Export of internal Abseil changes

--
91ca367a7548270155721bdda74611aeea2a2153 by Abseil Team <absl-team@google.com>:

Replace the only usage of btree_node::swap with simpler logic using transfers and delete btree_node::swap.

Add a benchmark for constructing small containers.

PiperOrigin-RevId: 301169874

--
ff9d73a7125b7f8ab5733cda877204dfbfac138e by Derek Mauro <dmauro@google.com>:

Ensure ABSL_CXX_STANDARD is set.
Fixes #640

PiperOrigin-RevId: 301160106

--
14ca0beee8c109e532134e7e9da7b072da1bf911 by Abseil Team <absl-team@google.com>:

Rollback the change to make Cord iterators a fixed size.  That change increased the iterator size, which can cause a deep recursion call to hit the stack memory limit, in turn causing a signal 11 failure.

PiperOrigin-RevId: 301084915

--
619e3cd9e56408bdb8b3b5a1e08dda1e95242264 by Matthew Brown <matthewbr@google.com>:

Internal Change

PiperOrigin-RevId: 300832828

--
64f8d62ab4c4c78077dbe85a9595a8eeb6d16608 by Gennadiy Rozental <rogeeff@google.com>:

Fix for empty braces support.

We will call proper aggregate construction in case when {} is used as default value. In other words instead of "new T", we'll call "new T{}".

PiperOrigin-RevId: 300715686

--
db3f65594d6db8b104b01262f884dff465b696ef by Abseil Team <absl-team@google.com>:

Emscripten supports thread-local storage nowadays.

PiperOrigin-RevId: 300675185
GitOrigin-RevId: 91ca367a7548270155721bdda74611aeea2a2153
Change-Id: I3344f745f9c3fc78775532b1808442fabd98e34a

11 files changed, 257 insertions, 286 deletions

diff --git a/absl/base/config.h b/absl/base/config.h
index ee99f946..f54466de 100644
--- a/absl/base/config.h
+++ b/absl/base/config.h
@@ -262,13 +262,6 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #endif
 #endif  // defined(__ANDROID__) && defined(__clang__)
 
-// Emscripten doesn't yet support `thread_local` or `__thread`.
-// https://github.com/emscripten-core/emscripten/issues/3502
-#if defined(__EMSCRIPTEN__)
-#undef ABSL_HAVE_TLS
-#undef ABSL_HAVE_THREAD_LOCAL
-#endif  // defined(__EMSCRIPTEN__)
-
 // ABSL_HAVE_INTRINSIC_INT128
 //
 // Checks whether the __int128 compiler extension for a 128-bit integral type is
diff --git a/absl/container/btree_benchmark.cc b/absl/container/btree_benchmark.cc
index ca4d575c..46798676 100644
--- a/absl/container/btree_benchmark.cc
+++ b/absl/container/btree_benchmark.cc
@@ -134,6 +134,27 @@ void BM_InsertEnd(benchmark::State& state) {
   }
 }
 
+// Benchmark inserting the first few elements in a container. In b-tree, this is
+// when the root node grows.
+template <typename T>
+void BM_InsertSmall(benchmark::State& state) {
+  using V = typename remove_pair_const<typename T::value_type>::type;
+
+  const int kSize = 8;
+  std::vector<V> values = GenerateValues<V>(kSize);
+  T container;
+
+  while (state.KeepRunningBatch(kSize)) {
+    for (int i = 0; i < kSize; ++i) {
+      benchmark::DoNotOptimize(container.insert(values[i]));
+    }
+    state.PauseTiming();
+    // Do not measure the time it takes to clear the container.
+    container.clear();
+    state.ResumeTiming();
+  }
+}
+
 template <typename T>
 void BM_LookupImpl(benchmark::State& state, bool sorted) {
   using V = typename remove_pair_const<typename T::value_type>::type;
@@ -493,6 +514,7 @@ BTREE_TYPES(Time);
   MY_BENCHMARK4(type, Insert);            \
   MY_BENCHMARK4(type, InsertSorted);      \
   MY_BENCHMARK4(type, InsertEnd);         \
+  MY_BENCHMARK4(type, InsertSmall);       \
   MY_BENCHMARK4(type, Lookup);            \
   MY_BENCHMARK4(type, FullLookup);        \
   MY_BENCHMARK4(type, Delete);            \
diff --git a/absl/container/internal/btree.h b/absl/container/internal/btree.h
index d986f81e..adf49f81 100644
--- a/absl/container/internal/btree.h
+++ b/absl/container/internal/btree.h
@@ -776,9 +776,6 @@ class btree_node {
   // delimiting key in the parent node onto itself.
   void merge(btree_node *src, allocator_type *alloc);
 
-  // Swaps the contents of `this` and `other`.
-  void swap(btree_node *other, allocator_type *alloc);
-
   // Node allocation/deletion routines.
   void init_leaf(btree_node *parent, int max_count) {
     set_parent(parent);
@@ -820,6 +817,14 @@ class btree_node {
     absl::container_internal::SanitizerPoisonObject(slot(i));
   }
 
+  // Transfers value from slot `src_i` in `src` to slot `dest_i` in `this`.
+  void transfer(const size_type dest_i, const size_type src_i, btree_node *src,
+                allocator_type *alloc) {
+    absl::container_internal::SanitizerUnpoisonObject(slot(dest_i));
+    params_type::transfer(alloc, slot(dest_i), src->slot(src_i));
+    absl::container_internal::SanitizerPoisonObject(src->slot(src_i));
+  }
+
   // Move n values starting at value i in this node into the values starting at
   // value j in dest_node.
   void uninitialized_move_n(const size_type n, const size_type i,
@@ -1752,54 +1757,6 @@ void btree_node<P>::merge(btree_node *src, allocator_type *alloc) {
   parent()->remove_value(position(), alloc);
 }
 
-template <typename P>
-void btree_node<P>::swap(btree_node *other, allocator_type *alloc) {
-  using std::swap;
-  assert(leaf() == other->leaf());
-
-  // Determine which is the smaller/larger node.
-  btree_node *smaller = this, *larger = other;
-  if (smaller->count() > larger->count()) {
-    swap(smaller, larger);
-  }
-
-  // Swap the values.
-  for (slot_type *a = smaller->start_slot(), *b = larger->start_slot(),
-                 *end = smaller->finish_slot();
-       a != end; ++a, ++b) {
-    params_type::swap(alloc, a, b);
-  }
-
-  // Move values that can't be swapped.
-  const size_type to_move = larger->count() - smaller->count();
-  larger->uninitialized_move_n(to_move, smaller->finish(), smaller->finish(),
-                               smaller, alloc);
-  larger->value_destroy_n(smaller->finish(), to_move, alloc);
-
-  if (!leaf()) {
-    // Swap the child pointers.
-    std::swap_ranges(&smaller->mutable_child(smaller->start()),
-                     &smaller->mutable_child(smaller->finish() + 1),
-                     &larger->mutable_child(larger->start()));
-    // Update swapped children's parent pointers.
-    int i = smaller->start();
-    int j = larger->start();
-    for (; i <= smaller->finish(); ++i, ++j) {
-      smaller->child(i)->set_parent(smaller);
-      larger->child(j)->set_parent(larger);
-    }
-    // Move the child pointers that couldn't be swapped.
-    for (; j <= larger->finish(); ++i, ++j) {
-      smaller->init_child(i, larger->child(j));
-      larger->clear_child(j);
-    }
-  }
-
-  // Swap the `finish`s.
-  // TODO(ezb): with floating storage, will also need to swap starts.
-  swap(mutable_finish(), other->mutable_finish());
-}
-
 ////
 // btree_iterator methods
 template <typename N, typename R, typename P>
@@ -2492,6 +2449,7 @@ inline auto btree<P>::internal_emplace(iterator iter, Args &&... args)
     ++iter.position;
   }
   const int max_count = iter.node->max_count();
+  allocator_type *alloc = mutable_allocator();
   if (iter.node->count() == max_count) {
     // Make room in the leaf for the new item.
     if (max_count < kNodeValues) {
@@ -2500,15 +2458,21 @@ inline auto btree<P>::internal_emplace(iterator iter, Args &&... args)
       assert(iter.node == root());
       iter.node =
           new_leaf_root_node((std::min<int>)(kNodeValues, 2 * max_count));
-      iter.node->swap(root(), mutable_allocator());
-      delete_leaf_node(root());
-      mutable_root() = rightmost_ = iter.node;
+      // Transfer the values from the old root to the new root.
+      node_type *old_root = root();
+      node_type *new_root = iter.node;
+      for (int i = old_root->start(), f = old_root->finish(); i < f; ++i) {
+        new_root->transfer(i, i, old_root, alloc);
+      }
+      new_root->set_finish(old_root->finish());
+      old_root->set_finish(old_root->start());
+      delete_leaf_node(old_root);
+      mutable_root() = rightmost_ = new_root;
     } else {
       rebalance_or_split(&iter);
     }
   }
-  iter.node->emplace_value(iter.position, mutable_allocator(),
-                           std::forward<Args>(args)...);
+  iter.node->emplace_value(iter.position, alloc, std::forward<Args>(args)...);
   ++size_;
   return iter;
 }
diff --git a/absl/copts/AbseilConfigureCopts.cmake b/absl/copts/AbseilConfigureCopts.cmake
index 390a07a0..9557e36f 100644
--- a/absl/copts/AbseilConfigureCopts.cmake
+++ b/absl/copts/AbseilConfigureCopts.cmake
@@ -63,3 +63,5 @@ else()
   set(ABSL_DEFAULT_COPTS "")
   set(ABSL_TEST_COPTS "")
 endif()
+
+set(ABSL_CXX_STANDARD "${CMAKE_CXX_STANDARD}")
diff --git a/absl/flags/flag_test.cc b/absl/flags/flag_test.cc
index 1e01b49c..3a025576 100644
--- a/absl/flags/flag_test.cc
+++ b/absl/flags/flag_test.cc
@@ -293,6 +293,18 @@ TEST_F(FlagTest, TestFlagDefinition) {
 // --------------------------------------------------------------------
 
 TEST_F(FlagTest, TestDefault) {
+  EXPECT_EQ(FLAGS_test_flag_01.DefaultValue(), "true");
+  EXPECT_EQ(FLAGS_test_flag_02.DefaultValue(), "1234");
+  EXPECT_EQ(FLAGS_test_flag_03.DefaultValue(), "-34");
+  EXPECT_EQ(FLAGS_test_flag_04.DefaultValue(), "189");
+  EXPECT_EQ(FLAGS_test_flag_05.DefaultValue(), "10765");
+  EXPECT_EQ(FLAGS_test_flag_06.DefaultValue(), "40000");
+  EXPECT_EQ(FLAGS_test_flag_07.DefaultValue(), "-1234567");
+  EXPECT_EQ(FLAGS_test_flag_08.DefaultValue(), "9876543");
+  EXPECT_EQ(FLAGS_test_flag_09.DefaultValue(), "-9.876e-50");
+  EXPECT_EQ(FLAGS_test_flag_10.DefaultValue(), "1.234e+12");
+  EXPECT_EQ(FLAGS_test_flag_11.DefaultValue(), "");
+
   EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_01), true);
   EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_02), 1234);
   EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_03), -34);
@@ -308,6 +320,61 @@ TEST_F(FlagTest, TestDefault) {
 
 // --------------------------------------------------------------------
 
+struct NonTriviallyCopyableAggregate {
+  NonTriviallyCopyableAggregate() = default;
+  NonTriviallyCopyableAggregate(const NonTriviallyCopyableAggregate& rhs)
+      : value(rhs.value) {}
+  NonTriviallyCopyableAggregate& operator=(
+      const NonTriviallyCopyableAggregate& rhs) {
+    value = rhs.value;
+    return *this;
+  }
+
+  int value;
+};
+bool AbslParseFlag(absl::string_view src, NonTriviallyCopyableAggregate* f,
+                   std::string* e) {
+  return absl::ParseFlag(src, &f->value, e);
+}
+std::string AbslUnparseFlag(const NonTriviallyCopyableAggregate& ntc) {
+  return absl::StrCat(ntc.value);
+}
+
+bool operator==(const NonTriviallyCopyableAggregate& ntc1,
+                const NonTriviallyCopyableAggregate& ntc2) {
+  return ntc1.value == ntc2.value;
+}
+
+}  // namespace
+
+ABSL_FLAG(bool, test_flag_eb_01, {}, "");
+ABSL_FLAG(int32_t, test_flag_eb_02, {}, "");
+ABSL_FLAG(int64_t, test_flag_eb_03, {}, "");
+ABSL_FLAG(double, test_flag_eb_04, {}, "");
+ABSL_FLAG(std::string, test_flag_eb_05, {}, "");
+ABSL_FLAG(NonTriviallyCopyableAggregate, test_flag_eb_06, {}, "");
+
+namespace {
+
+TEST_F(FlagTest, TestEmptyBracesDefault) {
+  EXPECT_EQ(FLAGS_test_flag_eb_01.DefaultValue(), "false");
+  EXPECT_EQ(FLAGS_test_flag_eb_02.DefaultValue(), "0");
+  EXPECT_EQ(FLAGS_test_flag_eb_03.DefaultValue(), "0");
+  EXPECT_EQ(FLAGS_test_flag_eb_04.DefaultValue(), "0");
+  EXPECT_EQ(FLAGS_test_flag_eb_05.DefaultValue(), "");
+  EXPECT_EQ(FLAGS_test_flag_eb_06.DefaultValue(), "0");
+
+  EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_eb_01), false);
+  EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_eb_02), 0);
+  EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_eb_03), 0);
+  EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_eb_04), 0.0);
+  EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_eb_05), "");
+  EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_eb_06),
+            NonTriviallyCopyableAggregate{});
+}
+
+// --------------------------------------------------------------------
+
 TEST_F(FlagTest, TestGetSet) {
   absl::SetFlag(&FLAGS_test_flag_01, false);
   EXPECT_EQ(absl::GetFlag(FLAGS_test_flag_01), false);
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index 344e31f6..0ef0ee74 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -647,7 +647,7 @@ T* MakeFromDefaultValue(T t) {
 
 template <typename T>
 T* MakeFromDefaultValue(EmptyBraces) {
-  return new T;
+  return new T{};
 }
 
 }  // namespace flags_internal
diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 415b239b..4f64f799 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -30,6 +30,7 @@
 #include "absl/base/internal/raw_logging.h"
 #include "absl/base/port.h"
 #include "absl/container/fixed_array.h"
+#include "absl/container/inlined_vector.h"
 #include "absl/strings/escaping.h"
 #include "absl/strings/internal/cord_internal.h"
 #include "absl/strings/internal/resize_uninitialized.h"
@@ -131,14 +132,6 @@ inline const CordRepExternal* CordRep::external() const {
   return static_cast<const CordRepExternal*>(this);
 }
 
-using CordTreeConstPath = CordTreePath<const CordRep*, MaxCordDepth()>;
-
-// This type is used to store the list of pending nodes during re-balancing.
-// Its maximum size is 2 * MaxCordDepth() because the tree has a maximum
-// possible depth of MaxCordDepth() and every concat node along a tree path
-// could theoretically be split during rebalancing.
-using RebalancingStack = CordTreePath<CordRep*, 2 * MaxCordDepth()>;
-
 }  // namespace cord_internal
 
 static const size_t kFlatOverhead = offsetof(CordRep, data);
@@ -187,78 +180,98 @@ static constexpr size_t TagToLength(uint8_t tag) {
 // Enforce that kMaxFlatSize maps to a well-known exact tag value.
 static_assert(TagToAllocatedSize(224) == kMaxFlatSize, "Bad tag logic");
 
-constexpr size_t Fibonacci(uint8_t n, const size_t a = 0, const size_t b = 1) {
-  return n == 0
-             ? a
-             : n == 1 ? b
-                      : Fibonacci(n - 1, b,
-                                  (a > (size_t(-1) - b)) ? size_t(-1) : a + b);
+constexpr uint64_t Fibonacci(unsigned char n, uint64_t a = 0, uint64_t b = 1) {
+  return n == 0 ? a : Fibonacci(n - 1, b, a + b);
 }
 
+static_assert(Fibonacci(63) == 6557470319842,
+              "Fibonacci values computed incorrectly");
+
 // Minimum length required for a given depth tree -- a tree is considered
 // balanced if
-//      length(t) >= kMinLength[depth(t)]
-// The node depth is allowed to become larger to reduce rebalancing
-// for larger strings (see ShouldRebalance).
-constexpr size_t kMinLength[] = {
-    Fibonacci(2),  Fibonacci(3),  Fibonacci(4),  Fibonacci(5),  Fibonacci(6),
-    Fibonacci(7),  Fibonacci(8),  Fibonacci(9),  Fibonacci(10), Fibonacci(11),
-    Fibonacci(12), Fibonacci(13), Fibonacci(14), Fibonacci(15), Fibonacci(16),
-    Fibonacci(17), Fibonacci(18), Fibonacci(19), Fibonacci(20), Fibonacci(21),
-    Fibonacci(22), Fibonacci(23), Fibonacci(24), Fibonacci(25), Fibonacci(26),
-    Fibonacci(27), Fibonacci(28), Fibonacci(29), Fibonacci(30), Fibonacci(31),
-    Fibonacci(32), Fibonacci(33), Fibonacci(34), Fibonacci(35), Fibonacci(36),
-    Fibonacci(37), Fibonacci(38), Fibonacci(39), Fibonacci(40), Fibonacci(41),
-    Fibonacci(42), Fibonacci(43), Fibonacci(44), Fibonacci(45), Fibonacci(46),
-    Fibonacci(47), Fibonacci(48), Fibonacci(49), Fibonacci(50), Fibonacci(51),
-    Fibonacci(52), Fibonacci(53), Fibonacci(54), Fibonacci(55), Fibonacci(56),
-    Fibonacci(57), Fibonacci(58), Fibonacci(59), Fibonacci(60), Fibonacci(61),
-    Fibonacci(62), Fibonacci(63), Fibonacci(64), Fibonacci(65), Fibonacci(66),
-    Fibonacci(67), Fibonacci(68), Fibonacci(69), Fibonacci(70), Fibonacci(71),
-    Fibonacci(72), Fibonacci(73), Fibonacci(74), Fibonacci(75), Fibonacci(76),
-    Fibonacci(77), Fibonacci(78), Fibonacci(79), Fibonacci(80), Fibonacci(81),
-    Fibonacci(82), Fibonacci(83), Fibonacci(84), Fibonacci(85), Fibonacci(86),
-    Fibonacci(87), Fibonacci(88), Fibonacci(89), Fibonacci(90), Fibonacci(91),
-    Fibonacci(92), Fibonacci(93), Fibonacci(94), Fibonacci(95)};
-
-static_assert(sizeof(kMinLength) / sizeof(size_t) >=
-                  (cord_internal::MaxCordDepth() + 1),
-              "Not enough elements in kMinLength array to cover all the "
-              "supported Cord depth(s)");
-
-inline bool ShouldRebalance(const CordRep* node) {
-  if (node->tag != CONCAT) return false;
-
-  size_t node_depth = node->concat()->depth();
-
-  if (node_depth <= 15) return false;
-
-  // Rebalancing Cords is expensive, so we reduce how often rebalancing occurs
-  // by allowing shallow Cords to have twice the depth that the Fibonacci rule
-  // would otherwise imply. Deep Cords need to follow the rule more closely,
-  // however to ensure algorithm correctness. We implement this with linear
-  // interpolation. Cords of depth 16 are treated as though they have a depth
-  // of 16 * 1/2, and Cords of depth MaxCordDepth() interpolate to
-  // MaxCordDepth() * 1.
-  return node->length <
-         kMinLength[(node_depth * (cord_internal::MaxCordDepth() - 16)) /
-                    (2 * cord_internal::MaxCordDepth() - 16 - node_depth)];
-}
-
-// Unlike root balancing condition this one is part of the re-balancing
-// algorithm and has to be always matching against right depth for
-// algorithm to be correct.
-inline bool IsNodeBalanced(const CordRep* node) {
-  if (node->tag != CONCAT) return true;
-
-  size_t node_depth = node->concat()->depth();
-
-  return node->length >= kMinLength[node_depth];
+//      length(t) >= min_length[depth(t)]
+// The root node depth is allowed to become twice as large to reduce rebalancing
+// for larger strings (see IsRootBalanced).
+static constexpr uint64_t min_length[] = {
+    Fibonacci(2),
+    Fibonacci(3),
+    Fibonacci(4),
+    Fibonacci(5),
+    Fibonacci(6),
+    Fibonacci(7),
+    Fibonacci(8),
+    Fibonacci(9),
+    Fibonacci(10),
+    Fibonacci(11),
+    Fibonacci(12),
+    Fibonacci(13),
+    Fibonacci(14),
+    Fibonacci(15),
+    Fibonacci(16),
+    Fibonacci(17),
+    Fibonacci(18),
+    Fibonacci(19),
+    Fibonacci(20),
+    Fibonacci(21),
+    Fibonacci(22),
+    Fibonacci(23),
+    Fibonacci(24),
+    Fibonacci(25),
+    Fibonacci(26),
+    Fibonacci(27),
+    Fibonacci(28),
+    Fibonacci(29),
+    Fibonacci(30),
+    Fibonacci(31),
+    Fibonacci(32),
+    Fibonacci(33),
+    Fibonacci(34),
+    Fibonacci(35),
+    Fibonacci(36),
+    Fibonacci(37),
+    Fibonacci(38),
+    Fibonacci(39),
+    Fibonacci(40),
+    Fibonacci(41),
+    Fibonacci(42),
+    Fibonacci(43),
+    Fibonacci(44),
+    Fibonacci(45),
+    Fibonacci(46),
+    Fibonacci(47),
+    0xffffffffffffffffull,  // Avoid overflow
+};
+
+static const int kMinLengthSize = ABSL_ARRAYSIZE(min_length);
+
+// The inlined size to use with absl::InlinedVector.
+//
+// Note: The InlinedVectors in this file (and in cord.h) do not need to use
+// the same value for their inlined size. The fact that they do is historical.
+// It may be desirable for each to use a different inlined size optimized for
+// that InlinedVector's usage.
+//
+// TODO(jgm): Benchmark to see if there's a more optimal value than 47 for
+// the inlined vector size (47 exists for backward compatibility).
+static const int kInlinedVectorSize = 47;
+
+static inline bool IsRootBalanced(CordRep* node) {
+  if (node->tag != CONCAT) {
+    return true;
+  } else if (node->concat()->depth() <= 15) {
+    return true;
+  } else if (node->concat()->depth() > kMinLengthSize) {
+    return false;
+  } else {
+    // Allow depth to become twice as large as implied by fibonacci rule to
+    // reduce rebalancing for larger strings.
+    return (node->length >= min_length[node->concat()->depth() / 2]);
+  }
 }
 
 static CordRep* Rebalance(CordRep* node);
-static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os);
-static bool VerifyNode(const CordRep* root, const CordRep* start_node,
+static void DumpNode(CordRep* rep, bool include_data, std::ostream* os);
+static bool VerifyNode(CordRep* root, CordRep* start_node,
                        bool full_validation);
 
 static inline CordRep* VerifyTree(CordRep* node) {
@@ -305,8 +318,7 @@ __attribute__((preserve_most))
 static void UnrefInternal(CordRep* rep) {
   assert(rep != nullptr);
 
-  cord_internal::RebalancingStack pending;
-
+  absl::InlinedVector<CordRep*, kInlinedVectorSize> pending;
   while (true) {
     if (rep->tag == CONCAT) {
       CordRepConcat* rep_concat = rep->concat();
@@ -388,11 +400,6 @@ static void SetConcatChildren(CordRepConcat* concat, CordRep* left,
 
   concat->length = left->length + right->length;
   concat->set_depth(1 + std::max(Depth(left), Depth(right)));
-
-  ABSL_INTERNAL_CHECK(concat->depth() <= cord_internal::MaxCordDepth(),
-                      "Cord depth exceeds max");
-  ABSL_INTERNAL_CHECK(concat->length >= left->length, "Cord is too long");
-  ABSL_INTERNAL_CHECK(concat->length >= right->length, "Cord is too long");
 }
 
 // Create a concatenation of the specified nodes.
@@ -418,7 +425,7 @@ static CordRep* RawConcat(CordRep* left, CordRep* right) {
 
 static CordRep* Concat(CordRep* left, CordRep* right) {
   CordRep* rep = RawConcat(left, right);
-  if (rep != nullptr && ShouldRebalance(rep)) {
+  if (rep != nullptr && !IsRootBalanced(rep)) {
     rep = Rebalance(rep);
   }
   return VerifyTree(rep);
@@ -909,7 +916,7 @@ void Cord::Prepend(absl::string_view src) {
 static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
   if (n >= node->length) return nullptr;
   if (n == 0) return Ref(node);
-  cord_internal::CordTreeMutablePath rhs_stack;
+  absl::InlinedVector<CordRep*, kInlinedVectorSize> rhs_stack;
 
   while (node->tag == CONCAT) {
     assert(n <= node->length);
@@ -950,7 +957,7 @@ static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
 static CordRep* RemoveSuffixFrom(CordRep* node, size_t n) {
   if (n >= node->length) return nullptr;
   if (n == 0) return Ref(node);
-  absl::cord_internal::CordTreeMutablePath lhs_stack;
+  absl::InlinedVector<CordRep*, kInlinedVectorSize> lhs_stack;
   bool inplace_ok = node->refcount.IsOne();
 
   while (node->tag == CONCAT) {
@@ -1021,7 +1028,6 @@ void Cord::RemoveSuffix(size_t n) {
 
 // Work item for NewSubRange().
 struct SubRange {
-  SubRange() = default;
   SubRange(CordRep* a_node, size_t a_pos, size_t a_n)
       : node(a_node), pos(a_pos), n(a_n) {}
   CordRep* node;  // nullptr means concat last 2 results.
@@ -1030,11 +1036,8 @@ struct SubRange {
 };
 
 static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
-  cord_internal::CordTreeMutablePath results;
-  // The algorithm below in worst case scenario adds up to 3 nodes to the `todo`
-  // list, but we also pop one out on every cycle. If original tree has depth d
-  // todo list can grew up to 2*d in size.
-  cord_internal::CordTreePath<SubRange, 2 * cord_internal::MaxCordDepth()> todo;
+  absl::InlinedVector<CordRep*, kInlinedVectorSize> results;
+  absl::InlinedVector<SubRange, kInlinedVectorSize> todo;
   todo.push_back(SubRange(node, pos, n));
   do {
     const SubRange& sr = todo.back();
@@ -1071,7 +1074,7 @@ static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
     }
   } while (!todo.empty());
   assert(results.size() == 1);
-  return results.back();
+  return results[0];
 }
 
 Cord Cord::Subcord(size_t pos, size_t new_size) const {
@@ -1110,12 +1113,11 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
 
 class CordForest {
  public:
-  explicit CordForest(size_t length) : root_length_(length), trees_({}) {}
+  explicit CordForest(size_t length)
+      : root_length_(length), trees_(kMinLengthSize, nullptr) {}
 
   void Build(CordRep* cord_root) {
-    // We are adding up to two nodes to the `pending` list, but we also popping
-    // one, so the size of `pending` will never exceed `MaxCordDepth()`.
-    cord_internal::CordTreeMutablePath pending(cord_root);
+    std::vector<CordRep*> pending = {cord_root};
 
     while (!pending.empty()) {
       CordRep* node = pending.back();
@@ -1127,20 +1129,21 @@ class CordForest {
       }
 
       CordRepConcat* concat_node = node->concat();
-      if (IsNodeBalanced(concat_node)) {
-        AddNode(node);
-        continue;
-      }
-      pending.push_back(concat_node->right);
-      pending.push_back(concat_node->left);
-
-      if (concat_node->refcount.IsOne()) {
-        concat_node->left = concat_freelist_;
-        concat_freelist_ = concat_node;
+      if (concat_node->depth() >= kMinLengthSize ||
+          concat_node->length < min_length[concat_node->depth()]) {
+        pending.push_back(concat_node->right);
+        pending.push_back(concat_node->left);
+
+        if (concat_node->refcount.IsOne()) {
+          concat_node->left = concat_freelist_;
+          concat_freelist_ = concat_node;
+        } else {
+          Ref(concat_node->right);
+          Ref(concat_node->left);
+          Unref(concat_node);
+        }
       } else {
-        Ref(concat_node->right);
-        Ref(concat_node->left);
-        Unref(concat_node);
+        AddNode(node);
       }
     }
   }
@@ -1172,7 +1175,7 @@ class CordForest {
 
     // Collect together everything with which we will merge with node
     int i = 0;
-    for (; node->length >= kMinLength[i + 1]; ++i) {
+    for (; node->length > min_length[i + 1]; ++i) {
       auto& tree_at_i = trees_[i];
 
       if (tree_at_i == nullptr) continue;
@@ -1183,7 +1186,7 @@ class CordForest {
     sum = AppendNode(node, sum);
 
     // Insert sum into appropriate place in the forest
-    for (; sum->length >= kMinLength[i]; ++i) {
+    for (; sum->length >= min_length[i]; ++i) {
       auto& tree_at_i = trees_[i];
       if (tree_at_i == nullptr) continue;
 
@@ -1191,7 +1194,7 @@ class CordForest {
       tree_at_i = nullptr;
     }
 
-    // kMinLength[0] == 1, which means sum->length >= kMinLength[0]
+    // min_length[0] == 1, which means sum->length >= min_length[0]
     assert(i > 0);
     trees_[i - 1] = sum;
   }
@@ -1224,7 +1227,9 @@ class CordForest {
   }
 
   size_t root_length_;
-  std::array<cord_internal::CordRep*, cord_internal::MaxCordDepth()> trees_;
+
+  // use an inlined vector instead of a flat array to get bounds checking
+  absl::InlinedVector<CordRep*, kInlinedVectorSize> trees_;
 
   // List of concat nodes we can re-use for Cord balancing.
   CordRepConcat* concat_freelist_ = nullptr;
@@ -1836,18 +1841,18 @@ absl::string_view Cord::FlattenSlowPath() {
   }
 }
 
-static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os) {
+static void DumpNode(CordRep* rep, bool include_data, std::ostream* os) {
   const int kIndentStep = 1;
   int indent = 0;
-  cord_internal::CordTreeConstPath stack;
-  cord_internal::CordTreePath<int, cord_internal::MaxCordDepth()> indents;
+  absl::InlinedVector<CordRep*, kInlinedVectorSize> stack;
+  absl::InlinedVector<int, kInlinedVectorSize> indents;
   for (;;) {
     *os << std::setw(3) << rep->refcount.Get();
     *os << " " << std::setw(7) << rep->length;
     *os << " [";
-    if (include_data) *os << static_cast<const void*>(rep);
+    if (include_data) *os << static_cast<void*>(rep);
     *os << "]";
-    *os << " " << (IsNodeBalanced(rep) ? 'b' : 'u');
+    *os << " " << (IsRootBalanced(rep) ? 'b' : 'u');
     *os << " " << std::setw(indent) << "";
     if (rep->tag == CONCAT) {
       *os << "CONCAT depth=" << Depth(rep) << "\n";
@@ -1868,7 +1873,7 @@ static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os) {
       } else {
         *os << "FLAT cap=" << TagToLength(rep->tag) << " [";
         if (include_data)
-          *os << absl::CEscape(absl::string_view(rep->data, rep->length));
+          *os << absl::CEscape(std::string(rep->data, rep->length));
         *os << "]\n";
       }
       if (stack.empty()) break;
@@ -1881,19 +1886,19 @@ static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os) {
   ABSL_INTERNAL_CHECK(indents.empty(), "");
 }
 
-static std::string ReportError(const CordRep* root, const CordRep* node) {
+static std::string ReportError(CordRep* root, CordRep* node) {
   std::ostringstream buf;
   buf << "Error at node " << node << " in:";
   DumpNode(root, true, &buf);
   return buf.str();
 }
 
-static bool VerifyNode(const CordRep* root, const CordRep* start_node,
+static bool VerifyNode(CordRep* root, CordRep* start_node,
                        bool full_validation) {
-  cord_internal::CordTreeConstPath worklist;
+  absl::InlinedVector<CordRep*, 2> worklist;
   worklist.push_back(start_node);
   do {
-    const CordRep* node = worklist.back();
+    CordRep* node = worklist.back();
     worklist.pop_back();
 
     ABSL_INTERNAL_CHECK(node != nullptr, ReportError(root, node));
@@ -1943,7 +1948,7 @@ static bool VerifyNode(const CordRep* root, const CordRep* start_node,
   // Iterate over the tree. cur_node is never a leaf node and leaf nodes will
   // never be appended to tree_stack. This reduces overhead from manipulating
   // tree_stack.
-  cord_internal::CordTreeConstPath tree_stack;
+  absl::InlinedVector<const CordRep*, kInlinedVectorSize> tree_stack;
   const CordRep* cur_node = rep;
   while (true) {
     const CordRep* next_node = nullptr;
diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index eb236e50..66645eef 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -48,6 +48,7 @@
 #include "absl/base/internal/per_thread_tls.h"
 #include "absl/base/macros.h"
 #include "absl/base/port.h"
+#include "absl/container/inlined_vector.h"
 #include "absl/functional/function_ref.h"
 #include "absl/meta/type_traits.h"
 #include "absl/strings/internal/cord_internal.h"
@@ -67,55 +68,6 @@ template <typename H>
 H HashFragmentedCord(H, const Cord&);
 }
 
-namespace cord_internal {
-
-// It's expensive to keep a tree perfectly balanced, so instead we keep trees
-// approximately balanced.  A tree node N of depth D(N) that contains a string
-// of L(N) characters is considered balanced if L >= Fibonacci(D + 2).
-// The "+ 2" is used to ensure that every balanced leaf node contains at least
-//  one character. Here we presume that
-//   Fibonacci(0) = 0
-//   Fibonacci(1) = 1
-//   Fibonacci(2) = 1
-//   Fibonacci(3) = 2
-//   ...
-// The algorithm is based on paper by Hans Boehm et al:
-// https://www.cs.rit.edu/usr/local/pub/jeh/courses/QUARTERS/FP/Labs/CedarRope/rope-paper.pdf
-// In this paper authors shows that rebalancing based on cord forest of already
-// balanced subtrees can be proven to never produce tree of depth larger than
-// largest Fibonacci number representable in the same integral type as cord size
-// For 64 bit integers this is the 93rd Fibonacci number. For 32 bit integrals
-// this is 47th Fibonacci number.
-constexpr size_t MaxCordDepth() { return sizeof(size_t) == 8 ? 93 : 47; }
-
-// This class models fixed max size stack of CordRep pointers.
-// The elements are being pushed back and popped from the back.
-template <typename CordRepPtr, size_t N>
-class CordTreePath {
- public:
-  CordTreePath() {}
-  explicit CordTreePath(CordRepPtr root) { push_back(root); }
-
-  bool empty() const { return size_ == 0; }
-  size_t size() const { return size_; }
-  void clear() { size_ = 0; }
-
-  CordRepPtr back() { return data_[size_ - 1]; }
-
-  void pop_back() {
-    --size_;
-    assert(size_ < N);
-  }
-  void push_back(CordRepPtr elem) { data_[size_++] = elem; }
-
- private:
-  CordRepPtr data_[N];
-  size_t size_ = 0;
-};
-
-using CordTreeMutablePath = CordTreePath<CordRep*, MaxCordDepth()>;
-}  // namespace cord_internal
-
 // A Cord is a sequence of characters.
 class Cord {
  private:
@@ -333,7 +285,8 @@ class Cord {
     absl::cord_internal::CordRep* current_leaf_ = nullptr;
     // The number of bytes left in the `Cord` over which we are iterating.
     size_t bytes_remaining_ = 0;
-    absl::cord_internal::CordTreeMutablePath stack_of_right_children_;
+    absl::InlinedVector<absl::cord_internal::CordRep*, 4>
+        stack_of_right_children_;
   };
 
   // Returns an iterator to the first chunk of the `Cord`.
diff --git a/absl/strings/cord_test.cc b/absl/strings/cord_test.cc
index f2d81d4c..4afa4a26 100644
--- a/absl/strings/cord_test.cc
+++ b/absl/strings/cord_test.cc
@@ -1402,53 +1402,6 @@ TEST(CordChunkIterator, Operations) {
   VerifyChunkIterator(subcords, 128);
 }
 
-TEST(CordChunkIterator, MaxLengthFullTree) {
-  // Start with a 1-byte cord, and then double its length in a loop.  We should
-  // be able to do this until the point where we would overflow size_t.
-
-  absl::Cord cord;
-  size_t size = 1;
-  AddExternalMemory("x", &cord);
-  EXPECT_EQ(cord.size(), size);
-
-  const int kCordLengthDoublingLimit = std::numeric_limits<size_t>::digits - 1;
-  for (int i = 0; i < kCordLengthDoublingLimit; ++i) {
-    cord.Prepend(absl::Cord(cord));
-    size <<= 1;
-
-    EXPECT_EQ(cord.size(), size);
-
-    auto chunk_it = cord.chunk_begin();
-    EXPECT_EQ(*chunk_it, "x");
-  }
-
-  EXPECT_DEATH_IF_SUPPORTED(
-      (cord.Prepend(absl::Cord(cord)), *cord.chunk_begin()),
-      "Cord is too long");
-}
-
-TEST(CordChunkIterator, MaxDepth) {
-  // By reusing nodes, it's possible in pathological cases to build a Cord that
-  // exceeds both the maximum permissible length and depth.  In this case, the
-  // violation of the maximum depth is reported.
-  absl::Cord left_child;
-  AddExternalMemory("x", &left_child);
-  absl::Cord root = left_child;
-
-  for (int i = 0; i < absl::cord_internal::MaxCordDepth() - 2; ++i) {
-    size_t new_size = left_child.size() + root.size();
-    root.Prepend(left_child);
-    EXPECT_EQ(root.size(), new_size);
-
-    auto chunk_it = root.chunk_begin();
-    EXPECT_EQ(*chunk_it, "x");
-
-    std::swap(left_child, root);
-  }
-
-  EXPECT_DEATH_IF_SUPPORTED(root.Prepend(left_child), "Cord is too long");
-}
-
 TEST(CordCharIterator, Traits) {
   static_assert(std::is_copy_constructible<absl::Cord::CharIterator>::value,
                 "");
diff --git a/absl/strings/internal/str_format/extension.h b/absl/strings/internal/str_format/extension.h
index d1665753..968850eb 100644
--- a/absl/strings/internal/str_format/extension.h
+++ b/absl/strings/internal/str_format/extension.h
@@ -24,6 +24,7 @@
 
 #include "absl/base/config.h"
 #include "absl/base/port.h"
+#include "absl/meta/type_traits.h"
 #include "absl/strings/internal/str_format/output.h"
 #include "absl/strings/string_view.h"
 
@@ -365,11 +366,22 @@ constexpr FormatConversionCharSet operator|(FormatConversionCharSet a,
                                  static_cast<uint64_t>(b));
 }
 
+// Overloaded conversion functions to support absl::ParsedFormat.
 // Get a conversion with a single character in it.
-constexpr FormatConversionCharSet ConversionCharToConv(char c) {
-  return FormatConversionCharSet(FormatConversionCharToConvValue(c));
+constexpr FormatConversionCharSet ToFormatConversionCharSet(char c) {
+  return static_cast<FormatConversionCharSet>(
+      FormatConversionCharToConvValue(c));
 }
 
+// Get a conversion with a single character in it.
+constexpr FormatConversionCharSet ToFormatConversionCharSet(
+    FormatConversionCharSet c) {
+  return c;
+}
+
+template <typename T>
+void ToFormatConversionCharSet(T) = delete;
+
 // Checks whether `c` exists in `set`.
 constexpr bool Contains(FormatConversionCharSet set, char c) {
   return (static_cast<uint64_t>(set) & FormatConversionCharToConvValue(c)) != 0;
diff --git a/absl/strings/str_format.h b/absl/strings/str_format.h
index 2f9b4b27..d40fca11 100644
--- a/absl/strings/str_format.h
+++ b/absl/strings/str_format.h
@@ -285,7 +285,7 @@ using FormatSpec =
 //   }
 template <char... Conv>
 using ParsedFormat = str_format_internal::ExtendedParsedFormat<
-    str_format_internal::ConversionCharToConv(Conv)...>;
+    absl::str_format_internal::ToFormatConversionCharSet(Conv)...>;
 
 // StrFormat()
 //