Update contrib/restricted/abseil-cpp to 20220623.0

12 files changed, 739 insertions, 358 deletions

diff --git a/contrib/restricted/abseil-cpp/absl/container/fixed_array.h b/contrib/restricted/abseil-cpp/absl/container/fixed_array.h
index 839ba0bc16..2aefae3bde 100644
--- a/contrib/restricted/abseil-cpp/absl/container/fixed_array.h
+++ b/contrib/restricted/abseil-cpp/absl/container/fixed_array.h
@@ -489,12 +489,14 @@ class FixedArray {
   Storage storage_;
 };
 
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 template <typename T, size_t N, typename A>
 constexpr size_t FixedArray<T, N, A>::kInlineBytesDefault;
 
 template <typename T, size_t N, typename A>
 constexpr typename FixedArray<T, N, A>::size_type
     FixedArray<T, N, A>::inline_elements;
+#endif
 
 template <typename T, size_t N, typename A>
 void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateConstruct(
diff --git a/contrib/restricted/abseil-cpp/absl/container/flat_hash_map.h b/contrib/restricted/abseil-cpp/absl/container/flat_hash_map.h
index 74def0df0e..e6bdbd9e4f 100644
--- a/contrib/restricted/abseil-cpp/absl/container/flat_hash_map.h
+++ b/contrib/restricted/abseil-cpp/absl/container/flat_hash_map.h
@@ -36,6 +36,7 @@
 #include <utility>
 
 #include "absl/algorithm/container.h"
+#include "absl/base/macros.h"
 #include "absl/container/internal/container_memory.h"
 #include "absl/container/internal/hash_function_defaults.h"  // IWYU pragma: export
 #include "absl/container/internal/raw_hash_map.h"  // IWYU pragma: export
@@ -75,6 +76,10 @@ struct FlatHashMapPolicy;
 // absl/hash/hash.h for information on extending Abseil hashing to user-defined
 // types.
 //
+// Using `absl::flat_hash_map` at interface boundaries in dynamically loaded
+// libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
+// be randomized across dynamically loaded libraries.
+//
 // NOTE: A `flat_hash_map` stores its value types directly inside its
 // implementation array to avoid memory indirection. Because a `flat_hash_map`
 // is designed to move data when rehashed, map values will not retain pointer
@@ -356,8 +361,8 @@ class flat_hash_map : public absl::container_internal::raw_hash_map<
   // `flat_hash_map`.
   //
   //   iterator try_emplace(const_iterator hint,
-  //                        const init_type& k, Args&&... args):
-  //   iterator try_emplace(const_iterator hint, init_type&& k, Args&&... args):
+  //                        const key_type& k, Args&&... args):
+  //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):
   //
   // Inserts (via copy or move) the element of the specified key into the
   // `flat_hash_map` using the position of `hint` as a non-binding suggestion
@@ -541,10 +546,12 @@ class flat_hash_map : public absl::container_internal::raw_hash_map<
 // erase_if(flat_hash_map<>, Pred)
 //
 // Erases all elements that satisfy the predicate `pred` from the container `c`.
+// Returns the number of erased elements.
 template <typename K, typename V, typename H, typename E, typename A,
           typename Predicate>
-void erase_if(flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
-  container_internal::EraseIf(pred, &c);
+typename flat_hash_map<K, V, H, E, A>::size_type erase_if(
+    flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
+  return container_internal::EraseIf(pred, &c);
 }
 
 namespace container_internal {
diff --git a/contrib/restricted/abseil-cpp/absl/container/flat_hash_set.h b/contrib/restricted/abseil-cpp/absl/container/flat_hash_set.h
index 6b89da6571..4938c703b7 100644
--- a/contrib/restricted/abseil-cpp/absl/container/flat_hash_set.h
+++ b/contrib/restricted/abseil-cpp/absl/container/flat_hash_set.h
@@ -67,11 +67,15 @@ struct FlatHashSetPolicy;
 //
 // By default, `flat_hash_set` uses the `absl::Hash` hashing framework. All
 // fundamental and Abseil types that support the `absl::Hash` framework have a
-// compatible equality operator for comparing insertions into `flat_hash_map`.
+// compatible equality operator for comparing insertions into `flat_hash_set`.
 // If your type is not yet supported by the `absl::Hash` framework, see
 // absl/hash/hash.h for information on extending Abseil hashing to user-defined
 // types.
 //
+// Using `absl::flat_hash_set` at interface boundaries in dynamically loaded
+// libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
+// be randomized across dynamically loaded libraries.
+//
 // NOTE: A `flat_hash_set` stores its keys directly inside its implementation
 // array to avoid memory indirection. Because a `flat_hash_set` is designed to
 // move data when rehashed, set keys will not retain pointer stability. If you
@@ -106,7 +110,7 @@ class flat_hash_set
  public:
   // Constructors and Assignment Operators
   //
-  // A flat_hash_set supports the same overload set as `std::unordered_map`
+  // A flat_hash_set supports the same overload set as `std::unordered_set`
   // for construction and assignment:
   //
   // *  Default constructor
@@ -173,7 +177,7 @@ class flat_hash_set
   // available within the `flat_hash_set`.
   //
   // NOTE: this member function is particular to `absl::flat_hash_set` and is
-  // not provided in the `std::unordered_map` API.
+  // not provided in the `std::unordered_set` API.
   using Base::capacity;
 
   // flat_hash_set::empty()
@@ -332,7 +336,7 @@ class flat_hash_set
   // flat_hash_set::swap(flat_hash_set& other)
   //
   // Exchanges the contents of this `flat_hash_set` with those of the `other`
-  // flat hash map, avoiding invocation of any move, copy, or swap operations on
+  // flat hash set, avoiding invocation of any move, copy, or swap operations on
   // individual elements.
   //
   // All iterators and references on the `flat_hash_set` remain valid, excepting
@@ -340,7 +344,7 @@ class flat_hash_set
   //
   // `swap()` requires that the flat hash set's hashing and key equivalence
   // functions be Swappable, and are exchaged using unqualified calls to
-  // non-member `swap()`. If the map's allocator has
+  // non-member `swap()`. If the set's allocator has
   // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
   // set to `true`, the allocators are also exchanged using an unqualified call
   // to non-member `swap()`; otherwise, the allocators are not swapped.
@@ -395,14 +399,14 @@ class flat_hash_set
   // flat_hash_set::bucket_count()
   //
   // Returns the number of "buckets" within the `flat_hash_set`. Note that
-  // because a flat hash map contains all elements within its internal storage,
+  // because a flat hash set contains all elements within its internal storage,
   // this value simply equals the current capacity of the `flat_hash_set`.
   using Base::bucket_count;
 
   // flat_hash_set::load_factor()
   //
   // Returns the current load factor of the `flat_hash_set` (the average number
-  // of slots occupied with a value within the hash map).
+  // of slots occupied with a value within the hash set).
   using Base::load_factor;
 
   // flat_hash_set::max_load_factor()
@@ -443,9 +447,11 @@ class flat_hash_set
 // erase_if(flat_hash_set<>, Pred)
 //
 // Erases all elements that satisfy the predicate `pred` from the container `c`.
+// Returns the number of erased elements.
 template <typename T, typename H, typename E, typename A, typename Predicate>
-void erase_if(flat_hash_set<T, H, E, A>& c, Predicate pred) {
-  container_internal::EraseIf(pred, &c);
+typename flat_hash_set<T, H, E, A>::size_type erase_if(
+    flat_hash_set<T, H, E, A>& c, Predicate pred) {
+  return container_internal::EraseIf(pred, &c);
 }
 
 namespace container_internal {
diff --git a/contrib/restricted/abseil-cpp/absl/container/inlined_vector.h b/contrib/restricted/abseil-cpp/absl/container/inlined_vector.h
index df9e09917d..bc1c4a776c 100644
--- a/contrib/restricted/abseil-cpp/absl/container/inlined_vector.h
+++ b/contrib/restricted/abseil-cpp/absl/container/inlined_vector.h
@@ -36,7 +36,6 @@
 #define ABSL_CONTAINER_INLINED_VECTOR_H_
 
 #include <algorithm>
-#include <cassert>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
@@ -152,7 +151,7 @@ class InlinedVector {
                 const allocator_type& allocator = allocator_type())
       : storage_(allocator) {
     storage_.Initialize(IteratorValueAdapter<A, ForwardIterator>(first),
-                        std::distance(first, last));
+                        static_cast<size_t>(std::distance(first, last)));
   }
 
   // Creates an inlined vector with elements constructed from the provided input
@@ -233,8 +232,8 @@ class InlinedVector {
   // specified allocator is also `noexcept`.
   InlinedVector(
       InlinedVector&& other,
-      const allocator_type& allocator)
-      noexcept(absl::allocator_is_nothrow<allocator_type>::value)
+      const allocator_type&
+          allocator) noexcept(absl::allocator_is_nothrow<allocator_type>::value)
       : storage_(allocator) {
     if (IsMemcpyOk<A>::value) {
       storage_.MemcpyFrom(other.storage_);
@@ -486,8 +485,8 @@ class InlinedVector {
   InlinedVector& operator=(InlinedVector&& other) {
     if (ABSL_PREDICT_TRUE(this != std::addressof(other))) {
       if (IsMemcpyOk<A>::value || other.storage_.GetIsAllocated()) {
-        inlined_vector_internal::DestroyElements<A>(storage_.GetAllocator(),
-                                                    data(), size());
+        inlined_vector_internal::DestroyAdapter<A>::DestroyElements(
+            storage_.GetAllocator(), data(), size());
         storage_.DeallocateIfAllocated();
         storage_.MemcpyFrom(other.storage_);
 
@@ -523,7 +522,7 @@ class InlinedVector {
             EnableIfAtLeastForwardIterator<ForwardIterator> = 0>
   void assign(ForwardIterator first, ForwardIterator last) {
     storage_.Assign(IteratorValueAdapter<A, ForwardIterator>(first),
-                    std::distance(first, last));
+                    static_cast<size_t>(std::distance(first, last)));
   }
 
   // Overload of `InlinedVector::assign(...)` to replace the contents of the
@@ -586,8 +585,20 @@ class InlinedVector {
 
     if (ABSL_PREDICT_TRUE(n != 0)) {
       value_type dealias = v;
+      // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102329#c2
+      // It appears that GCC thinks that since `pos` is a const pointer and may
+      // point to uninitialized memory at this point, a warning should be
+      // issued. But `pos` is actually only used to compute an array index to
+      // write to.
+#if !defined(__clang__) && defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
       return storage_.Insert(pos, CopyValueAdapter<A>(std::addressof(dealias)),
                              n);
+#if !defined(__clang__) && defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
     } else {
       return const_cast<iterator>(pos);
     }
@@ -721,8 +732,8 @@ class InlinedVector {
   // Destroys all elements in the inlined vector, setting the size to `0` and
   // deallocating any held memory.
   void clear() noexcept {
-    inlined_vector_internal::DestroyElements<A>(storage_.GetAllocator(), data(),
-                                                size());
+    inlined_vector_internal::DestroyAdapter<A>::DestroyElements(
+        storage_.GetAllocator(), data(), size());
     storage_.DeallocateIfAllocated();
 
     storage_.SetInlinedSize(0);
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/common.h b/contrib/restricted/abseil-cpp/absl/container/internal/common.h
index 030e9d4ab0..416d9aa32e 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/common.h
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/common.h
@@ -84,10 +84,11 @@ class node_handle_base {
     PolicyTraits::transfer(alloc(), slot(), s);
   }
 
-  struct move_tag_t {};
-  node_handle_base(move_tag_t, const allocator_type& a, slot_type* s)
+  struct construct_tag_t {};
+  template <typename... Args>
+  node_handle_base(construct_tag_t, const allocator_type& a, Args&&... args)
       : alloc_(a) {
-    PolicyTraits::construct(alloc(), slot(), s);
+    PolicyTraits::construct(alloc(), slot(), std::forward<Args>(args)...);
   }
 
   void destroy() {
@@ -186,8 +187,8 @@ struct CommonAccess {
   }
 
   template <typename T, typename... Args>
-  static T Move(Args&&... args) {
-    return T(typename T::move_tag_t{}, std::forward<Args>(args)...);
+  static T Construct(Args&&... args) {
+    return T(typename T::construct_tag_t{}, std::forward<Args>(args)...);
   }
 };
 
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/container_memory.h b/contrib/restricted/abseil-cpp/absl/container/internal/container_memory.h
index e67529ecb6..00e9f6d703 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/container_memory.h
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/container_memory.h
@@ -174,7 +174,7 @@ decltype(std::declval<F>()(std::declval<T>())) WithConstructed(
 //
 // 2. auto a = PairArgs(args...);
 //    std::pair<F, S> p(std::piecewise_construct,
-//                      std::move(p.first), std::move(p.second));
+//                      std::move(a.first), std::move(a.second));
 inline std::pair<std::tuple<>, std::tuple<>> PairArgs() { return {}; }
 template <class F, class S>
 std::pair<std::tuple<F&&>, std::tuple<S&&>> PairArgs(F&& f, S&& s) {
@@ -402,6 +402,15 @@ struct map_slot_policy {
     }
   }
 
+  // Construct this slot by copying from another slot.
+  template <class Allocator>
+  static void construct(Allocator* alloc, slot_type* slot,
+                        const slot_type* other) {
+    emplace(slot);
+    absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
+                                                 other->value);
+  }
+
   template <class Allocator>
   static void destroy(Allocator* alloc, slot_type* slot) {
     if (kMutableKeys::value) {
@@ -424,33 +433,6 @@ struct map_slot_policy {
     }
     destroy(alloc, old_slot);
   }
-
-  template <class Allocator>
-  static void swap(Allocator* alloc, slot_type* a, slot_type* b) {
-    if (kMutableKeys::value) {
-      using std::swap;
-      swap(a->mutable_value, b->mutable_value);
-    } else {
-      value_type tmp = std::move(a->value);
-      absl::allocator_traits<Allocator>::destroy(*alloc, &a->value);
-      absl::allocator_traits<Allocator>::construct(*alloc, &a->value,
-                                                   std::move(b->value));
-      absl::allocator_traits<Allocator>::destroy(*alloc, &b->value);
-      absl::allocator_traits<Allocator>::construct(*alloc, &b->value,
-                                                   std::move(tmp));
-    }
-  }
-
-  template <class Allocator>
-  static void move(Allocator* alloc, slot_type* src, slot_type* dest) {
-    if (kMutableKeys::value) {
-      dest->mutable_value = std::move(src->mutable_value);
-    } else {
-      absl::allocator_traits<Allocator>::destroy(*alloc, &dest->value);
-      absl::allocator_traits<Allocator>::construct(*alloc, &dest->value,
-                                                   std::move(src->value));
-    }
-  }
 };
 
 }  // namespace container_internal
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.cc b/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.cc
index 40cce0479e..efc1be5866 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.cc
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.cc
@@ -21,33 +21,43 @@
 #include <limits>
 
 #include "absl/base/attributes.h"
-#include "absl/container/internal/have_sse.h"
+#include "absl/base/config.h"
 #include "absl/debugging/stacktrace.h"
 #include "absl/memory/memory.h"
 #include "absl/profiling/internal/exponential_biased.h"
 #include "absl/profiling/internal/sample_recorder.h"
 #include "absl/synchronization/mutex.h"
+#include "absl/utility/utility.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace container_internal {
+
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr int HashtablezInfo::kMaxStackDepth;
+#endif
 
 namespace {
 ABSL_CONST_INIT std::atomic<bool> g_hashtablez_enabled{
     false
 };
 ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_sample_parameter{1 << 10};
+std::atomic<HashtablezConfigListener> g_hashtablez_config_listener{nullptr};
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 ABSL_PER_THREAD_TLS_KEYWORD absl::profiling_internal::ExponentialBiased
     g_exponential_biased_generator;
 #endif
 
+void TriggerHashtablezConfigListener() {
+  auto* listener = g_hashtablez_config_listener.load(std::memory_order_acquire);
+  if (listener != nullptr) listener();
+}
+
 }  // namespace
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample = 0;
+ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample = {0, 0};
 #endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 HashtablezSampler& GlobalHashtablezSampler() {
@@ -55,13 +65,11 @@ HashtablezSampler& GlobalHashtablezSampler() {
   return *sampler;
 }
 
-// TODO(bradleybear): The comments at this constructors declaration say that the
-// fields are not initialized, but this definition does initialize the fields.
-// Something needs to be cleaned up.
-HashtablezInfo::HashtablezInfo() { PrepareForSampling(); }
+HashtablezInfo::HashtablezInfo() = default;
 HashtablezInfo::~HashtablezInfo() = default;
 
-void HashtablezInfo::PrepareForSampling() {
+void HashtablezInfo::PrepareForSampling(int64_t stride,
+                                        size_t inline_element_size_value) {
   capacity.store(0, std::memory_order_relaxed);
   size.store(0, std::memory_order_relaxed);
   num_erases.store(0, std::memory_order_relaxed);
@@ -74,11 +82,13 @@ void HashtablezInfo::PrepareForSampling() {
   max_reserve.store(0, std::memory_order_relaxed);
 
   create_time = absl::Now();
+  weight = stride;
   // The inliner makes hardcoded skip_count difficult (especially when combined
   // with LTO).  We use the ability to exclude stacks by regex when encoding
   // instead.
   depth = absl::GetStackTrace(stack, HashtablezInfo::kMaxStackDepth,
                               /* skip_count= */ 0);
+  inline_element_size = inline_element_size_value;
 }
 
 static bool ShouldForceSampling() {
@@ -101,23 +111,32 @@ static bool ShouldForceSampling() {
   return state == kForce;
 }
 
-HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size) {
+HashtablezInfo* SampleSlow(SamplingState& next_sample,
+                           size_t inline_element_size) {
   if (ABSL_PREDICT_FALSE(ShouldForceSampling())) {
-    *next_sample = 1;
-    HashtablezInfo* result = GlobalHashtablezSampler().Register();
-    result->inline_element_size = inline_element_size;
+    next_sample.next_sample = 1;
+    const int64_t old_stride = exchange(next_sample.sample_stride, 1);
+    HashtablezInfo* result =
+        GlobalHashtablezSampler().Register(old_stride, inline_element_size);
     return result;
   }
 
 #if !defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-  *next_sample = std::numeric_limits<int64_t>::max();
+  next_sample = {
+      std::numeric_limits<int64_t>::max(),
+      std::numeric_limits<int64_t>::max(),
+  };
   return nullptr;
 #else
-  bool first = *next_sample < 0;
-  *next_sample = g_exponential_biased_generator.GetStride(
+  bool first = next_sample.next_sample < 0;
+
+  const int64_t next_stride = g_exponential_biased_generator.GetStride(
       g_hashtablez_sample_parameter.load(std::memory_order_relaxed));
+
+  next_sample.next_sample = next_stride;
+  const int64_t old_stride = exchange(next_sample.sample_stride, next_stride);
   // Small values of interval are equivalent to just sampling next time.
-  ABSL_ASSERT(*next_sample >= 1);
+  ABSL_ASSERT(next_stride >= 1);
 
   // g_hashtablez_enabled can be dynamically flipped, we need to set a threshold
   // low enough that we will start sampling in a reasonable time, so we just use
@@ -127,13 +146,11 @@ HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size) {
   // We will only be negative on our first count, so we should just retry in
   // that case.
   if (first) {
-    if (ABSL_PREDICT_TRUE(--*next_sample > 0)) return nullptr;
+    if (ABSL_PREDICT_TRUE(--next_sample.next_sample > 0)) return nullptr;
     return SampleSlow(next_sample, inline_element_size);
   }
 
-  HashtablezInfo* result = GlobalHashtablezSampler().Register();
-  result->inline_element_size = inline_element_size;
-  return result;
+  return GlobalHashtablezSampler().Register(old_stride, inline_element_size);
 #endif
 }
 
@@ -146,7 +163,7 @@ void RecordInsertSlow(HashtablezInfo* info, size_t hash,
   // SwissTables probe in groups of 16, so scale this to count items probes and
   // not offset from desired.
   size_t probe_length = distance_from_desired;
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef ABSL_INTERNAL_HAVE_SSE2
   probe_length /= 16;
 #else
   probe_length /= 8;
@@ -163,11 +180,33 @@ void RecordInsertSlow(HashtablezInfo* info, size_t hash,
   info->size.fetch_add(1, std::memory_order_relaxed);
 }
 
+void SetHashtablezConfigListener(HashtablezConfigListener l) {
+  g_hashtablez_config_listener.store(l, std::memory_order_release);
+}
+
+bool IsHashtablezEnabled() {
+  return g_hashtablez_enabled.load(std::memory_order_acquire);
+}
+
 void SetHashtablezEnabled(bool enabled) {
+  SetHashtablezEnabledInternal(enabled);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezEnabledInternal(bool enabled) {
   g_hashtablez_enabled.store(enabled, std::memory_order_release);
 }
 
+int32_t GetHashtablezSampleParameter() {
+  return g_hashtablez_sample_parameter.load(std::memory_order_acquire);
+}
+
 void SetHashtablezSampleParameter(int32_t rate) {
+  SetHashtablezSampleParameterInternal(rate);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezSampleParameterInternal(int32_t rate) {
   if (rate > 0) {
     g_hashtablez_sample_parameter.store(rate, std::memory_order_release);
   } else {
@@ -176,7 +215,16 @@ void SetHashtablezSampleParameter(int32_t rate) {
   }
 }
 
+int32_t GetHashtablezMaxSamples() {
+  return GlobalHashtablezSampler().GetMaxSamples();
+}
+
 void SetHashtablezMaxSamples(int32_t max) {
+  SetHashtablezMaxSamplesInternal(max);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezMaxSamplesInternal(int32_t max) {
   if (max > 0) {
     GlobalHashtablezSampler().SetMaxSamples(max);
   } else {
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.h b/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.h
index 91fcdb34a3..d4016d8a9f 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.h
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/hashtablez_sampler.h
@@ -44,9 +44,9 @@
 #include <memory>
 #include <vector>
 
+#include "absl/base/config.h"
 #include "absl/base/internal/per_thread_tls.h"
 #include "absl/base/optimization.h"
-#include "absl/container/internal/have_sse.h"
 #include "absl/profiling/internal/sample_recorder.h"
 #include "absl/synchronization/mutex.h"
 #include "absl/utility/utility.h"
@@ -67,7 +67,8 @@ struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> {
 
   // Puts the object into a clean state, fills in the logically `const` members,
   // blocking for any readers that are currently sampling the object.
-  void PrepareForSampling() ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu);
+  void PrepareForSampling(int64_t stride, size_t inline_element_size_value)
+      ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu);
 
   // These fields are mutated by the various Record* APIs and need to be
   // thread-safe.
@@ -84,18 +85,18 @@ struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> {
 
   // All of the fields below are set by `PrepareForSampling`, they must not be
   // mutated in `Record*` functions.  They are logically `const` in that sense.
-  // These are guarded by init_mu, but that is not externalized to clients, who
-  // can only read them during `HashtablezSampler::Iterate` which will hold the
-  // lock.
+  // These are guarded by init_mu, but that is not externalized to clients,
+  // which can read them only during `SampleRecorder::Iterate` which will hold
+  // the lock.
   static constexpr int kMaxStackDepth = 64;
   absl::Time create_time;
   int32_t depth;
   void* stack[kMaxStackDepth];
-  size_t inline_element_size;
+  size_t inline_element_size;  // How big is the slot?
 };
 
 inline void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length) {
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef ABSL_INTERNAL_HAVE_SSE2
   total_probe_length /= 16;
 #else
   total_probe_length /= 8;
@@ -144,7 +145,15 @@ inline void RecordEraseSlow(HashtablezInfo* info) {
       std::memory_order_relaxed);
 }
 
-HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size);
+struct SamplingState {
+  int64_t next_sample;
+  // When we make a sampling decision, we record that distance so we can weight
+  // each sample.
+  int64_t sample_stride;
+};
+
+HashtablezInfo* SampleSlow(SamplingState& next_sample,
+                           size_t inline_element_size);
 void UnsampleSlow(HashtablezInfo* info);
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
@@ -234,7 +243,7 @@ class HashtablezInfoHandle {
 #endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-extern ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample;
+extern ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample;
 #endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 // Returns an RAII sampling handle that manages registration and unregistation
@@ -242,11 +251,11 @@ extern ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample;
 inline HashtablezInfoHandle Sample(
     size_t inline_element_size ABSL_ATTRIBUTE_UNUSED) {
 #if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-  if (ABSL_PREDICT_TRUE(--global_next_sample > 0)) {
+  if (ABSL_PREDICT_TRUE(--global_next_sample.next_sample > 0)) {
     return HashtablezInfoHandle(nullptr);
   }
   return HashtablezInfoHandle(
-      SampleSlow(&global_next_sample, inline_element_size));
+      SampleSlow(global_next_sample, inline_element_size));
 #else
   return HashtablezInfoHandle(nullptr);
 #endif  // !ABSL_PER_THREAD_TLS
@@ -258,14 +267,23 @@ using HashtablezSampler =
 // Returns a global Sampler.
 HashtablezSampler& GlobalHashtablezSampler();
 
+using HashtablezConfigListener = void (*)();
+void SetHashtablezConfigListener(HashtablezConfigListener l);
+
 // Enables or disables sampling for Swiss tables.
+bool IsHashtablezEnabled();
 void SetHashtablezEnabled(bool enabled);
+void SetHashtablezEnabledInternal(bool enabled);
 
 // Sets the rate at which Swiss tables will be sampled.
+int32_t GetHashtablezSampleParameter();
 void SetHashtablezSampleParameter(int32_t rate);
+void SetHashtablezSampleParameterInternal(int32_t rate);
 
 // Sets a soft max for the number of samples that will be kept.
+int32_t GetHashtablezMaxSamples();
 void SetHashtablezMaxSamples(int32_t max);
+void SetHashtablezMaxSamplesInternal(int32_t max);
 
 // Configuration override.
 // This allows process-wide sampling without depending on order of
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/have_sse.h b/contrib/restricted/abseil-cpp/absl/container/internal/have_sse.h
deleted file mode 100644
index e75e1a16d3..0000000000
--- a/contrib/restricted/abseil-cpp/absl/container/internal/have_sse.h
+++ /dev/null
@@ -1,50 +0,0 @@
-// 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
-//
-//      https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-//
-// Shared config probing for SSE instructions used in Swiss tables.
-#ifndef ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
-#define ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
-
-#ifndef ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
-#if defined(__SSE2__) ||  \
-    (defined(_MSC_VER) && \
-     (defined(_M_X64) || (defined(_M_IX86) && _M_IX86_FP >= 2)))
-#define ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2 1
-#else
-#define ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2 0
-#endif
-#endif
-
-#ifndef ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
-#ifdef __SSSE3__
-#define ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3 1
-#else
-#define ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3 0
-#endif
-#endif
-
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3 && \
-    !ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
-#error "Bad configuration!"
-#endif
-
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
-#include <emmintrin.h>
-#endif
-
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
-#include <tmmintrin.h>
-#endif
-
-#endif  // ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/inlined_vector.h b/contrib/restricted/abseil-cpp/absl/container/internal/inlined_vector.h
index 1d7d6cda72..54c92a0106 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/inlined_vector.h
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/inlined_vector.h
@@ -40,7 +40,6 @@ namespace inlined_vector_internal {
 #if !defined(__clang__) && defined(__GNUC__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Warray-bounds"
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
 #endif
 
 template <typename A>
@@ -94,16 +93,30 @@ struct TypeIdentity {
 template <typename T>
 using NoTypeDeduction = typename TypeIdentity<T>::type;
 
+template <typename A, bool IsTriviallyDestructible =
+                          absl::is_trivially_destructible<ValueType<A>>::value>
+struct DestroyAdapter;
+
 template <typename A>
-void DestroyElements(NoTypeDeduction<A>& allocator, Pointer<A> destroy_first,
-                     SizeType<A> destroy_size) {
-  if (destroy_first != nullptr) {
+struct DestroyAdapter<A, /* IsTriviallyDestructible */ false> {
+  static void DestroyElements(A& allocator, Pointer<A> destroy_first,
+                              SizeType<A> destroy_size) {
     for (SizeType<A> i = destroy_size; i != 0;) {
       --i;
       AllocatorTraits<A>::destroy(allocator, destroy_first + i);
     }
   }
-}
+};
+
+template <typename A>
+struct DestroyAdapter<A, /* IsTriviallyDestructible */ true> {
+  static void DestroyElements(A& allocator, Pointer<A> destroy_first,
+                              SizeType<A> destroy_size) {
+    static_cast<void>(allocator);
+    static_cast<void>(destroy_first);
+    static_cast<void>(destroy_size);
+  }
+};
 
 template <typename A>
 struct Allocation {
@@ -133,7 +146,7 @@ void ConstructElements(NoTypeDeduction<A>& allocator,
   for (SizeType<A> i = 0; i < construct_size; ++i) {
     ABSL_INTERNAL_TRY { values.ConstructNext(allocator, construct_first + i); }
     ABSL_INTERNAL_CATCH_ANY {
-      DestroyElements<A>(allocator, construct_first, i);
+      DestroyAdapter<A>::DestroyElements(allocator, construct_first, i);
       ABSL_INTERNAL_RETHROW;
     }
   }
@@ -253,7 +266,7 @@ class ConstructionTransaction {
 
   ~ConstructionTransaction() {
     if (DidConstruct()) {
-      DestroyElements<A>(GetAllocator(), GetData(), GetSize());
+      DestroyAdapter<A>::DestroyElements(GetAllocator(), GetData(), GetSize());
     }
   }
 
@@ -297,10 +310,10 @@ class Storage {
   // Storage Constructors and Destructor
   // ---------------------------------------------------------------------------
 
-  Storage() : metadata_(A(), /* size and is_allocated */ 0) {}
+  Storage() : metadata_(A(), /* size and is_allocated */ 0u) {}
 
   explicit Storage(const A& allocator)
-      : metadata_(allocator, /* size and is_allocated */ 0) {}
+      : metadata_(allocator, /* size and is_allocated */ 0u) {}
 
   ~Storage() {
     if (GetSizeAndIsAllocated() == 0) {
@@ -416,7 +429,7 @@ class Storage {
   }
 
   void SubtractSize(SizeType<A> count) {
-    assert(count <= GetSize());
+    ABSL_HARDENING_ASSERT(count <= GetSize());
 
     GetSizeAndIsAllocated() -= count << static_cast<SizeType<A>>(1);
   }
@@ -427,7 +440,8 @@ class Storage {
   }
 
   void MemcpyFrom(const Storage& other_storage) {
-    assert(IsMemcpyOk<A>::value || other_storage.GetIsAllocated());
+    ABSL_HARDENING_ASSERT(IsMemcpyOk<A>::value ||
+                          other_storage.GetIsAllocated());
 
     GetSizeAndIsAllocated() = other_storage.GetSizeAndIsAllocated();
     data_ = other_storage.data_;
@@ -469,14 +483,14 @@ class Storage {
 template <typename T, size_t N, typename A>
 void Storage<T, N, A>::DestroyContents() {
   Pointer<A> data = GetIsAllocated() ? GetAllocatedData() : GetInlinedData();
-  DestroyElements<A>(GetAllocator(), data, GetSize());
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), data, GetSize());
   DeallocateIfAllocated();
 }
 
 template <typename T, size_t N, typename A>
 void Storage<T, N, A>::InitFrom(const Storage& other) {
   const SizeType<A> n = other.GetSize();
-  assert(n > 0);  // Empty sources handled handled in caller.
+  ABSL_HARDENING_ASSERT(n > 0);  // Empty sources handled handled in caller.
   ConstPointer<A> src;
   Pointer<A> dst;
   if (!other.GetIsAllocated()) {
@@ -508,8 +522,8 @@ template <typename ValueAdapter>
 auto Storage<T, N, A>::Initialize(ValueAdapter values, SizeType<A> new_size)
     -> void {
   // Only callable from constructors!
-  assert(!GetIsAllocated());
-  assert(GetSize() == 0);
+  ABSL_HARDENING_ASSERT(!GetIsAllocated());
+  ABSL_HARDENING_ASSERT(GetSize() == 0);
 
   Pointer<A> construct_data;
   if (new_size > GetInlinedCapacity()) {
@@ -566,7 +580,8 @@ auto Storage<T, N, A>::Assign(ValueAdapter values, SizeType<A> new_size)
   ConstructElements<A>(GetAllocator(), construct_loop.data(), values,
                        construct_loop.size());
 
-  DestroyElements<A>(GetAllocator(), destroy_loop.data(), destroy_loop.size());
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), destroy_loop.data(),
+                                     destroy_loop.size());
 
   if (allocation_tx.DidAllocate()) {
     DeallocateIfAllocated();
@@ -587,7 +602,7 @@ auto Storage<T, N, A>::Resize(ValueAdapter values, SizeType<A> new_size)
   A& alloc = GetAllocator();
   if (new_size <= size) {
     // Destroy extra old elements.
-    DestroyElements<A>(alloc, base + new_size, size - new_size);
+    DestroyAdapter<A>::DestroyElements(alloc, base + new_size, size - new_size);
   } else if (new_size <= storage_view.capacity) {
     // Construct new elements in place.
     ConstructElements<A>(alloc, base + size, values, new_size - size);
@@ -595,7 +610,7 @@ auto Storage<T, N, A>::Resize(ValueAdapter values, SizeType<A> new_size)
     // Steps:
     //  a. Allocate new backing store.
     //  b. Construct new elements in new backing store.
-    //  c. Move existing elements from old backing store to now.
+    //  c. Move existing elements from old backing store to new backing store.
     //  d. Destroy all elements in old backing store.
     // Use transactional wrappers for the first two steps so we can roll
     // back if necessary due to exceptions.
@@ -611,7 +626,7 @@ auto Storage<T, N, A>::Resize(ValueAdapter values, SizeType<A> new_size)
         (MoveIterator<A>(base)));
     ConstructElements<A>(alloc, new_data, move_values, size);
 
-    DestroyElements<A>(alloc, base, size);
+    DestroyAdapter<A>::DestroyElements(alloc, base, size);
     std::move(construction_tx).Commit();
     DeallocateIfAllocated();
     SetAllocation(std::move(allocation_tx).Release());
@@ -650,7 +665,8 @@ auto Storage<T, N, A>::Insert(ConstIterator<A> pos, ValueAdapter values,
     ConstructElements<A>(GetAllocator(), new_data + insert_end_index,
                          move_values, storage_view.size - insert_index);
 
-    DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+    DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                       storage_view.size);
 
     std::move(construction_tx).Commit();
     std::move(move_construction_tx).Commit();
@@ -753,7 +769,8 @@ auto Storage<T, N, A>::EmplaceBackSlow(Args&&... args) -> Reference<A> {
     ABSL_INTERNAL_RETHROW;
   }
   // Destroy elements in old backing store.
-  DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                     storage_view.size);
 
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());
@@ -778,9 +795,9 @@ auto Storage<T, N, A>::Erase(ConstIterator<A> from, ConstIterator<A> to)
   AssignElements<A>(storage_view.data + erase_index, move_values,
                     storage_view.size - erase_end_index);
 
-  DestroyElements<A>(GetAllocator(),
-                     storage_view.data + (storage_view.size - erase_size),
-                     erase_size);
+  DestroyAdapter<A>::DestroyElements(
+      GetAllocator(), storage_view.data + (storage_view.size - erase_size),
+      erase_size);
 
   SubtractSize(erase_size);
   return Iterator<A>(storage_view.data + erase_index);
@@ -804,7 +821,8 @@ auto Storage<T, N, A>::Reserve(SizeType<A> requested_capacity) -> void {
   ConstructElements<A>(GetAllocator(), new_data, move_values,
                        storage_view.size);
 
-  DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                     storage_view.size);
 
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());
@@ -814,7 +832,7 @@ auto Storage<T, N, A>::Reserve(SizeType<A> requested_capacity) -> void {
 template <typename T, size_t N, typename A>
 auto Storage<T, N, A>::ShrinkToFit() -> void {
   // May only be called on allocated instances!
-  assert(GetIsAllocated());
+  ABSL_HARDENING_ASSERT(GetIsAllocated());
 
   StorageView<A> storage_view{GetAllocatedData(), GetSize(),
                               GetAllocatedCapacity()};
@@ -847,7 +865,8 @@ auto Storage<T, N, A>::ShrinkToFit() -> void {
     ABSL_INTERNAL_RETHROW;
   }
 
-  DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                     storage_view.size);
 
   MallocAdapter<A>::Deallocate(GetAllocator(), storage_view.data,
                                storage_view.capacity);
@@ -862,7 +881,7 @@ auto Storage<T, N, A>::ShrinkToFit() -> void {
 template <typename T, size_t N, typename A>
 auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
   using std::swap;
-  assert(this != other_storage_ptr);
+  ABSL_HARDENING_ASSERT(this != other_storage_ptr);
 
   if (GetIsAllocated() && other_storage_ptr->GetIsAllocated()) {
     swap(data_.allocated, other_storage_ptr->data_.allocated);
@@ -883,9 +902,10 @@ auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
                          move_values,
                          large_ptr->GetSize() - small_ptr->GetSize());
 
-    DestroyElements<A>(large_ptr->GetAllocator(),
-                       large_ptr->GetInlinedData() + small_ptr->GetSize(),
-                       large_ptr->GetSize() - small_ptr->GetSize());
+    DestroyAdapter<A>::DestroyElements(
+        large_ptr->GetAllocator(),
+        large_ptr->GetInlinedData() + small_ptr->GetSize(),
+        large_ptr->GetSize() - small_ptr->GetSize());
   } else {
     Storage* allocated_ptr = this;
     Storage* inlined_ptr = other_storage_ptr;
@@ -904,23 +924,24 @@ auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
                            inlined_ptr->GetSize());
     }
     ABSL_INTERNAL_CATCH_ANY {
-      allocated_ptr->SetAllocation(
-          {allocated_storage_view.data, allocated_storage_view.capacity});
+      allocated_ptr->SetAllocation(Allocation<A>{
+          allocated_storage_view.data, allocated_storage_view.capacity});
       ABSL_INTERNAL_RETHROW;
     }
 
-    DestroyElements<A>(inlined_ptr->GetAllocator(),
-                       inlined_ptr->GetInlinedData(), inlined_ptr->GetSize());
+    DestroyAdapter<A>::DestroyElements(inlined_ptr->GetAllocator(),
+                                       inlined_ptr->GetInlinedData(),
+                                       inlined_ptr->GetSize());
 
-    inlined_ptr->SetAllocation(
-        {allocated_storage_view.data, allocated_storage_view.capacity});
+    inlined_ptr->SetAllocation(Allocation<A>{allocated_storage_view.data,
+                                             allocated_storage_view.capacity});
   }
 
   swap(GetSizeAndIsAllocated(), other_storage_ptr->GetSizeAndIsAllocated());
   swap(GetAllocator(), other_storage_ptr->GetAllocator());
 }
 
-// End ignore "array-bounds" and "maybe-uninitialized"
+// End ignore "array-bounds"
 #if !defined(__clang__) && defined(__GNUC__)
 #pragma GCC diagnostic pop
 #endif
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.cc b/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.cc
index 687bcb8a4d..c63a2e02d1 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.cc
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.cc
@@ -23,13 +23,17 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace container_internal {
 
+// A single block of empty control bytes for tables without any slots allocated.
+// This enables removing a branch in the hot path of find().
 alignas(16) ABSL_CONST_INIT ABSL_DLL const ctrl_t kEmptyGroup[16] = {
     ctrl_t::kSentinel, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty};
 
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr size_t Group::kWidth;
+#endif
 
 // Returns "random" seed.
 inline size_t RandomSeed() {
diff --git a/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.h b/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.h
index 12682b3532..ea912f8305 100644
--- a/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.h
+++ b/contrib/restricted/abseil-cpp/absl/container/internal/raw_hash_set.h
@@ -53,51 +53,121 @@
 //
 // IMPLEMENTATION DETAILS
 //
-// The table stores elements inline in a slot array. In addition to the slot
-// array the table maintains some control state per slot. The extra state is one
-// byte per slot and stores empty or deleted marks, or alternatively 7 bits from
-// the hash of an occupied slot. The table is split into logical groups of
-// slots, like so:
+// # Table Layout
+//
+// A raw_hash_set's backing array consists of control bytes followed by slots
+// that may or may not contain objects.
+//
+// The layout of the backing array, for `capacity` slots, is thus, as a
+// pseudo-struct:
+//
+//   struct BackingArray {
+//     // Control bytes for the "real" slots.
+//     ctrl_t ctrl[capacity];
+//     // Always `ctrl_t::kSentinel`. This is used by iterators to find when to
+//     // stop and serves no other purpose.
+//     ctrl_t sentinel;
+//     // A copy of the first `kWidth - 1` elements of `ctrl`. This is used so
+//     // that if a probe sequence picks a value near the end of `ctrl`,
+//     // `Group` will have valid control bytes to look at.
+//     ctrl_t clones[kWidth - 1];
+//     // The actual slot data.
+//     slot_type slots[capacity];
+//   };
+//
+// The length of this array is computed by `AllocSize()` below.
+//
+// Control bytes (`ctrl_t`) are bytes (collected into groups of a
+// platform-specific size) that define the state of the corresponding slot in
+// the slot array. Group manipulation is tightly optimized to be as efficient
+// as possible: SSE and friends on x86, clever bit operations on other arches.
 //
 //      Group 1         Group 2        Group 3
 // +---------------+---------------+---------------+
 // | | | | | | | | | | | | | | | | | | | | | | | | |
 // +---------------+---------------+---------------+
 //
-// On lookup the hash is split into two parts:
-// - H2: 7 bits (those stored in the control bytes)
-// - H1: the rest of the bits
-// The groups are probed using H1. For each group the slots are matched to H2 in
-// parallel. Because H2 is 7 bits (128 states) and the number of slots per group
-// is low (8 or 16) in almost all cases a match in H2 is also a lookup hit.
+// Each control byte is either a special value for empty slots, deleted slots
+// (sometimes called *tombstones*), and a special end-of-table marker used by
+// iterators, or, if occupied, seven bits (H2) from the hash of the value in the
+// corresponding slot.
+//
+// Storing control bytes in a separate array also has beneficial cache effects,
+// since more logical slots will fit into a cache line.
+//
+// # Hashing
+//
+// We compute two separate hashes, `H1` and `H2`, from the hash of an object.
+// `H1(hash(x))` is an index into `slots`, and essentially the starting point
+// for the probe sequence. `H2(hash(x))` is a 7-bit value used to filter out
+// objects that cannot possibly be the one we are looking for.
+//
+// # Table operations.
 //
-// On insert, once the right group is found (as in lookup), its slots are
-// filled in order.
+// The key operations are `insert`, `find`, and `erase`.
 //
-// On erase a slot is cleared. In case the group did not have any empty slots
-// before the erase, the erased slot is marked as deleted.
+// Since `insert` and `erase` are implemented in terms of `find`, we describe
+// `find` first. To `find` a value `x`, we compute `hash(x)`. From
+// `H1(hash(x))` and the capacity, we construct a `probe_seq` that visits every
+// group of slots in some interesting order.
 //
-// Groups without empty slots (but maybe with deleted slots) extend the probe
-// sequence. The probing algorithm is quadratic. Given N the number of groups,
-// the probing function for the i'th probe is:
+// We now walk through these indices. At each index, we select the entire group
+// starting with that index and extract potential candidates: occupied slots
+// with a control byte equal to `H2(hash(x))`. If we find an empty slot in the
+// group, we stop and return an error. Each candidate slot `y` is compared with
+// `x`; if `x == y`, we are done and return `&y`; otherwise we contine to the
+// next probe index. Tombstones effectively behave like full slots that never
+// match the value we're looking for.
 //
-//   P(0) = H1 % N
+// The `H2` bits ensure when we compare a slot to an object with `==`, we are
+// likely to have actually found the object.  That is, the chance is low that
+// `==` is called and returns `false`.  Thus, when we search for an object, we
+// are unlikely to call `==` many times.  This likelyhood can be analyzed as
+// follows (assuming that H2 is a random enough hash function).
 //
-//   P(i) = (P(i - 1) + i) % N
+// Let's assume that there are `k` "wrong" objects that must be examined in a
+// probe sequence.  For example, when doing a `find` on an object that is in the
+// table, `k` is the number of objects between the start of the probe sequence
+// and the final found object (not including the final found object).  The
+// expected number of objects with an H2 match is then `k/128`.  Measurements
+// and analysis indicate that even at high load factors, `k` is less than 32,
+// meaning that the number of "false positive" comparisons we must perform is
+// less than 1/8 per `find`.
+
+// `insert` is implemented in terms of `unchecked_insert`, which inserts a
+// value presumed to not be in the table (violating this requirement will cause
+// the table to behave erratically). Given `x` and its hash `hash(x)`, to insert
+// it, we construct a `probe_seq` once again, and use it to find the first
+// group with an unoccupied (empty *or* deleted) slot. We place `x` into the
+// first such slot in the group and mark it as full with `x`'s H2.
 //
-// This probing function guarantees that after N probes, all the groups of the
-// table will be probed exactly once.
+// To `insert`, we compose `unchecked_insert` with `find`. We compute `h(x)` and
+// perform a `find` to see if it's already present; if it is, we're done. If
+// it's not, we may decide the table is getting overcrowded (i.e. the load
+// factor is greater than 7/8 for big tables; `is_small()` tables use a max load
+// factor of 1); in this case, we allocate a bigger array, `unchecked_insert`
+// each element of the table into the new array (we know that no insertion here
+// will insert an already-present value), and discard the old backing array. At
+// this point, we may `unchecked_insert` the value `x`.
 //
-// The control state and slot array are stored contiguously in a shared heap
-// allocation. The layout of this allocation is: `capacity()` control bytes,
-// one sentinel control byte, `Group::kWidth - 1` cloned control bytes,
-// <possible padding>, `capacity()` slots. The sentinel control byte is used in
-// iteration so we know when we reach the end of the table. The cloned control
-// bytes at the end of the table are cloned from the beginning of the table so
-// groups that begin near the end of the table can see a full group. In cases in
-// which there are more than `capacity()` cloned control bytes, the extra bytes
-// are `kEmpty`, and these ensure that we always see at least one empty slot and
-// can stop an unsuccessful search.
+// Below, `unchecked_insert` is partly implemented by `prepare_insert`, which
+// presents a viable, initialized slot pointee to the caller.
+//
+// `erase` is implemented in terms of `erase_at`, which takes an index to a
+// slot. Given an offset, we simply create a tombstone and destroy its contents.
+// If we can prove that the slot would not appear in a probe sequence, we can
+// make the slot as empty, instead. We can prove this by observing that if a
+// group has any empty slots, it has never been full (assuming we never create
+// an empty slot in a group with no empties, which this heuristic guarantees we
+// never do) and find would stop at this group anyways (since it does not probe
+// beyond groups with empties).
+//
+// `erase` is `erase_at` composed with `find`: if we
+// have a value `x`, we can perform a `find`, and then `erase_at` the resulting
+// slot.
+//
+// To iterate, we simply traverse the array, skipping empty and deleted slots
+// and stopping when we hit a `kSentinel`.
 
 #ifndef ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
 #define ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
@@ -113,7 +183,9 @@
 #include <type_traits>
 #include <utility>
 
+#include "absl/base/config.h"
 #include "absl/base/internal/endian.h"
+#include "absl/base/internal/prefetch.h"
 #include "absl/base/optimization.h"
 #include "absl/base/port.h"
 #include "absl/container/internal/common.h"
@@ -122,12 +194,27 @@
 #include "absl/container/internal/hash_policy_traits.h"
 #include "absl/container/internal/hashtable_debug_hooks.h"
 #include "absl/container/internal/hashtablez_sampler.h"
-#include "absl/container/internal/have_sse.h"
 #include "absl/memory/memory.h"
 #include "absl/meta/type_traits.h"
 #include "absl/numeric/bits.h"
 #include "absl/utility/utility.h"
 
+#ifdef ABSL_INTERNAL_HAVE_SSE2
+#include <emmintrin.h>
+#endif
+
+#ifdef ABSL_INTERNAL_HAVE_SSSE3
+#include <tmmintrin.h>
+#endif
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+#ifdef ABSL_INTERNAL_HAVE_ARM_NEON
+#include <arm_neon.h>
+#endif
+
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace container_internal {
@@ -142,14 +229,40 @@ template <typename AllocType>
 void SwapAlloc(AllocType& /*lhs*/, AllocType& /*rhs*/,
                std::false_type /* propagate_on_container_swap */) {}
 
+// The state for a probe sequence.
+//
+// Currently, the sequence is a triangular progression of the form
+//
+//   p(i) := Width * (i^2 + i)/2 + hash (mod mask + 1)
+//
+// The use of `Width` ensures that each probe step does not overlap groups;
+// the sequence effectively outputs the addresses of *groups* (although not
+// necessarily aligned to any boundary). The `Group` machinery allows us
+// to check an entire group with minimal branching.
+//
+// Wrapping around at `mask + 1` is important, but not for the obvious reason.
+// As described above, the first few entries of the control byte array
+// are mirrored at the end of the array, which `Group` will find and use
+// for selecting candidates. However, when those candidates' slots are
+// actually inspected, there are no corresponding slots for the cloned bytes,
+// so we need to make sure we've treated those offsets as "wrapping around".
+//
+// It turns out that this probe sequence visits every group exactly once if the
+// number of groups is a power of two, since (i^2+i)/2 is a bijection in
+// Z/(2^m). See https://en.wikipedia.org/wiki/Quadratic_probing
 template <size_t Width>
 class probe_seq {
  public:
+  // Creates a new probe sequence using `hash` as the initial value of the
+  // sequence and `mask` (usually the capacity of the table) as the mask to
+  // apply to each value in the progression.
   probe_seq(size_t hash, size_t mask) {
     assert(((mask + 1) & mask) == 0 && "not a mask");
     mask_ = mask;
     offset_ = hash & mask_;
   }
+
+  // The offset within the table, i.e., the value `p(i)` above.
   size_t offset() const { return offset_; }
   size_t offset(size_t i) const { return (offset_ + i) & mask_; }
 
@@ -158,7 +271,7 @@ class probe_seq {
     offset_ += index_;
     offset_ &= mask_;
   }
-  // 0-based probe index. The i-th probe in the probe sequence.
+  // 0-based probe index, a multiple of `Width`.
   size_t index() const { return index_; }
 
  private:
@@ -182,9 +295,9 @@ struct IsDecomposable : std::false_type {};
 
 template <class Policy, class Hash, class Eq, class... Ts>
 struct IsDecomposable<
-    absl::void_t<decltype(
-        Policy::apply(RequireUsableKey<typename Policy::key_type, Hash, Eq>(),
-                      std::declval<Ts>()...))>,
+    absl::void_t<decltype(Policy::apply(
+        RequireUsableKey<typename Policy::key_type, Hash, Eq>(),
+        std::declval<Ts>()...))>,
     Policy, Hash, Eq, Ts...> : std::true_type {};
 
 // TODO(alkis): Switch to std::is_nothrow_swappable when gcc/clang supports it.
@@ -200,57 +313,84 @@ constexpr bool IsNoThrowSwappable(std::false_type /* is_swappable */) {
 
 template <typename T>
 uint32_t TrailingZeros(T x) {
-  ABSL_INTERNAL_ASSUME(x != 0);
-  return countr_zero(x);
+  ABSL_ASSUME(x != 0);
+  return static_cast<uint32_t>(countr_zero(x));
 }
 
-// An abstraction over a bitmask. It provides an easy way to iterate through the
-// indexes of the set bits of a bitmask.  When Shift=0 (platforms with SSE),
-// this is a true bitmask.  On non-SSE, platforms the arithematic used to
-// emulate the SSE behavior works in bytes (Shift=3) and leaves each bytes as
-// either 0x00 or 0x80.
+// An abstract bitmask, such as that emitted by a SIMD instruction.
 //
-// For example:
-//   for (int i : BitMask<uint32_t, 16>(0x5)) -> yields 0, 2
-//   for (int i : BitMask<uint64_t, 8, 3>(0x0000000080800000)) -> yields 2, 3
+// Specifically, this type implements a simple bitset whose representation is
+// controlled by `SignificantBits` and `Shift`. `SignificantBits` is the number
+// of abstract bits in the bitset, while `Shift` is the log-base-two of the
+// width of an abstract bit in the representation.
+// This mask provides operations for any number of real bits set in an abstract
+// bit. To add iteration on top of that, implementation must guarantee no more
+// than one real bit is set in an abstract bit.
 template <class T, int SignificantBits, int Shift = 0>
-class BitMask {
-  static_assert(std::is_unsigned<T>::value, "");
-  static_assert(Shift == 0 || Shift == 3, "");
-
+class NonIterableBitMask {
  public:
-  // These are useful for unit tests (gunit).
-  using value_type = int;
-  using iterator = BitMask;
-  using const_iterator = BitMask;
+  explicit NonIterableBitMask(T mask) : mask_(mask) {}
 
-  explicit BitMask(T mask) : mask_(mask) {}
-  BitMask& operator++() {
-    mask_ &= (mask_ - 1);
-    return *this;
-  }
-  explicit operator bool() const { return mask_ != 0; }
-  int operator*() const { return LowestBitSet(); }
+  explicit operator bool() const { return this->mask_ != 0; }
+
+  // Returns the index of the lowest *abstract* bit set in `self`.
   uint32_t LowestBitSet() const {
     return container_internal::TrailingZeros(mask_) >> Shift;
   }
+
+  // Returns the index of the highest *abstract* bit set in `self`.
   uint32_t HighestBitSet() const {
     return static_cast<uint32_t>((bit_width(mask_) - 1) >> Shift);
   }
 
-  BitMask begin() const { return *this; }
-  BitMask end() const { return BitMask(0); }
-
+  // Return the number of trailing zero *abstract* bits.
   uint32_t TrailingZeros() const {
     return container_internal::TrailingZeros(mask_) >> Shift;
   }
 
+  // Return the number of leading zero *abstract* bits.
   uint32_t LeadingZeros() const {
     constexpr int total_significant_bits = SignificantBits << Shift;
     constexpr int extra_bits = sizeof(T) * 8 - total_significant_bits;
-    return countl_zero(mask_ << extra_bits) >> Shift;
+    return static_cast<uint32_t>(countl_zero(mask_ << extra_bits)) >> Shift;
   }
 
+  T mask_;
+};
+
+// Mask that can be iterable
+//
+// For example, when `SignificantBits` is 16 and `Shift` is zero, this is just
+// an ordinary 16-bit bitset occupying the low 16 bits of `mask`. When
+// `SignificantBits` is 8 and `Shift` is 3, abstract bits are represented as
+// the bytes `0x00` and `0x80`, and it occupies all 64 bits of the bitmask.
+//
+// For example:
+//   for (int i : BitMask<uint32_t, 16>(0b101)) -> yields 0, 2
+//   for (int i : BitMask<uint64_t, 8, 3>(0x0000000080800000)) -> yields 2, 3
+template <class T, int SignificantBits, int Shift = 0>
+class BitMask : public NonIterableBitMask<T, SignificantBits, Shift> {
+  using Base = NonIterableBitMask<T, SignificantBits, Shift>;
+  static_assert(std::is_unsigned<T>::value, "");
+  static_assert(Shift == 0 || Shift == 3, "");
+
+ public:
+  explicit BitMask(T mask) : Base(mask) {}
+  // BitMask is an iterator over the indices of its abstract bits.
+  using value_type = int;
+  using iterator = BitMask;
+  using const_iterator = BitMask;
+
+  BitMask& operator++() {
+    this->mask_ &= (this->mask_ - 1);
+    return *this;
+  }
+
+  uint32_t operator*() const { return Base::LowestBitSet(); }
+
+  BitMask begin() const { return *this; }
+  BitMask end() const { return BitMask(0); }
+
  private:
   friend bool operator==(const BitMask& a, const BitMask& b) {
     return a.mask_ == b.mask_;
@@ -258,15 +398,27 @@ class BitMask {
   friend bool operator!=(const BitMask& a, const BitMask& b) {
     return a.mask_ != b.mask_;
   }
-
-  T mask_;
 };
 
 using h2_t = uint8_t;
 
 // The values here are selected for maximum performance. See the static asserts
-// below for details. We use an enum class so that when strict aliasing is
-// enabled, the compiler knows ctrl_t doesn't alias other types.
+// below for details.
+
+// A `ctrl_t` is a single control byte, which can have one of four
+// states: empty, deleted, full (which has an associated seven-bit h2_t value)
+// and the sentinel. They have the following bit patterns:
+//
+//      empty: 1 0 0 0 0 0 0 0
+//    deleted: 1 1 1 1 1 1 1 0
+//       full: 0 h h h h h h h  // h represents the hash bits.
+//   sentinel: 1 1 1 1 1 1 1 1
+//
+// These values are specifically tuned for SSE-flavored SIMD.
+// The static_asserts below detail the source of these choices.
+//
+// We use an enum class so that when strict aliasing is enabled, the compiler
+// knows ctrl_t doesn't alias other types.
 enum class ctrl_t : int8_t {
   kEmpty = -128,   // 0b10000000
   kDeleted = -2,   // 0b11111110
@@ -294,15 +446,17 @@ static_assert(
      static_cast<int8_t>(ctrl_t::kSentinel) & 0x7F) != 0,
     "ctrl_t::kEmpty and ctrl_t::kDeleted must share an unset bit that is not "
     "shared by ctrl_t::kSentinel to make the scalar test for "
-    "MatchEmptyOrDeleted() efficient");
+    "MaskEmptyOrDeleted() efficient");
 static_assert(ctrl_t::kDeleted == static_cast<ctrl_t>(-2),
               "ctrl_t::kDeleted must be -2 to make the implementation of "
               "ConvertSpecialToEmptyAndFullToDeleted efficient");
 
-// A single block of empty control bytes for tables without any slots allocated.
-// This enables removing a branch in the hot path of find().
 ABSL_DLL extern const ctrl_t kEmptyGroup[16];
+
+// Returns a pointer to a control byte group that can be used by empty tables.
 inline ctrl_t* EmptyGroup() {
+  // Const must be cast away here; no uses of this function will actually write
+  // to it, because it is only used for empty tables.
   return const_cast<ctrl_t*>(kEmptyGroup);
 }
 
@@ -310,28 +464,61 @@ inline ctrl_t* EmptyGroup() {
 // randomize insertion order within groups.
 bool ShouldInsertBackwards(size_t hash, const ctrl_t* ctrl);
 
-// Returns a hash seed.
+// Returns a per-table, hash salt, which changes on resize. This gets mixed into
+// H1 to randomize iteration order per-table.
 //
 // The seed consists of the ctrl_ pointer, which adds enough entropy to ensure
 // non-determinism of iteration order in most cases.
-inline size_t HashSeed(const ctrl_t* ctrl) {
+inline size_t PerTableSalt(const ctrl_t* ctrl) {
   // The low bits of the pointer have little or no entropy because of
   // alignment. We shift the pointer to try to use higher entropy bits. A
   // good number seems to be 12 bits, because that aligns with page size.
   return reinterpret_cast<uintptr_t>(ctrl) >> 12;
 }
-
+// Extracts the H1 portion of a hash: 57 bits mixed with a per-table salt.
 inline size_t H1(size_t hash, const ctrl_t* ctrl) {
-  return (hash >> 7) ^ HashSeed(ctrl);
+  return (hash >> 7) ^ PerTableSalt(ctrl);
 }
+
+// Extracts the H2 portion of a hash: the 7 bits not used for H1.
+//
+// These are used as an occupied control byte.
 inline h2_t H2(size_t hash) { return hash & 0x7F; }
 
+// Helpers for checking the state of a control byte.
 inline bool IsEmpty(ctrl_t c) { return c == ctrl_t::kEmpty; }
 inline bool IsFull(ctrl_t c) { return c >= static_cast<ctrl_t>(0); }
 inline bool IsDeleted(ctrl_t c) { return c == ctrl_t::kDeleted; }
 inline bool IsEmptyOrDeleted(ctrl_t c) { return c < ctrl_t::kSentinel; }
 
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef ABSL_INTERNAL_HAVE_SSE2
+// Quick reference guide for intrinsics used below:
+//
+// * __m128i: An XMM (128-bit) word.
+//
+// * _mm_setzero_si128: Returns a zero vector.
+// * _mm_set1_epi8:     Returns a vector with the same i8 in each lane.
+//
+// * _mm_subs_epi8:    Saturating-subtracts two i8 vectors.
+// * _mm_and_si128:    Ands two i128s together.
+// * _mm_or_si128:     Ors two i128s together.
+// * _mm_andnot_si128: And-nots two i128s together.
+//
+// * _mm_cmpeq_epi8: Component-wise compares two i8 vectors for equality,
+//                   filling each lane with 0x00 or 0xff.
+// * _mm_cmpgt_epi8: Same as above, but using > rather than ==.
+//
+// * _mm_loadu_si128:  Performs an unaligned load of an i128.
+// * _mm_storeu_si128: Performs an unaligned store of an i128.
+//
+// * _mm_sign_epi8:     Retains, negates, or zeroes each i8 lane of the first
+//                      argument if the corresponding lane of the second
+//                      argument is positive, negative, or zero, respectively.
+// * _mm_movemask_epi8: Selects the sign bit out of each i8 lane and produces a
+//                      bitmask consisting of those bits.
+// * _mm_shuffle_epi8:  Selects i8s from the first argument, using the low
+//                      four bits of each i8 lane in the second argument as
+//                      indices.
 
 // https://github.com/abseil/abseil-cpp/issues/209
 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87853
@@ -360,30 +547,32 @@ struct GroupSse2Impl {
   BitMask<uint32_t, kWidth> Match(h2_t hash) const {
     auto match = _mm_set1_epi8(hash);
     return BitMask<uint32_t, kWidth>(
-        _mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl)));
+        static_cast<uint32_t>(_mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl))));
   }
 
   // Returns a bitmask representing the positions of empty slots.
-  BitMask<uint32_t, kWidth> MatchEmpty() const {
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
+  NonIterableBitMask<uint32_t, kWidth> MaskEmpty() const {
+#ifdef ABSL_INTERNAL_HAVE_SSSE3
     // This only works because ctrl_t::kEmpty is -128.
-    return BitMask<uint32_t, kWidth>(
-        _mm_movemask_epi8(_mm_sign_epi8(ctrl, ctrl)));
+    return NonIterableBitMask<uint32_t, kWidth>(
+        static_cast<uint32_t>(_mm_movemask_epi8(_mm_sign_epi8(ctrl, ctrl))));
 #else
-    return Match(static_cast<h2_t>(ctrl_t::kEmpty));
+    auto match = _mm_set1_epi8(static_cast<h2_t>(ctrl_t::kEmpty));
+    return NonIterableBitMask<uint32_t, kWidth>(
+        static_cast<uint32_t>(_mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl))));
 #endif
   }
 
   // Returns a bitmask representing the positions of empty or deleted slots.
-  BitMask<uint32_t, kWidth> MatchEmptyOrDeleted() const {
-    auto special = _mm_set1_epi8(static_cast<int8_t>(ctrl_t::kSentinel));
-    return BitMask<uint32_t, kWidth>(
-        _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl)));
+  NonIterableBitMask<uint32_t, kWidth> MaskEmptyOrDeleted() const {
+    auto special = _mm_set1_epi8(static_cast<uint8_t>(ctrl_t::kSentinel));
+    return NonIterableBitMask<uint32_t, kWidth>(static_cast<uint32_t>(
+        _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl))));
   }
 
   // Returns the number of trailing empty or deleted elements in the group.
   uint32_t CountLeadingEmptyOrDeleted() const {
-    auto special = _mm_set1_epi8(static_cast<int8_t>(ctrl_t::kSentinel));
+    auto special = _mm_set1_epi8(static_cast<uint8_t>(ctrl_t::kSentinel));
     return TrailingZeros(static_cast<uint32_t>(
         _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl)) + 1));
   }
@@ -391,7 +580,7 @@ struct GroupSse2Impl {
   void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
     auto msbs = _mm_set1_epi8(static_cast<char>(-128));
     auto x126 = _mm_set1_epi8(126);
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
+#ifdef ABSL_INTERNAL_HAVE_SSSE3
     auto res = _mm_or_si128(_mm_shuffle_epi8(x126, ctrl), msbs);
 #else
     auto zero = _mm_setzero_si128();
@@ -405,6 +594,63 @@ struct GroupSse2Impl {
 };
 #endif  // ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
 
+#if defined(ABSL_INTERNAL_HAVE_ARM_NEON) && defined(ABSL_IS_LITTLE_ENDIAN)
+struct GroupAArch64Impl {
+  static constexpr size_t kWidth = 8;
+
+  explicit GroupAArch64Impl(const ctrl_t* pos) {
+    ctrl = vld1_u8(reinterpret_cast<const uint8_t*>(pos));
+  }
+
+  BitMask<uint64_t, kWidth, 3> Match(h2_t hash) const {
+    uint8x8_t dup = vdup_n_u8(hash);
+    auto mask = vceq_u8(ctrl, dup);
+    constexpr uint64_t msbs = 0x8080808080808080ULL;
+    return BitMask<uint64_t, kWidth, 3>(
+        vget_lane_u64(vreinterpret_u64_u8(mask), 0) & msbs);
+  }
+
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmpty() const {
+    uint64_t mask =
+        vget_lane_u64(vreinterpret_u64_u8(
+                          vceq_s8(vdup_n_s8(static_cast<h2_t>(ctrl_t::kEmpty)),
+                                  vreinterpret_s8_u8(ctrl))),
+                      0);
+    return NonIterableBitMask<uint64_t, kWidth, 3>(mask);
+  }
+
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmptyOrDeleted() const {
+    uint64_t mask =
+        vget_lane_u64(vreinterpret_u64_u8(vcgt_s8(
+                          vdup_n_s8(static_cast<int8_t>(ctrl_t::kSentinel)),
+                          vreinterpret_s8_u8(ctrl))),
+                      0);
+    return NonIterableBitMask<uint64_t, kWidth, 3>(mask);
+  }
+
+  uint32_t CountLeadingEmptyOrDeleted() const {
+    uint64_t mask = vget_lane_u64(vreinterpret_u64_u8(ctrl), 0);
+    // ctrl | ~(ctrl >> 7) will have the lowest bit set to zero for kEmpty and
+    // kDeleted. We lower all other bits and count number of trailing zeros.
+    // Clang and GCC optimize countr_zero to rbit+clz without any check for 0,
+    // so we should be fine.
+    constexpr uint64_t bits = 0x0101010101010101ULL;
+    return countr_zero((mask | ~(mask >> 7)) & bits) >> 3;
+  }
+
+  void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
+    uint64_t mask = vget_lane_u64(vreinterpret_u64_u8(ctrl), 0);
+    constexpr uint64_t msbs = 0x8080808080808080ULL;
+    constexpr uint64_t lsbs = 0x0101010101010101ULL;
+    auto x = mask & msbs;
+    auto res = (~x + (x >> 7)) & ~lsbs;
+    little_endian::Store64(dst, res);
+  }
+
+  uint8x8_t ctrl;
+};
+#endif  // ABSL_INTERNAL_HAVE_ARM_NEON && ABSL_IS_LITTLE_ENDIAN
+
 struct GroupPortableImpl {
   static constexpr size_t kWidth = 8;
 
@@ -431,19 +677,23 @@ struct GroupPortableImpl {
     return BitMask<uint64_t, kWidth, 3>((x - lsbs) & ~x & msbs);
   }
 
-  BitMask<uint64_t, kWidth, 3> MatchEmpty() const {
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmpty() const {
     constexpr uint64_t msbs = 0x8080808080808080ULL;
-    return BitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 6)) & msbs);
+    return NonIterableBitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 6)) &
+                                                   msbs);
   }
 
-  BitMask<uint64_t, kWidth, 3> MatchEmptyOrDeleted() const {
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmptyOrDeleted() const {
     constexpr uint64_t msbs = 0x8080808080808080ULL;
-    return BitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 7)) & msbs);
+    return NonIterableBitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 7)) &
+                                                   msbs);
   }
 
   uint32_t CountLeadingEmptyOrDeleted() const {
-    constexpr uint64_t gaps = 0x00FEFEFEFEFEFEFEULL;
-    return (TrailingZeros(((~ctrl & (ctrl >> 7)) | gaps) + 1) + 7) >> 3;
+    // ctrl | ~(ctrl >> 7) will have the lowest bit set to zero for kEmpty and
+    // kDeleted. We lower all other bits and count number of trailing zeros.
+    constexpr uint64_t bits = 0x0101010101010101ULL;
+    return countr_zero((ctrl | ~(ctrl >> 7)) & bits) >> 3;
   }
 
   void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
@@ -457,32 +707,40 @@ struct GroupPortableImpl {
   uint64_t ctrl;
 };
 
-#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef ABSL_INTERNAL_HAVE_SSE2
 using Group = GroupSse2Impl;
+#elif defined(ABSL_INTERNAL_HAVE_ARM_NEON) && defined(ABSL_IS_LITTLE_ENDIAN)
+using Group = GroupAArch64Impl;
 #else
 using Group = GroupPortableImpl;
 #endif
 
-// The number of cloned control bytes that we copy from the beginning to the
-// end of the control bytes array.
+// Returns he number of "cloned control bytes".
+//
+// This is the number of control bytes that are present both at the beginning
+// of the control byte array and at the end, such that we can create a
+// `Group::kWidth`-width probe window starting from any control byte.
 constexpr size_t NumClonedBytes() { return Group::kWidth - 1; }
 
 template <class Policy, class Hash, class Eq, class Alloc>
 class raw_hash_set;
 
+// Returns whether `n` is a valid capacity (i.e., number of slots).
+//
+// A valid capacity is a non-zero integer `2^m - 1`.
 inline bool IsValidCapacity(size_t n) { return ((n + 1) & n) == 0 && n > 0; }
 
+// Applies the following mapping to every byte in the control array:
+//   * kDeleted -> kEmpty
+//   * kEmpty -> kEmpty
+//   * _ -> kDeleted
 // PRECONDITION:
 //   IsValidCapacity(capacity)
 //   ctrl[capacity] == ctrl_t::kSentinel
 //   ctrl[i] != ctrl_t::kSentinel for all i < capacity
-// Applies mapping for every byte in ctrl:
-//   DELETED -> EMPTY
-//   EMPTY -> EMPTY
-//   FULL -> DELETED
 void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity);
 
-// Rounds up the capacity to the next power of 2 minus 1, with a minimum of 1.
+// Converts `n` into the next valid capacity, per `IsValidCapacity`.
 inline size_t NormalizeCapacity(size_t n) {
   return n ? ~size_t{} >> countl_zero(n) : 1;
 }
@@ -495,8 +753,8 @@ inline size_t NormalizeCapacity(size_t n) {
 //   never need to probe (the whole table fits in one group) so we don't need a
 //   load factor less than 1.
 
-// Given `capacity` of the table, returns the size (i.e. number of full slots)
-// at which we should grow the capacity.
+// Given `capacity`, applies the load factor; i.e., it returns the maximum
+// number of values we should put into the table before a resizing rehash.
 inline size_t CapacityToGrowth(size_t capacity) {
   assert(IsValidCapacity(capacity));
   // `capacity*7/8`
@@ -506,8 +764,12 @@ inline size_t CapacityToGrowth(size_t capacity) {
   }
   return capacity - capacity / 8;
 }
-// From desired "growth" to a lowerbound of the necessary capacity.
-// Might not be a valid one and requires NormalizeCapacity().
+
+// Given `growth`, "unapplies" the load factor to find how large the capacity
+// should be to stay within the load factor.
+//
+// This might not be a valid capacity and `NormalizeCapacity()` should be
+// called on this.
 inline size_t GrowthToLowerboundCapacity(size_t growth) {
   // `growth*8/7`
   if (Group::kWidth == 8 && growth == 7) {
@@ -533,16 +795,15 @@ size_t SelectBucketCountForIterRange(InputIter first, InputIter last,
   return 0;
 }
 
-inline void AssertIsFull(ctrl_t* ctrl) {
-  ABSL_HARDENING_ASSERT((ctrl != nullptr && IsFull(*ctrl)) &&
-                        "Invalid operation on iterator. The element might have "
-                        "been erased, or the table might have rehashed.");
-}
+#define ABSL_INTERNAL_ASSERT_IS_FULL(ctrl, msg) \
+  ABSL_HARDENING_ASSERT((ctrl != nullptr && IsFull(*ctrl)) && msg)
 
 inline void AssertIsValid(ctrl_t* ctrl) {
-  ABSL_HARDENING_ASSERT((ctrl == nullptr || IsFull(*ctrl)) &&
-                        "Invalid operation on iterator. The element might have "
-                        "been erased, or the table might have rehashed.");
+  ABSL_HARDENING_ASSERT(
+      (ctrl == nullptr || IsFull(*ctrl)) &&
+      "Invalid operation on iterator. The element might have "
+      "been erased, the table might have rehashed, or this may "
+      "be an end() iterator.");
 }
 
 struct FindInfo {
@@ -550,44 +811,40 @@ struct FindInfo {
   size_t probe_length;
 };
 
-// The representation of the object has two modes:
-//  - small: For capacities < kWidth-1
-//  - large: For the rest.
+// Whether a table is "small". A small table fits entirely into a probing
+// group, i.e., has a capacity < `Group::kWidth`.
 //
-// Differences:
-//  - In small mode we are able to use the whole capacity. The extra control
-//  bytes give us at least one "empty" control byte to stop the iteration.
-//  This is important to make 1 a valid capacity.
+// In small mode we are able to use the whole capacity. The extra control
+// bytes give us at least one "empty" control byte to stop the iteration.
+// This is important to make 1 a valid capacity.
 //
-//  - In small mode only the first `capacity()` control bytes after the
-//  sentinel are valid. The rest contain dummy ctrl_t::kEmpty values that do not
-//  represent a real slot. This is important to take into account on
-//  find_first_non_full(), where we never try ShouldInsertBackwards() for
-//  small tables.
+// In small mode only the first `capacity` control bytes after the sentinel
+// are valid. The rest contain dummy ctrl_t::kEmpty values that do not
+// represent a real slot. This is important to take into account on
+// `find_first_non_full()`, where we never try
+// `ShouldInsertBackwards()` for small tables.
 inline bool is_small(size_t capacity) { return capacity < Group::kWidth - 1; }
 
+// Begins a probing operation on `ctrl`, using `hash`.
 inline probe_seq<Group::kWidth> probe(const ctrl_t* ctrl, size_t hash,
                                       size_t capacity) {
   return probe_seq<Group::kWidth>(H1(hash, ctrl), capacity);
 }
 
-// Probes the raw_hash_set with the probe sequence for hash and returns the
-// pointer to the first empty or deleted slot.
-// NOTE: this function must work with tables having both ctrl_t::kEmpty and
-// ctrl_t::kDeleted in one group. Such tables appears during
-// drop_deletes_without_resize.
+// Probes an array of control bits using a probe sequence derived from `hash`,
+// and returns the offset corresponding to the first deleted or empty slot.
 //
-// This function is very useful when insertions happen and:
-// - the input is already a set
-// - there are enough slots
-// - the element with the hash is not in the table
+// Behavior when the entire table is full is undefined.
+//
+// NOTE: this function must work with tables having both empty and deleted
+// slots in the same group. Such tables appear during `erase()`.
 template <typename = void>
 inline FindInfo find_first_non_full(const ctrl_t* ctrl, size_t hash,
                                     size_t capacity) {
   auto seq = probe(ctrl, hash, capacity);
   while (true) {
     Group g{ctrl + seq.offset()};
-    auto mask = g.MatchEmptyOrDeleted();
+    auto mask = g.MaskEmptyOrDeleted();
     if (mask) {
 #if !defined(NDEBUG)
       // We want to add entropy even when ASLR is not enabled.
@@ -610,7 +867,8 @@ inline FindInfo find_first_non_full(const ctrl_t* ctrl, size_t hash,
 // corresponding translation unit.
 extern template FindInfo find_first_non_full(const ctrl_t*, size_t, size_t);
 
-// Reset all ctrl bytes back to ctrl_t::kEmpty, except the sentinel.
+// Sets `ctrl` to `{kEmpty, kSentinel, ..., kEmpty}`, marking the entire
+// array as marked as empty.
 inline void ResetCtrl(size_t capacity, ctrl_t* ctrl, const void* slot,
                       size_t slot_size) {
   std::memset(ctrl, static_cast<int8_t>(ctrl_t::kEmpty),
@@ -619,8 +877,10 @@ inline void ResetCtrl(size_t capacity, ctrl_t* ctrl, const void* slot,
   SanitizerPoisonMemoryRegion(slot, slot_size * capacity);
 }
 
-// Sets the control byte, and if `i < NumClonedBytes()`, set the cloned byte
-// at the end too.
+// Sets `ctrl[i]` to `h`.
+//
+// Unlike setting it directly, this function will perform bounds checks and
+// mirror the value to the cloned tail if necessary.
 inline void SetCtrl(size_t i, ctrl_t h, size_t capacity, ctrl_t* ctrl,
                     const void* slot, size_t slot_size) {
   assert(i < capacity);
@@ -636,25 +896,28 @@ inline void SetCtrl(size_t i, ctrl_t h, size_t capacity, ctrl_t* ctrl,
   ctrl[((i - NumClonedBytes()) & capacity) + (NumClonedBytes() & capacity)] = h;
 }
 
+// Overload for setting to an occupied `h2_t` rather than a special `ctrl_t`.
 inline void SetCtrl(size_t i, h2_t h, size_t capacity, ctrl_t* ctrl,
                     const void* slot, size_t slot_size) {
   SetCtrl(i, static_cast<ctrl_t>(h), capacity, ctrl, slot, slot_size);
 }
 
-// The allocated block consists of `capacity + 1 + NumClonedBytes()` control
-// bytes followed by `capacity` slots, which must be aligned to `slot_align`.
-// SlotOffset returns the offset of the slots into the allocated block.
+// Given the capacity of a table, computes the offset (from the start of the
+// backing allocation) at which the slots begin.
 inline size_t SlotOffset(size_t capacity, size_t slot_align) {
   assert(IsValidCapacity(capacity));
   const size_t num_control_bytes = capacity + 1 + NumClonedBytes();
   return (num_control_bytes + slot_align - 1) & (~slot_align + 1);
 }
 
-// Returns the size of the allocated block. See also above comment.
+// Given the capacity of a table, computes the total size of the backing
+// array.
 inline size_t AllocSize(size_t capacity, size_t slot_size, size_t slot_align) {
   return SlotOffset(capacity, slot_align) + capacity * slot_size;
 }
 
+// A SwissTable.
+//
 // Policy: a policy defines how to perform different operations on
 // the slots of the hashtable (see hash_policy_traits.h for the full interface
 // of policy).
@@ -769,16 +1032,22 @@ class raw_hash_set {
 
     // PRECONDITION: not an end() iterator.
     reference operator*() const {
-      AssertIsFull(ctrl_);
+      ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_,
+                                   "operator*() called on invalid iterator.");
       return PolicyTraits::element(slot_);
     }
 
     // PRECONDITION: not an end() iterator.
-    pointer operator->() const { return &operator*(); }
+    pointer operator->() const {
+      ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_,
+                                   "operator-> called on invalid iterator.");
+      return &operator*();
+    }
 
     // PRECONDITION: not an end() iterator.
     iterator& operator++() {
-      AssertIsFull(ctrl_);
+      ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_,
+                                   "operator++ called on invalid iterator.");
       ++ctrl_;
       ++slot_;
       skip_empty_or_deleted();
@@ -804,9 +1073,13 @@ class raw_hash_set {
     iterator(ctrl_t* ctrl, slot_type* slot) : ctrl_(ctrl), slot_(slot) {
       // This assumption helps the compiler know that any non-end iterator is
       // not equal to any end iterator.
-      ABSL_INTERNAL_ASSUME(ctrl != nullptr);
+      ABSL_ASSUME(ctrl != nullptr);
     }
 
+    // Fixes up `ctrl_` to point to a full by advancing it and `slot_` until
+    // they reach one.
+    //
+    // If a sentinel is reached, we null both of them out instead.
     void skip_empty_or_deleted() {
       while (IsEmptyOrDeleted(*ctrl_)) {
         uint32_t shift = Group{ctrl_}.CountLeadingEmptyOrDeleted();
@@ -1103,8 +1376,7 @@ class raw_hash_set {
   //   m.insert(std::make_pair("abc", 42));
   // TODO(cheshire): A type alias T2 is introduced as a workaround for the nvcc
   // bug.
-  template <class T, RequiresInsertable<T> = 0,
-            class T2 = T,
+  template <class T, RequiresInsertable<T> = 0, class T2 = T,
             typename std::enable_if<IsDecomposable<T2>::value, int>::type = 0,
             T* = nullptr>
   std::pair<iterator, bool> insert(T&& value) {
@@ -1324,7 +1596,8 @@ class raw_hash_set {
   // This overload is necessary because otherwise erase<K>(const K&) would be
   // a better match if non-const iterator is passed as an argument.
   void erase(iterator it) {
-    AssertIsFull(it.ctrl_);
+    ABSL_INTERNAL_ASSERT_IS_FULL(it.ctrl_,
+                                 "erase() called on invalid iterator.");
     PolicyTraits::destroy(&alloc_ref(), it.slot_);
     erase_meta_only(it);
   }
@@ -1358,7 +1631,8 @@ class raw_hash_set {
   }
 
   node_type extract(const_iterator position) {
-    AssertIsFull(position.inner_.ctrl_);
+    ABSL_INTERNAL_ASSERT_IS_FULL(position.inner_.ctrl_,
+                                 "extract() called on invalid iterator.");
     auto node =
         CommonAccess::Transfer<node_type>(alloc_ref(), position.inner_.slot_);
     erase_meta_only(position);
@@ -1445,12 +1719,13 @@ class raw_hash_set {
   template <class K = key_type>
   void prefetch(const key_arg<K>& key) const {
     (void)key;
-#if defined(__GNUC__)
+    // Avoid probing if we won't be able to prefetch the addresses received.
+#ifdef ABSL_INTERNAL_HAVE_PREFETCH
     prefetch_heap_block();
     auto seq = probe(ctrl_, hash_ref()(key), capacity_);
-    __builtin_prefetch(static_cast<const void*>(ctrl_ + seq.offset()));
-    __builtin_prefetch(static_cast<const void*>(slots_ + seq.offset()));
-#endif  // __GNUC__
+    base_internal::PrefetchT0(ctrl_ + seq.offset());
+    base_internal::PrefetchT0(slots_ + seq.offset());
+#endif  // ABSL_INTERNAL_HAVE_PREFETCH
   }
 
   // The API of find() has two extensions.
@@ -1465,13 +1740,13 @@ class raw_hash_set {
     auto seq = probe(ctrl_, hash, capacity_);
     while (true) {
       Group g{ctrl_ + seq.offset()};
-      for (int i : g.Match(H2(hash))) {
+      for (uint32_t i : g.Match(H2(hash))) {
         if (ABSL_PREDICT_TRUE(PolicyTraits::apply(
                 EqualElement<K>{key, eq_ref()},
                 PolicyTraits::element(slots_ + seq.offset(i)))))
           return iterator_at(seq.offset(i));
       }
-      if (ABSL_PREDICT_TRUE(g.MatchEmpty())) return end();
+      if (ABSL_PREDICT_TRUE(g.MaskEmpty())) return end();
       seq.next();
       assert(seq.index() <= capacity_ && "full table!");
     }
@@ -1538,6 +1813,14 @@ class raw_hash_set {
     return !(a == b);
   }
 
+  template <typename H>
+  friend typename std::enable_if<H::template is_hashable<value_type>::value,
+                                 H>::type
+  AbslHashValue(H h, const raw_hash_set& s) {
+    return H::combine(H::combine_unordered(std::move(h), s.begin(), s.end()),
+                      s.size());
+  }
+
   friend void swap(raw_hash_set& a,
                    raw_hash_set& b) noexcept(noexcept(a.swap(b))) {
     a.swap(b);
@@ -1603,17 +1886,17 @@ class raw_hash_set {
     slot_type&& slot;
   };
 
-  // "erases" the object from the container, except that it doesn't actually
-  // destroy the object. It only updates all the metadata of the class.
-  // This can be used in conjunction with Policy::transfer to move the object to
-  // another place.
+  // Erases, but does not destroy, the value pointed to by `it`.
+  //
+  // This merely updates the pertinent control byte. This can be used in
+  // conjunction with Policy::transfer to move the object to another place.
   void erase_meta_only(const_iterator it) {
     assert(IsFull(*it.inner_.ctrl_) && "erasing a dangling iterator");
     --size_;
-    const size_t index = it.inner_.ctrl_ - ctrl_;
+    const size_t index = static_cast<size_t>(it.inner_.ctrl_ - ctrl_);
     const size_t index_before = (index - Group::kWidth) & capacity_;
-    const auto empty_after = Group(it.inner_.ctrl_).MatchEmpty();
-    const auto empty_before = Group(ctrl_ + index_before).MatchEmpty();
+    const auto empty_after = Group(it.inner_.ctrl_).MaskEmpty();
+    const auto empty_before = Group(ctrl_ + index_before).MaskEmpty();
 
     // We count how many consecutive non empties we have to the right and to the
     // left of `it`. If the sum is >= kWidth then there is at least one probe
@@ -1629,6 +1912,11 @@ class raw_hash_set {
     infoz().RecordErase();
   }
 
+  // Allocates a backing array for `self` and initializes its control bytes.
+  // This reads `capacity_` and updates all other fields based on the result of
+  // the allocation.
+  //
+  // This does not free the currently held array; `capacity_` must be nonzero.
   void initialize_slots() {
     assert(capacity_);
     // Folks with custom allocators often make unwarranted assumptions about the
@@ -1657,6 +1945,10 @@ class raw_hash_set {
     infoz().RecordStorageChanged(size_, capacity_);
   }
 
+  // Destroys all slots in the backing array, frees the backing array, and
+  // clears all top-level book-keeping data.
+  //
+  // This essentially implements `map = raw_hash_set();`.
   void destroy_slots() {
     if (!capacity_) return;
     for (size_t i = 0; i != capacity_; ++i) {
@@ -1707,6 +1999,9 @@ class raw_hash_set {
     infoz().RecordRehash(total_probe_length);
   }
 
+  // Prunes control bytes to remove as many tombstones as possible.
+  //
+  // See the comment on `rehash_and_grow_if_necessary()`.
   void drop_deletes_without_resize() ABSL_ATTRIBUTE_NOINLINE {
     assert(IsValidCapacity(capacity_));
     assert(!is_small(capacity_));
@@ -1773,6 +2068,11 @@ class raw_hash_set {
     infoz().RecordRehash(total_probe_length);
   }
 
+  // Called whenever the table *might* need to conditionally grow.
+  //
+  // This function is an optimization opportunity to perform a rehash even when
+  // growth is unnecessary, because vacating tombstones is beneficial for
+  // performance in the long-run.
   void rehash_and_grow_if_necessary() {
     if (capacity_ == 0) {
       resize(1);
@@ -1832,12 +2132,12 @@ class raw_hash_set {
     auto seq = probe(ctrl_, hash, capacity_);
     while (true) {
       Group g{ctrl_ + seq.offset()};
-      for (int i : g.Match(H2(hash))) {
+      for (uint32_t i : g.Match(H2(hash))) {
         if (ABSL_PREDICT_TRUE(PolicyTraits::element(slots_ + seq.offset(i)) ==
                               elem))
           return true;
       }
-      if (ABSL_PREDICT_TRUE(g.MatchEmpty())) return false;
+      if (ABSL_PREDICT_TRUE(g.MaskEmpty())) return false;
       seq.next();
       assert(seq.index() <= capacity_ && "full table!");
     }
@@ -1857,6 +2157,9 @@ class raw_hash_set {
   }
 
  protected:
+  // Attempts to find `key` in the table; if it isn't found, returns a slot that
+  // the value can be inserted into, with the control byte already set to
+  // `key`'s H2.
   template <class K>
   std::pair<size_t, bool> find_or_prepare_insert(const K& key) {
     prefetch_heap_block();
@@ -1864,19 +2167,23 @@ class raw_hash_set {
     auto seq = probe(ctrl_, hash, capacity_);
     while (true) {
       Group g{ctrl_ + seq.offset()};
-      for (int i : g.Match(H2(hash))) {
+      for (uint32_t i : g.Match(H2(hash))) {
         if (ABSL_PREDICT_TRUE(PolicyTraits::apply(
                 EqualElement<K>{key, eq_ref()},
                 PolicyTraits::element(slots_ + seq.offset(i)))))
           return {seq.offset(i), false};
       }
-      if (ABSL_PREDICT_TRUE(g.MatchEmpty())) break;
+      if (ABSL_PREDICT_TRUE(g.MaskEmpty())) break;
       seq.next();
       assert(seq.index() <= capacity_ && "full table!");
     }
     return {prepare_insert(hash), true};
   }
 
+  // Given the hash of a value not currently in the table, finds the next
+  // viable slot index to insert it at.
+  //
+  // REQUIRES: At least one non-full slot available.
   size_t prepare_insert(size_t hash) ABSL_ATTRIBUTE_NOINLINE {
     auto target = find_first_non_full(ctrl_, hash, capacity_);
     if (ABSL_PREDICT_FALSE(growth_left() == 0 &&
@@ -1920,15 +2227,23 @@ class raw_hash_set {
     growth_left() = CapacityToGrowth(capacity()) - size_;
   }
 
+  // The number of slots we can still fill without needing to rehash.
+  //
+  // This is stored separately due to tombstones: we do not include tombstones
+  // in the growth capacity, because we'd like to rehash when the table is
+  // otherwise filled with tombstones: otherwise, probe sequences might get
+  // unacceptably long without triggering a rehash. Callers can also force a
+  // rehash via the standard `rehash(0)`, which will recompute this value as a
+  // side-effect.
+  //
+  // See `CapacityToGrowth()`.
   size_t& growth_left() { return settings_.template get<0>(); }
 
+  // Prefetch the heap-allocated memory region to resolve potential TLB misses.
+  // This is intended to overlap with execution of calculating the hash for a
+  // key.
   void prefetch_heap_block() const {
-    // Prefetch the heap-allocated memory region to resolve potential TLB
-    // misses.  This is intended to overlap with execution of calculating the
-    // hash for a key.
-#if defined(__GNUC__)
-    __builtin_prefetch(static_cast<const void*>(ctrl_), 0, 1);
-#endif  // __GNUC__
+    base_internal::PrefetchT2(ctrl_);
   }
 
   HashtablezInfoHandle& infoz() { return settings_.template get<1>(); }
@@ -1945,20 +2260,33 @@ class raw_hash_set {
   // TODO(alkis): Investigate removing some of these fields:
   // - ctrl/slots can be derived from each other
   // - size can be moved into the slot array
-  ctrl_t* ctrl_ = EmptyGroup();  // [(capacity + 1 + NumClonedBytes()) * ctrl_t]
-  slot_type* slots_ = nullptr;   // [capacity * slot_type]
-  size_t size_ = 0;              // number of full slots
-  size_t capacity_ = 0;          // total number of slots
+
+  // The control bytes (and, also, a pointer to the base of the backing array).
+  //
+  // This contains `capacity_ + 1 + NumClonedBytes()` entries, even
+  // when the table is empty (hence EmptyGroup).
+  ctrl_t* ctrl_ = EmptyGroup();
+  // The beginning of the slots, located at `SlotOffset()` bytes after
+  // `ctrl_`. May be null for empty tables.
+  slot_type* slots_ = nullptr;
+
+  // The number of filled slots.
+  size_t size_ = 0;
+
+  // The total number of available slots.
+  size_t capacity_ = 0;
   absl::container_internal::CompressedTuple<size_t /* growth_left */,
                                             HashtablezInfoHandle, hasher,
                                             key_equal, allocator_type>
-      settings_{0, HashtablezInfoHandle{}, hasher{}, key_equal{},
+      settings_{0u, HashtablezInfoHandle{}, hasher{}, key_equal{},
                 allocator_type{}};
 };
 
 // Erases all elements that satisfy the predicate `pred` from the container `c`.
 template <typename P, typename H, typename E, typename A, typename Predicate>
-void EraseIf(Predicate& pred, raw_hash_set<P, H, E, A>* c) {
+typename raw_hash_set<P, H, E, A>::size_type EraseIf(
+    Predicate& pred, raw_hash_set<P, H, E, A>* c) {
+  const auto initial_size = c->size();
   for (auto it = c->begin(), last = c->end(); it != last;) {
     if (pred(*it)) {
       c->erase(it++);
@@ -1966,6 +2294,7 @@ void EraseIf(Predicate& pred, raw_hash_set<P, H, E, A>* c) {
       ++it;
     }
   }
+  return initial_size - c->size();
 }
 
 namespace hashtable_debug_internal {
@@ -1981,7 +2310,7 @@ struct HashtableDebugAccess<Set, absl::void_t<typename Set::raw_hash_set>> {
     auto seq = probe(set.ctrl_, hash, set.capacity_);
     while (true) {
       container_internal::Group g{set.ctrl_ + seq.offset()};
-      for (int i : g.Match(container_internal::H2(hash))) {
+      for (uint32_t i : g.Match(container_internal::H2(hash))) {
         if (Traits::apply(
                 typename Set::template EqualElement<typename Set::key_type>{
                     key, set.eq_ref()},
@@ -1989,7 +2318,7 @@ struct HashtableDebugAccess<Set, absl::void_t<typename Set::raw_hash_set>> {
           return num_probes;
         ++num_probes;
       }
-      if (g.MatchEmpty()) return num_probes;
+      if (g.MaskEmpty()) return num_probes;
       seq.next();
       ++num_probes;
     }
@@ -2031,4 +2360,6 @@ struct HashtableDebugAccess<Set, absl::void_t<typename Set::raw_hash_set>> {
 ABSL_NAMESPACE_END
 }  // namespace absl
 
+#undef ABSL_INTERNAL_ASSERT_IS_FULL
+
 #endif  // ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_