From 3b61cd6ad738b8479bf216dcf736bb935e8812df Mon Sep 17 00:00:00 2001 From: Thiago Macieira Date: Sun, 20 Aug 2017 14:22:44 -0700 Subject: QStringView: De-inline the length calculation so we can use SSE2 Performance is more important in this case than the theoretical benefit of constexpr. This commit implements the SSE2 search for 16-bit null and it might be possible to implement the equivalent for AArch64 (investigation required). It also adds a fallback to wcslen() for systems where wchar_t is short (non-x86 Windows or 32-bit x86 build with -no-sse2). We can re-add the constexpr loop once the C++ language has a way of overloading constexpr and non-constexpr. GCC has a non-standard way to do that with __builtin_constant_p, which is also implemented in this commit, but note that the inline function is still not constexpr. Change-Id: I6e9274c1e7444ad48c81fffd14dcaacafda5ebdc Reviewed-by: Oswald Buddenhagen Reviewed-by: Thiago Macieira --- src/corelib/tools/qstring.cpp | 38 +++++++++++++++++++ src/corelib/tools/qstringalgorithms.h | 2 + src/corelib/tools/qstringview.h | 22 ++++++----- .../corelib/tools/qstringview/tst_qstringview.cpp | 44 ++++++++++++++++++++++ 4 files changed, 96 insertions(+), 10 deletions(-) diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp index 3826d7531a..a0c309c1cf 100644 --- a/src/corelib/tools/qstring.cpp +++ b/src/corelib/tools/qstring.cpp @@ -72,6 +72,7 @@ #include #include #include +#include #include "qchar.cpp" #include "qstringmatcher.cpp" @@ -159,6 +160,43 @@ static inline bool qt_ends_with(QStringView haystack, QStringView needle, Qt::Ca static inline bool qt_ends_with(QStringView haystack, QLatin1String needle, Qt::CaseSensitivity cs); static inline bool qt_ends_with(QStringView haystack, QChar needle, Qt::CaseSensitivity cs); +qssize_t qustrlen(const ushort *str) Q_DECL_NOTHROW +{ + qssize_t result = 0; + +#ifdef __SSE2__ + // progress until we get an aligned pointer + const ushort *ptr = str; + while (*ptr && quintptr(ptr) % 16) + ++ptr; + if (*ptr == 0) + return ptr - str; + + // load 16 bytes and see if we have a null + // (aligned loads can never segfault) + int mask; + const __m128i zeroes = _mm_setzero_si128(); + do { + __m128i data = _mm_load_si128(reinterpret_cast(ptr)); + ptr += 8; + + __m128i comparison = _mm_cmpeq_epi16(data, zeroes); + mask = _mm_movemask_epi8(comparison); + } while (mask == 0); + + // found a null + uint idx = qCountTrailingZeroBits(quint32(mask)); + return ptr - str - 8 + idx / 2; +#endif + + if (sizeof(wchar_t) == sizeof(ushort)) + return wcslen(reinterpret_cast(str)); + + while (*str++) + ++result; + return result; +} + #if defined(Q_COMPILER_LAMBDA) && !defined(__OPTIMIZE_SIZE__) namespace { template struct UnrollTailLoop diff --git a/src/corelib/tools/qstringalgorithms.h b/src/corelib/tools/qstringalgorithms.h index e1b8b90428..eaa7207bec 100644 --- a/src/corelib/tools/qstringalgorithms.h +++ b/src/corelib/tools/qstringalgorithms.h @@ -53,6 +53,8 @@ class QLatin1String; class QStringView; template class QVector; +Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION qssize_t qustrlen(const ushort *str) Q_DECL_NOTHROW; + Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int qCompareStrings(QStringView lhs, QStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) Q_DECL_NOTHROW; Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int qCompareStrings(QStringView lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) Q_DECL_NOTHROW; Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int qCompareStrings(QLatin1String lhs, QStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) Q_DECL_NOTHROW; diff --git a/src/corelib/tools/qstringview.h b/src/corelib/tools/qstringview.h index 24be441b00..764da71d0b 100644 --- a/src/corelib/tools/qstringview.h +++ b/src/corelib/tools/qstringview.h @@ -143,20 +143,22 @@ private: { return qssize_t(N - 1); } + template - static Q_DECL_RELAXED_CONSTEXPR qssize_t lengthHelperPointer(const Char *str) Q_DECL_NOTHROW + static qssize_t lengthHelperPointer(const Char *str) Q_DECL_NOTHROW { - qssize_t result = 0; - while (*str++) - ++result; - return result; +#if defined(Q_CC_GNU) && !defined(Q_CC_CLANG) && !defined(Q_CC_INTEL) + if (__builtin_constant_p(*str)) { + qssize_t result = 0; + while (*str++) + ++result; + } +#endif + return qustrlen(reinterpret_cast(str)); } - static Q_DECL_RELAXED_CONSTEXPR qssize_t lengthHelperPointer(const QChar *str) Q_DECL_NOTHROW + static qssize_t lengthHelperPointer(const QChar *str) Q_DECL_NOTHROW { - qssize_t result = 0; - while (!str++->isNull()) - ++result; - return result; + return qustrlen(reinterpret_cast(str)); } template diff --git a/tests/auto/corelib/tools/qstringview/tst_qstringview.cpp b/tests/auto/corelib/tools/qstringview/tst_qstringview.cpp index 9617afb651..48ea5a794c 100644 --- a/tests/auto/corelib/tools/qstringview/tst_qstringview.cpp +++ b/tests/auto/corelib/tools/qstringview/tst_qstringview.cpp @@ -136,6 +136,7 @@ class tst_QStringView : public QObject private Q_SLOTS: void constExpr() const; void basics() const; + void literals() const; void at() const; void fromQString() const; @@ -305,6 +306,12 @@ void tst_QStringView::constExpr() const Q_STATIC_ASSERT(!sv2.isNull()); Q_STATIC_ASSERT(!sv2.empty()); Q_STATIC_ASSERT(sv2.size() == 5); + + constexpr char16_t *null = nullptr; + constexpr QStringView sv3(null); + Q_STATIC_ASSERT(sv3.isNull()); + Q_STATIC_ASSERT(sv3.isEmpty()); + Q_STATIC_ASSERT(sv3.size() == 0); } #else // storage_type is wchar_t { @@ -328,6 +335,12 @@ void tst_QStringView::constExpr() const Q_STATIC_ASSERT(!sv2.isNull()); Q_STATIC_ASSERT(!sv2.empty()); Q_STATIC_ASSERT(sv2.size() == 5); + + constexpr wchar_t *null = nullptr; + constexpr QStringView sv3(null); + Q_STATIC_ASSERT(sv3.isNull()); + Q_STATIC_ASSERT(sv3.isEmpty()); + Q_STATIC_ASSERT(sv3.size() == 0); } #endif #endif @@ -348,6 +361,37 @@ void tst_QStringView::basics() const QVERIFY(!(sv2 != sv1)); } +void tst_QStringView::literals() const +{ +#if !defined(Q_OS_WIN) || defined(Q_COMPILER_UNICODE_STRINGS) + // the + ensures it's a pointer, not an array + QCOMPARE(QStringView(+u"Hello").size(), 5); + QStringView sv = u"Hello"; +#else // storage_type is wchar_t + // the + ensures it's a pointer, not an array + QCOMPARE(QStringView(+L"Hello").size(), 5); + QStringView sv = L"Hello"; +#endif + QCOMPARE(sv.size(), 5); + QVERIFY(!sv.empty()); + QVERIFY(!sv.isEmpty()); + QVERIFY(!sv.isNull()); + QCOMPARE(*sv.utf16(), 'H'); + QCOMPARE(sv[0], QLatin1Char('H')); + QCOMPARE(sv.at(0), QLatin1Char('H')); + QCOMPARE(sv.front(), QLatin1Char('H')); + QCOMPARE(sv.first(), QLatin1Char('H')); + QCOMPARE(sv[4], QLatin1Char('o')); + QCOMPARE(sv.at(4), QLatin1Char('o')); + QCOMPARE(sv.back(), QLatin1Char('o')); + QCOMPARE(sv.last(), QLatin1Char('o')); + + QStringView sv2(sv.utf16(), sv.utf16() + sv.size()); + QVERIFY(!sv2.isNull()); + QVERIFY(!sv2.empty()); + QCOMPARE(sv2.size(), 5); +} + void tst_QStringView::at() const { QString hello("Hello"); -- cgit v1.2.3