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, 9 insertions, 7 deletions

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index abc5af94cb..48d70f2747 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -182,16 +182,18 @@ void QCoreApplicationPrivate::processCommandLineArguments()
 {
     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.startsWith("-qmljsdebugger=")) {
-            qmljs_debug_arguments = QString::fromLocal8Bit(arg.right(arg.length() - 15));
-        } else if (arg == "-qmljsdebugger" && i < argc - 1) {
+        const char *arg = argv[i];
+        if (arg[1] == '-') // startsWith("--")
+            ++arg;
+        if (strncmp(arg, "-qmljsdebugger=", 15) == 0) {
+            qmljs_debug_arguments = QString::fromLocal8Bit(arg + 15);
+        } else if (strcmp(arg, "-qmljsdebugger") == 0 && i < argc - 1) {
             ++i;
             qmljs_debug_arguments = QString::fromLocal8Bit(argv[i]);
         } else {