Use QString::fromLatin1() less to avoid string allocations

QString::fromLatin1 always allocates memory, but there are
cases where we can avoid/reduce allocations or/and reduce
text size, e.g.:

QStringBuilder expressions
Fix: replace QString::fromLatin1 with QL1S

QString::fromLatin1().arg(String) pattern
Fix: replace with QStringBuilder

Overloaded functions with QL1S arg
Fix: replace QString::fromLatin1 with QL1S

In rare cases if there is no overloaded function
with QL1S and we have deal with string literal,
replace QString::fromLatin1 with QStringLiteral.

Change-Id: Iabe1a3cc0830f40ef78a0548afa4368583c31def
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

4 files changed, 10 insertions, 6 deletions

diff --git a/src/gui/image/qimagereader.cpp b/src/gui/image/qimagereader.cpp
index 0320d032b0..4390e46fde 100644
--- a/src/gui/image/qimagereader.cpp
+++ b/src/gui/image/qimagereader.cpp
@@ -569,7 +569,7 @@ bool QImageReaderPrivate::initHandler()
 
         do {
             file->setFileName(fileName + QLatin1Char('.')
-                    + QString::fromLatin1(extensions.at(currentExtension++).constData()));
+                    + QLatin1String(extensions.at(currentExtension++).constData()));
             file->open(QIODevice::ReadOnly);
         } while (!file->isOpen() && currentExtension < extensions.size());
 
diff --git a/src/gui/kernel/qkeysequence.cpp b/src/gui/kernel/qkeysequence.cpp
index 9a75f4bc83..d59bd63caf 100644
--- a/src/gui/kernel/qkeysequence.cpp
+++ b/src/gui/kernel/qkeysequence.cpp
@@ -1211,9 +1211,13 @@ QString QKeySequence::encodeString(int key)
 
 static inline void addKey(QString &str, const QString &theKey, QKeySequence::SequenceFormat format)
 {
-    if (!str.isEmpty())
-        str += (format == QKeySequence::NativeText) ? QCoreApplication::translate("QShortcut", "+")
-                                                    : QString::fromLatin1("+");
+    if (!str.isEmpty()) {
+        if (format == QKeySequence::NativeText)
+            str += QCoreApplication::translate("QShortcut", "+");
+        else
+            str += QLatin1Char('+');
+    }
+
     str += theKey;
 }
 
diff --git a/src/gui/text/qfontdatabase.cpp b/src/gui/text/qfontdatabase.cpp
index a3a3f20b18..7fcac9b9f2 100644
--- a/src/gui/text/qfontdatabase.cpp
+++ b/src/gui/text/qfontdatabase.cpp
@@ -2439,7 +2439,7 @@ int QFontDatabasePrivate::addAppFont(const QByteArray &fontData, const QString &
     }
 
     if (font.fileName.isEmpty() && !fontData.isEmpty())
-        font.fileName = QString::fromLatin1(":qmemoryfonts/") + QString::number(i);
+        font.fileName = QLatin1String(":qmemoryfonts/") + QString::number(i);
 
     registerFont(&font);
     if (font.families.isEmpty())
diff --git a/src/gui/text/qtextodfwriter.cpp b/src/gui/text/qtextodfwriter.cpp
index 73d2e545ba..e228b3c840 100644
--- a/src/gui/text/qtextodfwriter.cpp
+++ b/src/gui/text/qtextodfwriter.cpp
@@ -63,7 +63,7 @@ QT_BEGIN_NAMESPACE
 static QString pixelToPoint(qreal pixels)
 {
     // we hardcode 96 DPI, we do the same in the ODF importer to have a perfect roundtrip.
-    return QString::number(pixels * 72 / 96) + QString::fromLatin1("pt");
+    return QString::number(pixels * 72 / 96) + QLatin1String("pt");
 }
 
 // strategies