From bd52059eef7c96031972b5bee03067f3cb0f038d Mon Sep 17 00:00:00 2001 From: Marc Mutz Date: Thu, 12 Aug 2021 08:56:46 +0200 Subject: [PATCH] QMetaEnum: avoid quadratic behavior in valueToKeys() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit QByteArray (thankfully) doesn't have the prepend "optimization", so prepend() is a linear operation, calling it in a loop thus makes the algorithm quadratic. To fix, simply remember the parts in a QVLA (an upper bound on the size of which is easily calculated) and then build the result by reverse-iterating over the QVLA. This join_reversed() function is possibly useful elsewhere, but I left it locally in the unnamed namespace to ease cherry-picking. The new stringDataView() function is more universally useful, too, and will be used in a subsequent other change. It return QL1S instead of QByteArrayView because the latter is scheduled to become a non-string type, and already lacks certain features (e.g. qTokenize() doesn't work on QBA, due to lack of a Qt::CaseSensitivity argument in QBA::indexOf()). It's also a Qt 6 addition, so not available in 5.15. We can revisit this decision later, when QBAV (or, possibly, QU8SV) has caught up. Amends 05e0dfa0060aab80afc696161226b2ab0cddfbf9. Results indicate a ~2x speedup: PASS : tst_QMetaEnum::valueToKeys(1 bits set) - 0.00026 msecs per iteration (total: 70, iterations: 262144) + 0.00017 msecs per iteration (total: 90, iterations: 524288) PASS : tst_QMetaEnum::valueToKeys(2 bits set) - 0.00037 msecs per iteration (total: 98, iterations: 262144) + 0.00019 msecs per iteration (total: 52, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(3 bits set) - 0.00040 msecs per iteration (total: 53, iterations: 131072) + 0.00021 msecs per iteration (total: 56, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(4 bits set) - 0.00047 msecs per iteration (total: 62, iterations: 131072) + 0.00022 msecs per iteration (total: 60, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(5 bits set) - 0.00048 msecs per iteration (total: 63, iterations: 131072) + 0.00024 msecs per iteration (total: 64, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(6 bits set) - 0.00061 msecs per iteration (total: 80, iterations: 131072) + 0.00027 msecs per iteration (total: 71, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(7 bits set) - 0.00063 msecs per iteration (total: 83, iterations: 131072) + 0.00027 msecs per iteration (total: 73, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(8 bits set) - 0.00069 msecs per iteration (total: 91, iterations: 131072) + 0.00030 msecs per iteration (total: 81, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(9 bits set) - 0.00070 msecs per iteration (total: 92, iterations: 131072) + 0.00031 msecs per iteration (total: 83, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(10 bits set) - 0.00074 msecs per iteration (total: 98, iterations: 131072) + 0.00034 msecs per iteration (total: 91, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(11 bits set) - 0.000762 msecs per iteration (total: 100, iterations: 131072) + 0.00035 msecs per iteration (total: 92, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(12 bits set) - 0.00088 msecs per iteration (total: 58, iterations: 65536) + 0.000381 msecs per iteration (total: 100, iterations: 262144) PASS : tst_QMetaEnum::valueToKeys(13 bits set) - 0.00094 msecs per iteration (total: 62, iterations: 65536) + 0.00038 msecs per iteration (total: 51, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(14 bits set) - 0.00099 msecs per iteration (total: 65, iterations: 65536) + 0.00041 msecs per iteration (total: 55, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(15 bits set) - 0.0010 msecs per iteration (total: 67, iterations: 65536) + 0.00042 msecs per iteration (total: 56, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(16 bits set) - 0.0010 msecs per iteration (total: 70, iterations: 65536) + 0.00044 msecs per iteration (total: 58, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(17 bits set) - 0.0011 msecs per iteration (total: 73, iterations: 65536) + 0.00046 msecs per iteration (total: 61, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(18 bits set) - 0.0012 msecs per iteration (total: 79, iterations: 65536) + 0.00048 msecs per iteration (total: 63, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(19 bits set) - 0.0012 msecs per iteration (total: 79, iterations: 65536) + 0.00051 msecs per iteration (total: 67, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(20 bits set) - 0.0012 msecs per iteration (total: 80, iterations: 65536) + 0.00054 msecs per iteration (total: 71, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(21 bits set) - 0.0012 msecs per iteration (total: 83, iterations: 65536) + 0.00090 msecs per iteration (total: 59, iterations: 65536) PASS : tst_QMetaEnum::valueToKeys(22 bits set) - 0.0012 msecs per iteration (total: 85, iterations: 65536) + 0.00057 msecs per iteration (total: 76, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(23 bits set) - 0.0013 msecs per iteration (total: 87, iterations: 65536) + 0.00059 msecs per iteration (total: 78, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(24 bits set) - 0.0014 msecs per iteration (total: 93, iterations: 65536) + 0.00065 msecs per iteration (total: 86, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(25 bits set) - 0.0014 msecs per iteration (total: 94, iterations: 65536) + 0.00063 msecs per iteration (total: 83, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(26 bits set) - 0.00028 msecs per iteration (total: 74, iterations: 262144) + 0.00017 msecs per iteration (total: 94, iterations: 524288) PASS : tst_QMetaEnum::valueToKeys(27 bits set) - 0.0014 msecs per iteration (total: 98, iterations: 65536) + 0.00063 msecs per iteration (total: 83, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(28 bits set) - 0.0014 msecs per iteration (total: 96, iterations: 65536) + 0.00065 msecs per iteration (total: 86, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(29 bits set) - 0.0014 msecs per iteration (total: 98, iterations: 65536) + 0.00064 msecs per iteration (total: 84, iterations: 131072) PASS : tst_QMetaEnum::valueToKeys(30 bits set) - 0.0014 msecs per iteration (total: 97, iterations: 65536) + 0.00064 msecs per iteration (total: 84, iterations: 131072) Pick-to: 6.2 5.15 Change-Id: Ie456b71b39c118001987716e30642f08f5e8dcdb Reviewed-by: Mårten Nordheim Reviewed-by: Thiago Macieira --- src/corelib/kernel/qmetaobject.cpp | 38 ++++++++++++++++++++++++++---- 1 file changed, 33 insertions(+), 5 deletions(-) diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp index c50d17992b..25a09646af 100644 --- a/src/corelib/kernel/qmetaobject.cpp +++ b/src/corelib/kernel/qmetaobject.cpp @@ -157,13 +157,19 @@ static inline const char *rawStringData(const QMetaObject *mo, int index) return reinterpret_cast(mo->d.stringdata) + offset; } -static inline const QByteArray stringData(const QMetaObject *mo, int index) +static inline QLatin1String stringDataView(const QMetaObject *mo, int index) { Q_ASSERT(priv(mo->d.data)->revision >= 7); uint offset = mo->d.stringdata[2*index]; uint length = mo->d.stringdata[2*index + 1]; const char *string = reinterpret_cast(mo->d.stringdata) + offset; - return QByteArray::fromRawData(string, length); + return QLatin1String(string, length); +} + +static inline QByteArray stringData(const QMetaObject *mo, int index) +{ + const auto view = stringDataView(mo, index); + return QByteArray::fromRawData(view.data(), view.size()); } static inline const char *rawTypeNameFromTypeInfo(const QMetaObject *mo, uint typeInfo) @@ -2874,6 +2880,28 @@ int QMetaEnum::keysToValue(const char *keys, bool *ok) const return value; } +namespace +{ +template +void join_reversed(String &s, const Container &c, Separator sep) +{ + if (c.empty()) + return; + qsizetype len = qsizetype(c.size()) - 1; // N - 1 separators + for (auto &e : c) + len += qsizetype(e.size()); // N parts + s.reserve(len); + bool first = true; + for (auto rit = c.rbegin(), rend = c.rend(); rit != rend; ++rit) { + const auto &e = *rit; + if (!first) + s.append(sep); + first = false; + s.append(e.data(), e.size()); + } +} +} // unnamed namespace + /*! Returns a byte array of '|'-separated keys that represents the given \a value. @@ -2885,17 +2913,17 @@ QByteArray QMetaEnum::valueToKeys(int value) const QByteArray keys; if (!mobj) return keys; + QVarLengthArray parts; int v = value; // reverse iterate to ensure values like Qt::Dialog=0x2|Qt::Window are processed first. for (int i = data.keyCount() - 1; i >= 0; --i) { int k = mobj->d.data[data.data() + 2 * i + 1]; if ((k != 0 && (v & k) == k) || (k == value)) { v = v & ~k; - if (!keys.isEmpty()) - keys.prepend('|'); - keys.prepend(stringData(mobj, mobj->d.data[data.data() + 2 * i])); + parts.push_back(stringDataView(mobj, mobj->d.data[data.data() + 2 * i])); } } + join_reversed(keys, parts, '|'); return keys; }