Export of internal Abseil changes

--
00f5301405423005d9129935c05f20155536cc1a by CJ Johnson <johnsoncj@google.com>:

Removes usage of std::aligned_storage from Abseil implementation details

PiperOrigin-RevId: 296492301

--
fc11d15f91764612fba080669d2381dc181df52b by Abseil Team <absl-team@google.com>:

Fix absl::bind_front documentation.

PiperOrigin-RevId: 296482945

--
0164c595c129c46bf21ae74eba5399a1da5f140b by Gennadiy Rozental <rogeeff@google.com>:

Automated g4 rollback of changelist 296320700.

PiperOrigin-RevId: 296439968

--
1eb295700758ca0894d872b2de7c675b4ad679af by Abseil Team <absl-team@google.com>:

Removes duplicate comments.

PiperOrigin-RevId: 296433214

--
c30c01caae02d2fa4ef783d988de6bebb9757c39 by Derek Mauro <dmauro@google.com>:

Merge GitHub #621: Add RISCV support to GetProgramCounter()

Fixes #621

PiperOrigin-RevId: 296351174

--
95d4498167596fd7543e025bdfe9a8da9e2ca3c8 by Abseil Team <absl-team@google.com>:

Automated g4 rollback of changelist 296320700.

PiperOrigin-RevId: 296348701

--
b193f0543e0cec54dddb2ed51f45dc489c8d06d5 by Gennadiy Rozental <rogeeff@google.com>:

Change TryParse interface to return managed value.

In addition introduce companion StoreValue routine which consumes pointer to source value and stores the value inside of FlagImpl. In a follow up CL we will change StoreValue implementation to behave differently depending on "value storage kind".
We also rename default_src_ to default_value_.

PiperOrigin-RevId: 296320700

--
57e942b485d12912a0a8d0d0b35fa2a62847020f by Derek Mauro <dmauro@google.com>:

Merge GitHub #622
 * Add missing #ifdef conditionals for ABSL_HAVE_VDSO_SUPPORT

PiperOrigin-RevId: 296272830
GitOrigin-RevId: 00f5301405423005d9129935c05f20155536cc1a
Change-Id: I1b05eeaf1280f95fb0a2c5f3654995a87c792893

16 files changed, 130 insertions, 134 deletions

diff --git a/absl/base/exception_safety_testing_test.cc b/absl/base/exception_safety_testing_test.cc
index 575b535..a59be29 100644
--- a/absl/base/exception_safety_testing_test.cc
+++ b/absl/base/exception_safety_testing_test.cc
@@ -328,17 +328,15 @@ TEST(ThrowingValueTest, NonThrowingDelete) {
   UnsetCountdown();
 }
 
-using Storage =
-    absl::aligned_storage_t<sizeof(ThrowingValue<>), alignof(ThrowingValue<>)>;
-
 TEST(ThrowingValueTest, NonThrowingPlacementDelete) {
   constexpr int kArrayLen = 2;
   // We intentionally create extra space to store the tag allocated by placement
   // new[].
   constexpr int kStorageLen = 4;
 
-  Storage buf;
-  Storage array_buf[kStorageLen];
+  alignas(ThrowingValue<>) unsigned char buf[sizeof(ThrowingValue<>)];
+  alignas(ThrowingValue<>) unsigned char
+      array_buf[sizeof(ThrowingValue<>[kStorageLen])];
   auto* placed = new (&buf) ThrowingValue<>(1);
   auto placed_array = new (&array_buf) ThrowingValue<>[kArrayLen];
 
@@ -902,12 +900,12 @@ TEST(ConstructorTrackerTest, CreatedAfter) {
 }
 
 TEST(ConstructorTrackerTest, NotDestroyedAfter) {
-  absl::aligned_storage_t<sizeof(Tracked), alignof(Tracked)> storage;
+  alignas(Tracked) unsigned char storage[sizeof(Tracked)];
   EXPECT_NONFATAL_FAILURE(
       {
         exceptions_internal::ConstructorTracker ct(
             exceptions_internal::countdown);
-        new (&storage) Tracked;
+        new (&storage) Tracked();
       },
       "not destroyed");
 }
@@ -924,11 +922,11 @@ TEST(ConstructorTrackerTest, DestroyedTwice) {
 
 TEST(ConstructorTrackerTest, ConstructedTwice) {
   exceptions_internal::ConstructorTracker ct(exceptions_internal::countdown);
-  absl::aligned_storage_t<sizeof(Tracked), alignof(Tracked)> storage;
+  alignas(Tracked) unsigned char storage[sizeof(Tracked)];
   EXPECT_NONFATAL_FAILURE(
       {
-        new (&storage) Tracked;
-        new (&storage) Tracked;
+        new (&storage) Tracked();
+        new (&storage) Tracked();
         reinterpret_cast<Tracked*>(&storage)->~Tracked();
       },
       "re-constructed");
diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc
index 225abc2..1bf9443 100644
--- a/absl/base/internal/low_level_alloc.cc
+++ b/absl/base/internal/low_level_alloc.cc
@@ -220,16 +220,17 @@ struct LowLevelAlloc::Arena {
 };
 
 namespace {
-using ArenaStorage = std::aligned_storage<sizeof(LowLevelAlloc::Arena),
-                                          alignof(LowLevelAlloc::Arena)>::type;
-
 // Static storage space for the lazily-constructed, default global arena
 // instances.  We require this space because the whole point of LowLevelAlloc
 // is to avoid relying on malloc/new.
-ArenaStorage default_arena_storage;
-ArenaStorage unhooked_arena_storage;
+alignas(LowLevelAlloc::Arena) unsigned char default_arena_storage[sizeof(
+    LowLevelAlloc::Arena)];
+alignas(LowLevelAlloc::Arena) unsigned char unhooked_arena_storage[sizeof(
+    LowLevelAlloc::Arena)];
 #ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
-ArenaStorage unhooked_async_sig_safe_arena_storage;
+alignas(
+    LowLevelAlloc::Arena) unsigned char unhooked_async_sig_safe_arena_storage
+    [sizeof(LowLevelAlloc::Arena)];
 #endif
 
 // We must use LowLevelCallOnce here to construct the global arenas, rather than
diff --git a/absl/base/options.h b/absl/base/options.h
index 6868c77..234137c 100644
--- a/absl/base/options.h
+++ b/absl/base/options.h
@@ -123,14 +123,6 @@
 // compiler flags passed by the end user.  For more info, see
 // https://abseil.io/about/design/dropin-types.
 
-// A value of 2 means to detect the C++ version being used to compile Abseil,
-// and use an alias only if a working std::optional is available.  This option
-// should not be used when your program is not built from source -- for example,
-// if you are distributing Abseil in a binary package manager -- since in mode
-// 2, absl::optional will name a different template class, with a different
-// mangled name and binary layout, depending on the compiler flags passed by the
-// end user.
-//
 // User code should not inspect this macro.  To check in the preprocessor if
 // absl::optional is a typedef of std::optional, use the feature macro
 // ABSL_USES_STD_OPTIONAL.
diff --git a/absl/container/fixed_array_test.cc b/absl/container/fixed_array_test.cc
index 2b1cf47..c960fe5 100644
--- a/absl/container/fixed_array_test.cc
+++ b/absl/container/fixed_array_test.cc
@@ -604,19 +604,16 @@ TEST(FixedArrayTest, Fill) {
   empty.fill(fill_val);
 }
 
-// TODO(johnsoncj): Investigate InlinedStorage default initialization in GCC 4.x
 #ifndef __GNUC__
 TEST(FixedArrayTest, DefaultCtorDoesNotValueInit) {
   using T = char;
   constexpr auto capacity = 10;
   using FixedArrType = absl::FixedArray<T, capacity>;
-  using FixedArrBuffType =
-      absl::aligned_storage_t<sizeof(FixedArrType), alignof(FixedArrType)>;
   constexpr auto scrubbed_bits = 0x95;
   constexpr auto length = capacity / 2;
 
-  FixedArrBuffType buff;
-  std::memset(std::addressof(buff), scrubbed_bits, sizeof(FixedArrBuffType));
+  alignas(FixedArrType) unsigned char buff[sizeof(FixedArrType)];
+  std::memset(std::addressof(buff), scrubbed_bits, sizeof(FixedArrType));
 
   FixedArrType* arr =
       ::new (static_cast<void*>(std::addressof(buff))) FixedArrType(length);
diff --git a/absl/container/internal/common.h b/absl/container/internal/common.h
index 853a5b2..5037d80 100644
--- a/absl/container/internal/common.h
+++ b/absl/container/internal/common.h
@@ -56,7 +56,7 @@ class node_handle_base {
  public:
   using allocator_type = Alloc;
 
-  constexpr node_handle_base() {}
+  constexpr node_handle_base() = default;
   node_handle_base(node_handle_base&& other) noexcept {
     *this = std::move(other);
   }
@@ -109,9 +109,8 @@ class node_handle_base {
   allocator_type* alloc() { return std::addressof(*alloc_); }
 
  private:
-  absl::optional<allocator_type> alloc_;
-  mutable absl::aligned_storage_t<sizeof(slot_type), alignof(slot_type)>
-      slot_space_;
+  absl::optional<allocator_type> alloc_ = {};
+  alignas(slot_type) mutable unsigned char slot_space_[sizeof(slot_type)] = {};
 };
 
 // For sets.
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index 0d3d604..ca7be8d 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -1067,8 +1067,7 @@ class raw_hash_set {
   template <class... Args, typename std::enable_if<
                                !IsDecomposable<Args...>::value, int>::type = 0>
   std::pair<iterator, bool> emplace(Args&&... args) {
-    typename std::aligned_storage<sizeof(slot_type), alignof(slot_type)>::type
-        raw;
+    alignas(slot_type) unsigned char raw[sizeof(slot_type)];
     slot_type* slot = reinterpret_cast<slot_type*>(&raw);
 
     PolicyTraits::construct(&alloc_ref(), slot, std::forward<Args>(args)...);
@@ -1556,8 +1555,7 @@ class raw_hash_set {
     //       mark target as FULL
     //       repeat procedure for current slot with moved from element (target)
     ConvertDeletedToEmptyAndFullToDeleted(ctrl_, capacity_);
-    typename std::aligned_storage<sizeof(slot_type), alignof(slot_type)>::type
-        raw;
+    alignas(slot_type) unsigned char raw[sizeof(slot_type)];
     size_t total_probe_length = 0;
     slot_type* slot = reinterpret_cast<slot_type*>(&raw);
     for (size_t i = 0; i != capacity_; ++i) {
diff --git a/absl/debugging/internal/stacktrace_x86-inl.inc b/absl/debugging/internal/stacktrace_x86-inl.inc
index f87cafb..bc320ff 100644
--- a/absl/debugging/internal/stacktrace_x86-inl.inc
+++ b/absl/debugging/internal/stacktrace_x86-inl.inc
@@ -202,9 +202,9 @@ static void **NextStackFrame(void **old_fp, const void *uc) {
       } else {
         num_push_instructions = 0;
       }
-#else
+#else  // ABSL_HAVE_VDSO_SUPPORT
       num_push_instructions = 0;
-#endif
+#endif  // ABSL_HAVE_VDSO_SUPPORT
     }
     if (num_push_instructions != 0 && kernel_rt_sigreturn_address != nullptr &&
         old_fp[1] == kernel_rt_sigreturn_address) {
diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc
index 83ec8df..5a921e2 100644
--- a/absl/flags/internal/flag.cc
+++ b/absl/flags/internal/flag.cc
@@ -121,13 +121,21 @@ void FlagImpl::AssertValidType(FlagStaticTypeId type_id) const {
 std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const {
   void* res = nullptr;
   if (DefaultKind() == FlagDefaultKind::kDynamicValue) {
-    res = flags_internal::Clone(op_, default_src_.dynamic_value);
+    res = flags_internal::Clone(op_, default_value_.dynamic_value);
   } else {
-    res = (*default_src_.gen_func)();
+    res = (*default_value_.gen_func)();
   }
   return {res, DynValueDeleter{op_}};
 }
 
+void FlagImpl::StoreValue(const void* src) {
+  flags_internal::Copy(op_, src, value_.dynamic);
+  StoreAtomic();
+  modified_ = true;
+  ++counter_;
+  InvokeCallback();
+}
+
 absl::string_view FlagImpl::Name() const { return name_; }
 
 std::string FlagImpl::Filename() const {
@@ -220,23 +228,19 @@ bool FlagImpl::RestoreState(const void* value, bool modified,
 // argument. If parsing successful, this function replaces the dst with newly
 // parsed value. In case if any error is encountered in either step, the error
 // message is stored in 'err'
-bool FlagImpl::TryParse(void** dst, absl::string_view value,
-                        std::string* err) const {
-  auto tentative_value = MakeInitValue();
+std::unique_ptr<void, DynValueDeleter> FlagImpl::TryParse(
+    absl::string_view value, std::string* err) const {
+  std::unique_ptr<void, DynValueDeleter> tentative_value = MakeInitValue();
 
   std::string parse_err;
   if (!flags_internal::Parse(op_, value, tentative_value.get(), &parse_err)) {
     absl::string_view err_sep = parse_err.empty() ? "" : "; ";
     *err = absl::StrCat("Illegal value '", value, "' specified for flag '",
                         Name(), "'", err_sep, parse_err);
-    return false;
+    return nullptr;
   }
 
-  void* old_val = *dst;
-  *dst = tentative_value.release();
-  tentative_value.reset(old_val);
-
-  return true;
+  return tentative_value;
 }
 
 void FlagImpl::Read(void* dst) const {
@@ -266,22 +270,17 @@ void FlagImpl::Write(const void* src) {
   absl::MutexLock l(DataGuard());
 
   if (ShouldValidateFlagValue(flags_internal::StaticTypeId(op_))) {
-    void* obj = flags_internal::Clone(op_, src);
+    std::unique_ptr<void, DynValueDeleter> obj{flags_internal::Clone(op_, src),
+                                               DynValueDeleter{op_}};
     std::string ignored_error;
     std::string src_as_str = flags_internal::Unparse(op_, src);
-    if (!flags_internal::Parse(op_, src_as_str, obj, &ignored_error)) {
+    if (!flags_internal::Parse(op_, src_as_str, obj.get(), &ignored_error)) {
       ABSL_INTERNAL_LOG(ERROR, absl::StrCat("Attempt to set flag '", Name(),
                                             "' to invalid value ", src_as_str));
     }
-    flags_internal::Delete(op_, obj);
   }
 
-  modified_ = true;
-  counter_++;
-  flags_internal::Copy(op_, src, value_.dynamic);
-
-  StoreAtomic();
-  InvokeCallback();
+  StoreValue(src);
 }
 
 // Sets the value of the flag based on specified string `value`. If the flag
@@ -299,11 +298,10 @@ bool FlagImpl::SetFromString(absl::string_view value, FlagSettingMode set_mode,
   switch (set_mode) {
     case SET_FLAGS_VALUE: {
       // set or modify the flag's value
-      if (!TryParse(&value_.dynamic, value, err)) return false;
-      modified_ = true;
-      counter_++;
-      StoreAtomic();
-      InvokeCallback();
+      auto tentative_value = TryParse(value, err);
+      if (!tentative_value) return false;
+
+      StoreValue(tentative_value.get());
 
       if (source == kCommandLine) {
         on_command_line_ = true;
@@ -312,13 +310,7 @@ bool FlagImpl::SetFromString(absl::string_view value, FlagSettingMode set_mode,
     }
     case SET_FLAG_IF_DEFAULT: {
       // set the flag's value, but only if it hasn't been set by someone else
-      if (!modified_) {
-        if (!TryParse(&value_.dynamic, value, err)) return false;
-        modified_ = true;
-        counter_++;
-        StoreAtomic();
-        InvokeCallback();
-      } else {
+      if (modified_) {
         // TODO(rogeeff): review and fix this semantic. Currently we do not fail
         // in this case if flag is modified. This is misleading since the flag's
         // value is not updated even though we return true.
@@ -327,28 +319,29 @@ bool FlagImpl::SetFromString(absl::string_view value, FlagSettingMode set_mode,
         // return false;
         return true;
       }
+      auto tentative_value = TryParse(value, err);
+      if (!tentative_value) return false;
+
+      StoreValue(tentative_value.get());
       break;
     }
     case SET_FLAGS_DEFAULT: {
+      auto tentative_value = TryParse(value, err);
+      if (!tentative_value) return false;
+
       if (DefaultKind() == FlagDefaultKind::kDynamicValue) {
-        if (!TryParse(&default_src_.dynamic_value, value, err)) {
-          return false;
-        }
+        void* old_value = default_value_.dynamic_value;
+        default_value_.dynamic_value = tentative_value.release();
+        tentative_value.reset(old_value);
       } else {
-        void* new_default_val = nullptr;
-        if (!TryParse(&new_default_val, value, err)) {
-          return false;
-        }
-
-        default_src_.dynamic_value = new_default_val;
+        default_value_.dynamic_value = tentative_value.release();
         def_kind_ = static_cast<uint8_t>(FlagDefaultKind::kDynamicValue);
       }
 
       if (!modified_) {
         // Need to set both default value *and* current, in this case
-        flags_internal::Copy(op_, default_src_.dynamic_value, value_.dynamic);
-        StoreAtomic();
-        InvokeCallback();
+        StoreValue(default_value_.dynamic_value);
+        modified_ = false;
       }
       break;
     }
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index ec67348..c1beda8 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -363,7 +363,7 @@ struct DynValueDeleter {
     if (op != nullptr) Delete(op, ptr);
   }
 
-  const FlagOpFn op;
+  FlagOpFn op;
 };
 
 class FlagImpl {
@@ -380,7 +380,7 @@ class FlagImpl {
         on_command_line_(false),
         counter_(0),
         callback_(nullptr),
-        default_src_(default_value_gen),
+        default_value_(default_value_gen),
         data_guard_{} {}
 
   // Constant access methods
@@ -392,10 +392,6 @@ class FlagImpl {
   std::string DefaultValue() const ABSL_LOCKS_EXCLUDED(*DataGuard());
   std::string CurrentValue() const ABSL_LOCKS_EXCLUDED(*DataGuard());
   void Read(void* dst) const ABSL_LOCKS_EXCLUDED(*DataGuard());
-  // Attempts to parse supplied `value` std::string. If parsing is successful, then
-  // it replaces `dst` with the new value.
-  bool TryParse(void** dst, absl::string_view value, std::string* err) const
-      ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard());
 
   template <typename T, typename std::enable_if<
                             !IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
@@ -466,8 +462,15 @@ class FlagImpl {
   // Returns heap allocated value of type T initialized with default value.
   std::unique_ptr<void, DynValueDeleter> MakeInitValue() const
       ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard());
-  // Lazy initialization of the Flag's data.
+  // Flag initialization called via absl::call_once.
   void Init();
+  // Attempts to parse supplied `value` std::string. If parsing is successful,
+  // returns new value. Otherwsie returns nullptr.
+  std::unique_ptr<void, DynValueDeleter> TryParse(absl::string_view value,
+                                                  std::string* err) const
+      ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard());
+  // Stores the flag value based on the pointer to the source.
+  void StoreValue(const void* src) ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard());
 
   FlagHelpKind HelpSourceKind() const {
     return static_cast<FlagHelpKind>(help_source_kind_);
@@ -511,7 +514,7 @@ class FlagImpl {
 
   // Mutable flag's state (guarded by `data_guard_`).
 
-  // If def_kind_ == kDynamicValue, default_src_ holds a dynamically allocated
+  // If def_kind_ == kDynamicValue, default_value_ holds a dynamically allocated
   // value.
   uint8_t def_kind_ : 1 ABSL_GUARDED_BY(*DataGuard());
   // Has this flag's value been modified?
@@ -527,7 +530,7 @@ class FlagImpl {
   // value specified in ABSL_FLAG or pointer to the dynamically set default
   // value via SetCommandLineOptionWithMode. def_kind_ is used to distinguish
   // these two cases.
-  FlagDefaultSrc default_src_ ABSL_GUARDED_BY(*DataGuard());
+  FlagDefaultSrc default_value_ ABSL_GUARDED_BY(*DataGuard());
   // Current Flag Value
   FlagValue value_;
 
@@ -542,8 +545,8 @@ class FlagImpl {
 };
 
 ///////////////////////////////////////////////////////////////////////////////
-// The "unspecified" implementation of Flag object parameterized by the
-// flag's value type.
+// The Flag object parameterized by the flag's value type. This class implements
+// flag reflection handle interface.
 
 template <typename T>
 class Flag final : public flags_internal::CommandLineFlag {
diff --git a/absl/flags/internal/type_erased_test.cc b/absl/flags/internal/type_erased_test.cc
index 033e00e..4ce5981 100644
--- a/absl/flags/internal/type_erased_test.cc
+++ b/absl/flags/internal/type_erased_test.cc
@@ -119,6 +119,13 @@ TEST_F(TypeErasedTest, TestSetCommandLineOptionWithMode_SET_FLAGS_DEFAULT) {
   EXPECT_TRUE(flags::SetCommandLineOptionWithMode("int_flag", "101",
                                                   flags::SET_FLAGS_DEFAULT));
 
+  // Set it again to ensure that resetting logic is covered.
+  EXPECT_TRUE(flags::SetCommandLineOptionWithMode("int_flag", "102",
+                                                  flags::SET_FLAGS_DEFAULT));
+
+  EXPECT_TRUE(flags::SetCommandLineOptionWithMode("int_flag", "103",
+                                                  flags::SET_FLAGS_DEFAULT));
+
   EXPECT_TRUE(flags::SetCommandLineOptionWithMode("string_flag", "asdfgh",
                                                   flags::SET_FLAGS_DEFAULT));
   EXPECT_EQ(absl::GetFlag(FLAGS_string_flag), "asdfgh");
diff --git a/absl/functional/bind_front.h b/absl/functional/bind_front.h
index 8448d7b..5b47970 100644
--- a/absl/functional/bind_front.h
+++ b/absl/functional/bind_front.h
@@ -38,9 +38,7 @@ ABSL_NAMESPACE_BEGIN
 
 // bind_front()
 //
-// Binds the first N arguments of an invocable object and stores them by value,
-// except types of `std::reference_wrapper` which are 'unwound' and stored by
-// reference.
+// Binds the first N arguments of an invocable object and stores them by value.
 //
 // Like `std::bind()`, `absl::bind_front()` is implicitly convertible to
 // `std::function`.  In particular, it may be used as a simpler replacement for
@@ -140,7 +138,9 @@ ABSL_NAMESPACE_BEGIN
 //
 // Example: Storing bound arguments by reference.
 //
-//   void Print(const string& a, const string& b) { LOG(INFO) << a << b; }
+//   void Print(const std::string& a, const std::string& b) {
+//     std::cerr << a << b;
+//   }
 //
 //   std::string hi = "Hello, ";
 //   std::vector<std::string> names = {"Chuk", "Gek"};
@@ -152,6 +152,24 @@ ABSL_NAMESPACE_BEGIN
 //   // dangling references.
 //   foo->DoInFuture(absl::bind_front(Print, std::ref(hi), "Guest"));  // BAD!
 //   auto f = absl::bind_front(Print, std::ref(hi), "Guest"); // BAD!
+//
+// Example: Storing reference-like types.
+//
+//   void Print(absl::string_view a, const std::string& b) {
+//     std::cerr << a << b;
+//   }
+//
+//   std::string hi = "Hello, ";
+//   // Copies "hi".
+//   absl::bind_front(Print, hi)("Chuk");
+//
+//   // Compile error: std::reference_wrapper<const string> is not implicitly
+//   // convertible to string_view.
+//   // absl::bind_front(Print, std::cref(hi))("Chuk");
+//
+//   // Doesn't copy "hi".
+//   absl::bind_front(Print, absl::string_view(hi))("Chuk");
+//
 template <class F, class... BoundArgs>
 constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
     F&& func, BoundArgs&&... args) {
diff --git a/absl/memory/memory_exception_safety_test.cc b/absl/memory/memory_exception_safety_test.cc
index c0910dc..1df7261 100644
--- a/absl/memory/memory_exception_safety_test.cc
+++ b/absl/memory/memory_exception_safety_test.cc
@@ -27,9 +27,6 @@ namespace {
 
 constexpr int kLength = 50;
 using Thrower = testing::ThrowingValue<testing::TypeSpec::kEverythingThrows>;
-using ThrowerStorage =
-    absl::aligned_storage_t<sizeof(Thrower), alignof(Thrower)>;
-using ThrowerList = std::array<ThrowerStorage, kLength>;
 
 TEST(MakeUnique, CheckForLeaks) {
   constexpr int kValue = 321;
diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index cc0cc9d..d9503ae 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -63,16 +63,16 @@ namespace {
 // Type used with std::allocator for allocating and deallocating
 // `CordRepExternal`. std::allocator is used because it opaquely handles the
 // different new / delete overloads available on a given platform.
-using ExternalAllocType =
-    absl::aligned_storage_t<absl::cord_internal::ExternalRepAlignment(),
-                            absl::cord_internal::ExternalRepAlignment()>;
+struct alignas(absl::cord_internal::ExternalRepAlignment()) ExternalAllocType {
+  unsigned char value[absl::cord_internal::ExternalRepAlignment()];
+};
 
 // Returns the number of objects to pass in to std::allocator<ExternalAllocType>
 // allocate() and deallocate() to create enough room for `CordRepExternal` with
 // `releaser_size` bytes on the end.
 constexpr size_t GetExternalAllocNumObjects(size_t releaser_size) {
   // Be sure to round up since `releaser_size` could be smaller than
-  // sizeof(ExternalAllocType)`.
+  // `sizeof(ExternalAllocType)`.
   return (sizeof(CordRepExternal) + releaser_size + sizeof(ExternalAllocType) -
           1) /
          sizeof(ExternalAllocType);
diff --git a/absl/synchronization/internal/mutex_nonprod.inc b/absl/synchronization/internal/mutex_nonprod.inc
index 85dae0f..a1502e7 100644
--- a/absl/synchronization/internal/mutex_nonprod.inc
+++ b/absl/synchronization/internal/mutex_nonprod.inc
@@ -252,8 +252,8 @@ class SynchronizationStorage {
 
   absl::once_flag once_;
 
-  // An aligned space for T.
-  typename std::aligned_storage<sizeof(T), alignof(T)>::type space_;
+  // An aligned space for the T.
+  alignas(T) unsigned char space_[sizeof(T)];
 };
 
 }  // namespace synchronization_internal
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index ddd6081..2949f5a 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -368,31 +368,29 @@ class Waiter::WinHelper {
     return reinterpret_cast<CONDITION_VARIABLE *>(&w->cv_storage_);
   }
 
-  static_assert(sizeof(SRWLOCK) == sizeof(Waiter::SRWLockStorage),
-                "SRWLockStorage does not have the same size as SRWLOCK");
+  static_assert(sizeof(SRWLOCK) == sizeof(void *),
+                "`mu_storage_` does not have the same size as SRWLOCK");
+  static_assert(alignof(SRWLOCK) == alignof(void *),
+                "`mu_storage_` does not have the same alignment as SRWLOCK");
+
+  static_assert(sizeof(CONDITION_VARIABLE) == sizeof(void *),
+                "`ABSL_CONDITION_VARIABLE_STORAGE` does not have the same size "
+                "as `CONDITION_VARIABLE`");
   static_assert(
-      alignof(SRWLOCK) == alignof(Waiter::SRWLockStorage),
-      "SRWLockStorage does not have the same alignment as SRWLOCK");
-
-  static_assert(sizeof(CONDITION_VARIABLE) ==
-                    sizeof(Waiter::ConditionVariableStorage),
-                "ABSL_CONDITION_VARIABLE_STORAGE does not have the same size "
-                "as CONDITION_VARIABLE");
-  static_assert(alignof(CONDITION_VARIABLE) ==
-                    alignof(Waiter::ConditionVariableStorage),
-                "ConditionVariableStorage does not have the same "
-                "alignment as CONDITION_VARIABLE");
+      alignof(CONDITION_VARIABLE) == alignof(void *),
+      "`cv_storage_` does not have the same alignment as `CONDITION_VARIABLE`");
 
   // The SRWLOCK and CONDITION_VARIABLE types must be trivially constructible
   // and destructible because we never call their constructors or destructors.
   static_assert(std::is_trivially_constructible<SRWLOCK>::value,
-                "The SRWLOCK type must be trivially constructible");
-  static_assert(std::is_trivially_constructible<CONDITION_VARIABLE>::value,
-                "The CONDITION_VARIABLE type must be trivially constructible");
+                "The `SRWLOCK` type must be trivially constructible");
+  static_assert(
+      std::is_trivially_constructible<CONDITION_VARIABLE>::value,
+      "The `CONDITION_VARIABLE` type must be trivially constructible");
   static_assert(std::is_trivially_destructible<SRWLOCK>::value,
-                "The SRWLOCK type must be trivially destructible");
+                "The `SRWLOCK` type must be trivially destructible");
   static_assert(std::is_trivially_destructible<CONDITION_VARIABLE>::value,
-                "The CONDITION_VARIABLE type must be trivially destructible");
+                "The `CONDITION_VARIABLE` type must be trivially destructible");
 };
 
 class LockHolder {
diff --git a/absl/synchronization/internal/waiter.h b/absl/synchronization/internal/waiter.h
index 5af5c28..a6e6d4c 100644
--- a/absl/synchronization/internal/waiter.h
+++ b/absl/synchronization/internal/waiter.h
@@ -133,13 +133,6 @@ class Waiter {
   std::atomic<int> wakeups_;
 
 #elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_WIN32
-  // We can't include Windows.h in our headers, so we use aligned storage
-  // buffers to define the storage of SRWLOCK and CONDITION_VARIABLE.
-  using SRWLockStorage =
-      typename std::aligned_storage<sizeof(void*), alignof(void*)>::type;
-  using ConditionVariableStorage =
-      typename std::aligned_storage<sizeof(void*), alignof(void*)>::type;
-
   // WinHelper - Used to define utilities for accessing the lock and
   // condition variable storage once the types are complete.
   class WinHelper;
@@ -147,8 +140,10 @@ class Waiter {
   // REQUIRES: WinHelper::GetLock(this) must be held.
   void InternalCondVarPoke();
 
-  SRWLockStorage mu_storage_;
-  ConditionVariableStorage cv_storage_;
+  // We can't include Windows.h in our headers, so we use aligned charachter
+  // buffers to define the storage of SRWLOCK and CONDITION_VARIABLE.
+  alignas(void*) unsigned char mu_storage_[sizeof(void*)];
+  alignas(void*) unsigned char cv_storage_[sizeof(void*)];
   int waiter_count_;
   int wakeup_count_;