CoreLib: use QStringRef to optimize memory allocation

Replace substring functions that return QString with
corresponding functions that return QStringRef where
it's possible.

Create QString from QStringRef only where necessary.

Change-Id: Id9ea11b16947220cd27787c0b529de62d10b6c26
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

3 files changed, 9 insertions, 7 deletions

diff --git a/src/corelib/mimetypes/qmimeglobpattern.cpp b/src/corelib/mimetypes/qmimeglobpattern.cpp
index 94be5385f3..568f9bf4de 100644
--- a/src/corelib/mimetypes/qmimeglobpattern.cpp
+++ b/src/corelib/mimetypes/qmimeglobpattern.cpp
@@ -124,7 +124,7 @@ bool QMimeGlobPattern::matchFileName(const QString &inputFilename) const
     if (starCount == 1 && m_pattern.at(pattern_len - 1) == QLatin1Char('*')) {
         if (len + 1 < pattern_len) return false;
         if (m_pattern.at(0) == QLatin1Char('*'))
-            return filename.indexOf(m_pattern.mid(1, pattern_len - 2)) != -1;
+            return filename.indexOf(m_pattern.midRef(1, pattern_len - 2)) != -1;
 
         const QChar *c1 = m_pattern.unicode();
         const QChar *c2 = filename.unicode();
diff --git a/src/corelib/mimetypes/qmimeprovider.cpp b/src/corelib/mimetypes/qmimeprovider.cpp
index dc6eb05d9a..e72f9a30d0 100644
--- a/src/corelib/mimetypes/qmimeprovider.cpp
+++ b/src/corelib/mimetypes/qmimeprovider.cpp
@@ -63,7 +63,7 @@ QT_BEGIN_NAMESPACE
 
 static QString fallbackParent(const QString &mimeTypeName)
 {
-    const QString myGroup = mimeTypeName.left(mimeTypeName.indexOf(QLatin1Char('/')));
+    const QStringRef myGroup = mimeTypeName.leftRef(mimeTypeName.indexOf(QLatin1Char('/')));
     // All text/* types are subclasses of text/plain.
     if (myGroup == QLatin1String("text") && mimeTypeName != QLatin1String("text/plain"))
         return QLatin1String("text/plain");
@@ -363,7 +363,8 @@ bool QMimeBinaryProvider::matchSuffixTree(QMimeGlobMatchResult &result, QMimeBin
                     const int weight = flagsAndWeight & 0xff;
                     const bool caseSensitive = flagsAndWeight & 0x100;
                     if (caseSensitiveCheck || !caseSensitive) {
-                        result.addMatch(QLatin1String(mimeType), weight, QLatin1Char('*') + fileName.mid(charPos+1));
+                        result.addMatch(QLatin1String(mimeType), weight,
+                                        QLatin1Char('*') + fileName.midRef(charPos + 1));
                         success = true;
                     }
                 }
diff --git a/src/corelib/mimetypes/qmimetype.cpp b/src/corelib/mimetypes/qmimetype.cpp
index 80b6a76ecc..5d18b67e8d 100644
--- a/src/corelib/mimetypes/qmimetype.cpp
+++ b/src/corelib/mimetypes/qmimetype.cpp
@@ -286,11 +286,12 @@ QString QMimeType::genericIconName() const
         // then the mimetype is used to generate the generic icon by using the top-level
         // media type (e.g.  "video" in "video/ogg") and appending "-x-generic"
         // (i.e. "video-x-generic" in the previous example).
-        QString group = name();
-        const int slashindex = group.indexOf(QLatin1Char('/'));
+        const QString group = name();
+        QStringRef groupRef(&group);
+        const int slashindex = groupRef.indexOf(QLatin1Char('/'));
         if (slashindex != -1)
-            group = group.left(slashindex);
-        return group + QLatin1String("-x-generic");
+            groupRef = groupRef.left(slashindex);
+        return groupRef + QLatin1String("-x-generic");
     }
     return d->genericIconName;
 }