Add rvalue-ref qualified QString::to{Upper,Lower,CaseFolded}

This is even more common than the QByteArray equivalents.

                Qt                   Qt Creator
        const &         &&      const &         &&
toLower      71         50           45         26
toUpper      35          8           46         35

Change-Id: I8b797d2321b22ce414c23656c5f1709ac649c423
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

3 files changed, 81 insertions, 13 deletions

diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index 23329224e7..5ac11c71c6 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -5547,16 +5547,16 @@ struct CasefoldTraits
     { return prop->caseFoldSpecial; }
 };
 
-template <typename Traits>
+template <typename Traits, typename T>
 #ifdef Q_CC_MSVC
 __declspec(noinline)
 #elif defined(Q_CC_GNU)
 __attribute__((noinline))
 #endif
-static QString detachAndConvertCase(const QString &str, QStringIterator it)
+static QString detachAndConvertCase(T &str, QStringIterator it)
 {
-    QString s(str);
-    QChar *pp = s.begin() + it.index();
+    QString s = qMove(str);             // will copy if T is const QString
+    QChar *pp = s.begin() + it.index(); // will detach if necessary
     uint uc = it.nextUnchecked();
     forever {
         const QUnicodeTables::Properties *prop = qGetProp(uc);
@@ -5583,8 +5583,8 @@ static QString detachAndConvertCase(const QString &str, QStringIterator it)
     }
 }
 
-template <typename Traits>
-static inline QString convertCase(const QString &str)
+template <typename Traits, typename T>
+static QString convertCase(T &str)
 {
     const QChar *p = str.constBegin();
     const QChar *e = p + str.size();
@@ -5600,25 +5600,40 @@ static inline QString convertCase(const QString &str)
         if (Traits::caseDiff(prop))
             return detachAndConvertCase<Traits>(str, it);
     }
-    return str;
+    return qMove(str);
 }
 } // namespace QUnicodeTables
 
-QString QString::toLower() const
+QString QString::toLower_helper(const QString &str)
 {
-    return QUnicodeTables::convertCase<QUnicodeTables::LowercaseTraits>(*this);
+    return QUnicodeTables::convertCase<QUnicodeTables::LowercaseTraits>(str);
+}
+
+QString QString::toLower_helper(QString &str)
+{
+    return QUnicodeTables::convertCase<QUnicodeTables::LowercaseTraits>(str);
 }
 
 /*!
+    \fn QString QString::toCaseFolded() const
+
     Returns the case folded equivalent of the string. For most Unicode
     characters this is the same as toLower().
 */
-QString QString::toCaseFolded() const
+
+QString QString::toCaseFolded_helper(const QString &str)
+{
+    return QUnicodeTables::convertCase<QUnicodeTables::CasefoldTraits>(str);
+}
+
+QString QString::toCaseFolded_helper(QString &str)
 {
-    return QUnicodeTables::convertCase<QUnicodeTables::CasefoldTraits>(*this);
+    return QUnicodeTables::convertCase<QUnicodeTables::CasefoldTraits>(str);
 }
 
 /*!
+    \fn QString QString::toUpper() const
+
     Returns an uppercase copy of the string.
 
     \snippet qstring/main.cpp 81
@@ -5628,11 +5643,18 @@ QString QString::toCaseFolded() const
 
     \sa toLower(), QLocale::toLower()
 */
-QString QString::toUpper() const
+
+QString QString::toUpper_helper(const QString &str)
 {
-    return QUnicodeTables::convertCase<QUnicodeTables::UppercaseTraits>(*this);
+    return QUnicodeTables::convertCase<QUnicodeTables::UppercaseTraits>(str);
 }
 
+QString QString::toUpper_helper(QString &str)
+{
+    return QUnicodeTables::convertCase<QUnicodeTables::UppercaseTraits>(str);
+}
+
+
 // ### Qt 6: Consider whether this function shouldn't be removed See task 202871.
 /*!
     Safely builds a formatted string from the format string \a cformat
diff --git a/src/corelib/tools/qstring.h b/src/corelib/tools/qstring.h
index dfb98ffaa2..a6e13e37b5 100644
--- a/src/corelib/tools/qstring.h
+++ b/src/corelib/tools/qstring.h
@@ -377,9 +377,34 @@ public:
     QString leftJustified(int width, QChar fill = QLatin1Char(' '), bool trunc = false) const Q_REQUIRED_RESULT;
     QString rightJustified(int width, QChar fill = QLatin1Char(' '), bool trunc = false) const Q_REQUIRED_RESULT;
 
+#if defined(Q_COMPILER_REF_QUALIFIERS) && !defined(QT_COMPILING_QSTRING_COMPAT_CPP)
+#  if defined(Q_CC_GNU)
+    // required due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61941
+#    pragma push_macro("Q_REQUIRED_RESULT")
+#    undef Q_REQUIRED_RESULT
+#    define Q_REQUIRED_RESULT
+#    define Q_REQUIRED_RESULT_pushed
+#  endif
+    QString toLower() const & Q_REQUIRED_RESULT
+    { return toLower_helper(*this); }
+    QString toLower() && Q_REQUIRED_RESULT
+    { return toLower_helper(*this); }
+    QString toUpper() const & Q_REQUIRED_RESULT
+    { return toUpper_helper(*this); }
+    QString toUpper() && Q_REQUIRED_RESULT
+    { return toUpper_helper(*this); }
+    QString toCaseFolded() const & Q_REQUIRED_RESULT
+    { return toCaseFolded_helper(*this); }
+    QString toCaseFolded() && Q_REQUIRED_RESULT
+    { return toCaseFolded_helper(*this); }
+#  ifdef Q_REQUIRED_RESULT_pushed
+#    pragma pop_macro("Q_REQUIRED_RESULT")
+#  endif
+#else
     QString toLower() const Q_REQUIRED_RESULT;
     QString toUpper() const Q_REQUIRED_RESULT;
     QString toCaseFolded() const Q_REQUIRED_RESULT;
+#endif
 
     QString trimmed() const Q_REQUIRED_RESULT;
     QString simplified() const Q_REQUIRED_RESULT;
@@ -742,6 +767,12 @@ private:
                               Qt::CaseSensitivity cs = Qt::CaseSensitive);
     static int localeAwareCompare_helper(const QChar *data1, int length1,
                                          const QChar *data2, int length2);
+    static QString toLower_helper(const QString &str);
+    static QString toLower_helper(QString &str);
+    static QString toUpper_helper(const QString &str);
+    static QString toUpper_helper(QString &str);
+    static QString toCaseFolded_helper(const QString &str);
+    static QString toCaseFolded_helper(QString &str);
     static Data *fromLatin1_helper(const char *str, int size = -1);
     static Data *fromAscii_helper(const char *str, int size = -1);
     static QString fromUtf8_helper(const char *str, int size);
diff --git a/src/corelib/tools/qstring_compat.cpp b/src/corelib/tools/qstring_compat.cpp
index be74775c1a..b42f49d86d 100644
--- a/src/corelib/tools/qstring_compat.cpp
+++ b/src/corelib/tools/qstring_compat.cpp
@@ -50,6 +50,21 @@
 QT_BEGIN_NAMESPACE
 
 // all these implementations must be the same as the inline versions in qstring.h
+QString QString::toLower() const
+{
+    return toLower_helper(*this);
+}
+
+QString QString::toCaseFolded() const
+{
+    return toCaseFolded_helper(*this);
+}
+
+QString QString::toUpper() const
+{
+    return toUpper_helper(*this);
+}
+
 QByteArray QString::toLatin1() const
 {
     return toLatin1_helper(*this);