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.

While touching the code, also port loops to C++11 style.

Change-Id: I04c99b24ea6afd3715e3edf9ea00bfab838fd53c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>
Reviewed-by: Frank Meerkoetter <frank.meerkoetter@basyskom.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@theqtcompany.com>
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

9 files changed, 65 insertions, 62 deletions

diff --git a/src/quick/items/context2d/qquickcontext2d.cpp b/src/quick/items/context2d/qquickcontext2d.cpp
index 734cadf49a..1b0670aabf 100644
--- a/src/quick/items/context2d/qquickcontext2d.cpp
+++ b/src/quick/items/context2d/qquickcontext2d.cpp
@@ -65,6 +65,7 @@
 #include <private/qv4scopedvalue_p.h>
 
 #include <QtCore/qmath.h>
+#include <QtCore/qvector.h>
 #include <QtCore/private/qnumeric_p.h>
 #include <QtCore/QRunnable>
 #include <QtGui/qguiapplication.h>
@@ -200,7 +201,7 @@ QColor qt_color_from_string(const QV4::Value &name)
     return QColor();
 }
 
-static int qParseFontSizeFromToken(const QString &fontSizeToken, bool &ok)
+static int qParseFontSizeFromToken(const QStringRef &fontSizeToken, bool &ok)
 {
     ok = false;
     float size = fontSizeToken.trimmed().toFloat(&ok);
@@ -216,11 +217,11 @@ static int qParseFontSizeFromToken(const QString &fontSizeToken, bool &ok)
     \c true if successful. If the font size is invalid, \c false is returned
     and a warning is printed.
 */
-static bool qSetFontSizeFromToken(QFont &font, const QString &fontSizeToken)
+static bool qSetFontSizeFromToken(QFont &font, const QStringRef &fontSizeToken)
 {
-    const QString trimmedToken = fontSizeToken.trimmed();
-    const QString unitStr = trimmedToken.right(2);
-    const QString value = trimmedToken.left(trimmedToken.size() - 2);
+    const QStringRef trimmedToken = fontSizeToken.trimmed();
+    const QStringRef unitStr = trimmedToken.right(2);
+    const QStringRef value = trimmedToken.left(trimmedToken.size() - 2);
     bool ok = false;
     int size = 0;
     if (unitStr == QLatin1String("px")) {
@@ -246,7 +247,7 @@ static bool qSetFontSizeFromToken(QFont &font, const QString &fontSizeToken)
     each family is separated by spaces. Families with spaces in their name
     must be quoted.
 */
-static QStringList qExtractFontFamiliesFromString(const QString &fontFamiliesString)
+static QStringList qExtractFontFamiliesFromString(const QStringRef &fontFamiliesString)
 {
     QStringList extractedFamilies;
     int quoteIndex = -1;
@@ -259,7 +260,7 @@ static QStringList qExtractFontFamiliesFromString(const QString &fontFamiliesStr
             } else {
                 if (ch == fontFamiliesString.at(quoteIndex)) {
                     // Found the matching quote. +1/-1 because we don't want the quote as part of the name.
-                    const QString family = fontFamiliesString.mid(quoteIndex + 1, index - quoteIndex - 1);
+                    const QString family = fontFamiliesString.mid(quoteIndex + 1, index - quoteIndex - 1).toString();
                     extractedFamilies.push_back(family);
                     currentFamily.clear();
                     quoteIndex = -1;
@@ -390,16 +391,17 @@ static QFont qt_font_from_string(const QString& fontString, const QFont &current
     fontSizeEnd += 3;
 
     QFont newFont;
-    if (!qSetFontSizeFromToken(newFont, fontString.mid(fontSizeStart, fontSizeEnd - fontSizeStart)))
+    if (!qSetFontSizeFromToken(newFont, fontString.midRef(fontSizeStart, fontSizeEnd - fontSizeStart)))
         return currentFont;
 
     // We don't want to parse the size twice, so remove it now.
     QString remainingFontString = fontString;
     remainingFontString.remove(fontSizeStart, fontSizeEnd - fontSizeStart);
+    QStringRef remainingFontStringRef(&remainingFontString);
 
     // Next, we have to take any font families out, as QString::split() will ruin quoted family names.
-    const QString fontFamiliesString = remainingFontString.mid(fontSizeStart);
-    remainingFontString.chop(remainingFontString.length() - fontSizeStart);
+    const QStringRef fontFamiliesString = remainingFontStringRef.mid(fontSizeStart);
+    remainingFontStringRef.truncate(fontSizeStart);
     QStringList fontFamilies = qExtractFontFamiliesFromString(fontFamiliesString);
     if (fontFamilies.isEmpty()) {
         return currentFont;
@@ -408,16 +410,16 @@ static QFont qt_font_from_string(const QString& fontString, const QFont &current
         return currentFont;
 
     // Now that we've removed the messy parts, we can split the font string on spaces.
-    const QString trimmedTokensStr = remainingFontString.trimmed();
+    const QStringRef trimmedTokensStr = remainingFontStringRef.trimmed();
     if (trimmedTokensStr.isEmpty()) {
         // No optional properties.
         return newFont;
     }
-    const QStringList tokens = trimmedTokensStr.split(QLatin1Char(' '));
+    const auto tokens = trimmedTokensStr.split(QLatin1Char(' '));
 
     int usedTokens = NoTokens;
     // Optional properties can be in any order, but font-size and font-family must be last.
-    for (const QString &token : tokens) {
+    for (const QStringRef &token : tokens) {
         if (token.compare(QLatin1String("normal")) == 0) {
             if (!(usedTokens & FontStyle) || !(usedTokens & FontVariant) || !(usedTokens & FontWeight)) {
                 // Could be font-style, font-variant or font-weight.
diff --git a/src/quick/items/qquickpathview.cpp b/src/quick/items/qquickpathview.cpp
index f0bbb1e732..a56d0fc06e 100644
--- a/src/quick/items/qquickpathview.cpp
+++ b/src/quick/items/qquickpathview.cpp
@@ -1910,7 +1910,7 @@ void QQuickPathView::refill()
         if (lcItemViewDelegateLifecycle().isDebugEnabled()) {
             QQuickText *text = qmlobject_cast<QQuickText*>(item);
             if (text)
-                qCDebug(lcItemViewDelegateLifecycle) << "idx" << idx << "@" << pos << ": QQuickText" << text->objectName() << text->text().left(40);
+                qCDebug(lcItemViewDelegateLifecycle) << "idx" << idx << "@" << pos << ": QQuickText" << text->objectName() << text->text().leftRef(40);
             else
                 qCDebug(lcItemViewDelegateLifecycle) << "idx" << idx << "@" << pos << ":" << item;
         }
diff --git a/src/quick/items/qquickscalegrid.cpp b/src/quick/items/qquickscalegrid.cpp
index f860c08bad..d7a0f1b681 100644
--- a/src/quick/items/qquickscalegrid.cpp
+++ b/src/quick/items/qquickscalegrid.cpp
@@ -136,39 +136,38 @@ QQuickGridScaledImage::QQuickGridScaledImage(QIODevice *data)
         if (colonId <= 0)
             return;
 
-        QStringList list;
-        list.append(line.left(colonId).trimmed());
-        list.append(line.mid(colonId+1).trimmed());
-
-        if (list[0] == QLatin1String("border.left"))
-            l = list[1].toInt();
-        else if (list[0] == QLatin1String("border.right"))
-            r = list[1].toInt();
-        else if (list[0] == QLatin1String("border.top"))
-            t = list[1].toInt();
-        else if (list[0] == QLatin1String("border.bottom"))
-            b = list[1].toInt();
-        else if (list[0] == QLatin1String("source"))
-            imgFile = list[1];
-        else if (list[0] == QLatin1String("horizontalTileRule") || list[0] == QLatin1String("horizontalTileMode"))
-            _h = stringToRule(list[1]);
-        else if (list[0] == QLatin1String("verticalTileRule") || list[0] == QLatin1String("verticalTileMode"))
-            _v = stringToRule(list[1]);
+        const QStringRef property = line.leftRef(colonId).trimmed();
+        QStringRef value = line.midRef(colonId + 1).trimmed();
+
+        if (property == QLatin1String("border.left")) {
+            l = value.toInt();
+        } else if (property == QLatin1String("border.right")) {
+            r = value.toInt();
+        } else if (property == QLatin1String("border.top")) {
+            t = value.toInt();
+        } else if (property == QLatin1String("border.bottom")) {
+            b = value.toInt();
+        } else if (property == QLatin1String("source")) {
+            if (value.startsWith(QLatin1Char('"')) && value.endsWith(QLatin1Char('"')))
+                value = value.mid(1, value.size() - 2); // remove leading/trailing quotes.
+            imgFile = value.toString();
+        } else if (property == QLatin1String("horizontalTileRule") || property == QLatin1String("horizontalTileMode")) {
+            _h = stringToRule(value);
+        } else if (property == QLatin1String("verticalTileRule") || property == QLatin1String("verticalTileMode")) {
+            _v = stringToRule(value);
+        }
     }
 
     if (l < 0 || r < 0 || t < 0 || b < 0 || imgFile.isEmpty())
         return;
 
     _l = l; _r = r; _t = t; _b = b;
-
     _pix = imgFile;
-    if (_pix.startsWith(QLatin1Char('"')) && _pix.endsWith(QLatin1Char('"')))
-        _pix = _pix.mid(1, _pix.size() - 2); // remove leading/trailing quotes.
 }
 
-QQuickBorderImage::TileMode QQuickGridScaledImage::stringToRule(const QString &s)
+QQuickBorderImage::TileMode QQuickGridScaledImage::stringToRule(const QStringRef &s)
 {
-    QString string = s;
+    QStringRef string = s;
     if (string.startsWith(QLatin1Char('"')) && string.endsWith(QLatin1Char('"')))
         string = string.mid(1, string.size() - 2); // remove leading/trailing quotes.
 
diff --git a/src/quick/items/qquickscalegrid_p_p.h b/src/quick/items/qquickscalegrid_p_p.h
index a424002dfb..7f6a31a7bd 100644
--- a/src/quick/items/qquickscalegrid_p_p.h
+++ b/src/quick/items/qquickscalegrid_p_p.h
@@ -116,7 +116,7 @@ public:
     QString pixmapUrl() const;
 
 private:
-    static QQuickBorderImage::TileMode stringToRule(const QString &);
+    static QQuickBorderImage::TileMode stringToRule(const QStringRef &);
 
 private:
     int _l;
diff --git a/src/quick/items/qquicktextinput.cpp b/src/quick/items/qquicktextinput.cpp
index ab7a0f02dd..504dece0d1 100644
--- a/src/quick/items/qquicktextinput.cpp
+++ b/src/quick/items/qquicktextinput.cpp
@@ -1874,7 +1874,7 @@ QVariant QQuickTextInput::inputMethodQuery(Qt::InputMethodQuery property, QVaria
         return QVariant(d->m_text.mid(d->m_cursor));
     case Qt::ImTextBeforeCursor:
         if (argument.isValid())
-            return QVariant(d->m_text.left(d->m_cursor).right(argument.toInt()));
+            return QVariant(d->m_text.leftRef(d->m_cursor).right(argument.toInt()).toString());
         return QVariant(d->m_text.left(d->m_cursor));
     default:
         return QQuickItem::inputMethodQuery(property);
diff --git a/src/quick/scenegraph/util/qsgshadersourcebuilder.cpp b/src/quick/scenegraph/util/qsgshadersourcebuilder.cpp
index ec1d316f78..caa296451e 100644
--- a/src/quick/scenegraph/util/qsgshadersourcebuilder.cpp
+++ b/src/quick/scenegraph/util/qsgshadersourcebuilder.cpp
@@ -382,9 +382,9 @@ QString QSGShaderSourceBuilder::resolveShaderPath(const QString &path) const
         int idx = path.lastIndexOf(QLatin1Char('.'));
         QString resolvedPath;
         if (idx != -1)
-            resolvedPath = path.left(idx)
-                         + QStringLiteral("_core")
-                         + path.right(path.length() - idx);
+            resolvedPath = path.leftRef(idx)
+                         + QLatin1String("_core")
+                         + path.rightRef(path.length() - idx);
         return resolvedPath;
     }
 }
diff --git a/src/quick/util/qquickanimation.cpp b/src/quick/util/qquickanimation.cpp
index adf8f600a0..741a583803 100644
--- a/src/quick/util/qquickanimation.cpp
+++ b/src/quick/util/qquickanimation.cpp
@@ -986,7 +986,7 @@ void QQuickScriptActionPrivate::debugAction(QDebug d, int indentLevel) const
         QByteArray ind(indentLevel, ' ');
         QString exprStr = expr.expression();
         int endOfFirstLine = exprStr.indexOf('\n');
-        d << "\n" << ind.constData() << exprStr.left(endOfFirstLine);
+        d << "\n" << ind.constData() << exprStr.leftRef(endOfFirstLine);
         if (endOfFirstLine != -1 && endOfFirstLine < exprStr.length())
             d << "...";
     }
diff --git a/src/quick/util/qquickglobal.cpp b/src/quick/util/qquickglobal.cpp
index ef54917434..be4c968ab2 100644
--- a/src/quick/util/qquickglobal.cpp
+++ b/src/quick/util/qquickglobal.cpp
@@ -172,8 +172,8 @@ public:
             int index = s.indexOf(QLatin1Char(','));
 
             bool xGood, yGood;
-            float xCoord = s.left(index).toFloat(&xGood);
-            float yCoord = s.mid(index+1).toFloat(&yGood);
+            float xCoord = s.leftRef(index).toFloat(&xGood);
+            float yCoord = s.midRef(index + 1).toFloat(&yGood);
 
             if (xGood && yGood) {
                 if (ok) *ok = true;
@@ -192,9 +192,9 @@ public:
             int index2 = s.indexOf(QLatin1Char(','), index+1);
 
             bool xGood, yGood, zGood;
-            float xCoord = s.left(index).toFloat(&xGood);
-            float yCoord = s.mid(index+1, index2-index-1).toFloat(&yGood);
-            float zCoord = s.mid(index2+1).toFloat(&zGood);
+            float xCoord = s.leftRef(index).toFloat(&xGood);
+            float yCoord = s.midRef(index + 1, index2 - index - 1).toFloat(&yGood);
+            float zCoord = s.midRef(index2 + 1).toFloat(&zGood);
 
             if (xGood && yGood && zGood) {
                 if (ok) *ok = true;
@@ -214,10 +214,10 @@ public:
             int index3 = s.indexOf(QLatin1Char(','), index2+1);
 
             bool xGood, yGood, zGood, wGood;
-            float xCoord = s.left(index).toFloat(&xGood);
-            float yCoord = s.mid(index+1, index2-index-1).toFloat(&yGood);
-            float zCoord = s.mid(index2+1, index3-index2-1).toFloat(&zGood);
-            float wCoord = s.mid(index3+1).toFloat(&wGood);
+            float xCoord = s.leftRef(index).toFloat(&xGood);
+            float yCoord = s.midRef(index + 1, index2 - index - 1).toFloat(&yGood);
+            float zCoord = s.midRef(index2 + 1, index3 - index2 - 1).toFloat(&zGood);
+            float wCoord = s.midRef(index3 + 1).toFloat(&wGood);
 
             if (xGood && yGood && zGood && wGood) {
                 if (ok) *ok = true;
@@ -257,10 +257,10 @@ public:
         if (s.count(QLatin1Char(',')) == 15) {
             float matValues[16];
             bool vOK = true;
-            QString mutableStr = s;
+            QStringRef mutableStr(&s);
             for (int i = 0; vOK && i < 16; ++i) {
                 int cidx = mutableStr.indexOf(QLatin1Char(','));
-                matValues[i] = mutableStr.leftRef(cidx).toDouble(&vOK);
+                matValues[i] = mutableStr.left(cidx).toDouble(&vOK);
                 mutableStr = mutableStr.mid(cidx + 1);
             }
 
diff --git a/src/quick/util/qquickstategroup.cpp b/src/quick/util/qquickstategroup.cpp
index 791e38e45d..c163b401fb 100644
--- a/src/quick/util/qquickstategroup.cpp
+++ b/src/quick/util/qquickstategroup.cpp
@@ -47,6 +47,7 @@
 #include <QtCore/qstringbuilder.h>
 #include <QtCore/qstringlist.h>
 #include <QtCore/qdebug.h>
+#include <QtCore/qvector.h>
 
 #include <private/qobject_p.h>
 #include <qqmlinfo.h>
@@ -379,28 +380,29 @@ QQuickTransition *QQuickStateGroupPrivate::findTransition(const QString &from, c
                       (t->fromState() == QLatin1String("*") &&
                        t->toState() == QLatin1String("*"))))
                 break;
-            QStringList fromState;
-            QStringList toState;
+            const QString fromStateStr = t->fromState();
+            const QString toStateStr = t->toState();
 
-            fromState = t->fromState().split(QLatin1Char(','));
+            QVector<QStringRef> fromState = fromStateStr.splitRef(QLatin1Char(','));
             for (int jj = 0; jj < fromState.count(); ++jj)
                 fromState[jj] = fromState.at(jj).trimmed();
-            toState = t->toState().split(QLatin1Char(','));
+            QVector<QStringRef> toState = toStateStr.splitRef(QLatin1Char(','));
             for (int jj = 0; jj < toState.count(); ++jj)
                 toState[jj] = toState.at(jj).trimmed();
             if (ii == 1)
                 qSwap(fromState, toState);
             int tScore = 0;
-            if (fromState.contains(from))
+            const QString asterisk = QStringLiteral("*");
+            if (fromState.contains(QStringRef(&from)))
                 tScore += 2;
-            else if (fromState.contains(QLatin1String("*")))
+            else if (fromState.contains(QStringRef(&asterisk)))
                 tScore += 1;
             else
                 continue;
 
-            if (toState.contains(to))
+            if (toState.contains(QStringRef(&to)))
                 tScore += 2;
-            else if (toState.contains(QLatin1String("*")))
+            else if (toState.contains(QStringRef(&asterisk)))
                 tScore += 1;
             else
                 continue;