Use QStringRef to optimize memory allocation

Replace substring functions that return QString
with corresponding functions that return QStringRef.

Change-Id: I3c485f89352a1ee66076fba74fd486da9349c354
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

5 files changed, 10 insertions, 10 deletions

diff --git a/src/corelib/io/qfilesystemengine_win.cpp b/src/corelib/io/qfilesystemengine_win.cpp
index abf346a717..cdb64d08e1 100644
--- a/src/corelib/io/qfilesystemengine_win.cpp
+++ b/src/corelib/io/qfilesystemengine_win.cpp
@@ -349,7 +349,7 @@ static QString readSymLink(const QFileSystemEntry &link)
         if (matchVolName.indexIn(result) == 0) {
             DWORD len;
             wchar_t buffer[MAX_PATH];
-            QString volumeName = result.mid(0, matchVolName.matchedLength()).prepend(QLatin1String("\\\\?\\"));
+            const QString volumeName = QLatin1String("\\\\?\\") + result.leftRef(matchVolName.matchedLength());
             if (GetVolumePathNamesForVolumeName(reinterpret_cast<LPCWSTR>(volumeName.utf16()), buffer, MAX_PATH, &len) != 0)
                 result.replace(0,matchVolName.matchedLength(), QString::fromWCharArray(buffer));
         }
diff --git a/src/gui/text/qcssparser.cpp b/src/gui/text/qcssparser.cpp
index 72c5d5ff33..3e36a6d1c9 100644
--- a/src/gui/text/qcssparser.cpp
+++ b/src/gui/text/qcssparser.cpp
@@ -2107,7 +2107,7 @@ QString Scanner::preprocess(const QString &input, bool *hasEscapeSequences)
 
             hexCount = qMin(hexCount, 6);
             bool ok = false;
-            ushort code = output.mid(hexStart, hexCount).toUShort(&ok, 16);
+            ushort code = output.midRef(hexStart, hexCount).toUShort(&ok, 16);
             if (ok) {
                 output.replace(hexStart - 1, hexCount + 1, QChar(code));
                 i = hexStart;
diff --git a/src/gui/text/qtextdocument_p.cpp b/src/gui/text/qtextdocument_p.cpp
index 3537adba9e..7107c7c26e 100644
--- a/src/gui/text/qtextdocument_p.cpp
+++ b/src/gui/text/qtextdocument_p.cpp
@@ -131,7 +131,7 @@ static bool isValidBlockSeparator(QChar ch)
         || ch == QTextEndOfFrame;
 }
 
-static bool noBlockInString(const QString &str)
+static bool noBlockInString(const QStringRef &str)
 {
     return !str.contains(QChar::ParagraphSeparator)
         && !str.contains(QTextBeginningOfFrame)
@@ -320,7 +320,7 @@ void QTextDocumentPrivate::setLayout(QAbstractTextDocumentLayout *layout)
 void QTextDocumentPrivate::insert_string(int pos, uint strPos, uint length, int format, QTextUndoCommand::Operation op)
 {
     // ##### optimize when only appending to the fragment!
-    Q_ASSERT(noBlockInString(text.mid(strPos, length)));
+    Q_ASSERT(noBlockInString(text.midRef(strPos, length)));
 
     split(pos);
     uint x = fragments.insert_single(pos, length);
@@ -476,7 +476,7 @@ void QTextDocumentPrivate::insert(int pos, const QString &str, int format)
     if (str.size() == 0)
         return;
 
-    Q_ASSERT(noBlockInString(str));
+    Q_ASSERT(noBlockInString(QStringRef(&str)));
 
     int strPos = text.length();
     text.append(str);
@@ -494,7 +494,7 @@ int QTextDocumentPrivate::remove_string(int pos, uint length, QTextUndoCommand::
 
     Q_ASSERT(blocks.size(b) > length);
     Q_ASSERT(x && fragments.position(x) == (uint)pos && fragments.size(x) == length);
-    Q_ASSERT(noBlockInString(text.mid(fragments.fragment(x)->stringPosition, length)));
+    Q_ASSERT(noBlockInString(text.midRef(fragments.fragment(x)->stringPosition, length)));
 
     blocks.setSize(b, blocks.size(b)-length);
 
@@ -629,7 +629,7 @@ void QTextDocumentPrivate::move(int pos, int to, int length, QTextUndoCommand::O
 
         if (key+1 != blocks.position(b)) {
 //          qDebug("remove_string from %d length %d", key, X->size_array[0]);
-            Q_ASSERT(noBlockInString(text.mid(X->stringPosition, X->size_array[0])));
+            Q_ASSERT(noBlockInString(text.midRef(X->stringPosition, X->size_array[0])));
             w = remove_string(key, X->size_array[0], op);
 
             if (needsInsert) {
diff --git a/src/gui/text/qtextengine.cpp b/src/gui/text/qtextengine.cpp
index d11f8c34b1..d9b648b170 100644
--- a/src/gui/text/qtextengine.cpp
+++ b/src/gui/text/qtextengine.cpp
@@ -2711,7 +2711,7 @@ static QString stringMidRetainingBidiCC(const QString &string,
             suffix += c;
     }
 
-    return prefix + ellidePrefix + string.mid(midStart, midLength) + ellideSuffix + suffix;
+    return prefix + ellidePrefix + string.midRef(midStart, midLength) + ellideSuffix + suffix;
 }
 
 QString QTextEngine::elidedText(Qt::TextElideMode mode, const QFixed &width, int flags, int from, int count) const
@@ -2874,7 +2874,7 @@ QString QTextEngine::elidedText(Qt::TextElideMode mode, const QFixed &width, int
         if (prevCharJoins(layoutData->string, rightPos))
             ellipsisText.append(QChar(0x200d) /* ZWJ */);
 
-        return layoutData->string.mid(from, leftPos - from) + ellipsisText + layoutData->string.mid(rightPos, to - rightPos);
+        return layoutData->string.midRef(from, leftPos - from) + ellipsisText + layoutData->string.midRef(rightPos, to - rightPos);
     }
 
     return layoutData->string.mid(from, to - from);
diff --git a/src/tools/uic/cpp/cppwriteinitialization.cpp b/src/tools/uic/cpp/cppwriteinitialization.cpp
index ade3c5db35..031b34b67e 100644
--- a/src/tools/uic/cpp/cppwriteinitialization.cpp
+++ b/src/tools/uic/cpp/cppwriteinitialization.cpp
@@ -2023,7 +2023,7 @@ void WriteInitialization::addInitializer(Item *item,
         const QString &name, int column, const QString &value, const QString &directive, bool translatable) const
 {
     if (!value.isEmpty())
-        item->addSetter(QLatin1String("->set") + name.at(0).toUpper() + name.mid(1) +
+        item->addSetter(QLatin1String("->set") + name.at(0).toUpper() + name.midRef(1) +
                     QLatin1Char('(') + (column < 0 ? QString() : QString::number(column) +
                     QLatin1String(", ")) + value + QLatin1String(");"), directive, translatable);
 }