Export of internal Abseil changes

--
6cfac39ea1266f01f195de5eb4c9a6fc9ea9b20a by Matt Kulukundis <kfm@google.com>:

Fix a typo

PiperOrigin-RevId: 366174890

--
6ee8c58647aef171d394e59fa06f9bf8cd0306ec by Derek Mauro <dmauro@google.com>:

Adds `ABSL_ATTRIBUTE_LIFETIME_BOUND` and applies it to the
`const std::string&` constructor of `absl::string_view`.

Compilers that support this attribute will emit a warning
if the parameter does not have sufficient lifetime.

PiperOrigin-RevId: 366027738

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b944427d96e4b436b8fa0fe396c2a1118dbbbd13 by Abseil Team <absl-team@google.com>:

Calls to `ResetToEmpty()` from `ClearSlow` use ~3% of the time in assignment. However, `ClearSlow()` is only used in contexts where `data_` is immediately reassigned.

Rename `ClearSlow()` into `UnrefTree()` and remove `data_` resetting.

PiperOrigin-RevId: 365977213

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7428b3147a5672c8bb55649efa3a1cfe19b52a8b by Abseil Team <absl-team@google.com>:

Fix CordRepRing diabolical growth

The 'Mutable' function in CordRepRing was over-eager in doubling capacity, which lead to 'ludicrous' growth in the diabolical test case as added to cord_test. This CL fixes the doubling for growing shared reps, and tempers CordRepRing growth for non shared capacity to 1.5 instead of 2, which is more inline with a conservative growth we also have in tree cord.

After this change, CordRepRing no longer swamps the heap into the shadow realm, and is in effect reducing the memory used compared to the tree implementation. With a diabolical 5000 bytes growth pattern:

Tree cord: 1523520 bytes
Ring cord:  274232 bytes

PiperOrigin-RevId: 365915857

--
f24d4aee48b03c5a7980664df903f947cbb198e8 by Andy Getzendanner <durandal@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 365873932
GitOrigin-RevId: 6cfac39ea1266f01f195de5eb4c9a6fc9ea9b20a
Change-Id: I9737aa215ac732c9785a1d0032c77aba62330f12

5 files changed, 31 insertions, 10 deletions

diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 1c03a61..1aea396 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -491,7 +491,7 @@ static bool RepMemoryUsageLeaf(const CordRep* rep, size_t* total_mem_usage) {
 }
 
 void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
-  ClearSlow();
+  UnrefTree();
 
   data_ = src.data_;
   if (is_tree()) {
@@ -501,11 +501,10 @@ void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
   }
 }
 
-void Cord::InlineRep::ClearSlow() {
+void Cord::InlineRep::UnrefTree() {
   if (is_tree()) {
     CordRep::Unref(tree());
   }
-  ResetToEmpty();
 }
 
 // --------------------------------------------------------------------
diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index fa9cb91..cb2ffc5 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -776,8 +776,8 @@ class Cord {
     friend class Cord;
 
     void AssignSlow(const InlineRep& src);
-    // Unrefs the tree, stops profiling, and zeroes the contents
-    void ClearSlow();
+    // Unrefs the tree and stops profiling.
+    void UnrefTree();
 
     void ResetToEmpty() { data_ = {}; }
 
@@ -966,7 +966,7 @@ inline Cord::InlineRep& Cord::InlineRep::operator=(const Cord::InlineRep& src) {
 inline Cord::InlineRep& Cord::InlineRep::operator=(
     Cord::InlineRep&& src) noexcept {
   if (is_tree()) {
-    ClearSlow();
+    UnrefTree();
   }
   data_ = src.data_;
   src.ResetToEmpty();
diff --git a/absl/strings/cord_test.cc b/absl/strings/cord_test.cc
index fb67341..710a1b4 100644
--- a/absl/strings/cord_test.cc
+++ b/absl/strings/cord_test.cc
@@ -1316,6 +1316,26 @@ TEST(Cord, Concat_Append) {
   EXPECT_EQ(s2.size(), size + 1);
 }
 
+TEST(Cord, DiabolicalGrowth) {
+  // This test exercises a diabolical Append(<one char>) on a cord, making the
+  // cord shared before each Append call resulting in a terribly fragmented
+  // resulting cord.
+  // TODO(b/183983616): Apply some minimum compaction when copying a shared
+  // source cord into a mutable copy for updates in CordRepRing.
+  RandomEngine rng(testing::GTEST_FLAG(random_seed));
+  const std::string expected = RandomLowercaseString(&rng, 5000);
+  absl::Cord cord;
+  for (char c : expected) {
+    absl::Cord shared(cord);
+    cord.Append(absl::string_view(&c, 1));
+  }
+  std::string value;
+  absl::CopyCordToString(cord, &value);
+  EXPECT_EQ(value, expected);
+  ABSL_RAW_LOG(INFO, "Diabolical size allocated = %zu",
+               cord.EstimatedMemoryUsage());
+}
+
 TEST(MakeFragmentedCord, MakeFragmentedCordFromInitializerList) {
   absl::Cord fragmented =
       absl::MakeFragmentedCord({"A ", "fragmented ", "Cord"});
diff --git a/absl/strings/internal/cord_rep_ring.cc b/absl/strings/internal/cord_rep_ring.cc
index 4d31d1d..cb95b19 100644
--- a/absl/strings/internal/cord_rep_ring.cc
+++ b/absl/strings/internal/cord_rep_ring.cc
@@ -400,10 +400,11 @@ CordRepRing* CordRepRing::Mutable(CordRepRing* rep, size_t extra) {
   // Get current number of entries, and check for max capacity.
   size_t entries = rep->entries();
 
-  size_t min_extra = (std::max)(extra, rep->capacity() * 2 - entries);
   if (!rep->refcount.IsOne()) {
-    return Copy(rep, rep->head(), rep->tail(), min_extra);
+    return Copy(rep, rep->head(), rep->tail(), extra);
   } else if (entries + extra > rep->capacity()) {
+    const size_t min_grow = rep->capacity() + rep->capacity() / 2;
+    const size_t min_extra = (std::max)(extra, min_grow - entries);
     CordRepRing* newrep = CordRepRing::New(entries, min_extra);
     newrep->Fill<false>(rep, rep->head(), rep->tail());
     CordRepRing::Delete(rep);
diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
index b276bdb..1f14a75 100644
--- a/absl/strings/string_view.h
+++ b/absl/strings/string_view.h
@@ -36,6 +36,7 @@
 #include <limits>
 #include <string>
 
+#include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/base/internal/throw_delegate.h"
 #include "absl/base/macros.h"
@@ -180,8 +181,8 @@ class string_view {
 
   template <typename Allocator>
   string_view(  // NOLINT(runtime/explicit)
-      const std::basic_string<char, std::char_traits<char>, Allocator>&
-          str) noexcept
+      const std::basic_string<char, std::char_traits<char>, Allocator>& str
+          ABSL_ATTRIBUTE_LIFETIME_BOUND) noexcept
       // This is implemented in terms of `string_view(p, n)` so `str.size()`
       // doesn't need to be reevaluated after `ptr_` is set.
       : string_view(str.data(), str.size()) {}