Export of internal Abseil changes

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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

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

Ensure ABSL_CXX_STANDARD is set.
Fixes #640

PiperOrigin-RevId: 301160106

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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

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

Internal Change

PiperOrigin-RevId: 300832828

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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

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

Emscripten supports thread-local storage nowadays.

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

2 files changed, 42 insertions, 56 deletions

diff --git a/absl/container/btree_benchmark.cc b/absl/container/btree_benchmark.cc
index ca4d575c48b9..467986768aa1 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 d986f81e85e5..adf49f81c571 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;
 }