From a4798817e824a5c45689933bc62338f3c7d6961b Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Mon, 9 Nov 2020 04:09:55 -0800
Subject: 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
---
 absl/strings/internal/str_split_internal.h | 51 ++++++++----------------------
 1 file changed, 13 insertions(+), 38 deletions(-)

(limited to 'absl/strings/internal/str_split_internal.h')

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_;
 };
-- 
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