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Optimize qLastIndexOf<QString> to not detach the QString 

The call to data() on a non-const QString led to a detach(), which is
unexpected and unwanted from QString::lastIndexOf() const.

Found by looking at why QFileSystemEntry::fileName() was expensive, in
the hotspot profiler.

The solution is to instanciate QLastIndexOf with QStringView() rather
than QString(). I added a deleted QString overload to make sure nobody
ever instanciates it with a QString argument again.

Change-Id: I06a1b2f937425e83f0779eb215e099aef78c50a7
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
bb10
David Faure 2019-12-02 21:16:24 +01:00
parent 97ac281c1d
commit aa504fc2fa
1 changed files with 5 additions and 2 deletions
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7
src/corelib/text/qstring.cpp
View File

@ -146,6 +146,9 @@ qsizetype qFindStringBoyerMoore(QStringView haystack, qsizetype from, QStringVie
static inline qsizetype qFindChar(QStringView str, QChar ch, qsizetype from, Qt::CaseSensitivity cs) noexcept;
template <typename Haystack>
static inline qsizetype qLastIndexOf(Haystack haystack, QChar needle, qsizetype from, Qt::CaseSensitivity cs) noexcept;
template <>
inline qsizetype qLastIndexOf(QString haystack, QChar needle,
qsizetype from, Qt::CaseSensitivity cs) noexcept = delete; // unwanted, would detach
static inline qsizetype qt_string_count(QStringView haystack, QStringView needle, Qt::CaseSensitivity cs);
static inline qsizetype qt_string_count(QStringView haystack, QChar needle, Qt::CaseSensitivity cs);
@ -3817,7 +3820,7 @@ int QString::indexOf(const QStringRef &str, int from, Qt::CaseSensitivity cs) co
int QString::lastIndexOf(const QString &str, int from, Qt::CaseSensitivity cs) const
{
// ### Qt6: qsizetype
return int(QtPrivate::lastIndexOf(*this, from, str, cs));
return int(QtPrivate::lastIndexOf(QStringView(*this), from, str, cs));
}
#endif // QT_STRINGVIEW_LEVEL < 2
@ -3856,7 +3859,7 @@ int QString::lastIndexOf(QLatin1String str, int from, Qt::CaseSensitivity cs) co
int QString::lastIndexOf(QChar ch, int from, Qt::CaseSensitivity cs) const
{
// ### Qt6: qsizetype
return int(qLastIndexOf(*this, ch, from, cs));
return int(qLastIndexOf(QStringView(*this), ch, from, cs));
}
#if QT_STRINGVIEW_LEVEL < 2