From 3c38efbfe46300ea480a842a2704e2f1a0665658 Mon Sep 17 00:00:00 2001 From: Dennis Oberst Date: Wed, 9 Aug 2023 14:53:23 +0200 Subject: [PATCH] QByteArray: use new assign() in operator=(const char *) operator=(~) and assign(~) share similar names but, until now, have not shared the same functionality. This patch introduces the usage of QByteArray::assign() within the non-sharing assignment operator to effectively boost efficiency by reusing the available capacity. Since these assignment operators are frequently used in many places, both within Qt and non-Qt code, this patch comes with benchmarks. The preview of the benchmark results are compared with this patch and before this patch. The findings indicate a slight enhancement in performance associated with the assignment operator. Despite the results displaying only a minor improvement, progress has been made. Therefore use assign(QByteArrayView) as replacement. (x86_64-little_endian-lp64 shared (dynamic) release build (O3); by gcc 13.2.1, endeavouros ; 13th Gen Intel(R) Core(TM) i9-13900K benchmarks executed with -perf -iterations 1000000 * The last value at the EOL represent the string size. QByteArray &operator=(const char *ch) (current) 65 cycles/iter; 317 instructions/iter; 16.0 nsec/iter (5) 71.7 cycles/iter; 383 instructions/iter; 13.0 nsec/iter (10) 59.8 cycles/iter; 318 instructions/iter; 10.9 nsec/iter (20) 70.8 cycles/iter; 340 instructions/iter; 12.9 nsec/iter (50) 80.2 cycles/iter; 419 instructions/iter; 14.6 nsec/iter (100) 164.2 cycles/iter; 899 instructions/iter; 29.9 nsec/iter (500) 260.5 cycles/iter; 1522 instructions/iter; 45.6 nsec/iter (1'000) QByteArray &operator=(const char *ch) (before) 66.8 cycles/iter; 317 instructions/iter; 16.9 nsec/iter (5) 76.5 cycles/iter; 383 instructions/iter; 13.9 nsec/iter (10) 63.7 cycles/iter; 318 instructions/iter; 11.6 nsec/iter (20) 71.6 cycles/iter; 344 instructions/iter; 13.0 nsec/iter (50) 77.5 cycles/iter; 419 instructions/iter; 14.1 nsec/iter (100) 143.4 cycles/iter; 893 instructions/iter; 26.1 nsec/iter (500) 270.8 cycles/iter; 1516 instructions/iter; 48.2 nsec/iter (1'000) Task-number: QTBUG-106201 Change-Id: I0745c33f0f61f1d844a60960cc55f565320d5945 Reviewed-by: Thiago Macieira --- src/corelib/text/qbytearray.cpp | 9 +---- .../text/qbytearray/tst_bench_qbytearray.cpp | 35 +++++++++++++++++++ 2 files changed, 36 insertions(+), 8 deletions(-) diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp index 42921e99d76..4628c55ce50 100644 --- a/src/corelib/text/qbytearray.cpp +++ b/src/corelib/text/qbytearray.cpp @@ -1342,14 +1342,7 @@ QByteArray &QByteArray::operator=(const char *str) } else if (!*str) { d = DataPointer::fromRawData(&_empty, 0); } else { - const qsizetype len = qsizetype(strlen(str)); - const auto capacityAtEnd = d->allocatedCapacity() - d.freeSpaceAtBegin(); - if (d->needsDetach() || len > capacityAtEnd - || (len < size() && len < (capacityAtEnd >> 1))) - // ### inefficient! reallocData() does copy the old data and we then overwrite it in the next line - reallocData(len, QArrayData::KeepSize); - memcpy(d.data(), str, len + 1); // include null terminator - d.size = len; + assign(str); } return *this; } diff --git a/tests/benchmarks/corelib/text/qbytearray/tst_bench_qbytearray.cpp b/tests/benchmarks/corelib/text/qbytearray/tst_bench_qbytearray.cpp index 05e20645d70..5a8008a7eff 100644 --- a/tests/benchmarks/corelib/text/qbytearray/tst_bench_qbytearray.cpp +++ b/tests/benchmarks/corelib/text/qbytearray/tst_bench_qbytearray.cpp @@ -31,6 +31,9 @@ private slots: void toPercentEncoding_data(); void toPercentEncoding(); + + void operator_assign_char(); + void operator_assign_char_data(); }; void tst_QByteArray::initTestCase() @@ -353,6 +356,38 @@ void tst_QByteArray::toPercentEncoding() QTEST(encoded, "expected"); } +void tst_QByteArray::operator_assign_char() +{ + QFETCH(QByteArray, data); + QString str(data.size(), Qt::Uninitialized); + + const char *tdata = data.constData(); + QBENCHMARK { + str.operator=(tdata); + } +} + +void tst_QByteArray::operator_assign_char_data() +{ + QTest::addColumn("data"); + + QByteArray data; + data.fill('a', 5); + QTest::newRow("length: 5") << data; + data.fill('b', 10); + QTest::newRow("length: 10") << data; + data.fill('c', 20); + QTest::newRow("length: 20") << data; + data.fill('d', 50); + QTest::newRow("length: 50") << data; + data.fill('e', 100); + QTest::newRow("length: 100") << data; + data.fill('f', 500); + QTest::newRow("length: 500") << data; + data.fill('g', 1'000); + QTest::newRow("length: 1'000") << data; +} + QTEST_MAIN(tst_QByteArray) #include "tst_bench_qbytearray.moc"