QMimeTypeParser: use QStringRef more

Keep the return values of QXmlStream*::value() around as QStringRefs
for as long as possible. Avoids conversions to QString, among other
things, for:

- comparison to another string
- conversion to int
- conversion to UTF-8 or Latin-1 byte arrays

Add a pair of Q_UNLIKELY as a drive-by.

Saves ~900b in text size on optimized GCC 5.3 Linux AMD64 builds.

Change-Id: I17d440a11aeb8675979483f89e66d0a088ccc605
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/corelib/mimetypes/qmimemagicrule.cpp b/src/corelib/mimetypes/qmimemagicrule.cpp
index 09473caa78..06628fa323 100644
--- a/src/corelib/mimetypes/qmimemagicrule.cpp
+++ b/src/corelib/mimetypes/qmimemagicrule.cpp
@@ -238,10 +238,10 @@ QMimeMagicRule::QMimeMagicRule(const QString &type,
 
     // Parse for offset as "1" or "1:10"
     const int colonIndex = offsets.indexOf(QLatin1Char(':'));
-    const QString startPosStr = colonIndex == -1 ? offsets : offsets.mid(0, colonIndex);
-    const QString endPosStr   = colonIndex == -1 ? offsets : offsets.mid(colonIndex + 1);
-    if (!QMimeTypeParserBase::parseNumber(startPosStr, &m_startPos, errorString) ||
-        !QMimeTypeParserBase::parseNumber(endPosStr, &m_endPos, errorString)) {
+    const QStringRef startPosStr = offsets.midRef(0, colonIndex); // \ These decay to returning 'offsets'
+    const QStringRef endPosStr   = offsets.midRef(colonIndex + 1);// / unchanged when colonIndex == -1
+    if (Q_UNLIKELY(!QMimeTypeParserBase::parseNumber(startPosStr, &m_startPos, errorString)) ||
+        Q_UNLIKELY(!QMimeTypeParserBase::parseNumber(endPosStr, &m_endPos, errorString))) {
         m_type = Invalid;
         return;
     }