cs = transition.from;
       }
       if (cs.year() > 2037) break;  // limit test time (and to 32-bit time_t)
       const auto cl_zi = zi.lookup(cs);
diff --git a/absl/time/time.h b/absl/time/time.h
index 1be5727c..33a4a630 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -527,59 +527,30 @@ std::chrono::seconds ToChronoSeconds(Duration d);
 std::chrono::minutes ToChronoMinutes(Duration d);
 std::chrono::hours ToChronoHours(Duration d);
 
-
 // FormatDuration()
 //
-// Returns a string represention of the duration in a format consisting of a
-// possibly-signed prefix and a sequence of decimal numbers, each with an
-// optional fractional part and a unit suffix.
-//
-// Valid unit suffixes are "ns", "us" "ms", "s", "m", and "h".
-//
-// Simple examples include "300ms", "-1.5h", and "2h45m". Returns "inf" or
-// "-inf" for +/- `InfiniteDuration()` values and "0" for `ZeroDuration()`
-// values.
-//
-// This string format is used both as an input for parsing (when handling
-// command-line flags of type `absl::Duration`) and as an output in
-// `FormatDuration()`
+// Returns a string representing the duration in the form "72h3m0.5s".
+// Returns "inf" or "-inf" for +/- `InfiniteDuration()`.
 std::string FormatDuration(Duration d);
 
+// Output stream operator.
+inline std::ostream& operator<<(std::ostream& os, Duration d) {
+  return os << FormatDuration(d);
+}
+
 // ParseDuration()
 //
-// Parses a `dur_string` of the format noted above into an `absl::Duration`
-// value.
-//
-// Parses "0" as a zero-length duration value. Parses "-inf" or "+inf" as
-// infinite durations values.
+// Parses a duration string consisting of a possibly signed sequence of
+// decimal numbers, each with an optional fractional part and a unit
+// suffix.  The valid suffixes are "ns", "us" "ms", "s", "m", and "h".
+// Simple examples include "300ms", "-1.5h", and "2h45m".  Parses "0" as
+// `ZeroDuration()`. Parses "inf" and "-inf" as +/- `InfiniteDuration()`.
 bool ParseDuration(const std::string& dur_string, Duration* d);
 
-// AbslParseFlag()
-//
-// Parses the command-line flag string representation `text` (using the format
-// noted above) into an `absl::Duration` destination, setting `error` on
-// failure.
-//
-// Example:
-//
-//   --timeout=6h30m
-//   --timeout=inf       // Equivalent to `InfiniteDuration()`
-//   --timeout=0         // Equivalent to `ZeroDuration()`
+// Support for flag values of type Duration. Duration flags must be specified
+// in a format that is valid input for absl::ParseDuration().
 bool AbslParseFlag(absl::string_view text, Duration* dst, std::string* error);
-
-// AbslUnparseFlag()
-//
-// Unparses an `absl::Duration` into a command-line string representation using
-// the format noted above.
 std::string AbslUnparseFlag(Duration d);
-
-// operator<<()
-//
-// Output stream operator, returning a stream in the format noted above.
-inline std::ostream& operator<<(std::ostream& os, Duration d) {
-  return os << FormatDuration(d);
-}
-
 ABSL_DEPRECATED("Use AbslParseFlag() instead.")
 bool ParseFlag(const std::string& text, Duration* dst, std::string* error);
 ABSL_DEPRECATED("Use AbslUnparseFlag() instead.")
@@ -842,29 +813,18 @@ Time FromChrono(const std::chrono::system_clock::time_point& tp);
 //   // tp == std::chrono::system_clock::from_time_t(123);
 std::chrono::system_clock::time_point ToChronoTime(Time);
 
-// AbslParseFlag()
-//
-// Parses the command-line flag string representation `text` into an
-// `absl::Time` destination, setting `error` on failure. Time flag string
-// representations must be specified in a format that matches
-// `absl::RFC3339_full`.
-//
-// Example:
+// Support for flag values of type Time. Time flags must be specified in a
+// format that matches absl::RFC3339_full. For example:
 //
 //   --start_time=2016-01-02T03:04:05.678+08:00
 //
 // Note: A UTC offset (or 'Z' indicating a zero-offset from UTC) is required.
 //
 // Additionally, if you'd like to specify a time as a count of
-// seconds/milliseconds/etc from the Unix epoch, use an `absl::Duration` flag
-// and add that duration to `absl::UnixEpoch()` to get an `absl::Time`.
+// seconds/milliseconds/etc from the Unix epoch, use an absl::Duration flag
+// and add that duration to absl::UnixEpoch() to get an absl::Time.
 bool AbslParseFlag(absl::string_view text, Time* t, std::string* error);
-
-// AbslUnparseFlag()
-//
-// Unparses an `absl::Time` into a command-line string format as noted above.
 std::string AbslUnparseFlag(Time t);
-
 ABSL_DEPRECATED("Use AbslParseFlag() instead.")
 bool ParseFlag(const std::string& text, Time* t, std::string* error);
 ABSL_DEPRECATED("Use AbslUnparseFlag() instead.")
@@ -1243,15 +1203,18 @@ struct tm ToTM(Time t, TimeZone tz);
 // time with UTC offset.  Also note the use of "%Y": RFC3339 mandates that
 // years have exactly four digits, but we allow them to take their natural
 // width.
-extern const char RFC3339_full[];  // %Y-%m-%dT%H:%M:%E*S%Ez
-extern const char RFC3339_sec[];   // %Y-%m-%dT%H:%M:%S%Ez
+ABSL_DLL extern const char
+    RFC3339_full[];  // %Y-%m-%dT%H:%M:%E*S%Ez
+ABSL_DLL extern const char RFC3339_sec[];  // %Y-%m-%dT%H:%M:%S%Ez
 
 // RFC1123_full
 // RFC1123_no_wday
 //
 // FormatTime()/ParseTime() format specifiers for RFC1123 date/time strings.
-extern const char RFC1123_full[];     // %a, %d %b %E4Y %H:%M:%S %z
-extern const char RFC1123_no_wday[];  // %d %b %E4Y %H:%M:%S %z
+ABSL_DLL extern const char
+    RFC1123_full[];  // %a, %d %b %E4Y %H:%M:%S %z
+ABSL_DLL extern const char
+    RFC1123_no_wday[];  // %d %b %E4Y %H:%M:%S %z
 
 // FormatTime()
 //