Optimize equality operators for string classes

Using compare() for those operators is not a good idea, as we can't
shortcut comparisons if the string sizes are different. This alone
made our HTML parser in QtGui around 15% slower.

Don't go through QAnyStringView to implement compare() for
QUtf8StringView, use QtPrivate::compareStrings() directly instead.

Task-number: QTBUG-86354
Change-Id: I04869c29c9918161990dc1baf8e943b3a264ff3c
Reviewed-by: Karsten Heimrich <karsten.heimrich@qt.io>

5 files changed, 82 insertions, 13 deletions

diff --git a/src/corelib/text/qanystringview.h b/src/corelib/text/qanystringview.h
index 647f43f265..c073eda3b6 100644
--- a/src/corelib/text/qanystringview.h
+++ b/src/corelib/text/qanystringview.h
@@ -200,6 +200,7 @@ public:
     [[nodiscard]] constexpr const void *data() const noexcept { return m_data; }
 
     [[nodiscard]] Q_CORE_EXPORT static int compare(QAnyStringView lhs, QAnyStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+    [[nodiscard]] Q_CORE_EXPORT static bool equal(QAnyStringView lhs, QAnyStringView rhs) noexcept;
 
     //
     // STL compatibility API:
@@ -224,9 +225,9 @@ public:
 
 private:
     [[nodiscard]] friend inline bool operator==(QAnyStringView lhs, QAnyStringView rhs) noexcept
-    { return QAnyStringView::compare(lhs, rhs) == 0; }
+    { return QAnyStringView::equal(lhs, rhs); }
     [[nodiscard]] friend inline bool operator!=(QAnyStringView lhs, QAnyStringView rhs) noexcept
-    { return !operator==(lhs, rhs); }
+    { return !QAnyStringView::equal(lhs, rhs); }
 
 #ifdef __cpp_impl_three_way_comparison
     [[nodiscard]] friend inline auto operator<=>(QAnyStringView lhs, QAnyStringView rhs) noexcept
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 2838e513f1..71e51ab0fc 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -1325,6 +1325,63 @@ int QAnyStringView::compare(QAnyStringView lhs, QAnyStringView rhs, Qt::CaseSens
     });
 }
 
+bool QtPrivate::equalStrings(QStringView lhs, QStringView rhs) noexcept
+{
+    return ucstrcmp(lhs.begin(), lhs.size(), rhs.begin(), rhs.size()) == 0;
+}
+
+bool QtPrivate::equalStrings(QStringView lhs, QLatin1String rhs) noexcept
+{
+    return ucstrcmp(lhs.begin(), lhs.size(), rhs.begin(), rhs.size()) == 0;
+}
+
+bool QtPrivate::equalStrings(QLatin1String lhs, QStringView rhs) noexcept
+{
+    return QtPrivate::equalStrings(rhs, lhs);
+}
+
+bool QtPrivate::equalStrings(QLatin1String lhs, QLatin1String rhs) noexcept
+{
+    return lhs.size() == rhs.size() && (!lhs.size() || qstrncmp(lhs.data(), rhs.data(), lhs.size()) == 0);
+}
+
+bool QtPrivate::equalStrings(QBasicUtf8StringView<false> lhs, QStringView rhs) noexcept
+{
+    return QUtf8::compareUtf8(lhs, rhs) == 0;
+}
+
+bool QtPrivate::equalStrings(QStringView lhs, QBasicUtf8StringView<false> rhs) noexcept
+{
+    return QtPrivate::equalStrings(rhs, lhs);
+}
+
+bool QtPrivate::equalStrings(QLatin1String lhs, QBasicUtf8StringView<false> rhs) noexcept
+{
+    QString r = rhs.toString();
+    return QtPrivate::equalStrings(lhs, r); // ### optimize!
+}
+
+bool QtPrivate::equalStrings(QBasicUtf8StringView<false> lhs, QLatin1String rhs) noexcept
+{
+    return QtPrivate::equalStrings(rhs, lhs);
+}
+
+bool QtPrivate::equalStrings(QBasicUtf8StringView<false> lhs, QBasicUtf8StringView<false> rhs) noexcept
+{
+    return lhs.size() == rhs.size() && (!lhs.size() || qstrncmp(lhs.data(), rhs.data(), lhs.size()) == 0);
+}
+
+bool QAnyStringView::equal(QAnyStringView lhs, QAnyStringView rhs) noexcept
+{
+    if (lhs.size() != rhs.size() && lhs.isUtf8() == rhs.isUtf8())
+        return false;
+    return lhs.visit([rhs](auto lhs) {
+        return rhs.visit([lhs](auto rhs) {
+            return QtPrivate::equalStrings(lhs, rhs);
+        });
+    });
+}
+
 /*!
     \relates QStringView
     \internal
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index 5c809592e8..00efa8d1b0 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -1042,11 +1042,6 @@ QString QBasicUtf8StringView<UseChar8T>::toString() const
     return QString::fromUtf8(data(), int(size()));
 }
 
-template<bool UseChar8T>
-inline int QBasicUtf8StringView<UseChar8T>::compare(QBasicUtf8StringView lhs, QBasicUtf8StringView rhs,
-                                                    Qt::CaseSensitivity cs) noexcept
-{ return QAnyStringView::compare(lhs, rhs, cs); }
-
 //
 // QAnyStringView inline members that require QString:
 //
@@ -1444,7 +1439,7 @@ inline bool operator<=(QLatin1String lhs, QChar rhs) noexcept { return !(rhs <
 inline bool operator>=(QLatin1String lhs, QChar rhs) noexcept { return !(rhs >  lhs); }
 
 // QStringView <> QStringView
-inline bool operator==(QStringView lhs, QStringView rhs) noexcept { return lhs.size() == rhs.size() && QtPrivate::compareStrings(lhs, rhs) == 0; }
+inline bool operator==(QStringView lhs, QStringView rhs) noexcept { return lhs.size() == rhs.size() && QtPrivate::equalStrings(lhs, rhs); }
 inline bool operator!=(QStringView lhs, QStringView rhs) noexcept { return !(lhs == rhs); }
 inline bool operator< (QStringView lhs, QStringView rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) <  0; }
 inline bool operator<=(QStringView lhs, QStringView rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) <= 0; }
@@ -1467,14 +1462,14 @@ inline bool operator> (QChar lhs, QStringView rhs) noexcept { return QStringView
 inline bool operator>=(QChar lhs, QStringView rhs) noexcept { return QStringView(&lhs, 1) >= rhs; }
 
 // QStringView <> QLatin1String
-inline bool operator==(QStringView lhs, QLatin1String rhs) noexcept { return lhs.size() == rhs.size() && QtPrivate::compareStrings(lhs, rhs) == 0; }
+inline bool operator==(QStringView lhs, QLatin1String rhs) noexcept { return lhs.size() == rhs.size() && QtPrivate::equalStrings(lhs, rhs); }
 inline bool operator!=(QStringView lhs, QLatin1String rhs) noexcept { return !(lhs == rhs); }
 inline bool operator< (QStringView lhs, QLatin1String rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) <  0; }
 inline bool operator<=(QStringView lhs, QLatin1String rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) <= 0; }
 inline bool operator> (QStringView lhs, QLatin1String rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) >  0; }
 inline bool operator>=(QStringView lhs, QLatin1String rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) >= 0; }
 
-inline bool operator==(QLatin1String lhs, QStringView rhs) noexcept { return lhs.size() == rhs.size() && QtPrivate::compareStrings(lhs, rhs) == 0; }
+inline bool operator==(QLatin1String lhs, QStringView rhs) noexcept { return lhs.size() == rhs.size() && QtPrivate::equalStrings(lhs, rhs); }
 inline bool operator!=(QLatin1String lhs, QStringView rhs) noexcept { return !(lhs == rhs); }
 inline bool operator< (QLatin1String lhs, QStringView rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) <  0; }
 inline bool operator<=(QLatin1String lhs, QStringView rhs) noexcept { return QtPrivate::compareStrings(lhs, rhs) <= 0; }
diff --git a/src/corelib/text/qstringalgorithms.h b/src/corelib/text/qstringalgorithms.h
index 5e2eb1912a..6d8fe114f1 100644
--- a/src/corelib/text/qstringalgorithms.h
+++ b/src/corelib/text/qstringalgorithms.h
@@ -86,6 +86,16 @@ namespace QtPrivate {
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QBasicUtf8StringView<false> lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QBasicUtf8StringView<false> lhs, QBasicUtf8StringView<false> rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QStringView   lhs, QStringView   rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QStringView   lhs, QLatin1String rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QStringView   lhs, QBasicUtf8StringView<false> rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QLatin1String lhs, QStringView   rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QLatin1String lhs, QLatin1String rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QLatin1String lhs, QBasicUtf8StringView<false> rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QBasicUtf8StringView<false> lhs, QStringView   rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QBasicUtf8StringView<false> lhs, QLatin1String rhs) noexcept;
+[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool equalStrings(QBasicUtf8StringView<false> lhs, QBasicUtf8StringView<false> rhs) noexcept;
+
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool startsWith(QStringView   haystack, QStringView   needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool startsWith(QStringView   haystack, QLatin1String needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool startsWith(QLatin1String haystack, QStringView   needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
diff --git a/src/corelib/text/qutf8stringview.h b/src/corelib/text/qutf8stringview.h
index 98357ae5a9..55621588bd 100644
--- a/src/corelib/text/qutf8stringview.h
+++ b/src/corelib/text/qutf8stringview.h
@@ -306,11 +306,17 @@ public:
 #endif
 
 private:
-    [[nodiscard]] static inline int compare(QBasicUtf8StringView lhs, QBasicUtf8StringView rhs,
-                                            Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+    [[nodiscard]] static inline int compare(QBasicUtf8StringView lhs, QBasicUtf8StringView rhs) noexcept
+    {
+        return QtPrivate::compareStrings(QBasicUtf8StringView<false>(lhs.data(), lhs.size()),
+                                         QBasicUtf8StringView<false>(rhs.data(), rhs.size()));
+    }
 
     [[nodiscard]] friend inline bool operator==(QBasicUtf8StringView lhs, QBasicUtf8StringView rhs) noexcept
-    { return QBasicUtf8StringView::compare(lhs, rhs) == 0; }
+    {
+        return QtPrivate::equalStrings(QBasicUtf8StringView<false>(lhs.data(), lhs.size()),
+                                       QBasicUtf8StringView<false>(rhs.data(), rhs.size()));
+    }
     [[nodiscard]] friend inline bool operator!=(QBasicUtf8StringView lhs, QBasicUtf8StringView rhs) noexcept
     { return !operator==(lhs, rhs); }