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QPair: add constexpr liberally

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On templates, adding constexpr makes a given instantiation constexpr
if it can be.

This turns qMakePair(0,0), say, into a compile-time constant.

The effects on existing code are small, but exist:

  $ size lib/*{-baseline,-paircexp} | sort -nr
  6516727  211192    2608 6730527  66b31f lib/libQt5Widgets.so.5.4.0-baseline
  6516711  211192    2608 6730511  66b30f lib/libQt5Widgets.so.5.4.0-paircexp
  5373720   44492   15976 5434188  52eb4c lib/libQt5Core.so.5.4.0-baseline
  5373504   44492   15976 5433972  52ea74 lib/libQt5Core.so.5.4.0-paircexp
  5107206  125072    6080 5238358  4fee56 lib/libQt5Gui.so.5.4.0-baseline
  5107030  125072    6080 5238182  4feda6 lib/libQt5Gui.so.5.4.0-paircexp
  1341290   30180    2600 1374070  14f776 lib/libQt5Network.so.5.4.0-baseline
  1341210   30180    2600 1373990  14f726 lib/libQt5Network.so.5.4.0-paircexp
  # no other libraries benefit

[ChangeLog][QtCore][QPair] Can now be used in C++11 constexpr contexts.

Change-Id: I3872e6aa33a7d02a168516f4dfa7119efcac8c40
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
This commit is contained in:
Marc Mutz 2014-08-08 10:31:36 +02:00 committed by Oswald Buddenhagen
parent 31f2b7e591
commit e41b45f1ae
2 changed files with 27 additions and 12 deletions
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22
src/corelib/tools/qpair.h
View File

@ -53,18 +53,18 @@ struct QPair
typedef T1 first_type;
typedef T2 second_type;
QPair() : first(), second() {}
QPair(const T1 &t1, const T2 &t2) : first(t1), second(t2) {}
Q_DECL_CONSTEXPR QPair() : first(), second() {}
Q_DECL_CONSTEXPR QPair(const T1 &t1, const T2 &t2) : first(t1), second(t2) {}
// compiler-generated copy/move ctor/assignment operators are fine!
template <typename TT1, typename TT2>
QPair(const QPair<TT1, TT2> &p) : first(p.first), second(p.second) {}
Q_DECL_CONSTEXPR QPair(const QPair<TT1, TT2> &p) : first(p.first), second(p.second) {}
template <typename TT1, typename TT2>
QPair &operator=(const QPair<TT1, TT2> &p)
{ first = p.first; second = p.second; return *this; }
#ifdef Q_COMPILER_RVALUE_REFS
template <typename TT1, typename TT2>
QPair(QPair<TT1, TT2> &&p) : first(std::move(p.first)), second(std::move(p.second)) {}
Q_DECL_CONSTEXPR QPair(QPair<TT1, TT2> &&p) : first(std::move(p.first)), second(std::move(p.second)) {}
template <typename TT1, typename TT2>
QPair &operator=(QPair<TT1, TT2> &&p)
{ first = std::move(p.first); second = std::move(p.second); return *this; }
@ -80,39 +80,39 @@ template<class T1, class T2>
class QTypeInfo<QPair<T1, T2> > : public QTypeInfoMerger<QPair<T1, T2>, T1, T2> {}; // Q_DECLARE_TYPEINFO
template <class T1, class T2>
Q_INLINE_TEMPLATE bool operator==(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator==(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
{ return p1.first == p2.first && p1.second == p2.second; }
template <class T1, class T2>
Q_INLINE_TEMPLATE bool operator!=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator!=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
{ return !(p1 == p2); }
template <class T1, class T2>
Q_INLINE_TEMPLATE bool operator<(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator<(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
{
return p1.first < p2.first || (!(p2.first < p1.first) && p1.second < p2.second);
}
template <class T1, class T2>
Q_INLINE_TEMPLATE bool operator>(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator>(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
{
return p2 < p1;
}
template <class T1, class T2>
Q_INLINE_TEMPLATE bool operator<=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator<=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
{
return !(p2 < p1);
}
template <class T1, class T2>
Q_INLINE_TEMPLATE bool operator>=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator>=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
{
return !(p1 < p2);
}
template <class T1, class T2>
Q_OUTOFLINE_TEMPLATE QPair<T1, T2> qMakePair(const T1 &x, const T2 &y)
Q_DECL_CONSTEXPR Q_OUTOFLINE_TEMPLATE QPair<T1, T2> qMakePair(const T1 &x, const T2 &y)
{
return QPair<T1, T2>(x, y);
}

17
tests/auto/corelib/tools/qpair/tst_qpair.cpp
View File

@ -42,12 +42,13 @@
#include <QtTest/QtTest>
#include <QPair>
#include <QSize>
class tst_QPair : public QObject
{
Q_OBJECT
private Q_SLOTS:
void dummy() {}
void testConstexpr();
};
class C { char _[4]; };
@ -101,5 +102,19 @@ Q_STATIC_ASSERT(!QTypeInfo<QPairPP>::isDummy );
Q_STATIC_ASSERT(!QTypeInfo<QPairPP>::isPointer);
void tst_QPair::testConstexpr()
{
Q_CONSTEXPR QPair<int, double> pID = qMakePair(0, 0.0);
Q_UNUSED(pID);
Q_CONSTEXPR QPair<double, double> pDD = qMakePair(0.0, 0.0);
Q_CONSTEXPR QPair<double, double> pDD2 = qMakePair(0, 0.0); // involes (rvalue) conversion ctor
Q_CONSTEXPR bool equal = pDD2 == pDD;
QVERIFY(equal);
Q_CONSTEXPR QPair<QSize, int> pSI = qMakePair(QSize(4, 5), 6);
Q_UNUSED(pSI);
}
QTEST_APPLESS_MAIN(tst_QPair)
#include "tst_qpair.moc"