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-rw-r--r--absl/container/BUILD.bazel20
-rw-r--r--absl/container/CMakeLists.txt1
-rw-r--r--absl/container/fixed_array.h154
-rw-r--r--absl/container/fixed_array_test.cc213
-rw-r--r--absl/container/internal/compressed_tuple.h175
-rw-r--r--absl/container/internal/compressed_tuple_test.cc166
-rw-r--r--absl/memory/memory.h56
-rw-r--r--absl/memory/memory_exception_safety_test.cc11
-rw-r--r--absl/memory/memory_test.cc43
-rw-r--r--absl/meta/type_traits.h44
-rw-r--r--absl/meta/type_traits_test.cc81
-rw-r--r--absl/strings/numbers_test.cc7
-rw-r--r--absl/time/duration.cc5
-rw-r--r--absl/time/duration_benchmark.cc78
-rw-r--r--absl/time/duration_test.cc124
-rw-r--r--absl/time/time.h97
-rw-r--r--absl/types/internal/variant.h28
17 files changed, 1066 insertions, 237 deletions
diff --git a/absl/container/BUILD.bazel b/absl/container/BUILD.bazel
index 07df3675207e..6d5c958f382b 100644
--- a/absl/container/BUILD.bazel
+++ b/absl/container/BUILD.bazel
@@ -26,10 +26,30 @@ package(default_visibility = ["//visibility:public"])
 licenses(["notice"])  # Apache 2.0
 
 cc_library(
+    name = "compressed_tuple",
+    hdrs = ["internal/compressed_tuple.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        "//absl/utility",
+    ],
+)
+
+cc_test(
+    name = "compressed_tuple_test",
+    srcs = ["internal/compressed_tuple_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":compressed_tuple",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
     name = "fixed_array",
     hdrs = ["fixed_array.h"],
     copts = ABSL_DEFAULT_COPTS,
     deps = [
+        ":compressed_tuple",
         "//absl/algorithm",
         "//absl/base:core_headers",
         "//absl/base:dynamic_annotations",
diff --git a/absl/container/CMakeLists.txt b/absl/container/CMakeLists.txt
index d580b48976cb..123e4c4849aa 100644
--- a/absl/container/CMakeLists.txt
+++ b/absl/container/CMakeLists.txt
@@ -52,7 +52,6 @@ absl_library(
     ${TEST_INSTANCE_TRACKER_LIB_SRC}
   PUBLIC_LIBRARIES
     absl::container
-  DISABLE_INSTALL
 )
 
 
diff --git a/absl/container/fixed_array.h b/absl/container/fixed_array.h
index 62600df05be3..f480047a5db4 100644
--- a/absl/container/fixed_array.h
+++ b/absl/container/fixed_array.h
@@ -47,6 +47,7 @@
 #include "absl/base/macros.h"
 #include "absl/base/optimization.h"
 #include "absl/base/port.h"
+#include "absl/container/internal/compressed_tuple.h"
 #include "absl/memory/memory.h"
 
 namespace absl {
@@ -76,73 +77,99 @@ constexpr static auto kFixedArrayUseDefault = static_cast<size_t>(-1);
 // heap allocation, it will do so with global `::operator new[]()` and
 // `::operator delete[]()`, even if T provides class-scope overrides for these
 // operators.
-template <typename T, size_t inlined = kFixedArrayUseDefault>
+template <typename T, size_t N = kFixedArrayUseDefault,
+          typename A = std::allocator<T>>
 class FixedArray {
   static_assert(!std::is_array<T>::value || std::extent<T>::value > 0,
                 "Arrays with unknown bounds cannot be used with FixedArray.");
+
   static constexpr size_t kInlineBytesDefault = 256;
 
+  using AllocatorTraits = std::allocator_traits<A>;
   // std::iterator_traits isn't guaranteed to be SFINAE-friendly until C++17,
   // but this seems to be mostly pedantic.
   template <typename Iterator>
   using EnableIfForwardIterator = absl::enable_if_t<std::is_convertible<
       typename std::iterator_traits<Iterator>::iterator_category,
       std::forward_iterator_tag>::value>;
+  static constexpr bool NoexceptCopyable() {
+    return std::is_nothrow_copy_constructible<StorageElement>::value &&
+           absl::allocator_is_nothrow<allocator_type>::value;
+  }
+  static constexpr bool NoexceptMovable() {
+    return std::is_nothrow_move_constructible<StorageElement>::value &&
+           absl::allocator_is_nothrow<allocator_type>::value;
+  }
+  static constexpr bool DefaultConstructorIsNonTrivial() {
+    return !absl::is_trivially_default_constructible<StorageElement>::value;
+  }
 
  public:
-  using value_type = T;
-  using iterator = T*;
-  using const_iterator = const T*;
+  using allocator_type = typename AllocatorTraits::allocator_type;
+  using value_type = typename allocator_type::value_type;
+  using pointer = typename allocator_type::pointer;
+  using const_pointer = typename allocator_type::const_pointer;
+  using reference = typename allocator_type::reference;
+  using const_reference = typename allocator_type::const_reference;
+  using size_type = typename allocator_type::size_type;
+  using difference_type = typename allocator_type::difference_type;
+  using iterator = pointer;
+  using const_iterator = const_pointer;
   using reverse_iterator = std::reverse_iterator<iterator>;
   using const_reverse_iterator = std::reverse_iterator<const_iterator>;
-  using reference = T&;
-  using const_reference = const T&;
-  using pointer = T*;
-  using const_pointer = const T*;
-  using difference_type = ptrdiff_t;
-  using size_type = size_t;
 
   static constexpr size_type inline_elements =
-      inlined == kFixedArrayUseDefault
-          ? kInlineBytesDefault / sizeof(value_type)
-          : inlined;
+      (N == kFixedArrayUseDefault ? kInlineBytesDefault / sizeof(value_type)
+                                  : static_cast<size_type>(N));
 
-  FixedArray(const FixedArray& other)
-      : FixedArray(other.begin(), other.end()) {}
+  FixedArray(
+      const FixedArray& other,
+      const allocator_type& a = allocator_type()) noexcept(NoexceptCopyable())
+      : FixedArray(other.begin(), other.end(), a) {}
 
-  FixedArray(FixedArray&& other) noexcept(
-      absl::conjunction<absl::allocator_is_nothrow<std::allocator<value_type>>,
-                        std::is_nothrow_move_constructible<value_type>>::value)
+  FixedArray(
+      FixedArray&& other,
+      const allocator_type& a = allocator_type()) noexcept(NoexceptMovable())
       : FixedArray(std::make_move_iterator(other.begin()),
-                   std::make_move_iterator(other.end())) {}
+                   std::make_move_iterator(other.end()), a) {}
 
   // Creates an array object that can store `n` elements.
   // Note that trivially constructible elements will be uninitialized.
-  explicit FixedArray(size_type n) : storage_(n) {
-    absl::memory_internal::uninitialized_default_construct_n(storage_.begin(),
-                                                             size());
+  explicit FixedArray(size_type n, const allocator_type& a = allocator_type())
+      : storage_(n, a) {
+    if (DefaultConstructorIsNonTrivial()) {
+      memory_internal::ConstructStorage(storage_.alloc(), storage_.begin(),
+                                        storage_.end());
+    }
   }
 
   // Creates an array initialized with `n` copies of `val`.
-  FixedArray(size_type n, const value_type& val) : storage_(n) {
-    std::uninitialized_fill_n(data(), size(), val);
+  FixedArray(size_type n, const value_type& val,
+             const allocator_type& a = allocator_type())
+      : storage_(n, a) {
+    memory_internal::ConstructStorage(storage_.alloc(), storage_.begin(),
+                                      storage_.end(), val);
   }
 
+  // Creates an array initialized with the size and contents of `init_list`.
+  FixedArray(std::initializer_list<value_type> init_list,
+             const allocator_type& a = allocator_type())
+      : FixedArray(init_list.begin(), init_list.end(), a) {}
+
   // Creates an array initialized with the elements from the input
   // range. The array's size will always be `std::distance(first, last)`.
   // REQUIRES: Iterator must be a forward_iterator or better.
   template <typename Iterator, EnableIfForwardIterator<Iterator>* = nullptr>
-  FixedArray(Iterator first, Iterator last)
-      : storage_(std::distance(first, last)) {
-    std::uninitialized_copy(first, last, data());
+  FixedArray(Iterator first, Iterator last,
+             const allocator_type& a = allocator_type())
+      : storage_(std::distance(first, last), a) {
+    memory_internal::CopyToStorageFromRange(storage_.alloc(), storage_.begin(),
+                                            first, last);
   }
 
-  FixedArray(std::initializer_list<value_type> init_list)
-      : FixedArray(init_list.begin(), init_list.end()) {}
-
   ~FixedArray() noexcept {
-    for (const StorageElement& cur : storage_) {
-      cur.~StorageElement();
+    for (auto* cur = storage_.begin(); cur != storage_.end(); ++cur) {
+      AllocatorTraits::destroy(*storage_.alloc(), cur);
     }
   }
 
@@ -332,7 +359,6 @@ class FixedArray {
   friend bool operator>=(const FixedArray& lhs, const FixedArray& rhs) {
     return !(lhs < rhs);
   }
-
  private:
   // StorageElement
   //
@@ -364,6 +390,8 @@ class FixedArray {
   using StorageElement =
       absl::conditional_t<std::is_array<value_type>::value,
                           StorageElementWrapper<value_type>, value_type>;
+  using StorageElementBuffer =
+      absl::aligned_storage_t<sizeof(StorageElement), alignof(StorageElement)>;
 
   static pointer AsValueType(pointer ptr) { return ptr; }
   static pointer AsValueType(StorageElementWrapper<value_type>* ptr) {
@@ -374,9 +402,6 @@ class FixedArray {
   static_assert(alignof(StorageElement) == alignof(value_type), "");
 
   struct NonEmptyInlinedStorage {
-    using StorageElementBuffer =
-        absl::aligned_storage_t<sizeof(StorageElement),
-                                alignof(StorageElement)>;
     StorageElement* data() {
       return reinterpret_cast<StorageElement*>(inlined_storage_.data());
     }
@@ -386,8 +411,8 @@ class FixedArray {
     void* RedzoneEnd() { return &redzone_end_ + 1; }
 #endif  // ADDRESS_SANITIZER
 
-    void AnnotateConstruct(size_t);
-    void AnnotateDestruct(size_t);
+    void AnnotateConstruct(size_type);
+    void AnnotateDestruct(size_type);
 
     ADDRESS_SANITIZER_REDZONE(redzone_begin_);
     std::array<StorageElementBuffer, inline_elements> inlined_storage_;
@@ -396,8 +421,8 @@ class FixedArray {
 
   struct EmptyInlinedStorage {
     StorageElement* data() { return nullptr; }
-    void AnnotateConstruct(size_t) {}
-    void AnnotateDestruct(size_t) {}
+    void AnnotateConstruct(size_type) {}
+    void AnnotateDestruct(size_type) {}
   };
 
   using InlinedStorage =
@@ -414,48 +439,57 @@ class FixedArray {
   //
   class Storage : public InlinedStorage {
    public:
-    explicit Storage(size_type n) : data_(CreateStorage(n)), size_(n) {}
+    Storage(size_type n, const allocator_type& a)
+        : size_alloc_(n, a), data_(InitializeData()) {}
+
     ~Storage() noexcept {
       if (UsingInlinedStorage(size())) {
-        this->AnnotateDestruct(size());
+        InlinedStorage::AnnotateDestruct(size());
       } else {
-        std::allocator<StorageElement>().deallocate(begin(), size());
+        AllocatorTraits::deallocate(*alloc(), AsValueType(begin()), size());
       }
     }
 
-    size_type size() const { return size_; }
+    size_type size() const { return size_alloc_.template get<0>(); }
     StorageElement* begin() const { return data_; }
     StorageElement* end() const { return begin() + size(); }
+    allocator_type* alloc() {
+      return std::addressof(size_alloc_.template get<1>());
+    }
 
    private:
     static bool UsingInlinedStorage(size_type n) {
       return n <= inline_elements;
     }
 
-    StorageElement* CreateStorage(size_type n) {
-      if (UsingInlinedStorage(n)) {
-        this->AnnotateConstruct(n);
+    StorageElement* InitializeData() {
+      if (UsingInlinedStorage(size())) {
+        InlinedStorage::AnnotateConstruct(size());
         return InlinedStorage::data();
       } else {
-        return std::allocator<StorageElement>().allocate(n);
+        return reinterpret_cast<StorageElement*>(
+            AllocatorTraits::allocate(*alloc(), size()));
       }
     }
 
-    StorageElement* const data_;
-    const size_type size_;
+    // `CompressedTuple` takes advantage of EBCO for stateless `allocator_type`s
+    container_internal::CompressedTuple<size_type, allocator_type> size_alloc_;
+    StorageElement* data_;
   };
 
-  const Storage storage_;
+  Storage storage_;
 };
 
-template <typename T, size_t N>
-constexpr size_t FixedArray<T, N>::inline_elements;
+template <typename T, size_t N, typename A>
+constexpr size_t FixedArray<T, N, A>::kInlineBytesDefault;
 
-template <typename T, size_t N>
-constexpr size_t FixedArray<T, N>::kInlineBytesDefault;
+template <typename T, size_t N, typename A>
+constexpr typename FixedArray<T, N, A>::size_type
+    FixedArray<T, N, A>::inline_elements;
 
-template <typename T, size_t N>
-void FixedArray<T, N>::NonEmptyInlinedStorage::AnnotateConstruct(size_t n) {
+template <typename T, size_t N, typename A>
+void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateConstruct(
+    typename FixedArray<T, N, A>::size_type n) {
 #ifdef ADDRESS_SANITIZER
   if (!n) return;
   ANNOTATE_CONTIGUOUS_CONTAINER(data(), RedzoneEnd(), RedzoneEnd(), data() + n);
@@ -464,8 +498,9 @@ void FixedArray<T, N>::NonEmptyInlinedStorage::AnnotateConstruct(size_t n) {
   static_cast<void>(n);  // Mark used when not in asan mode
 }
 
-template <typename T, size_t N>
-void FixedArray<T, N>::NonEmptyInlinedStorage::AnnotateDestruct(size_t n) {
+template <typename T, size_t N, typename A>
+void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateDestruct(
+    typename FixedArray<T, N, A>::size_type n) {
 #ifdef ADDRESS_SANITIZER
   if (!n) return;
   ANNOTATE_CONTIGUOUS_CONTAINER(data(), RedzoneEnd(), data() + n, RedzoneEnd());
@@ -473,6 +508,5 @@ void FixedArray<T, N>::NonEmptyInlinedStorage::AnnotateDestruct(size_t n) {
 #endif                   // ADDRESS_SANITIZER
   static_cast<void>(n);  // Mark used when not in asan mode
 }
-
 }  // namespace absl
 #endif  // ABSL_CONTAINER_FIXED_ARRAY_H_
diff --git a/absl/container/fixed_array_test.cc b/absl/container/fixed_array_test.cc
index 2142132d1352..b07ebcb6d9ca 100644
--- a/absl/container/fixed_array_test.cc
+++ b/absl/container/fixed_array_test.cc
@@ -15,9 +15,11 @@
 #include "absl/container/fixed_array.h"
 
 #include <stdio.h>
+#include <cstring>
 #include <list>
 #include <memory>
 #include <numeric>
+#include <scoped_allocator>
 #include <stdexcept>
 #include <string>
 #include <vector>
@@ -607,6 +609,216 @@ 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));
+
+  FixedArrType* arr =
+      ::new (static_cast<void*>(std::addressof(buff))) FixedArrType(length);
+  EXPECT_THAT(*arr, testing::Each(scrubbed_bits));
+  arr->~FixedArrType();
+}
+#endif  // __GNUC__
+
+// This is a stateful allocator, but the state lives outside of the
+// allocator (in whatever test is using the allocator). This is odd
+// but helps in tests where the allocator is propagated into nested
+// containers - that chain of allocators uses the same state and is
+// thus easier to query for aggregate allocation information.
+template <typename T>
+class CountingAllocator : public std::allocator<T> {
+ public:
+  using Alloc = std::allocator<T>;
+  using pointer = typename Alloc::pointer;
+  using size_type = typename Alloc::size_type;
+
+  CountingAllocator() : bytes_used_(nullptr), instance_count_(nullptr) {}
+  explicit CountingAllocator(int64_t* b)
+      : bytes_used_(b), instance_count_(nullptr) {}
+  CountingAllocator(int64_t* b, int64_t* a)
+      : bytes_used_(b), instance_count_(a) {}
+
+  template <typename U>
+  explicit CountingAllocator(const CountingAllocator<U>& x)
+      : Alloc(x),
+        bytes_used_(x.bytes_used_),
+        instance_count_(x.instance_count_) {}
+
+  pointer allocate(size_type n, const void* const hint = nullptr) {
+    assert(bytes_used_ != nullptr);
+    *bytes_used_ += n * sizeof(T);
+    return Alloc::allocate(n, hint);
+  }
+
+  void deallocate(pointer p, size_type n) {
+    Alloc::deallocate(p, n);
+    assert(bytes_used_ != nullptr);
+    *bytes_used_ -= n * sizeof(T);
+  }
+
+  template <typename... Args>
+  void construct(pointer p, Args&&... args) {
+    Alloc::construct(p, absl::forward<Args>(args)...);
+    if (instance_count_) {
+      *instance_count_ += 1;
+    }
+  }
+
+  void destroy(pointer p) {
+    Alloc::destroy(p);
+    if (instance_count_) {
+      *instance_count_ -= 1;
+    }
+  }
+
+  template <typename U>
+  class rebind {
+   public:
+    using other = CountingAllocator<U>;
+  };
+
+  int64_t* bytes_used_;
+  int64_t* instance_count_;
+};
+
+TEST(AllocatorSupportTest, CountInlineAllocations) {
+  constexpr size_t inlined_size = 4;
+  using Alloc = CountingAllocator<int>;
+  using AllocFxdArr = absl::FixedArray<int, inlined_size, Alloc>;
+
+  int64_t allocated = 0;
+  int64_t active_instances = 0;
+
+  {
+    const int ia[] = {0, 1, 2, 3, 4, 5, 6, 7};
+
+    Alloc alloc(&allocated, &active_instances);
+
+    AllocFxdArr arr(ia, ia + inlined_size, alloc);
+    static_cast<void>(arr);
+  }
+
+  EXPECT_EQ(allocated, 0);
+  EXPECT_EQ(active_instances, 0);
+}
+
+TEST(AllocatorSupportTest, CountOutoflineAllocations) {
+  constexpr size_t inlined_size = 4;
+  using Alloc = CountingAllocator<int>;
+  using AllocFxdArr = absl::FixedArray<int, inlined_size, Alloc>;
+
+  int64_t allocated = 0;
+  int64_t active_instances = 0;
+
+  {
+    const int ia[] = {0, 1, 2, 3, 4, 5, 6, 7};
+    Alloc alloc(&allocated, &active_instances);
+
+    AllocFxdArr arr(ia, ia + ABSL_ARRAYSIZE(ia), alloc);
+
+    EXPECT_EQ(allocated, arr.size() * sizeof(int));
+    static_cast<void>(arr);
+  }
+
+  EXPECT_EQ(active_instances, 0);
+}
+
+TEST(AllocatorSupportTest, CountCopyInlineAllocations) {
+  constexpr size_t inlined_size = 4;
+  using Alloc = CountingAllocator<int>;
+  using AllocFxdArr = absl::FixedArray<int, inlined_size, Alloc>;
+
+  int64_t allocated1 = 0;
+  int64_t allocated2 = 0;
+  int64_t active_instances = 0;
+  Alloc alloc(&allocated1, &active_instances);
+  Alloc alloc2(&allocated2, &active_instances);
+
+  {
+    int initial_value = 1;
+
+    AllocFxdArr arr1(inlined_size / 2, initial_value, alloc);
+
+    EXPECT_EQ(allocated1, 0);
+
+    AllocFxdArr arr2(arr1, alloc2);
+
+    EXPECT_EQ(allocated2, 0);
+    static_cast<void>(arr1);
+    static_cast<void>(arr2);
+  }
+
+  EXPECT_EQ(active_instances, 0);
+}
+
+TEST(AllocatorSupportTest, CountCopyOutoflineAllocations) {
+  constexpr size_t inlined_size = 4;
+  using Alloc = CountingAllocator<int>;
+  using AllocFxdArr = absl::FixedArray<int, inlined_size, Alloc>;
+
+  int64_t allocated1 = 0;
+  int64_t allocated2 = 0;
+  int64_t active_instances = 0;
+  Alloc alloc(&allocated1, &active_instances);
+  Alloc alloc2(&allocated2, &active_instances);
+
+  {
+    int initial_value = 1;
+
+    AllocFxdArr arr1(inlined_size * 2, initial_value, alloc);
+
+    EXPECT_EQ(allocated1, arr1.size() * sizeof(int));
+
+    AllocFxdArr arr2(arr1, alloc2);
+
+    EXPECT_EQ(allocated2, inlined_size * 2 * sizeof(int));
+    static_cast<void>(arr1);
+    static_cast<void>(arr2);
+  }
+
+  EXPECT_EQ(active_instances, 0);
+}
+
+TEST(AllocatorSupportTest, SizeValAllocConstructor) {
+  using testing::AllOf;
+  using testing::Each;
+  using testing::SizeIs;
+
+  constexpr size_t inlined_size = 4;
+  using Alloc = CountingAllocator<int>;
+  using AllocFxdArr = absl::FixedArray<int, inlined_size, Alloc>;
+
+  {
+    auto len = inlined_size / 2;
+    auto val = 0;
+    int64_t allocated = 0;
+    AllocFxdArr arr(len, val, Alloc(&allocated));
+
+    EXPECT_EQ(allocated, 0);
+    EXPECT_THAT(arr, AllOf(SizeIs(len), Each(0)));
+  }
+
+  {
+    auto len = inlined_size * 2;
+    auto val = 0;
+    int64_t allocated = 0;
+    AllocFxdArr arr(len, val, Alloc(&allocated));
+
+    EXPECT_EQ(allocated, len * sizeof(int));
+    EXPECT_THAT(arr, AllOf(SizeIs(len), Each(0)));
+  }
+}
+
 #ifdef ADDRESS_SANITIZER
 TEST(FixedArrayTest, AddressSanitizerAnnotations1) {
   absl::FixedArray<int, 32> a(10);
@@ -655,5 +867,4 @@ TEST(FixedArrayTest, AddressSanitizerAnnotations4) {
   EXPECT_DEATH(raw[21] = ThreeInts(), "container-overflow");
 }
 #endif  // ADDRESS_SANITIZER
-
 }  // namespace
diff --git a/absl/container/internal/compressed_tuple.h b/absl/container/internal/compressed_tuple.h
new file mode 100644
index 000000000000..cc52614f5b37
--- /dev/null
+++ b/absl/container/internal/compressed_tuple.h
@@ -0,0 +1,175 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Helper class to perform the Empty Base Optimization.
+// Ts can contain classes and non-classes, empty or not. For the ones that
+// are empty classes, we perform the optimization. If all types in Ts are empty
+// classes, then CompressedTuple<Ts...> is itself an empty class.
+//
+// To access the members, use member get<N>() function.
+//
+// Eg:
+//   absl::container_internal::CompressedTuple<int, T1, T2, T3> value(7, t1, t2,
+//                                                                    t3);
+//   assert(value.get<0>() == 7);
+//   T1& t1 = value.get<1>();
+//   const T2& t2 = value.get<2>();
+//   ...
+//
+// http://en.cppreference.com/w/cpp/language/ebo
+
+#ifndef ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_
+#define ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_
+
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "absl/utility/utility.h"
+
+#ifdef _MSC_VER
+// We need to mark these classes with this declspec to ensure that
+// CompressedTuple happens.
+#define ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC __declspec(empty_bases)
+#else  // _MSC_VER
+#define ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC
+#endif  // _MSC_VER
+
+namespace absl {
+namespace container_internal {
+
+template <typename... Ts>
+class CompressedTuple;
+
+namespace internal_compressed_tuple {
+
+template <typename D, size_t I>
+struct Elem;
+template <typename... B, size_t I>
+struct Elem<CompressedTuple<B...>, I>
+    : std::tuple_element<I, std::tuple<B...>> {};
+template <typename D, size_t I>
+using ElemT = typename Elem<D, I>::type;
+
+// Use the __is_final intrinsic if available. Where it's not available, classes
+// declared with the 'final' specifier cannot be used as CompressedTuple
+// elements.
+// TODO(sbenza): Replace this with std::is_final in C++14.
+template <typename T>
+constexpr bool IsFinal() {
+#if defined(__clang__) || defined(__GNUC__)
+  return __is_final(T);
+#else
+  return false;
+#endif
+}
+
+template <typename T>
+constexpr bool ShouldUseBase() {
+  return std::is_class<T>::value && std::is_empty<T>::value && !IsFinal<T>();
+}
+
+// The storage class provides two specializations:
+//  - For empty classes, it stores T as a base class.
+//  - For everything else, it stores T as a member.
+template <typename D, size_t I, bool = ShouldUseBase<ElemT<D, I>>()>
+struct Storage {
+  using T = ElemT<D, I>;
+  T value;
+  constexpr Storage() = default;
+  explicit constexpr Storage(T&& v) : value(absl::forward<T>(v)) {}
+  constexpr const T& get() const { return value; }
+  T& get() { return value; }
+};
+
+template <typename D, size_t I>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC Storage<D, I, true>
+    : ElemT<D, I> {
+  using T = internal_compressed_tuple::ElemT<D, I>;
+  constexpr Storage() = default;
+  explicit constexpr Storage(T&& v) : T(absl::forward<T>(v)) {}
+  constexpr const T& get() const { return *this; }
+  T& get() { return *this; }
+};
+
+template <typename D, typename I>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl;
+
+template <typename... Ts, size_t... I>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC
+    CompressedTupleImpl<CompressedTuple<Ts...>, absl::index_sequence<I...>>
+    // We use the dummy identity function through std::integral_constant to
+    // convince MSVC of accepting and expanding I in that context. Without it
+    // you would get:
+    //   error C3548: 'I': parameter pack cannot be used in this context
+    : Storage<CompressedTuple<Ts...>,
+              std::integral_constant<size_t, I>::value>... {
+  constexpr CompressedTupleImpl() = default;
+  explicit constexpr CompressedTupleImpl(Ts&&... args)
+      : Storage<CompressedTuple<Ts...>, I>(absl::forward<Ts>(args))... {}
+};
+
+}  // namespace internal_compressed_tuple
+
+// Helper class to perform the Empty Base Class Optimization.
+// Ts can contain classes and non-classes, empty or not. For the ones that
+// are empty classes, we perform the CompressedTuple. If all types in Ts are
+// empty classes, then CompressedTuple<Ts...> is itself an empty class.
+//
+// To access the members, use member .get<N>() function.
+//
+// Eg:
+//   absl::container_internal::CompressedTuple<int, T1, T2, T3> value(7, t1, t2,
+//                                                                    t3);
+//   assert(value.get<0>() == 7);
+//   T1& t1 = value.get<1>();
+//   const T2& t2 = value.get<2>();
+//   ...
+//
+// http://en.cppreference.com/w/cpp/language/ebo
+template <typename... Ts>
+class ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTuple
+    : private internal_compressed_tuple::CompressedTupleImpl<
+          CompressedTuple<Ts...>, absl::index_sequence_for<Ts...>> {
+ private:
+  template <int I>
+  using ElemT = internal_compressed_tuple::ElemT<CompressedTuple, I>;
+
+ public:
+  constexpr CompressedTuple() = default;
+  explicit constexpr CompressedTuple(Ts... base)
+      : CompressedTuple::CompressedTupleImpl(absl::forward<Ts>(base)...) {}
+
+  template <int I>
+  ElemT<I>& get() {
+    return internal_compressed_tuple::Storage<CompressedTuple, I>::get();
+  }
+
+  template <int I>
+  constexpr const ElemT<I>& get() const {
+    return internal_compressed_tuple::Storage<CompressedTuple, I>::get();
+  }
+};
+
+// Explicit specialization for a zero-element tuple
+// (needed to avoid ambiguous overloads for the default constructor).
+template <>
+class ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTuple<> {};
+
+}  // namespace container_internal
+}  // namespace absl
+
+#undef ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC
+
+#endif  // ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_
diff --git a/absl/container/internal/compressed_tuple_test.cc b/absl/container/internal/compressed_tuple_test.cc
new file mode 100644
index 000000000000..45030c675ee1
--- /dev/null
+++ b/absl/container/internal/compressed_tuple_test.cc
@@ -0,0 +1,166 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/container/internal/compressed_tuple.h"
+
+#include <string>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+namespace absl {
+namespace container_internal {
+namespace {
+
+template <int>
+struct Empty {};
+
+template <typename T>
+struct NotEmpty {
+  T value;
+};
+
+template <typename T, typename U>
+struct TwoValues {
+  T value1;
+  U value2;
+};
+
+TEST(CompressedTupleTest, Sizeof) {
+  EXPECT_EQ(sizeof(int), sizeof(CompressedTuple<int>));
+  EXPECT_EQ(sizeof(int), sizeof(CompressedTuple<int, Empty<0>>));
+  EXPECT_EQ(sizeof(int), sizeof(CompressedTuple<int, Empty<0>, Empty<1>>));
+  EXPECT_EQ(sizeof(int),
+            sizeof(CompressedTuple<int, Empty<0>, Empty<1>, Empty<2>>));
+
+  EXPECT_EQ(sizeof(TwoValues<int, double>),
+            sizeof(CompressedTuple<int, NotEmpty<double>>));
+  EXPECT_EQ(sizeof(TwoValues<int, double>),
+            sizeof(CompressedTuple<int, Empty<0>, NotEmpty<double>>));
+  EXPECT_EQ(sizeof(TwoValues<int, double>),
+            sizeof(CompressedTuple<int, Empty<0>, NotEmpty<double>, Empty<1>>));
+}
+
+TEST(CompressedTupleTest, Access) {
+  struct S {
+    std::string x;
+  };
+  CompressedTuple<int, Empty<0>, S> x(7, {}, S{"ABC"});
+  EXPECT_EQ(sizeof(x), sizeof(TwoValues<int, S>));
+  EXPECT_EQ(7, x.get<0>());
+  EXPECT_EQ("ABC", x.get<2>().x);
+}
+
+TEST(CompressedTupleTest, NonClasses) {
+  CompressedTuple<int, const char*> x(7, "ABC");
+  EXPECT_EQ(7, x.get<0>());
+  EXPECT_STREQ("ABC", x.get<1>());
+}
+
+TEST(CompressedTupleTest, MixClassAndNonClass) {
+  CompressedTuple<int, const char*, Empty<0>, NotEmpty<double>> x(7, "ABC", {},
+                                                                  {1.25});
+  struct Mock {
+    int v;
+    const char* p;
+    double d;
+  };
+  EXPECT_EQ(sizeof(x), sizeof(Mock));
+  EXPECT_EQ(7, x.get<0>());
+  EXPECT_STREQ("ABC", x.get<1>());
+  EXPECT_EQ(1.25, x.get<3>().value);
+}
+
+TEST(CompressedTupleTest, Nested) {
+  CompressedTuple<int, CompressedTuple<int>,
+                  CompressedTuple<int, CompressedTuple<int>>>
+      x(1, CompressedTuple<int>(2),
+        CompressedTuple<int, CompressedTuple<int>>(3, CompressedTuple<int>(4)));
+  EXPECT_EQ(1, x.get<0>());
+  EXPECT_EQ(2, x.get<1>().get<0>());
+  EXPECT_EQ(3, x.get<2>().get<0>());
+  EXPECT_EQ(4, x.get<2>().get<1>().get<0>());
+
+  CompressedTuple<Empty<0>, Empty<0>,
+                  CompressedTuple<Empty<0>, CompressedTuple<Empty<0>>>>
+      y;
+  std::set<Empty<0>*> empties{&y.get<0>(), &y.get<1>(), &y.get<2>().get<0>(),
+                              &y.get<2>().get<1>().get<0>()};
+#ifdef _MSC_VER
+  // MSVC has a bug where many instances of the same base class are layed out in
+  // the same address when using __declspec(empty_bases).
+  // This will be fixed in a future version of MSVC.
+  int expected = 1;
+#else
+  int expected = 4;
+#endif
+  EXPECT_EQ(expected, sizeof(y));
+  EXPECT_EQ(expected, empties.size());
+  EXPECT_EQ(sizeof(y), sizeof(Empty<0>) * empties.size());
+
+  EXPECT_EQ(4 * sizeof(char),
+            sizeof(CompressedTuple<CompressedTuple<char, char>,
+                                   CompressedTuple<char, char>>));
+  EXPECT_TRUE(
+      (std::is_empty<CompressedTuple<CompressedTuple<Empty<0>>,
+                                     CompressedTuple<Empty<1>>>>::value));
+}
+
+TEST(CompressedTupleTest, Reference) {
+  int i = 7;
+  std::string s = "Very long std::string that goes in the heap";
+  CompressedTuple<int, int&, std::string, std::string&> x(i, i, s, s);
+
+  // Sanity check. We should have not moved from `s`
+  EXPECT_EQ(s, "Very long std::string that goes in the heap");
+
+  EXPECT_EQ(x.get<0>(), x.get<1>());
+  EXPECT_NE(&x.get<0>(), &x.get<1>());
+  EXPECT_EQ(&x.get<1>(), &i);
+
+  EXPECT_EQ(x.get<2>(), x.get<3>());
+  EXPECT_NE(&x.get<2>(), &x.get<3>());
+  EXPECT_EQ(&x.get<3>(), &s);
+}
+
+TEST(CompressedTupleTest, NoElements) {
+  CompressedTuple<> x;
+  static_cast<void>(x);  // Silence -Wunused-variable.
+  EXPECT_TRUE(std::is_empty<CompressedTuple<>>::value);
+}
+
+TEST(CompressedTupleTest, Constexpr) {
+  constexpr CompressedTuple<int, double, CompressedTuple<int>> x(
+      7, 1.25, CompressedTuple<int>(5));
+  constexpr int x0 = x.get<0>();
+  constexpr double x1 = x.get<1>();
+  constexpr int x2 = x.get<2>().get<0>();
+  EXPECT_EQ(x0, 7);
+  EXPECT_EQ(x1, 1.25);
+  EXPECT_EQ(x2, 5);
+}
+
+#if defined(__clang__) || defined(__GNUC__)
+TEST(CompressedTupleTest, EmptyFinalClass) {
+  struct S final {
+    int f() const { return 5; }
+  };
+  CompressedTuple<S> x;
+  EXPECT_EQ(x.get<0>().f(), 5);
+}
+#endif
+
+}  // namespace
+}  // namespace container_internal
+}  // namespace absl
diff --git a/absl/memory/memory.h b/absl/memory/memory.h
index f207169a6885..c7caf8b94dc9 100644
--- a/absl/memory/memory.h
+++ b/absl/memory/memory.h
@@ -641,38 +641,56 @@ struct default_allocator_is_nothrow : std::false_type {};
 #endif
 
 namespace memory_internal {
-// TODO(b110200014): Implement proper backports
-template <typename ForwardIt>
-void DefaultConstruct(ForwardIt it) {
-  using value_type = typename std::iterator_traits<ForwardIt>::value_type;
-  ::new (static_cast<void*>(std::addressof(*it))) value_type;
-}  // namespace memory_internal
-
 #ifdef ABSL_HAVE_EXCEPTIONS
-template <typename ForwardIt, typename Size>
-void uninitialized_default_construct_n(ForwardIt first, Size size) {
-  for (ForwardIt cur = first; size > 0; static_cast<void>(++cur), --size) {
+template <typename Allocator, typename StorageElement, typename... Args>
+void ConstructStorage(Allocator* alloc, StorageElement* first,
+                      StorageElement* last, const Args&... args) {
+  for (StorageElement* cur = first; cur != last; ++cur) {
+    try {
+      std::allocator_traits<Allocator>::construct(*alloc, cur, args...);
+    } catch (...) {
+      while (cur != first) {
+        --cur;
+        std::allocator_traits<Allocator>::destroy(*alloc, cur);
+      }
+      throw;
+    }
+  }
+}
+template <typename Allocator, typename StorageElement, typename Iterator>
+void CopyToStorageFromRange(Allocator* alloc, StorageElement* destination,
+                            Iterator first, Iterator last) {
+  for (StorageElement* cur = destination; first != last;
+       static_cast<void>(++cur), static_cast<void>(++first)) {
     try {
-      absl::memory_internal::DefaultConstruct(cur);
+      std::allocator_traits<Allocator>::construct(*alloc, cur, *first);
     } catch (...) {
-      using value_type = typename std::iterator_traits<ForwardIt>::value_type;
-      for (; first != cur; ++first) {
-        first->~value_type();
+      while (cur != destination) {
+        --cur;
+        std::allocator_traits<Allocator>::destroy(*alloc, cur);
       }
       throw;
     }
   }
 }
 #else   // ABSL_HAVE_EXCEPTIONS
-template <typename ForwardIt, typename Size>
-void uninitialized_default_construct_n(ForwardIt first, Size size) {
-  for (; size > 0; static_cast<void>(++first), --size) {
-    absl::memory_internal::DefaultConstruct(first);
+template <typename Allocator, typename StorageElement, typename... Args>
+void ConstructStorage(Allocator* alloc, StorageElement* first,
+                      StorageElement* last, const Args&... args) {
+  for (; first != last; ++first) {
+    std::allocator_traits<Allocator>::construct(*alloc, first, args...);
+  }
+}
+template <typename Allocator, typename StorageElement, typename Iterator>
+void CopyToStorageFromRange(Allocator* alloc, StorageElement* destination,
+                            Iterator first, Iterator last) {
+  for (; first != last;
+       static_cast<void>(++destination), static_cast<void>(++first)) {
+    std::allocator_traits<Allocator>::construct(*alloc, destination, *first);
   }
 }
 #endif  // ABSL_HAVE_EXCEPTIONS
 }  // namespace memory_internal
-
 }  // namespace absl
 
 #endif  // ABSL_MEMORY_MEMORY_H_
diff --git a/absl/memory/memory_exception_safety_test.cc b/absl/memory/memory_exception_safety_test.cc
index fb8b561d59fb..d1f6e84f10f8 100644
--- a/absl/memory/memory_exception_safety_test.cc
+++ b/absl/memory/memory_exception_safety_test.cc
@@ -48,16 +48,5 @@ TEST(MakeUnique, CheckForLeaks) {
   }));
 }
 
-TEST(MemoryInternal, UninitDefaultConstructNNonTrivial) {
-  EXPECT_TRUE(testing::MakeExceptionSafetyTester()
-                  .WithInitialValue(ThrowerList{})
-                  .WithOperation([&](ThrowerList* list_ptr) {
-                    absl::memory_internal::uninitialized_default_construct_n(
-                        list_ptr->data(), kLength);
-                  })
-                  .WithInvariants([&](...) { return true; })
-                  .Test());
-}
-
 }  // namespace
 }  // namespace absl
diff --git a/absl/memory/memory_test.cc b/absl/memory/memory_test.cc
index 8ff1945debe5..dee9b486a30d 100644
--- a/absl/memory/memory_test.cc
+++ b/absl/memory/memory_test.cc
@@ -611,47 +611,4 @@ TEST(AllocatorNoThrowTest, CustomAllocator) {
   EXPECT_FALSE(absl::allocator_is_nothrow<UnspecifiedAllocator>::value);
 }
 
-TEST(MemoryInternal, UninitDefaultConstructNTrivial) {
-  constexpr int kInitialValue = 123;
-  constexpr int kExpectedValue = kInitialValue;  // Expect no-op behavior
-  constexpr int len = 5;
-
-  struct TestObj {
-    int val;
-  };
-  static_assert(absl::is_trivially_default_constructible<TestObj>::value, "");
-  static_assert(absl::is_trivially_destructible<TestObj>::value, "");
-
-  TestObj objs[len];
-  for (auto& obj : objs) {
-    obj.val = kInitialValue;
-  }
-
-  absl::memory_internal::uninitialized_default_construct_n(objs, len);
-  for (auto& obj : objs) {
-    EXPECT_EQ(obj.val, kExpectedValue);
-  }
-}
-
-TEST(MemoryInternal, UninitDefaultConstructNNonTrivial) {
-  constexpr int kInitialValue = 123;
-  constexpr int kExpectedValue = 0;  // Expect value-construction behavior
-  constexpr int len = 5;
-
-  struct TestObj {
-    int val{kExpectedValue};
-  };
-  static_assert(absl::is_trivially_destructible<TestObj>::value, "");
-
-  TestObj objs[len];
-  for (auto& obj : objs) {
-    obj.val = kInitialValue;
-  }
-
-  absl::memory_internal::uninitialized_default_construct_n(objs, len);
-  for (auto& obj : objs) {
-    EXPECT_EQ(obj.val, kExpectedValue);
-  }
-}
-
 }  // namespace
diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h
index 8d3264f100db..457b890841a6 100644
--- a/absl/meta/type_traits.h
+++ b/absl/meta/type_traits.h
@@ -44,6 +44,7 @@
 namespace absl {
 
 namespace type_traits_internal {
+
 template <typename... Ts>
 struct VoidTImpl {
   using type = void;
@@ -61,6 +62,49 @@ struct default_alignment_of_aligned_storage<Len,
   static constexpr size_t value = Align;
 };
 
+////////////////////////////////
+// Library Fundamentals V2 TS //
+////////////////////////////////
+
+// NOTE: The `is_detected` family of templates here differ from the library
+// fundamentals specification in that for library fundamentals, `Op<Args...>` is
+// evaluated as soon as the type `is_detected<Op, Args...>` undergoes
+// substitution, regardless of whether or not the `::value` is accessed. That
+// is inconsistent with all other standard traits and prevents lazy evaluation
+// in larger contexts (such as if the `is_detected` check is a trailing argument
+// of a `conjunction`. This implementation opts to instead be lazy in the same
+// way that the standard traits are (this "defect" of the detection idiom
+// specifications has been reported).
+
+template <class Enabler, template <class...> class Op, class... Args>
+struct is_detected_impl {
+  using type = std::false_type;
+};
+
+template <template <class...> class Op, class... Args>
+struct is_detected_impl<typename VoidTImpl<Op<Args...>>::type, Op, Args...> {
+  using type = std::true_type;
+};
+
+template <template <class...> class Op, class... Args>
+struct is_detected : is_detected_impl<void, Op, Args...>::type {};
+
+template <class Enabler, class To, template <class...> class Op, class... Args>
+struct is_detected_convertible_impl {
+  using type = std::false_type;
+};
+
+template <class To, template <class...> class Op, class... Args>
+struct is_detected_convertible_impl<
+    typename std::enable_if<std::is_convertible<Op<Args...>, To>::value>::type,
+    To, Op, Args...> {
+  using type = std::true_type;
+};
+
+template <class To, template <class...> class Op, class... Args>
+struct is_detected_convertible
+    : is_detected_convertible_impl<void, To, Op, Args...>::type {};
+
 }  // namespace type_traits_internal
 
 // void_t()
diff --git a/absl/meta/type_traits_test.cc b/absl/meta/type_traits_test.cc
index 9dd95429a5a1..81b4bd323977 100644
--- a/absl/meta/type_traits_test.cc
+++ b/absl/meta/type_traits_test.cc
@@ -34,6 +34,83 @@ struct simple_pair {
 
 struct Dummy {};
 
+struct ReturnType {};
+struct ConvertibleToReturnType {
+  operator ReturnType() const;  // NOLINT
+};
+
+// Unique types used as parameter types for testing the detection idiom.
+struct StructA {};
+struct StructB {};
+struct StructC {};
+
+struct TypeWithBarFunction {
+  template <class T,
+            absl::enable_if_t<std::is_same<T&&, StructA&>::value, int> = 0>
+  ReturnType bar(T&&, const StructB&, StructC&&) &&;  // NOLINT
+};
+
+struct TypeWithBarFunctionAndConvertibleReturnType {
+  template <class T,
+            absl::enable_if_t<std::is_same<T&&, StructA&>::value, int> = 0>
+  ConvertibleToReturnType bar(T&&, const StructB&, StructC&&) &&;  // NOLINT
+};
+
+template <class Class, class... Ts>
+using BarIsCallableImpl =
+    decltype(std::declval<Class>().bar(std::declval<Ts>()...));
+
+template <class Class, class... T>
+using BarIsCallable =
+    absl::type_traits_internal::is_detected<BarIsCallableImpl, Class, T...>;
+
+template <class Class, class... T>
+using BarIsCallableConv = absl::type_traits_internal::is_detected_convertible<
+    ReturnType, BarIsCallableImpl, Class, T...>;
+
+// NOTE: Test of detail type_traits_internal::is_detected.
+TEST(IsDetectedTest, BasicUsage) {
+  EXPECT_TRUE((BarIsCallable<TypeWithBarFunction, StructA&, const StructB&,
+                             StructC>::value));
+  EXPECT_TRUE(
+      (BarIsCallable<TypeWithBarFunction, StructA&, StructB&, StructC>::value));
+  EXPECT_TRUE(
+      (BarIsCallable<TypeWithBarFunction, StructA&, StructB, StructC>::value));
+
+  EXPECT_FALSE((BarIsCallable<int, StructA&, const StructB&, StructC>::value));
+  EXPECT_FALSE((BarIsCallable<TypeWithBarFunction&, StructA&, const StructB&,
+                              StructC>::value));
+  EXPECT_FALSE((BarIsCallable<TypeWithBarFunction, StructA, const StructB&,
+                              StructC>::value));
+}
+
+// NOTE: Test of detail type_traits_internal::is_detected_convertible.
+TEST(IsDetectedConvertibleTest, BasicUsage) {
+  EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunction, StructA&, const StructB&,
+                                 StructC>::value));
+  EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunction, StructA&, StructB&,
+                                 StructC>::value));
+  EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunction, StructA&, StructB,
+                                 StructC>::value));
+  EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType,
+                                 StructA&, const StructB&, StructC>::value));
+  EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType,
+                                 StructA&, StructB&, StructC>::value));
+  EXPECT_TRUE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType,
+                                 StructA&, StructB, StructC>::value));
+
+  EXPECT_FALSE(
+      (BarIsCallableConv<int, StructA&, const StructB&, StructC>::value));
+  EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunction&, StructA&,
+                                  const StructB&, StructC>::value));
+  EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunction, StructA, const StructB&,
+                                  StructC>::value));
+  EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType&,
+                                  StructA&, const StructB&, StructC>::value));
+  EXPECT_FALSE((BarIsCallableConv<TypeWithBarFunctionAndConvertibleReturnType,
+                                  StructA, const StructB&, StructC>::value));
+}
+
 TEST(VoidTTest, BasicUsage) {
   StaticAssertTypeEq<void, absl::void_t<Dummy>>();
   StaticAssertTypeEq<void, absl::void_t<Dummy, Dummy, Dummy>>();
@@ -718,8 +795,8 @@ TEST(TypeTraitsTest, TestDecay) {
   ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int[][1]);
 
   ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int());
-  ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(float));
-  ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(char, ...));
+  ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(float));  // NOLINT
+  ABSL_INTERNAL_EXPECT_ALIAS_EQUIVALENCE(decay, int(char, ...));  // NOLINT
 }
 
 struct TypeA {};
diff --git a/absl/strings/numbers_test.cc b/absl/strings/numbers_test.cc
index 24e7138cfae2..8ebb090e76a6 100644
--- a/absl/strings/numbers_test.cc
+++ b/absl/strings/numbers_test.cc
@@ -56,16 +56,11 @@ using testing::Eq;
 using testing::MatchesRegex;
 
 // Number of floats to test with.
-// 10,000,000 is a reasonable default for a test that only takes a few seconds.
+// 5,000,000 is a reasonable default for a test that only takes a few seconds.
 // 1,000,000,000+ triggers checking for all possible mantissa values for
 // double-precision tests. 2,000,000,000+ triggers checking for every possible
 // single-precision float.
-#ifdef _MSC_VER
-// Use a smaller number on MSVC to avoid test time out (1 min)
 const int kFloatNumCases = 5000000;
-#else
-const int kFloatNumCases = 10000000;
-#endif
 
 // This is a slow, brute-force routine to compute the exact base-10
 // representation of a double-precision floating-point number.  It
diff --git a/absl/time/duration.cc b/absl/time/duration.cc
index c13fa79b7fa3..f402137b0a65 100644
--- a/absl/time/duration.cc
+++ b/absl/time/duration.cc
@@ -895,13 +895,10 @@ bool ParseDuration(const std::string& dur_string, Duration* d) {
   *d = dur;
   return true;
 }
-
 bool ParseFlag(const std::string& text, Duration* dst, std::string* ) {
   return ParseDuration(text, dst);
 }
 
-std::string UnparseFlag(Duration d) {
-  return FormatDuration(d);
-}
+std::string UnparseFlag(Duration d) { return FormatDuration(d); }
 
 }  // namespace absl
diff --git a/absl/time/duration_benchmark.cc b/absl/time/duration_benchmark.cc
index 54f89a1f000d..d5657bd576a5 100644
--- a/absl/time/duration_benchmark.cc
+++ b/absl/time/duration_benchmark.cc
@@ -27,47 +27,113 @@ namespace {
 //
 
 void BM_Duration_Factory_Nanoseconds(benchmark::State& state) {
+  int64_t i = 0;
   while (state.KeepRunning()) {
-    benchmark::DoNotOptimize(absl::Nanoseconds(1));
+    benchmark::DoNotOptimize(absl::Nanoseconds(i));
+    i += 314159;
   }
 }
 BENCHMARK(BM_Duration_Factory_Nanoseconds);
 
 void BM_Duration_Factory_Microseconds(benchmark::State& state) {
+  int64_t i = 0;
   while (state.KeepRunning()) {
-    benchmark::DoNotOptimize(absl::Microseconds(1));
+    benchmark::DoNotOptimize(absl::Microseconds(i));
+    i += 314;
   }
 }
 BENCHMARK(BM_Duration_Factory_Microseconds);
 
 void BM_Duration_Factory_Milliseconds(benchmark::State& state) {
+  int64_t i = 0;
   while (state.KeepRunning()) {
-    benchmark::DoNotOptimize(absl::Milliseconds(1));
+    benchmark::DoNotOptimize(absl::Milliseconds(i));
+    i += 1;
   }
 }
 BENCHMARK(BM_Duration_Factory_Milliseconds);
 
 void BM_Duration_Factory_Seconds(benchmark::State& state) {
+  int64_t i = 0;
   while (state.KeepRunning()) {
-    benchmark::DoNotOptimize(absl::Seconds(1));
+    benchmark::DoNotOptimize(absl::Seconds(i));
+    i += 1;
   }
 }
 BENCHMARK(BM_Duration_Factory_Seconds);
 
 void BM_Duration_Factory_Minutes(benchmark::State& state) {
+  int64_t i = 0;
   while (state.KeepRunning()) {
-    benchmark::DoNotOptimize(absl::Minutes(1));
+    benchmark::DoNotOptimize(absl::Minutes(i));
+    i += 1;
   }
 }
 BENCHMARK(BM_Duration_Factory_Minutes);
 
 void BM_Duration_Factory_Hours(benchmark::State& state) {
+  int64_t i = 0;
   while (state.KeepRunning()) {
-    benchmark::DoNotOptimize(absl::Hours(1));
+    benchmark::DoNotOptimize(absl::Hours(i));
+    i += 1;
   }
 }
 BENCHMARK(BM_Duration_Factory_Hours);
 
+void BM_Duration_Factory_DoubleNanoseconds(benchmark::State& state) {
+  double d = 1;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(absl::Nanoseconds(d));
+    d = d * 1.00000001 + 1;
+  }
+}
+BENCHMARK(BM_Duration_Factory_DoubleNanoseconds);
+
+void BM_Duration_Factory_DoubleMicroseconds(benchmark::State& state) {
+  double d = 1e-3;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(absl::Microseconds(d));
+    d = d * 1.00000001 + 1e-3;
+  }
+}
+BENCHMARK(BM_Duration_Factory_DoubleMicroseconds);
+
+void BM_Duration_Factory_DoubleMilliseconds(benchmark::State& state) {
+  double d = 1e-6;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(absl::Milliseconds(d));
+    d = d * 1.00000001 + 1e-6;
+  }
+}
+BENCHMARK(BM_Duration_Factory_DoubleMilliseconds);
+
+void BM_Duration_Factory_DoubleSeconds(benchmark::State& state) {
+  double d = 1e-9;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(absl::Seconds(d));
+    d = d * 1.00000001 + 1e-9;
+  }
+}
+BENCHMARK(BM_Duration_Factory_DoubleSeconds);
+
+void BM_Duration_Factory_DoubleMinutes(benchmark::State& state) {
+  double d = 1e-9;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(absl::Minutes(d));
+    d = d * 1.00000001 + 1e-9;
+  }
+}
+BENCHMARK(BM_Duration_Factory_DoubleMinutes);
+
+void BM_Duration_Factory_DoubleHours(benchmark::State& state) {
+  double d = 1e-9;
+  while (state.KeepRunning()) {
+    benchmark::DoNotOptimize(absl::Hours(d));
+    d = d * 1.00000001 + 1e-9;
+  }
+}
+BENCHMARK(BM_Duration_Factory_DoubleHours);
+
 //
 // Arithmetic
 //
diff --git a/absl/time/duration_test.cc b/absl/time/duration_test.cc
index 704684edb34e..7ae25dc68f9a 100644
--- a/absl/time/duration_test.cc
+++ b/absl/time/duration_test.cc
@@ -16,7 +16,9 @@
 #include <cmath>
 #include <cstdint>
 #include <ctime>
+#include <iomanip>
 #include <limits>
+#include <random>
 #include <string>
 
 #include "gmock/gmock.h"
@@ -105,22 +107,22 @@ TEST(Duration, Factories) {
 }
 
 TEST(Duration, ToConversion) {
-#define TEST_DURATION_CONVERSION(UNIT)                              \
-  do {                                                              \
-    const absl::Duration d = absl::UNIT(1.5);                       \
-    const absl::Duration z = absl::ZeroDuration();                  \
-    const absl::Duration inf = absl::InfiniteDuration();            \
-    const double dbl_inf = std::numeric_limits<double>::infinity(); \
-    EXPECT_EQ(kint64min, absl::ToInt64##UNIT(-inf));                \
-    EXPECT_EQ(-1, absl::ToInt64##UNIT(-d));                         \
-    EXPECT_EQ(0, absl::ToInt64##UNIT(z));                           \
-    EXPECT_EQ(1, absl::ToInt64##UNIT(d));                           \
-    EXPECT_EQ(kint64max, absl::ToInt64##UNIT(inf));                 \
-    EXPECT_EQ(-dbl_inf, absl::ToDouble##UNIT(-inf));                \
-    EXPECT_EQ(-1.5, absl::ToDouble##UNIT(-d));                      \
-    EXPECT_EQ(0, absl::ToDouble##UNIT(z));                          \
-    EXPECT_EQ(1.5, absl::ToDouble##UNIT(d));                        \
-    EXPECT_EQ(dbl_inf, absl::ToDouble##UNIT(inf));                  \
+#define TEST_DURATION_CONVERSION(UNIT)                                  \
+  do {                                                                  \
+    const absl::Duration d = absl::UNIT(1.5);                           \
+    constexpr absl::Duration z = absl::ZeroDuration();                  \
+    constexpr absl::Duration inf = absl::InfiniteDuration();            \
+    constexpr double dbl_inf = std::numeric_limits<double>::infinity(); \
+    EXPECT_EQ(kint64min, absl::ToInt64##UNIT(-inf));                    \
+    EXPECT_EQ(-1, absl::ToInt64##UNIT(-d));                             \
+    EXPECT_EQ(0, absl::ToInt64##UNIT(z));                               \
+    EXPECT_EQ(1, absl::ToInt64##UNIT(d));                               \
+    EXPECT_EQ(kint64max, absl::ToInt64##UNIT(inf));                     \
+    EXPECT_EQ(-dbl_inf, absl::ToDouble##UNIT(-inf));                    \
+    EXPECT_EQ(-1.5, absl::ToDouble##UNIT(-d));                          \
+    EXPECT_EQ(0, absl::ToDouble##UNIT(z));                              \
+    EXPECT_EQ(1.5, absl::ToDouble##UNIT(d));                            \
+    EXPECT_EQ(dbl_inf, absl::ToDouble##UNIT(inf));                      \
   } while (0)
 
   TEST_DURATION_CONVERSION(Nanoseconds);
@@ -1284,6 +1286,16 @@ TEST(Duration, SmallConversions) {
   EXPECT_EQ(absl::Nanoseconds(1), absl::Seconds(0.875e-9));
   EXPECT_EQ(absl::Nanoseconds(1), absl::Seconds(1.000e-9));
 
+  EXPECT_EQ(absl::ZeroDuration(), absl::Seconds(-0.124999999e-9));
+  EXPECT_EQ(-absl::Nanoseconds(1) / 4, absl::Seconds(-0.125e-9));
+  EXPECT_EQ(-absl::Nanoseconds(1) / 4, absl::Seconds(-0.250e-9));
+  EXPECT_EQ(-absl::Nanoseconds(1) / 2, absl::Seconds(-0.375e-9));
+  EXPECT_EQ(-absl::Nanoseconds(1) / 2, absl::Seconds(-0.500e-9));
+  EXPECT_EQ(-absl::Nanoseconds(3) / 4, absl::Seconds(-0.625e-9));
+  EXPECT_EQ(-absl::Nanoseconds(3) / 4, absl::Seconds(-0.750e-9));
+  EXPECT_EQ(-absl::Nanoseconds(1), absl::Seconds(-0.875e-9));
+  EXPECT_EQ(-absl::Nanoseconds(1), absl::Seconds(-1.000e-9));
+
   timespec ts;
   ts.tv_sec = 0;
   ts.tv_nsec = 0;
@@ -1313,6 +1325,86 @@ TEST(Duration, SmallConversions) {
   EXPECT_THAT(ToTimeval(absl::Nanoseconds(2000)), TimevalMatcher(tv));
 }
 
+void VerifySameAsMul(double time_as_seconds, int* const misses) {
+  auto direct_seconds = absl::Seconds(time_as_seconds);
+  auto mul_by_one_second = time_as_seconds * absl::Seconds(1);
+  if (direct_seconds != mul_by_one_second) {
+    if (*misses > 10) return;
+    ASSERT_LE(++(*misses), 10) << "Too many errors, not reporting more.";
+    EXPECT_EQ(direct_seconds, mul_by_one_second)
+        << "given double time_as_seconds = " << std::setprecision(17)
+        << time_as_seconds;
+  }
+}
+
+// For a variety of interesting durations, we find the exact point
+// where one double converts to that duration, and the very next double
+// converts to the next duration.  For both of those points, verify that
+// Seconds(point) returns the same duration as point * Seconds(1.0)
+TEST(Duration, ToDoubleSecondsCheckEdgeCases) {
+  constexpr uint32_t kTicksPerSecond = absl::time_internal::kTicksPerSecond;
+  constexpr auto duration_tick = absl::time_internal::MakeDuration(0, 1u);
+  int misses = 0;
+  for (int64_t seconds = 0; seconds < 99; ++seconds) {
+    uint32_t tick_vals[] = {0, +999, +999999, +999999999, kTicksPerSecond - 1,
+                            0, 1000, 1000000, 1000000000, kTicksPerSecond,
+                            1, 1001, 1000001, 1000000001, kTicksPerSecond + 1,
+                            2, 1002, 1000002, 1000000002, kTicksPerSecond + 2,
+                            3, 1003, 1000003, 1000000003, kTicksPerSecond + 3,
+                            4, 1004, 1000004, 1000000004, kTicksPerSecond + 4,
+                            5, 6,    7,       8,          9};
+    for (uint32_t ticks : tick_vals) {
+      absl::Duration s_plus_t = absl::Seconds(seconds) + ticks * duration_tick;
+      for (absl::Duration d : {s_plus_t, -s_plus_t}) {
+        absl::Duration after_d = d + duration_tick;
+        EXPECT_NE(d, after_d);
+        EXPECT_EQ(after_d - d, duration_tick);
+
+        double low_edge = ToDoubleSeconds(d);
+        EXPECT_EQ(d, absl::Seconds(low_edge));
+
+        double high_edge = ToDoubleSeconds(after_d);
+        EXPECT_EQ(after_d, absl::Seconds(high_edge));
+
+        for (;;) {
+          double midpoint = low_edge + (high_edge - low_edge) / 2;
+          if (midpoint == low_edge || midpoint == high_edge) break;
+          absl::Duration mid_duration = absl::Seconds(midpoint);
+          if (mid_duration == d) {
+            low_edge = midpoint;
+          } else {
+            EXPECT_EQ(mid_duration, after_d);
+            high_edge = midpoint;
+          }
+        }
+        // Now low_edge is the highest double that converts to Duration d,
+        // and high_edge is the lowest double that converts to Duration after_d.
+        VerifySameAsMul(low_edge, &misses);
+        VerifySameAsMul(high_edge, &misses);
+      }
+    }
+  }
+}
+
+TEST(Duration, ToDoubleSecondsCheckRandom) {
+  std::random_device rd;
+  std::seed_seq seed({rd(), rd(), rd(), rd(), rd(), rd(), rd(), rd()});
+  std::mt19937_64 gen(seed);
+  // We want doubles distributed from 1/8ns up to 2^63, where
+  // as many values are tested from 1ns to 2ns as from 1sec to 2sec,
+  // so even distribute along a log-scale of those values, and
+  // exponentiate before using them.  (9.223377e+18 is just slightly
+  // out of bounds for absl::Duration.)
+  std::uniform_real_distribution<double> uniform(std::log(0.125e-9),
+                                                 std::log(9.223377e+18));
+  int misses = 0;
+  for (int i = 0; i < 1000000; ++i) {
+    double d = std::exp(uniform(gen));
+    VerifySameAsMul(d, &misses);
+    VerifySameAsMul(-d, &misses);
+  }
+}
+
 TEST(Duration, ConversionSaturation) {
   absl::Duration d;
 
diff --git a/absl/time/time.h b/absl/time/time.h
index 880fc783ae4a..c41cb89c5eff 100644
--- a/absl/time/time.h
+++ b/absl/time/time.h
@@ -81,6 +81,7 @@ constexpr int64_t GetRepHi(Duration d);
 constexpr uint32_t GetRepLo(Duration d);
 constexpr Duration MakeDuration(int64_t hi, uint32_t lo);
 constexpr Duration MakeDuration(int64_t hi, int64_t lo);
+inline Duration MakePosDoubleDuration(double n);
 constexpr int64_t kTicksPerNanosecond = 4;
 constexpr int64_t kTicksPerSecond = 1000 * 1000 * 1000 * kTicksPerNanosecond;
 template <std::intmax_t N>
@@ -295,6 +296,39 @@ Duration Floor(Duration d, Duration unit);
 //   absl::Duration c = absl::Ceil(d, absl::Microseconds(1));   // 123457us
 Duration Ceil(Duration d, Duration unit);
 
+// InfiniteDuration()
+//
+// Returns an infinite `Duration`.  To get a `Duration` representing negative
+// infinity, use `-InfiniteDuration()`.
+//
+// Duration arithmetic overflows to +/- infinity and saturates. In general,
+// arithmetic with `Duration` infinities is similar to IEEE 754 infinities
+// except where IEEE 754 NaN would be involved, in which case +/-
+// `InfiniteDuration()` is used in place of a "nan" Duration.
+//
+// Examples:
+//
+//   constexpr absl::Duration inf = absl::InfiniteDuration();
+//   const absl::Duration d = ... any finite duration ...
+//
+//   inf == inf + inf
+//   inf == inf + d
+//   inf == inf - inf
+//   -inf == d - inf
+//
+//   inf == d * 1e100
+//   inf == inf / 2
+//   0 == d / inf
+//   INT64_MAX == inf / d
+//
+//   // Division by zero returns infinity, or INT64_MIN/MAX where appropriate.
+//   inf == d / 0
+//   INT64_MAX == d / absl::ZeroDuration()
+//
+// The examples involving the `/` operator above also apply to `IDivDuration()`
+// and `FDivDuration()`.
+constexpr Duration InfiniteDuration();
+
 // Nanoseconds()
 // Microseconds()
 // Milliseconds()
@@ -344,7 +378,13 @@ Duration Milliseconds(T n) {
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
 Duration Seconds(T n) {
-  return n * Seconds(1);
+  if (n >= 0) {
+    if (n >= std::numeric_limits<int64_t>::max()) return InfiniteDuration();
+    return time_internal::MakePosDoubleDuration(n);
+  } else {
+    if (n <= std::numeric_limits<int64_t>::min()) return -InfiniteDuration();
+    return -time_internal::MakePosDoubleDuration(-n);
+  }
 }
 template <typename T, time_internal::EnableIfFloat<T> = 0>
 Duration Minutes(T n) {
@@ -439,39 +479,6 @@ std::chrono::seconds ToChronoSeconds(Duration d);
 std::chrono::minutes ToChronoMinutes(Duration d);
 std::chrono::hours ToChronoHours(Duration d);
 
-// InfiniteDuration()
-//
-// Returns an infinite `Duration`.  To get a `Duration` representing negative
-// infinity, use `-InfiniteDuration()`.
-//
-// Duration arithmetic overflows to +/- infinity and saturates. In general,
-// arithmetic with `Duration` infinities is similar to IEEE 754 infinities
-// except where IEEE 754 NaN would be involved, in which case +/-
-// `InfiniteDuration()` is used in place of a "nan" Duration.
-//
-// Examples:
-//
-//   constexpr absl::Duration inf = absl::InfiniteDuration();
-//   const absl::Duration d = ... any finite duration ...
-//
-//   inf == inf + inf
-//   inf == inf + d
-//   inf == inf - inf
-//   -inf == d - inf
-//
-//   inf == d * 1e100
-//   inf == inf / 2
-//   0 == d / inf
-//   INT64_MAX == inf / d
-//
-//   // Division by zero returns infinity, or INT64_MIN/MAX where appropriate.
-//   inf == d / 0
-//   INT64_MAX == d / absl::ZeroDuration()
-//
-// The examples involving the `/` operator above also apply to `IDivDuration()`
-// and `FDivDuration()`.
-constexpr Duration InfiniteDuration();
-
 // FormatDuration()
 //
 // Returns a std::string representing the duration in the form "72h3m0.5s".
@@ -492,12 +499,9 @@ inline std::ostream& operator<<(std::ostream& os, Duration d) {
 // `ZeroDuration()`.  Parses "inf" and "-inf" as +/- `InfiniteDuration()`.
 bool ParseDuration(const std::string& dur_string, Duration* d);
 
-// ParseFlag()
-//
+// Support for flag values of type Duration. Duration flags must be specified
+// in a format that is valid input for absl::ParseDuration().
 bool ParseFlag(const std::string& text, Duration* dst, std::string* error);
-
-// UnparseFlag()
-//
 std::string UnparseFlag(Duration d);
 
 // Time
@@ -991,9 +995,6 @@ bool ParseTime(const std::string& format, const std::string& input, Time* time,
 bool ParseTime(const std::string& format, const std::string& input, TimeZone tz,
                Time* time, std::string* err);
 
-// ParseFlag()
-// UnparseFlag()
-//
 // Support for flag values of type Time. Time flags must be specified in a
 // format that matches absl::RFC3339_full. For example:
 //
@@ -1114,6 +1115,18 @@ constexpr Duration MakeDuration(int64_t hi, int64_t lo) {
   return MakeDuration(hi, static_cast<uint32_t>(lo));
 }
 
+// Make a Duration value from a floating-point number, as long as that number
+// is in the range [ 0 .. numeric_limits<int64_t>::max ), that is, as long as
+// it's positive and can be converted to int64_t without risk of UB.
+inline Duration MakePosDoubleDuration(double n) {
+  const int64_t int_secs = static_cast<int64_t>(n);
+  const uint32_t ticks =
+      static_cast<uint32_t>((n - int_secs) * kTicksPerSecond + 0.5);
+  return ticks < kTicksPerSecond
+             ? MakeDuration(int_secs, ticks)
+             : MakeDuration(int_secs + 1, ticks - kTicksPerSecond);
+}
+
 // Creates a normalized Duration from an almost-normalized (sec,ticks)
 // pair. sec may be positive or negative.  ticks must be in the range
 // -kTicksPerSecond < *ticks < kTicksPerSecond.  If ticks is negative it
diff --git a/absl/types/internal/variant.h b/absl/types/internal/variant.h
index 7db5e0535f68..7708e67cb14f 100644
--- a/absl/types/internal/variant.h
+++ b/absl/types/internal/variant.h
@@ -1062,32 +1062,6 @@ struct OverloadSet<> {
   static void Overload(...);
 };
 
-////////////////////////////////
-// Library Fundamentals V2 TS //
-////////////////////////////////
-
-// TODO(calabrese): Consider moving this to absl/meta/type_traits.h
-
-// The following is a rough implementation of parts of the detection idiom.
-// It is used for the comparison operator checks.
-
-template <class Enabler, class To, template <class...> class Op, class... Args>
-struct is_detected_convertible_impl {
-  using type = std::false_type;
-};
-
-template <class To, template <class...> class Op, class... Args>
-struct is_detected_convertible_impl<
-    absl::enable_if_t<std::is_convertible<Op<Args...>, To>::value>, To, Op,
-    Args...> {
-  using type = std::true_type;
-};
-
-// NOTE: This differs from library fundamentals by being lazy.
-template <class To, template <class...> class Op, class... Args>
-struct is_detected_convertible
-    : is_detected_convertible_impl<void, To, Op, Args...>::type {};
-
 template <class T>
 using LessThanResult = decltype(std::declval<T>() < std::declval<T>());
 
@@ -1107,6 +1081,8 @@ using EqualResult = decltype(std::declval<T>() == std::declval<T>());
 template <class T>
 using NotEqualResult = decltype(std::declval<T>() != std::declval<T>());
 
+using type_traits_internal::is_detected_convertible;
+
 template <class... T>
 using RequireAllHaveEqualT = absl::enable_if_t<
     absl::conjunction<is_detected_convertible<bool, EqualResult, T>...>::value,
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