Export of internal Abseil changes

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6e9f93888bbe6718997ed90bbd049f1f3572b066 by Abseil Team <absl-team@google.com>:

Fix status to be safe for self move assignment.

PiperOrigin-RevId: 346815392

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35cae74a977f258e81dfbe925fb5a34cb6632036 by Gennadiy Rozental <rogeeff@google.com>:

Eliminate unnecessary access to the global vars.

PiperOrigin-RevId: 346777168

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e7e786c243069060f5d6c1c945decb4b0b83f95b by Andy Getzendanner <durandal@google.com>:

Internal change.

PiperOrigin-RevId: 346685656

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4ccd41c48f1a83cfa20b3ea534f743dd7d788376 by Abseil Team <absl-team@google.com>:

Move CordRep Ref() and Unref() logic into cord_internal.h

This change moves Ref() and Unref() logic out of cord.cc into cord_internal. The main purpose is to make upcoming ring buffer changes easier to isolate from existing cord.cc code. Notice that this removes the nullptr check from Unref() and now requires it to be non null (which held true most times). We may need to rethink if the 'unref unlikely one' is the common case: are cordreps most likely shared? This may be something between 'root' and non root nodes, i.e., is it more likely for leaf / flat nodes in large cords to be shared than top level cordreps being shared? Vice versa? Benchmarks say that we mostly shouldn't care, the caveat being that atomic ops seem more expensive on upcoming archs (arcadia) so we should error on the side of an extra IsOne() branch saving us single owned atomic ops.

PiperOrigin-RevId: 346676121

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f0babab103b9e60d61ba09482d468985e43eceb3 by Samuel Benzaquen <sbenza@google.com>:

Fix iterator based constructor and `.insert` members to only require
EmplaceConstructible as the standard specifies.

PiperOrigin-RevId: 346616707

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8f48eedda02277f9c96a88ed7726e34b557cce20 by Evan Brown <ezb@google.com>:

Fix a bug in binary_search_impl when there's a transparent, three-way comparator that has different equivalence classes for different lookup types.

Add a new can_have_multiple_equivalent_keys method to share the common logic for these cases.

PiperOrigin-RevId: 346605948

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649183cb3cc9383431de9c81fb1c0f885d4001ae by Abseil Team <absl-team@google.com>:

Add benchmark for accessing a Duration flag.

PiperOrigin-RevId: 346594843

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fefdb046520871af63ce2229e2f7cccfc0483dea by Abseil Team <absl-team@google.com>:

Restructure CordReader for upcoming ring buffer changes.

PiperOrigin-RevId: 346410642

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8b2f50e7da0ebab06ead5f94e366e984ca23cb6a by Abseil Team <absl-team@google.com>:

Wire in an internal-only flag to toggle upcoming ring buffer changes on/off for experimentation.

PiperOrigin-RevId: 346199111
GitOrigin-RevId: 6e9f93888bbe6718997ed90bbd049f1f3572b066
Change-Id: I8f34866b25a79209cb5448bbb28dd3044111d2e9

1 files changed, 107 insertions, 0 deletions

diff --git a/absl/strings/internal/cord_internal.h b/absl/strings/internal/cord_internal.h
index 6fb75c4f..f1af8e6e 100644
--- a/absl/strings/internal/cord_internal.h
+++ b/absl/strings/internal/cord_internal.h
@@ -22,6 +22,7 @@
 #include <type_traits>
 
 #include "absl/base/internal/invoke.h"
+#include "absl/base/optimization.h"
 #include "absl/container/internal/compressed_tuple.h"
 #include "absl/meta/type_traits.h"
 #include "absl/strings/string_view.h"
@@ -30,6 +31,28 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
+extern std::atomic<bool> cord_ring_buffer_enabled;
+
+inline void enable_cord_ring_buffer(bool enable) {
+  cord_ring_buffer_enabled.store(enable, std::memory_order_relaxed);
+}
+
+enum Constants {
+  // 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).
+  kInlinedVectorSize = 47,
+
+  // Prefer copying blocks of at most this size, otherwise reference count.
+  kMaxBytesToCopy = 511
+};
+
 // Wraps std::atomic for reference counting.
 class Refcount {
  public:
@@ -151,6 +174,34 @@ struct CordRep {
   inline const CordRepExternal* external() const;
   inline CordRepFlat* flat();
   inline const CordRepFlat* flat() const;
+
+  // --------------------------------------------------------------------
+  // Memory management
+
+  // This internal routine is called from the cold path of Unref below. Keeping
+  // it in a separate routine allows good inlining of Unref into many profitable
+  // call sites. However, the call to this function can be highly disruptive to
+  // the register pressure in those callers. To minimize the cost to callers, we
+  // use a special LLVM calling convention that preserves most registers. This
+  // allows the call to this routine in cold paths to not disrupt the caller's
+  // register pressure. This calling convention is not available on all
+  // platforms; we intentionally allow LLVM to ignore the attribute rather than
+  // attempting to hardcode the list of supported platforms.
+#if defined(__clang__) && !defined(__i386__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wattributes"
+  __attribute__((preserve_most))
+#pragma clang diagnostic pop
+#endif
+  static void Destroy(CordRep* rep);
+
+  // Increments the reference count of `rep`.
+  // Requires `rep` to be a non-null pointer value.
+  static inline CordRep* Ref(CordRep* rep);
+
+  // Decrements the reference count of `rep`. Destroys rep if count reaches
+  // zero. Requires `rep` to be a non-null pointer value.
+  static inline void Unref(CordRep* rep);
 };
 
 struct CordRepConcat : public CordRep {
@@ -284,7 +335,63 @@ static_assert(sizeof(InlineData) == kMaxInline + 1, "");
 static_assert(sizeof(AsTree) == sizeof(InlineData), "");
 static_assert(offsetof(AsTree, tagged_size) == kMaxInline, "");
 
+inline CordRepConcat* CordRep::concat() {
+  assert(tag == CONCAT);
+  return static_cast<CordRepConcat*>(this);
+}
+
+inline const CordRepConcat* CordRep::concat() const {
+  assert(tag == CONCAT);
+  return static_cast<const CordRepConcat*>(this);
+}
+
+inline CordRepSubstring* CordRep::substring() {
+  assert(tag == SUBSTRING);
+  return static_cast<CordRepSubstring*>(this);
+}
+
+inline const CordRepSubstring* CordRep::substring() const {
+  assert(tag == SUBSTRING);
+  return static_cast<const CordRepSubstring*>(this);
+}
+
+inline CordRepExternal* CordRep::external() {
+  assert(tag == EXTERNAL);
+  return static_cast<CordRepExternal*>(this);
+}
+
+inline const CordRepExternal* CordRep::external() const {
+  assert(tag == EXTERNAL);
+  return static_cast<const CordRepExternal*>(this);
+}
+
+inline CordRepFlat* CordRep::flat() {
+  assert(tag >= FLAT && tag <= MAX_FLAT_TAG);
+  return reinterpret_cast<CordRepFlat*>(this);
+}
+
+inline const CordRepFlat* CordRep::flat() const {
+  assert(tag >= FLAT && tag <= MAX_FLAT_TAG);
+  return reinterpret_cast<const CordRepFlat*>(this);
+}
+
+inline CordRep* CordRep::Ref(CordRep* rep) {
+  assert(rep != nullptr);
+  rep->refcount.Increment();
+  return rep;
+}
+
+inline void CordRep::Unref(CordRep* rep) {
+  assert(rep != nullptr);
+  // Expect refcount to be 0. Avoiding the cost of an atomic decrement should
+  // typically outweigh the cost of an extra branch checking for ref == 1.
+  if (ABSL_PREDICT_FALSE(!rep->refcount.DecrementExpectHighRefcount())) {
+    Destroy(rep);
+  }
+}
+
 }  // namespace cord_internal
+
 ABSL_NAMESPACE_END
 }  // namespace absl
 #endif  // ABSL_STRINGS_INTERNAL_CORD_INTERNAL_H_