Export of internal Abseil changes

--
197bd3e5e315f408bdc2f7111a0652be7f47609f by Jorg Brown <jorg@google.com>:

ConvertibleToStringView wastes a lot of cycles initializing a std::string
member that it never uses.  This CL restricts ConvertibleToStringView to just
the cases that don't nned a std::string member, and uses an additional StrSplit
overload to catch when users pass a temporary string.

This makes StrSplit() 0-30% faster depending on the use case.

PiperOrigin-RevId: 341378221
GitOrigin-RevId: 197bd3e5e315f408bdc2f7111a0652be7f47609f
Change-Id: Id863f2a3d298ed5a086ac912afab42dc30601be5

2 files changed, 51 insertions, 42 deletions

diff --git a/absl/strings/internal/str_split_internal.h b/absl/strings/internal/str_split_internal.h
index 49ec5392..a2f41c15 100644
--- a/absl/strings/internal/str_split_internal.h
+++ b/absl/strings/internal/str_split_internal.h
@@ -51,9 +51,9 @@ ABSL_NAMESPACE_BEGIN
 namespace strings_internal {
 
 // This class is implicitly constructible from everything that absl::string_view
-// is implicitly constructible from. If it's constructed from a temporary
-// string, the data is moved into a data member so its lifetime matches that of
-// the ConvertibleToStringView instance.
+// is implicitly constructible from, except for rvalue strings.  This means it
+// can be used as a function parameter in places where passing a temporary
+// string might cause memory lifetime issues.
 class ConvertibleToStringView {
  public:
   ConvertibleToStringView(const char* s)  // NOLINT(runtime/explicit)
@@ -65,41 +65,12 @@ class ConvertibleToStringView {
       : value_(s) {}
 
   // Matches rvalue strings and moves their data to a member.
-  ConvertibleToStringView(std::string&& s)  // NOLINT(runtime/explicit)
-      : copy_(std::move(s)), value_(copy_) {}
-
-  ConvertibleToStringView(const ConvertibleToStringView& other)
-      : copy_(other.copy_),
-        value_(other.IsSelfReferential() ? copy_ : other.value_) {}
-
-  ConvertibleToStringView(ConvertibleToStringView&& other) {
-    StealMembers(std::move(other));
-  }
-
-  ConvertibleToStringView& operator=(ConvertibleToStringView other) {
-    StealMembers(std::move(other));
-    return *this;
-  }
+  ConvertibleToStringView(std::string&& s) = delete;
+  ConvertibleToStringView(const std::string&& s) = delete;
 
   absl::string_view value() const { return value_; }
 
  private:
-  // 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_;
-    }
-  }
-
-  // Holds the data moved from temporary std::string arguments. Declared first
-  // so that 'value' can refer to 'copy_'.
-  std::string copy_;
   absl::string_view value_;
 };
 
@@ -273,7 +244,11 @@ struct SplitterIsConvertibleTo
 // the split strings: only strings for which the predicate returns true will be
 // kept. A Predicate object is any unary functor that takes an absl::string_view
 // and returns bool.
-template <typename Delimiter, typename Predicate>
+//
+// The StringType parameter can be either string_view or string, depending on
+// whether the Splitter refers to a string stored elsewhere, or if the string
+// resides inside the Splitter itself.
+template <typename Delimiter, typename Predicate, typename StringType>
 class Splitter {
  public:
   using DelimiterType = Delimiter;
@@ -281,12 +256,12 @@ class Splitter {
   using const_iterator = strings_internal::SplitIterator<Splitter>;
   using value_type = typename std::iterator_traits<const_iterator>::value_type;
 
-  Splitter(ConvertibleToStringView input_text, Delimiter d, Predicate p)
+  Splitter(StringType input_text, Delimiter d, Predicate p)
       : text_(std::move(input_text)),
         delimiter_(std::move(d)),
         predicate_(std::move(p)) {}
 
-  absl::string_view text() const { return text_.value(); }
+  absl::string_view text() const { return text_; }
   const Delimiter& delimiter() const { return delimiter_; }
   const Predicate& predicate() const { return predicate_; }
 
@@ -443,7 +418,7 @@ class Splitter {
     };
   };
 
-  ConvertibleToStringView text_;
+  StringType text_;
   Delimiter delimiter_;
   Predicate predicate_;
 };
diff --git a/absl/strings/str_split.h b/absl/strings/str_split.h
index 1ce17f38..bfbca422 100644
--- a/absl/strings/str_split.h
+++ b/absl/strings/str_split.h
@@ -369,6 +369,12 @@ struct SkipWhitespace {
   }
 };
 
+template <typename T>
+using EnableSplitIfString =
+    typename std::enable_if<std::is_same<T, std::string>::value ||
+                            std::is_same<T, const std::string>::value,
+                            int>::type;
+
 //------------------------------------------------------------------------------
 //                                  StrSplit()
 //------------------------------------------------------------------------------
@@ -489,22 +495,50 @@ struct SkipWhitespace {
 // Try not to depend on this distinction because the bug may one day be fixed.
 template <typename Delimiter>
 strings_internal::Splitter<
-    typename strings_internal::SelectDelimiter<Delimiter>::type, AllowEmpty>
+    typename strings_internal::SelectDelimiter<Delimiter>::type, AllowEmpty,
+    absl::string_view>
 StrSplit(strings_internal::ConvertibleToStringView text, Delimiter d) {
   using DelimiterType =
       typename strings_internal::SelectDelimiter<Delimiter>::type;
-  return strings_internal::Splitter<DelimiterType, AllowEmpty>(
+  return strings_internal::Splitter<DelimiterType, AllowEmpty,
+                                    absl::string_view>(
+      text.value(), DelimiterType(d), AllowEmpty());
+}
+
+template <typename Delimiter, typename StringType,
+          EnableSplitIfString<StringType> = 0>
+strings_internal::Splitter<
+    typename strings_internal::SelectDelimiter<Delimiter>::type, AllowEmpty,
+    std::string>
+StrSplit(StringType&& text, Delimiter d) {
+  using DelimiterType =
+      typename strings_internal::SelectDelimiter<Delimiter>::type;
+  return strings_internal::Splitter<DelimiterType, AllowEmpty, std::string>(
       std::move(text), DelimiterType(d), AllowEmpty());
 }
 
 template <typename Delimiter, typename Predicate>
 strings_internal::Splitter<
-    typename strings_internal::SelectDelimiter<Delimiter>::type, Predicate>
+    typename strings_internal::SelectDelimiter<Delimiter>::type, Predicate,
+    absl::string_view>
 StrSplit(strings_internal::ConvertibleToStringView text, Delimiter d,
          Predicate p) {
   using DelimiterType =
       typename strings_internal::SelectDelimiter<Delimiter>::type;
-  return strings_internal::Splitter<DelimiterType, Predicate>(
+  return strings_internal::Splitter<DelimiterType, Predicate,
+                                    absl::string_view>(
+      text.value(), DelimiterType(d), std::move(p));
+}
+
+template <typename Delimiter, typename Predicate, typename StringType,
+          EnableSplitIfString<StringType> = 0>
+strings_internal::Splitter<
+    typename strings_internal::SelectDelimiter<Delimiter>::type, Predicate,
+    std::string>
+StrSplit(StringType&& text, Delimiter d, Predicate p) {
+  using DelimiterType =
+      typename strings_internal::SelectDelimiter<Delimiter>::type;
+  return strings_internal::Splitter<DelimiterType, Predicate, std::string>(
       std::move(text), DelimiterType(d), std::move(p));
 }