Export of internal Abseil changes

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587e6db882749fa7faa12815e614afab04d218b9 by Derek Mauro <dmauro@google.com>:

Use attribute detection for other sanitizer related attributes

PiperOrigin-RevId: 324077073

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3ee55e4935b4235516b1fcac3c55945e510f7afc by Evan Brown <ezb@google.com>:

Simplify CordRepExternal allocation/deallocation.

I think this can save some memory when `Releaser` is empty and when on platforms where alignof(CordRepExternal) < (default `::operator new` alignment).

We no longer need the API requirement that alignof(Releaser) <= (default `::operator new` alignment).

Also remove another static_assert from a TODO in cord_internal.h and fix some warnings about calling std::move on a forwarding reference.

PiperOrigin-RevId: 324053720

--
9fc78436565eb3b204d4aa425ee3773354392f45 by Derek Mauro <dmauro@google.com>:

Use auto-detected sanitizer attributes for ASAN, MSAN, and TSAN builds

PiperOrigin-RevId: 323831461
GitOrigin-RevId: 587e6db882749fa7faa12815e614afab04d218b9
Change-Id: Ie0e4a2846d7f66988a2d81a5e50721b62fdb3d6d

6 files changed, 66 insertions, 138 deletions

diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index ef412639..64a13cef 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -258,6 +258,8 @@ cc_library(
     visibility = ["//visibility:private"],
     deps = [
         ":strings",
+        "//absl/base:base_internal",
+        "//absl/container:compressed_tuple",
         "//absl/meta:type_traits",
     ],
 )
@@ -277,7 +279,6 @@ cc_library(
         ":str_format",
         ":strings",
         "//absl/base",
-        "//absl/base:base_internal",
         "//absl/base:core_headers",
         "//absl/base:endian",
         "//absl/base:raw_logging_internal",
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index d7237231..d6c2126d 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -548,6 +548,7 @@ absl_cc_library(
   DEPS
     absl::base
     absl::base_internal
+    absl::compressed_tuple
     absl::core_headers
     absl::endian
     absl::fixed_array
diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 920dcc67..763dcc45 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -61,48 +61,6 @@ enum CordRepKind {
   FLAT          = 3,
 };
 
-namespace {
-
-// Type used with std::allocator for allocating and deallocating
-// `CordRepExternal`. std::allocator is used because it opaquely handles the
-// different new / delete overloads available on a given platform.
-struct alignas(absl::cord_internal::ExternalRepAlignment()) ExternalAllocType {
-  unsigned char value[absl::cord_internal::ExternalRepAlignment()];
-};
-
-// Returns the number of objects to pass in to std::allocator<ExternalAllocType>
-// allocate() and deallocate() to create enough room for `CordRepExternal` with
-// `releaser_size` bytes on the end.
-constexpr size_t GetExternalAllocNumObjects(size_t releaser_size) {
-  // Be sure to round up since `releaser_size` could be smaller than
-  // `sizeof(ExternalAllocType)`.
-  return (sizeof(CordRepExternal) + releaser_size + sizeof(ExternalAllocType) -
-          1) /
-         sizeof(ExternalAllocType);
-}
-
-// Allocates enough memory for `CordRepExternal` and a releaser with size
-// `releaser_size` bytes.
-void* AllocateExternal(size_t releaser_size) {
-  return std::allocator<ExternalAllocType>().allocate(
-      GetExternalAllocNumObjects(releaser_size));
-}
-
-// Deallocates the memory for a `CordRepExternal` assuming it was allocated with
-// a releaser of given size and alignment.
-void DeallocateExternal(CordRepExternal* p, size_t releaser_size) {
-  std::allocator<ExternalAllocType>().deallocate(
-      reinterpret_cast<ExternalAllocType*>(p),
-      GetExternalAllocNumObjects(releaser_size));
-}
-
-// Returns a pointer to the type erased releaser for the given CordRepExternal.
-void* GetExternalReleaser(CordRepExternal* rep) {
-  return rep + 1;
-}
-
-}  // namespace
-
 namespace cord_internal {
 
 inline CordRepConcat* CordRep::concat() {
@@ -304,11 +262,7 @@ static void UnrefInternal(CordRep* rep) {
       }
     } else if (rep->tag == EXTERNAL) {
       CordRepExternal* rep_external = rep->external();
-      absl::string_view data(rep_external->base, rep->length);
-      void* releaser = GetExternalReleaser(rep_external);
-      size_t releaser_size = rep_external->releaser_invoker(releaser, data);
-      rep_external->~CordRepExternal();
-      DeallocateExternal(rep_external, releaser_size);
+      rep_external->releaser_invoker(rep_external);
       rep = nullptr;
     } else if (rep->tag == SUBSTRING) {
       CordRepSubstring* rep_substring = rep->substring();
@@ -458,18 +412,12 @@ static CordRep* NewTree(const char* data,
 
 namespace cord_internal {
 
-ExternalRepReleaserPair NewExternalWithUninitializedReleaser(
-    absl::string_view data, ExternalReleaserInvoker invoker,
-    size_t releaser_size) {
+void InitializeCordRepExternal(absl::string_view data, CordRepExternal* rep) {
   assert(!data.empty());
-
-  void* raw_rep = AllocateExternal(releaser_size);
-  auto* rep = new (raw_rep) CordRepExternal();
   rep->length = data.size();
   rep->tag = EXTERNAL;
   rep->base = data.data();
-  rep->releaser_invoker = invoker;
-  return {VerifyTree(rep), GetExternalReleaser(rep)};
+  VerifyTree(rep);
 }
 
 }  // namespace cord_internal
@@ -721,12 +669,12 @@ Cord::Cord(T&& src) {
       std::string data;
     };
     const absl::string_view original_data = src;
-    CordRepExternal* rep =
-        static_cast<CordRepExternal*>(absl::cord_internal::NewExternalRep(
-            original_data, StringReleaser{std::move(src)}));
+    auto* rep = static_cast<
+        ::absl::cord_internal::CordRepExternalImpl<StringReleaser>*>(
+        absl::cord_internal::NewExternalRep(
+            original_data, StringReleaser{std::forward<T>(src)}));
     // Moving src may have invalidated its data pointer, so adjust it.
-    rep->base =
-        static_cast<StringReleaser*>(GetExternalReleaser(rep))->data.data();
+    rep->base = rep->template get<0>().data.data();
     contents_.set_tree(rep);
   }
 }
@@ -775,7 +723,7 @@ Cord& Cord::operator=(T&& src) {
   if (src.size() <= kMaxBytesToCopy) {
     *this = absl::string_view(src);
   } else {
-    *this = Cord(std::move(src));
+    *this = Cord(std::forward<T>(src));
   }
   return *this;
 }
@@ -898,7 +846,7 @@ void Cord::Append(T&& src) {
   if (src.size() <= kMaxBytesToCopy) {
     Append(absl::string_view(src));
   } else {
-    Append(Cord(std::move(src)));
+    Append(Cord(std::forward<T>(src)));
   }
 }
 
@@ -938,7 +886,7 @@ inline void Cord::Prepend(T&& src) {
   if (src.size() <= kMaxBytesToCopy) {
     Prepend(absl::string_view(src));
   } else {
-    Prepend(Cord(std::move(src)));
+    Prepend(Cord(std::forward<T>(src)));
   }
 }
 
diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index 8580d803..a0db2797 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -71,7 +71,6 @@
 #include <type_traits>
 
 #include "absl/base/internal/endian.h"
-#include "absl/base/internal/invoke.h"
 #include "absl/base/internal/per_thread_tls.h"
 #include "absl/base/macros.h"
 #include "absl/base/port.h"
@@ -173,10 +172,6 @@ class Cord {
   //
   //   * be move constructible
   //   * support `void operator()(absl::string_view) const` or `void operator()`
-  //   * not have alignment requirement greater than what is guaranteed by
-  //     `::operator new`. This alignment is dictated by
-  //     `alignof(std::max_align_t)` (pre-C++17 code) or
-  //     `__STDCPP_DEFAULT_NEW_ALIGNMENT__` (C++17 code).
   //
   // Example:
   //
@@ -842,47 +837,15 @@ inline void SmallMemmove(char* dst, const char* src, size_t n,
   }
 }
 
-struct ExternalRepReleaserPair {
-  CordRep* rep;
-  void* releaser_address;
-};
-
-// Allocates a new external `CordRep` and returns a pointer to it and a pointer
-// to `releaser_size` bytes where the desired releaser can be constructed.
+// Does non-template-specific `CordRepExternal` initialization.
 // Expects `data` to be non-empty.
-ExternalRepReleaserPair NewExternalWithUninitializedReleaser(
-    absl::string_view data, ExternalReleaserInvoker invoker,
-    size_t releaser_size);
-
-struct Rank1 {};
-struct Rank0 : Rank1 {};
-
-template <typename Releaser, typename = ::absl::base_internal::invoke_result_t<
-                                 Releaser, absl::string_view>>
-void InvokeReleaser(Rank0, Releaser&& releaser, absl::string_view data) {
-  ::absl::base_internal::invoke(std::forward<Releaser>(releaser), data);
-}
-
-template <typename Releaser,
-          typename = ::absl::base_internal::invoke_result_t<Releaser>>
-void InvokeReleaser(Rank1, Releaser&& releaser, absl::string_view) {
-  ::absl::base_internal::invoke(std::forward<Releaser>(releaser));
-}
+void InitializeCordRepExternal(absl::string_view data, CordRepExternal* rep);
 
 // Creates a new `CordRep` that owns `data` and `releaser` and returns a pointer
 // to it, or `nullptr` if `data` was empty.
 template <typename Releaser>
 // NOLINTNEXTLINE - suppress clang-tidy raw pointer return.
 CordRep* NewExternalRep(absl::string_view data, Releaser&& releaser) {
-  static_assert(
-#if defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
-      alignof(Releaser) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__,
-#else
-      alignof(Releaser) <= alignof(max_align_t),
-#endif
-      "Releasers with alignment requirement greater than what is returned by "
-      "default `::operator new()` are not supported.");
-
   using ReleaserType = absl::decay_t<Releaser>;
   if (data.empty()) {
     // Never create empty external nodes.
@@ -891,18 +854,10 @@ CordRep* NewExternalRep(absl::string_view data, Releaser&& releaser) {
     return nullptr;
   }
 
-  auto releaser_invoker = [](void* type_erased_releaser, absl::string_view d) {
-    auto* my_releaser = static_cast<ReleaserType*>(type_erased_releaser);
-    InvokeReleaser(Rank0{}, std::move(*my_releaser), d);
-    my_releaser->~ReleaserType();
-    return sizeof(Releaser);
-  };
-
-  ExternalRepReleaserPair external = NewExternalWithUninitializedReleaser(
-      data, releaser_invoker, sizeof(releaser));
-  ::new (external.releaser_address)
-      ReleaserType(std::forward<Releaser>(releaser));
-  return external.rep;
+  CordRepExternal* rep = new CordRepExternalImpl<ReleaserType>(
+      std::forward<Releaser>(releaser), 0);
+  InitializeCordRepExternal(data, rep);
+  return rep;
 }
 
 // Overload for function reference types that dispatches using a function
diff --git a/absl/strings/internal/cord_internal.h b/absl/strings/internal/cord_internal.h
index 830ceaf4..d456eef8 100644
--- a/absl/strings/internal/cord_internal.h
+++ b/absl/strings/internal/cord_internal.h
@@ -21,6 +21,8 @@
 #include <cstdint>
 #include <type_traits>
 
+#include "absl/base/internal/invoke.h"
+#include "absl/container/internal/compressed_tuple.h"
 #include "absl/meta/type_traits.h"
 #include "absl/strings/string_view.h"
 
@@ -114,35 +116,56 @@ struct CordRepSubstring : public CordRep {
   CordRep* child;
 };
 
-// TODO(strel): replace the following logic (and related functions in cord.cc)
-// with container_internal::Layout.
-
-// Alignment requirement for CordRepExternal so that the type erased releaser
-// will be stored at a suitably aligned address.
-constexpr size_t ExternalRepAlignment() {
-#if defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
-  return __STDCPP_DEFAULT_NEW_ALIGNMENT__;
-#else
-  return alignof(max_align_t);
-#endif
-}
-
-// Type for function pointer that will invoke and destroy the type-erased
-// releaser function object. Accepts a pointer to the releaser and the
-// `string_view` that were passed in to `NewExternalRep` below. The return value
-// is the size of the `Releaser` type.
-using ExternalReleaserInvoker = size_t (*)(void*, absl::string_view);
+// Type for function pointer that will invoke the releaser function and also
+// delete the `CordRepExternalImpl` corresponding to the passed in
+// `CordRepExternal`.
+using ExternalReleaserInvoker = void (*)(CordRepExternal*);
 
 // External CordReps are allocated together with a type erased releaser. The
 // releaser is stored in the memory directly following the CordRepExternal.
-struct alignas(ExternalRepAlignment()) CordRepExternal : public CordRep {
+struct CordRepExternal : public CordRep {
   const char* base;
   // Pointer to function that knows how to call and destroy the releaser.
   ExternalReleaserInvoker releaser_invoker;
 };
 
-// TODO(strel): look into removing, it doesn't seem like anything relies on this
-static_assert(sizeof(CordRepConcat) == sizeof(CordRepSubstring), "");
+struct Rank1 {};
+struct Rank0 : Rank1 {};
+
+template <typename Releaser, typename = ::absl::base_internal::invoke_result_t<
+                                 Releaser, absl::string_view>>
+void InvokeReleaser(Rank0, Releaser&& releaser, absl::string_view data) {
+  ::absl::base_internal::invoke(std::forward<Releaser>(releaser), data);
+}
+
+template <typename Releaser,
+          typename = ::absl::base_internal::invoke_result_t<Releaser>>
+void InvokeReleaser(Rank1, Releaser&& releaser, absl::string_view) {
+  ::absl::base_internal::invoke(std::forward<Releaser>(releaser));
+}
+
+// We use CompressedTuple so that we can benefit from EBCO.
+template <typename Releaser>
+struct CordRepExternalImpl
+    : public CordRepExternal,
+      public ::absl::container_internal::CompressedTuple<Releaser> {
+  // The extra int arg is so that we can avoid interfering with copy/move
+  // constructors while still benefitting from perfect forwarding.
+  template <typename T>
+  CordRepExternalImpl(T&& releaser, int)
+      : CordRepExternalImpl::CompressedTuple(std::forward<T>(releaser)) {
+    this->releaser_invoker = &Release;
+  }
+
+  ~CordRepExternalImpl() {
+    InvokeReleaser(Rank0{}, std::move(this->template get<0>()),
+                   absl::string_view(base, length));
+  }
+
+  static void Release(CordRepExternal* rep) {
+    delete static_cast<CordRepExternalImpl*>(rep);
+  }
+};
 
 }  // namespace cord_internal
 ABSL_NAMESPACE_END
diff --git a/absl/strings/string_view_test.cc b/absl/strings/string_view_test.cc
index 41dbc97b..dcebb150 100644
--- a/absl/strings/string_view_test.cc
+++ b/absl/strings/string_view_test.cc
@@ -1177,7 +1177,7 @@ TEST(FindOneCharTest, EdgeCases) {
   EXPECT_EQ(absl::string_view::npos, a.rfind('x'));
 }
 
-#ifndef THREAD_SANITIZER  // Allocates too much memory for tsan.
+#ifndef ABSL_HAVE_THREAD_SANITIZER  // Allocates too much memory for tsan.
 TEST(HugeStringView, TwoPointTwoGB) {
   if (sizeof(size_t) <= 4)
     return;
@@ -1191,7 +1191,7 @@ TEST(HugeStringView, TwoPointTwoGB) {
   sp.remove_suffix(2);
   EXPECT_EQ(size - 1 - 2, sp.length());
 }
-#endif  // THREAD_SANITIZER
+#endif  // ABSL_HAVE_THREAD_SANITIZER
 
 #if !defined(NDEBUG) && !defined(ABSL_USES_STD_STRING_VIEW)
 TEST(NonNegativeLenTest, NonNegativeLen) {