Avoid unnecessary string and list copies

Change-Id: I78bc4d307be69ce3bbfaa3ca3dd7c85e654af8d6
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/libs/cplusplus/FastPreprocessor.cpp

@@ -38,7 +38,7 @@ QByteArray FastPreprocessor::run(Document::Ptr newDoc,
                 mergeEnvironment(i.key());
         }
 
-        const QList<Document::Include> includes = doc->resolvedIncludes();
+        const QList<Document::Include> &includes = doc->resolvedIncludes();
         for (const Document::Include &i : includes)
             mergeEnvironment(i.resolvedFileName());
 
@@ -69,7 +69,7 @@ void FastPreprocessor::mergeEnvironment(const FilePath &filePath)
 {
     if (Utils::insert(_merged, filePath)) {
         if (Document::Ptr doc = _snapshot.document(filePath)) {
-            const QList<Document::Include> includes = doc->resolvedIncludes();
+            const QList<Document::Include> &includes = doc->resolvedIncludes();
             for (const Document::Include &i : includes)
                 mergeEnvironment(i.resolvedFileName());
 

src/libs/utils/filepath.cpp

@@ -453,7 +453,7 @@ QStringView FilePath::host() const
 
 QStringView FilePath::pathView() const
 {
-    return QStringView(m_data).left(m_pathLen);
+    return QStringView(m_data.constData(), m_pathLen);
 }
 
 QString FilePath::path() const
@@ -469,7 +469,17 @@ void FilePath::setParts(const QStringView scheme, const QStringView host, QStrin
         path = path.mid(3);
 
     m_hash = 0;
-    m_data = path.toString() + scheme.toString() + host.toString();
+
+    // The equivalent of:
+    //   m_data = path.toString() + scheme.toString() + host.toString();
+    // but with less copying.
+    // Note: The QStringBuilder optimization does not currently work in this case.
+    m_data.resize(0);
+    m_data.reserve(m_schemeLen + m_hostLen + m_pathLen);
+    m_data.append(path);
+    m_data.append(scheme);
+    m_data.append(host);
+
     m_schemeLen = scheme.size();
     m_hostLen = host.size();
     m_pathLen = path.size();
@@ -1480,7 +1490,7 @@ FilePath FilePath::relativePathFrom(const FilePath &anchor) const
         absoluteAnchorPath = anchor.absoluteFilePath();
     else
         return {};
-    QString relativeFilePath = calcRelativePath(absPath.path(), absoluteAnchorPath.path());
+    QString relativeFilePath = calcRelativePath(absPath.pathView(), absoluteAnchorPath.pathView());
     if (!filename.isEmpty()) {
         if (relativeFilePath == ".")
             relativeFilePath.clear();
@@ -1505,14 +1515,14 @@ FilePath FilePath::relativePathFrom(const FilePath &anchor) const
 
     \see FilePath::isRelativePath(), FilePath::relativePathFrom(), FilePath::relativeChildPath()
 */
-QString FilePath::calcRelativePath(const QString &absolutePath, const QString &absoluteAnchorPath)
+QString FilePath::calcRelativePath(QStringView absolutePath, QStringView absoluteAnchorPath)
 {
     if (absolutePath.isEmpty() || absoluteAnchorPath.isEmpty())
         return QString();
     // TODO using split() instead of parsing the strings by char index is slow
     // and needs more memory (but the easiest implementation for now)
-    const QStringList splits1 = absolutePath.split('/');
+    const QList<QStringView> splits1 = absolutePath.split('/');
-    const QStringList splits2 = absoluteAnchorPath.split('/');
+    const QList<QStringView> splits2 = absoluteAnchorPath.split('/');
     int i = 0;
     while (i < splits1.count() && i < splits2.count() && splits1.at(i) == splits2.at(i))
         ++i;

src/libs/utils/filepath.h

@@ -258,7 +258,7 @@ public:
     [[nodiscard]] static int rootLength(const QStringView path); // Assumes no scheme and host
     [[nodiscard]] static int schemeAndHostLength(const QStringView path);
 
-    static QString calcRelativePath(const QString &absolutePath, const QString &absoluteAnchorPath);
+    static QString calcRelativePath(QStringView absolutePath, QStringView absoluteAnchorPath);
     //! Returns a filepath the represents the same file on a local drive
     expected_str<FilePath> localSource() const;
 

src/libs/utils/templateengine.cpp

@@ -46,11 +46,11 @@ PreprocessStackEntry::PreprocessStackEntry(PreprocessorSection s, bool p, bool c
 class PreprocessContext {
 public:
     PreprocessContext();
-    bool process(const QString &in, QString *out, QString *errorMessage);
+    bool process(QStringView in, QString *out, QString *errorMessage);
 
 private:
     void reset();
-    PreprocessorSection preprocessorLine(const QString & in, QString *ifExpression) const;
+    PreprocessorSection preprocessorLine(QStringView in, QString *ifExpression) const;
 
     mutable QRegularExpression m_ifPattern;
     mutable QRegularExpression m_elsifPattern;
@@ -81,7 +81,7 @@ void PreprocessContext::reset()
 
 // Determine type of line and return enumeration, cut out
 // expression for '@if/@elsif'.
-PreprocessorSection PreprocessContext::preprocessorLine(const QString &in,
+PreprocessorSection PreprocessContext::preprocessorLine(QStringView in,
                                                         QString *ifExpression) const
 {
     QRegularExpressionMatch match = m_ifPattern.match(in);
@@ -111,7 +111,7 @@ static inline QString msgEmptyStack(int line)
     return QString::fromLatin1("Unmatched '@endif' at line %1.").arg(line);
 }
 
-bool PreprocessContext::process(const QString &in, QString *out, QString *errorMessage)
+bool PreprocessContext::process(QStringView in, QString *out, QString *errorMessage)
 {
     out->clear();
     if (in.isEmpty())
@@ -121,7 +121,7 @@ bool PreprocessContext::process(const QString &in, QString *out, QString *errorM
     reset();
 
     const QChar newLine = QLatin1Char('\n');
-    const QStringList lines = in.split(newLine);
+    const QList<QStringView> lines = in.split(newLine);
     const int lineCount = lines.size();
     bool first = true;
     for (int l = 0; l < lineCount; l++) {