QChar: optimize comparison with QString{,Ref}

Instead of relying on the QString relational operators to
implicitly convert the QChar to a QString, add relational
operator overloads that compare the QChar without first
turning it into a QString, saving one memory allocation
per comparison, and allowing to mark the operation as
nothrow.

Consequently, in tst_QStringBinOps, verify now that all
relational operations are noexcept.

The added overloads make QChar ==/!= int comparisons
ambiguous. De-ambiguate by providing a constrained
template that matches int and nothing but int (otherwise,
the QChar and the int versions would compete for a
QChar::SpecialCharacter argument, and end up creating
new ambiguities). This solution may not be perfect, but
it can be easily extended should more ambiguities crop up.
The existing overload deals with all patterns found in
qtbase.

Change-Id: I4156d918e9b9134c1da684b8b69e0ee526ad24e3
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

3 files changed, 47 insertions, 0 deletions

diff --git a/src/corelib/tools/qchar.h b/src/corelib/tools/qchar.h
index f01fbc109c..a83e5e6f98 100644
--- a/src/corelib/tools/qchar.h
+++ b/src/corelib/tools/qchar.h
@@ -578,6 +578,18 @@ Q_DECL_CONSTEXPR inline bool operator>=(QChar c1, QChar c2) Q_DECL_NOTHROW { ret
 Q_DECL_CONSTEXPR inline bool operator> (QChar c1, QChar c2) Q_DECL_NOTHROW { return  operator< (c2, c1); }
 Q_DECL_CONSTEXPR inline bool operator<=(QChar c1, QChar c2) Q_DECL_NOTHROW { return !operator< (c2, c1); }
 
+// disambiguate QChar == int (but only that, so constrain template to exactly 'int'):
+template <typename T>
+Q_DECL_DEPRECATED_X("don't compare ints to QChars, compare them to QChar::unicode() instead")
+Q_DECL_CONSTEXPR inline
+typename std::enable_if<std::is_same<typename std::remove_cv<T>::type, int>::value, bool>::type
+operator==(QChar lhs, T rhs) Q_DECL_NOEXCEPT { return lhs == QChar(rhs); }
+template <typename T>
+Q_DECL_DEPRECATED_X("don't compare ints to QChars, compare them to QChar::unicode() instead")
+Q_DECL_CONSTEXPR inline
+typename std::enable_if<std::is_same<typename std::remove_cv<T>::type, int>::value, bool>::type
+operator!=(QChar lhs, T rhs) Q_DECL_NOEXCEPT { return lhs != QChar(rhs); }
+
 #ifndef QT_NO_DATASTREAM
 Q_CORE_EXPORT QDataStream &operator<<(QDataStream &, QChar);
 Q_CORE_EXPORT QDataStream &operator>>(QDataStream &, QChar &);
diff --git a/src/corelib/tools/qstring.h b/src/corelib/tools/qstring.h
index 3413a87085..3b85818221 100644
--- a/src/corelib/tools/qstring.h
+++ b/src/corelib/tools/qstring.h
@@ -814,6 +814,10 @@ private:
 
     Data *d;
 
+    friend inline bool operator==(QChar, const QString &) Q_DECL_NOTHROW;
+    friend inline bool operator< (QChar, const QString &) Q_DECL_NOTHROW;
+    friend inline bool operator> (QChar, const QString &) Q_DECL_NOTHROW;
+    friend inline bool operator==(QChar, const QStringRef &) Q_DECL_NOTHROW;
     friend inline bool operator< (QChar, const QStringRef &) Q_DECL_NOTHROW;
     friend inline bool operator> (QChar, const QStringRef &) Q_DECL_NOTHROW;
     friend inline bool operator==(QChar, QLatin1String) Q_DECL_NOTHROW;
@@ -1589,15 +1593,39 @@ inline bool operator> (const QStringRef &lhs, QLatin1String rhs) Q_DECL_NOTHROW
 inline bool operator<=(const QStringRef &lhs, QLatin1String rhs) Q_DECL_NOTHROW { return rhs >= lhs; }
 inline bool operator>=(const QStringRef &lhs, QLatin1String rhs) Q_DECL_NOTHROW { return rhs <= lhs; }
 
+// QChar <> QString
+inline bool operator==(QChar lhs, const QString &rhs) Q_DECL_NOTHROW
+{ return QString::compare_helper(&lhs, 1, rhs.data(), rhs.size()) == 0; }
+inline bool operator< (QChar lhs, const QString &rhs) Q_DECL_NOTHROW
+{ return QString::compare_helper(&lhs, 1, rhs.data(), rhs.size()) <  0; }
+inline bool operator> (QChar lhs, const QString &rhs) Q_DECL_NOTHROW
+{ return QString::compare_helper(&lhs, 1, rhs.data(), rhs.size()) >  0; }
+
+inline bool operator!=(QChar lhs, const QString &rhs) Q_DECL_NOTHROW { return !(lhs == rhs); }
+inline bool operator<=(QChar lhs, const QString &rhs) Q_DECL_NOTHROW { return !(lhs >  rhs); }
+inline bool operator>=(QChar lhs, const QString &rhs) Q_DECL_NOTHROW { return !(lhs <  rhs); }
+
+inline bool operator==(const QString &lhs, QChar rhs) Q_DECL_NOTHROW { return   rhs == lhs; }
+inline bool operator!=(const QString &lhs, QChar rhs) Q_DECL_NOTHROW { return !(rhs == lhs); }
+inline bool operator< (const QString &lhs, QChar rhs) Q_DECL_NOTHROW { return   rhs >  lhs; }
+inline bool operator> (const QString &lhs, QChar rhs) Q_DECL_NOTHROW { return   rhs <  lhs; }
+inline bool operator<=(const QString &lhs, QChar rhs) Q_DECL_NOTHROW { return !(rhs <  lhs); }
+inline bool operator>=(const QString &lhs, QChar rhs) Q_DECL_NOTHROW { return !(rhs >  lhs); }
+
 // QChar <> QStringRef
+inline bool operator==(QChar lhs, const QStringRef &rhs) Q_DECL_NOTHROW
+{ return QString::compare_helper(&lhs, 1, rhs.data(), rhs.size()) == 0; }
 inline bool operator< (QChar lhs, const QStringRef &rhs) Q_DECL_NOTHROW
 { return QString::compare_helper(&lhs, 1, rhs.data(), rhs.size()) <  0; }
 inline bool operator> (QChar lhs, const QStringRef &rhs) Q_DECL_NOTHROW
 { return QString::compare_helper(&lhs, 1, rhs.data(), rhs.size()) >  0; }
 
+inline bool operator!=(QChar lhs, const QStringRef &rhs) Q_DECL_NOTHROW { return !(lhs == rhs); }
 inline bool operator<=(QChar lhs, const QStringRef &rhs) Q_DECL_NOTHROW { return !(lhs >  rhs); }
 inline bool operator>=(QChar lhs, const QStringRef &rhs) Q_DECL_NOTHROW { return !(lhs <  rhs); }
 
+inline bool operator==(const QStringRef &lhs, QChar rhs) Q_DECL_NOTHROW { return   rhs == lhs; }
+inline bool operator!=(const QStringRef &lhs, QChar rhs) Q_DECL_NOTHROW { return !(rhs == lhs); }
 inline bool operator< (const QStringRef &lhs, QChar rhs) Q_DECL_NOTHROW { return   rhs >  lhs; }
 inline bool operator> (const QStringRef &lhs, QChar rhs) Q_DECL_NOTHROW { return   rhs <  lhs; }
 inline bool operator<=(const QStringRef &lhs, QChar rhs) Q_DECL_NOTHROW { return !(rhs <  lhs); }
diff --git a/tests/auto/corelib/tools/qstringapisymmetry/tst_qstringapisymmetry.cpp b/tests/auto/corelib/tools/qstringapisymmetry/tst_qstringapisymmetry.cpp
index f0d7cb5698..f6d2579074 100644
--- a/tests/auto/corelib/tools/qstringapisymmetry/tst_qstringapisymmetry.cpp
+++ b/tests/auto/corelib/tools/qstringapisymmetry/tst_qstringapisymmetry.cpp
@@ -148,7 +148,14 @@ void tst_QStringApiSymmetry::compare_impl() const
     const LHS lhs = make<LHS>(lhsUnicode, lhsLatin1);
     const RHS rhs = make<RHS>(rhsUnicode, rhsLatin1);
 
+#ifdef Q_COMPILER_NOEXCEPT
+# define QVERIFY_NOEXCEPT(expr) QVERIFY(noexcept(expr))
+#else
+# define QVERIFY_NOEXCEPT(expr)
+#endif
+
 #define CHECK(op) \
+    QVERIFY_NOEXCEPT(lhs op rhs); \
     do { if (caseSensitiveCompareResult op 0) { \
         QVERIFY(lhs op rhs); \
     } else { \