Q*Application: don't allocate memory just to compare C strings

Instead of creating a QByteArray, possibly normalizing a leading
'--' (one allocation, plus possibly one copy), simply use the
old 'ol str(n)cmp, skipping the first character if the argument
starts with '--'.

It also fixes parsing of -stylesheet and other options which
were erroneously parsed using indexOf() != -1, when they
should have used startsWith().

Also saves 504/742/522b in text size for QtCore/QtGui/QtWidgets,
resp., on optimized GCC 5.3 Linux AMD64 builds.

Change-Id: Ida868badac3fb9b77285417ee537c861ccc4fc06
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 26 insertions, 22 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 0f015af2b9..7d469dd25e 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -1181,30 +1181,32 @@ void QGuiApplicationPrivate::createPlatformIntegration()
 
     int j = argc ? 1 : 0;
     for (int i=1; i<argc; i++) {
-        if (argv[i] && *argv[i] != '-') {
+        if (!argv[i])
+            continue;
+        if (*argv[i] != '-') {
             argv[j++] = argv[i];
             continue;
         }
         const bool isXcb = platformName == "xcb";
-        QByteArray arg = argv[i];
-        if (arg.startsWith("--"))
-            arg.remove(0, 1);
-        if (arg == "-platformpluginpath") {
+        const char *arg = argv[i];
+        if (arg[1] == '-') // startsWith("--")
+            ++arg;
+        if (strcmp(arg, "-platformpluginpath") == 0) {
             if (++i < argc)
                 platformPluginPath = QString::fromLocal8Bit(argv[i]);
-        } else if (arg == "-platform") {
+        } else if (strcmp(arg, "-platform") == 0) {
             if (++i < argc)
                 platformName = argv[i];
-        } else if (arg == "-platformtheme") {
+        } else if (strcmp(arg, "-platformtheme") == 0) {
             if (++i < argc)
                 platformThemeName = QString::fromLocal8Bit(argv[i]);
-        } else if (arg == "-qwindowgeometry" || (isXcb && arg == "-geometry")) {
+        } else if (strcmp(arg, "-qwindowgeometry") == 0 || (isXcb && strcmp(arg, "-geometry") == 0)) {
             if (++i < argc)
                 windowGeometrySpecification = QWindowGeometrySpecification::fromArgument(argv[i]);
-        } else if (arg == "-qwindowtitle" || (isXcb && arg == "-title")) {
+        } else if (strcmp(arg, "-qwindowtitle") == 0 || (isXcb && strcmp(arg, "-title") == 0)) {
             if (++i < argc)
                 firstWindowTitle = QString::fromLocal8Bit(argv[i]);
-        } else if (arg == "-qwindowicon" || (isXcb && arg == "-icon")) {
+        } else if (strcmp(arg, "-qwindowicon") == 0 || (isXcb && strcmp(arg, "-icon") == 0)) {
             if (++i < argc) {
                 icon = QString::fromLocal8Bit(argv[i]);
             }
@@ -1280,20 +1282,22 @@ void QGuiApplicationPrivate::init()
     QString s;
     int j = argc ? 1 : 0;
     for (int i=1; i<argc; i++) {
-        if (argv[i] && *argv[i] != '-') {
+        if (!argv[i])
+            continue;
+        if (*argv[i] != '-') {
             argv[j++] = argv[i];
             continue;
         }
-        QByteArray arg = argv[i];
-        if (arg.startsWith("--"))
-            arg.remove(0, 1);
-        if (arg == "-plugin") {
+        const char *arg = argv[i];
+        if (arg[1] == '-') // startsWith("--")
+            ++arg;
+        if (strcmp(arg, "-plugin") == 0) {
             if (++i < argc)
                 pluginList << argv[i];
-        } else if (arg == "-reverse") {
+        } else if (strcmp(arg, "-reverse") == 0) {
             force_reverse = true;
 #ifdef Q_OS_MAC
-        } else if (arg.startsWith("-psn_")) {
+        } else if (strncmp(arg, "-psn_", 5) == 0) {
             // eat "-psn_xxxx" on Mac, which is passed when starting an app from Finder.
             // special hack to change working directory (for an app bundle) when running from finder
             if (QDir::currentPath() == QLatin1String("/")) {
@@ -1305,7 +1309,7 @@ void QGuiApplicationPrivate::init()
             }
 #endif
 #ifndef QT_NO_SESSIONMANAGER
-        } else if (arg == "-session" && i < argc-1) {
+        } else if (strcmp(arg, "-session") == 0 && i < argc - 1) {
             ++i;
             if (argv[i] && *argv[i]) {
                 session_id = QString::fromLatin1(argv[i]);
@@ -1317,11 +1321,11 @@ void QGuiApplicationPrivate::init()
                 is_session_restored = true;
             }
 #endif
-        } else if (arg == "-testability") {
+        } else if (strcmp(arg, "-testability") == 0) {
             loadTestability = true;
-        } else if (arg.indexOf("-style=", 0) != -1) {
-            s = QString::fromLocal8Bit(arg.right(arg.length() - 7).toLower());
-        } else if (arg == "-style" && i < argc-1) {
+        } else if (strncmp(arg, "-style=", 7) == 0) {
+            s = QString::fromLocal8Bit(arg + 7).toLower();
+        } else if (strcmp(arg, "-style") == 0 && i < argc - 1) {
             s = QString::fromLocal8Bit(argv[++i]).toLower();
         } else {
             argv[j++] = argv[i];