Export of internal Abseil changes

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76c5eb1cf346a1a64e0a5e2edf032546d600075a by Andy Getzendanner <durandal@google.com>:

Fix stacktrace on aarch64 architecture. Fixes #805

Import of https://github.com/abseil/abseil-cpp/pull/827

PiperOrigin-RevId: 340886173

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28f48f7bcadd4681854cddb0a7736d26d7dab000 by Andy Getzendanner <durandal@google.com>:

Some attribute cleanups in and around statusor:
* mark statusor_internal::Helper::Crash ABSL_ATTRIBUTE_NORETURN
* add ABSL_INTERNAL_UNREACHABLE to ABSL_INTERNAL_LOG when severity is FATAL
* create ABSL_INTERNAL_UNREACHABLE to wrap __builtin_unreachable and __assume(0)
* use ABSL_ATTRIBUTE_NONNULL instead of __builtin_unreachable in statusor_internal::PlacementNew (https://godbolt.org/z/n691fa)

PiperOrigin-RevId: 340868438

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33905d1d2d01eb6f81b04abaf24170bfebb6df09 by Andy Getzendanner <durandal@google.com>:

moved deleted functions to public for better compiler errors.

Import of https://github.com/abseil/abseil-cpp/pull/828

PiperOrigin-RevId: 340863976

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5e502222dfc3f5a0ef146535a9e16c743b005092 by Jorg Brown <jorg@google.com>:

ConvertibleToStringView wastes a lot of cycles initializing members just to reset them immediately after. Only initialize the string storage when needed. This makes StrSplit() 0-30% faster depending on the use case.

PiperOrigin-RevId: 340732039
GitOrigin-RevId: 76c5eb1cf346a1a64e0a5e2edf032546d600075a
Change-Id: I2ba1f717c4eaad384cd0a22694fd05f9e6a2d8fa

4 files changed, 40 insertions, 45 deletions

diff --git a/absl/base/internal/raw_logging.h b/absl/base/internal/raw_logging.h
index 2508f3cf..20f4291b 100644
--- a/absl/base/internal/raw_logging.h
+++ b/absl/base/internal/raw_logging.h
@@ -72,12 +72,14 @@
 //
 // The API is a subset of the above: each macro only takes two arguments.  Use
 // StrCat if you need to build a richer message.
-#define ABSL_INTERNAL_LOG(severity, message)                             \
-  do {                                                                   \
-    constexpr const char* absl_raw_logging_internal_filename = __FILE__; \
-    ::absl::raw_logging_internal::internal_log_function(                 \
-        ABSL_RAW_LOGGING_INTERNAL_##severity,                            \
-        absl_raw_logging_internal_filename, __LINE__, message);          \
+#define ABSL_INTERNAL_LOG(severity, message)                                 \
+  do {                                                                       \
+    constexpr const char* absl_raw_logging_internal_filename = __FILE__;     \
+    ::absl::raw_logging_internal::internal_log_function(                     \
+        ABSL_RAW_LOGGING_INTERNAL_##severity,                                \
+        absl_raw_logging_internal_filename, __LINE__, message);              \
+    if (ABSL_RAW_LOGGING_INTERNAL_##severity == ::absl::LogSeverity::kFatal) \
+      ABSL_INTERNAL_UNREACHABLE;                                             \
   } while (0)
 
 #define ABSL_INTERNAL_CHECK(condition, message)                    \
diff --git a/absl/base/macros.h b/absl/base/macros.h
index 02dd9ff4..3e085a91 100644
--- a/absl/base/macros.h
+++ b/absl/base/macros.h
@@ -144,4 +144,15 @@ ABSL_NAMESPACE_END
 #define ABSL_INTERNAL_RETHROW do {} while (false)
 #endif  // ABSL_HAVE_EXCEPTIONS
 
+// `ABSL_INTERNAL_UNREACHABLE` is an unreachable statement.  A program which
+// reaches one has undefined behavior, and the compiler may optimize
+// accordingly.
+#if defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable)
+#define ABSL_INTERNAL_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define ABSL_INTERNAL_UNREACHABLE __assume(0)
+#else
+#define ABSL_INTERNAL_UNREACHABLE
+#endif
+
 #endif  // ABSL_BASE_MACROS_H_
diff --git a/absl/status/internal/statusor_internal.h b/absl/status/internal/statusor_internal.h
index 7cc76256..eaac2c0b 100644
--- a/absl/status/internal/statusor_internal.h
+++ b/absl/status/internal/statusor_internal.h
@@ -17,6 +17,7 @@
 #include <type_traits>
 #include <utility>
 
+#include "absl/base/attributes.h"
 #include "absl/meta/type_traits.h"
 #include "absl/status/status.h"
 #include "absl/utility/utility.h"
@@ -135,18 +136,14 @@ class Helper {
  public:
   // Move type-agnostic error handling to the .cc.
   static void HandleInvalidStatusCtorArg(Status*);
-  static void Crash(const absl::Status& status);
+  ABSL_ATTRIBUTE_NORETURN static void Crash(const absl::Status& status);
 };
 
 // Construct an instance of T in `p` through placement new, passing Args... to
 // the constructor.
 // This abstraction is here mostly for the gcc performance fix.
 template <typename T, typename... Args>
-void PlacementNew(void* p, Args&&... args) {
-#if defined(__GNUC__) && !defined(__clang__)
-  // Teach gcc that 'p' cannot be null, fixing code size issues.
-  if (p == nullptr) __builtin_unreachable();
-#endif
+ABSL_ATTRIBUTE_NONNULL(1) void PlacementNew(void* p, Args&&... args) {
   new (p) T(std::forward<Args>(args)...);
 }
 
diff --git a/absl/strings/internal/str_split_internal.h b/absl/strings/internal/str_split_internal.h
index 76924771..49ec5392 100644
--- a/absl/strings/internal/str_split_internal.h
+++ b/absl/strings/internal/str_split_internal.h
@@ -66,56 +66,41 @@ class ConvertibleToStringView {
 
   // Matches rvalue strings and moves their data to a member.
   ConvertibleToStringView(std::string&& s)  // NOLINT(runtime/explicit)
-      : copy_(std::move(s)), value_(copy_), self_referential_(true) {}
+      : copy_(std::move(s)), value_(copy_) {}
 
   ConvertibleToStringView(const ConvertibleToStringView& other)
-      : value_(other.value_), self_referential_(other.self_referential_) {
-    if (other.self_referential_) {
-      new (&copy_) std::string(other.copy_);
-      value_ = copy_;
-    }
-  }
+      : copy_(other.copy_),
+        value_(other.IsSelfReferential() ? copy_ : other.value_) {}
 
-  ConvertibleToStringView(ConvertibleToStringView&& other)
-      : value_(other.value_), self_referential_(other.self_referential_) {
-    if (other.self_referential_) {
-      new (&copy_) std::string(std::move(other.copy_));
-      value_ = copy_;
-    }
+  ConvertibleToStringView(ConvertibleToStringView&& other) {
+    StealMembers(std::move(other));
   }
 
   ConvertibleToStringView& operator=(ConvertibleToStringView other) {
-    this->~ConvertibleToStringView();
-    new (this) ConvertibleToStringView(std::move(other));
+    StealMembers(std::move(other));
     return *this;
   }
 
   absl::string_view value() const { return value_; }
 
-  ~ConvertibleToStringView() { MaybeReleaseCopy(); }
-
  private:
-  void MaybeReleaseCopy() {
-    if (self_referential_) {
-      // An explicit destructor call cannot be a qualified name such as
-      // std::string. The "using" declaration works around this
-      // issue by creating an unqualified name for the destructor.
-      using string_type = std::string;
-      copy_.~string_type();
+  // Returns true if ctsp's value refers to its internal copy_ member.
+  bool IsSelfReferential() const { return value_.data() == copy_.data(); }
+
+  void StealMembers(ConvertibleToStringView&& other) {
+    if (other.IsSelfReferential()) {
+      copy_ = std::move(other.copy_);
+      value_ = copy_;
+      other.value_ = other.copy_;
+    } else {
+      value_ = other.value_;
     }
   }
-  struct Unused {  // MSVC disallows unions with only 1 member.
-  };
+
   // Holds the data moved from temporary std::string arguments. Declared first
   // so that 'value' can refer to 'copy_'.
-  union {
-    std::string copy_;
-    Unused unused_;
-  };
-
+  std::string copy_;
   absl::string_view value_;
-  // true if value_ refers to the internal copy_ member.
-  bool self_referential_ = false;
 };
 
 // An iterator that enumerates the parts of a string from a Splitter. The text