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Dennis Oberst b134718c11 QString: use new assign() in operator=({QByteArray, QChar, char *}) 
operator=(~) and assign() share similar names but, until now, have not
shared the same functionality. This patch introduces the usage of
QString::assign() within the non-sharing assignment operators to
effectively boost efficiency by reusing the available capacity.

Since we're re-using the capacity we update the test case in places
where they don't hold true anymore.

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 results show a boost in performance for the
QByteArray and 'const char*' overload. The QLatin1StringView overload
already preserved the capacity and has a better performance than the
assign() alternative, so don't us it there.

(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.

QString &operator=(const QByteArray &a) (current)
  64.3  cycles/iter; 300  instructions/iter; 17   nsec/iter (5)
  65.8  cycles/iter; 366  instructions/iter; 12   nsec/iter (10)
  62.9  cycles/iter; 301  instructions/iter; 11.5 nsec/iter (20)
  61.3  cycles/iter; 315  instructions/iter; 11.1 nsec/iter (50)
  71.4  cycles/iter; 386  instructions/iter; 13   nsec/iter (100)
  136.9 cycles/iter; 811  instructions/iter; 24.5 nsec/iter (500)
  245.8 cycles/iter; 1394 instructions/iter; 42.5 nsec/iter (1'000)

QString &operator=(const QByteArray &a) (before)
  78   cycles/iter; 399  instructions/iter; 15.3 nsec/iter (5)
  82.3 cycles/iter; 465  instructions/iter; 15   nsec/iter (10)
  76.7 cycles/iter; 400  instructions/iter; 14   nsec/iter (20)
  79.5 cycles/iter; 414  instructions/iter; 14.5 nsec/iter (50)
  91.4 cycles/iter; 485  instructions/iter; 16.7 nsec/iter (100)
  189  cycles/iter; 910  instructions/iter; 34.4 nsec/iter (500)
  320  cycles/iter; 1666 instructions/iter; 56   nsec/iter (1'000)

QString &operator=(const char *ch) (current)
  70  cycles/iter; 317  instructions/iter; 12   nsec/iter (5)
  71  cycles/iter; 383  instructions/iter; 12.3 nsec/iter (10)
  64  cycles/iter; 318  instructions/iter; 11.1 nsec/iter (20)
  69  cycles/iter; 340  instructions/iter; 12   nsec/iter (50)
  77  cycles/iter; 419  instructions/iter; 13.5 nsec/iter (100)
  141 cycles/iter; 899  instructions/iter; 24.4 nsec/iter (500)
  280 cycles/iter; 1518 instructions/iter; 48.4 nsec/iter (1'000)

QString &operator=(const char *ch) (before)
  86.7  cycles/iter; 416  instructions/iter; 15   nsec/iter (5)
  87.8  cycles/iter; 482  instructions/iter; 15.7 nsec/iter (10)
  82.4  cycles/iter; 417  instructions/iter; 14.3 nsec/iter (20)
  90.2  cycles/iter; 443  instructions/iter; 15.6 nsec/iter (50)
  101.4 cycles/iter; 518  instructions/iter; 17.7 nsec/iter (100)
  204.4 cycles/iter; 994  instructions/iter; 36.5 nsec/iter (500)
  337.9 cycles/iter; 1789 instructions/iter; 58.9 nsec/iter (1'000)

 * current implemented as: assign(other)
QString &operator=(QLatin1StringView other) (current)
  47.4 cycles/iter; 237 instructions/iter; 8.2  nsec/iter (5)
  46.2 cycles/iter; 237 instructions/iter; 7.9  nsec/iter (10)
  46.8 cycles/iter; 255 instructions/iter; 8    nsec/iter (20)
  59   cycles/iter; 273 instructions/iter; 10.2 nsec/iter (50)
  55   cycles/iter; 300 instructions/iter; 9.5  nsec/iter (100)
  94.3 cycles/iter; 525 instructions/iter; 16.3 nsec/iter (500)
  166  cycles/iter; 804 instructions/iter; 28.7 nsec/iter (1'000)

QString &operator=(QLatin1StringView other) (before)
  14  cycles/iter; 79  instructions/iter; 2.5  nsec/iter (5)
  14  cycles/iter; 79  instructions/iter; 2.6  nsec/iter (10)
  16  cycles/iter; 97  instructions/iter; 3    nsec/iter (20)
  19  cycles/iter; 115 instructions/iter; 3.5  nsec/iter (50)
  23  cycles/iter; 142 instructions/iter; 4.2  nsec/iter (100)
  91  cycles/iter; 367 instructions/iter; 16.6 nsec/iter (500)
  131 cycles/iter; 646 instructions/iter; 23.4 nsec/iter (1'000)

Task-number: QTBUG-106201
Change-Id: Ie852f6abd1cf16164802acddb048eae5df59758f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
2023-09-05 20:58:47 +02:00
.github/workflows Repair github action workflow 2021-11-10 18:57:33 +01:00
bin Add simple project generation based on existing source files 2023-02-08 12:59:19 +01:00
cmake Add enablers to expose semi-public APIs for QtQuick3D 2023-09-05 13:42:50 +02:00
coin Enable binfmts incase it is disabled 2023-08-31 06:31:36 +00:00
config.tests Remove the mandatory x86-64 features from its feature list 2023-05-31 14:55:37 -07:00
dist Add Qt 6.0.0 changes file 2020-11-16 10:02:08 +02:00
doc Docs: Add a macro for documenting something as a technical preview 2023-08-02 12:47:15 +00:00
examples Update datastream converter to use Qt_6_0 instead of Qt_5_0 2023-09-05 16:50:53 +02:00
lib Purge all fonts 2015-08-18 19:59:14 +00:00
libexec Remove syncqt.pl 2023-06-30 13:23:46 +02:00
LICENSES Clarify license of SHA-1 algorithm 2023-04-26 16:36:18 +02:00
mkspecs undef READ and WRITE on VxWorks 2023-08-31 22:30:35 +00:00
qmake Doc: Document TR_EXCLUDE 2023-08-25 17:56:28 +02:00
src QString: use new assign() in operator=({QByteArray, QChar, char *}) 2023-09-05 20:58:47 +02:00
tests QString: use new assign() in operator=({QByteArray, QChar, char *}) 2023-09-05 20:58:47 +02:00
util Change enumdata.py names so comments read more naturally 2023-08-09 17:53:45 +02:00
.cmake.conf CMake: Require CMake 3.21 when building/using Qt on Apple platforms 2023-06-28 22:09:20 +02:00
.gitattributes Give batch files CRLF line endings 2020-11-04 15:02:29 +00:00
.gitignore Add CMakeUserPresets.json to .gitignore 2023-06-23 12:13:08 +02:00
.lgtm.yml Skip LGTM analysis for the bootstrap library and tools 2020-07-16 01:04:34 +02:00
.tag Update the git-archive export options 2012-09-07 15:39:31 +02:00
CMakeLists.txt CMake: Fix find_package(Qt6*Tools) in non-qtbase tests 2023-08-23 16:21:58 +02:00
config_help.txt CMake: remove test for eventfd, replace with __has_include 2023-08-29 07:41:11 -07:00
configure Retrieve an old -redo behavior 2023-02-07 18:51:58 +00:00
configure.bat Retrieve an old -redo behavior 2023-02-07 18:51:58 +00:00
configure.cmake CMake: Don't add no-prefix define to qconfig_p.h 2023-09-05 16:33:40 +02:00
dependencies.yaml Re-add dependencies.yaml now that qt5.git wip/qt6 builds fine 2019-09-18 13:19:31 +02:00
qt_cmdline.cmake CMake: Allow installation of example sources into the Qt prefix 2023-08-16 19:04:40 +02:00