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>

src/corelib/global/qlibraryinfo.cpp

@@ -532,7 +532,7 @@ QLibraryInfo::rawLocation(LibraryLocation loc, PathGroup group)
             reg_var.setMinimal(true);
             while((rep = reg_var.indexIn(ret)) != -1) {
                 ret.replace(rep, reg_var.matchedLength(),
-                            QString::fromLocal8Bit(qgetenv(ret.mid(rep + 2,
+                            QString::fromLocal8Bit(qgetenv(ret.midRef(rep + 2,
                                 reg_var.matchedLength() - 3).toLatin1().constData()).constData()));
             }
 

src/corelib/io/qdir.cpp

@@ -146,9 +146,11 @@ inline QStringList QDirPrivate::splitFilters(const QString &nameFilter, QChar se
 {
     if (sep.isNull())
         sep = getFilterSepChar(nameFilter);
-    QStringList ret = nameFilter.split(sep);
+    const QVector<QStringRef> split = nameFilter.splitRef(sep);
-    for (int i = 0; i < ret.count(); ++i)
+    QStringList ret;
-        ret[i] = ret[i].trimmed();
+    ret.reserve(split.size());
+    for (const auto &e : split)
+        ret.append(e.trimmed().toString());
     return ret;
 }
 

src/corelib/io/qfilesystemengine.cpp

@@ -91,7 +91,7 @@ QString QFileSystemEngine::slowCanonicalized(const QString &path)
                 if (separatorPos != -1) {
                     if (fi.isDir() && !target.endsWith(slash))
                         target.append(slash);
-                    target.append(tmpPath.mid(separatorPos));
+                    target.append(tmpPath.midRef(separatorPos));
                 }
                 tmpPath = QDir::cleanPath(target);
                 separatorPos = 0;

src/corelib/io/qfilesystemengine_unix.cpp

@@ -182,8 +182,9 @@ QFileSystemEntry QFileSystemEngine::getLinkTarget(const QFileSystemEntry &link,
 #endif
 
         if (!ret.startsWith(QLatin1Char('/'))) {
-            if (link.filePath().startsWith(QLatin1Char('/'))) {
+            const QString linkFilePath = link.filePath();
-                ret.prepend(link.filePath().left(link.filePath().lastIndexOf(QLatin1Char('/')))
+            if (linkFilePath.startsWith(QLatin1Char('/'))) {
+                ret.prepend(linkFilePath.leftRef(linkFilePath.lastIndexOf(QLatin1Char('/')))
                             + QLatin1Char('/'));
             } else {
                 ret.prepend(QDir::currentPath() + QLatin1Char('/'));

src/corelib/io/qfilesystemengine_win.cpp

@@ -52,6 +52,7 @@
 #include "qvarlengtharray.h"
 #include "qdatetime.h"
 #include "qt_windows.h"
+#include "qvector.h"
 
 #include <sys/types.h>
 #include <direct.h>
@@ -407,11 +408,11 @@ static QString readLink(const QFileSystemEntry &link)
 static bool uncShareExists(const QString &server)
 {
     // This code assumes the UNC path is always like \\?\UNC\server...
-    QStringList parts = server.split(QLatin1Char('\\'), QString::SkipEmptyParts);
+    const QVector<QStringRef> parts = server.splitRef(QLatin1Char('\\'), QString::SkipEmptyParts);
     if (parts.count() >= 3) {
         QStringList shares;
         if (QFileSystemEngine::uncListSharesOnServer(QLatin1String("\\\\") + parts.at(2), &shares))
-            return parts.count() >= 4 ? shares.contains(parts.at(3), Qt::CaseInsensitive) : true;
+            return parts.count() < 4 || shares.contains(parts.at(3).toString(), Qt::CaseInsensitive);
     }
     return false;
 }
@@ -1106,9 +1107,10 @@ bool QFileSystemEngine::removeDirectory(const QFileSystemEntry &entry, bool remo
     if (removeEmptyParents) {
         dirName = QDir::toNativeSeparators(QDir::cleanPath(dirName));
         for (int oldslash = 0, slash=dirName.length(); slash > 0; oldslash = slash) {
-            QString chunk = dirName.left(slash);
+            const QStringRef chunkRef = dirName.leftRef(slash);
-            if (chunk.length() == 2 && chunk.at(0).isLetter() && chunk.at(1) == QLatin1Char(':'))
+            if (chunkRef.length() == 2 && chunkRef.at(0).isLetter() && chunkRef.at(1) == QLatin1Char(':'))
                 break;
+            const QString chunk = chunkRef.toString();
             if (!isDirPath(chunk, 0))
                 return false;
             if (!rmDir(chunk))

src/corelib/io/qfilesystemiterator_win.cpp

@@ -40,6 +40,7 @@
 #include "qfilesystemiterator_p.h"
 #include "qfilesystemengine_p.h"
 #include "qplatformdefs.h"
+#include "qvector.h"
 
 #include <QtCore/qt_windows.h>
 
@@ -103,7 +104,7 @@ bool QFileSystemIterator::advance(QFileSystemEntry &fileEntry, QFileSystemMetaDa
                                          FINDEX_SEARCH_OPS(searchOps), 0, dwAdditionalFlags);
         if (findFileHandle == INVALID_HANDLE_VALUE) {
             if (nativePath.startsWith(QLatin1String("\\\\?\\UNC\\"))) {
-                QStringList parts = nativePath.split(QLatin1Char('\\'), QString::SkipEmptyParts);
+                const QVector<QStringRef> parts = nativePath.splitRef(QLatin1Char('\\'), QString::SkipEmptyParts);
                 if (parts.count() == 4 && QFileSystemEngine::uncListSharesOnServer(
                         QLatin1String("\\\\") + parts.at(2), &uncShares)) {
                     if (uncShares.isEmpty())

src/corelib/io/qresource.cpp

@@ -303,12 +303,12 @@ QResourcePrivate::ensureInitialized() const
     if(!that->absoluteFilePath.startsWith(QLatin1Char(':')))
         that->absoluteFilePath.prepend(QLatin1Char(':'));
 
-    QString path = fileName;
+    QStringRef path(&fileName);
     if(path.startsWith(QLatin1Char(':')))
         path = path.mid(1);
 
     if(path.startsWith(QLatin1Char('/'))) {
-        that->load(path);
+        that->load(path.toString());
     } else {
         QMutexLocker lock(resourceMutex());
         QStringList searchPaths = *resourceSearchPaths();

src/corelib/io/qstandardpaths_unix.cpp

@@ -223,7 +223,7 @@ QString QStandardPaths::writableLocation(StandardLocation type)
             if (!value.isEmpty()) {
                 // value can start with $HOME
                 if (value.startsWith(QLatin1String("$HOME")))
-                    value = QDir::homePath() + value.mid(5);
+                    value = QDir::homePath() + value.midRef(5);
                 if (value.length() > 1 && value.endsWith(QLatin1Char('/')))
                     value.chop(1);
                 return value;

src/corelib/io/qurl.cpp

@@ -3784,13 +3784,13 @@ QUrl QUrl::fromLocalFile(const QString &localFile)
     } else if (deslashified.startsWith(QLatin1String("//"))) {
         // magic for shared drive on windows
         int indexOfPath = deslashified.indexOf(QLatin1Char('/'), 2);
-        QString hostSpec = deslashified.mid(2, indexOfPath - 2);
+        QStringRef hostSpec = deslashified.midRef(2, indexOfPath - 2);
         // Check for Windows-specific WebDAV specification: "//host@SSL/path".
         if (hostSpec.endsWith(webDavSslTag(), Qt::CaseInsensitive)) {
-            hostSpec.chop(4);
+            hostSpec.truncate(hostSpec.size() - 4);
             scheme = webDavScheme();
         }
-        url.setHost(hostSpec);
+        url.setHost(hostSpec.toString());
 
         if (indexOfPath > 2)
             deslashified = deslashified.right(deslashified.length() - indexOfPath);
@@ -4255,8 +4255,8 @@ QUrl QUrl::fromUserInput(const QString &userInput)
     if (urlPrepended.isValid() && (!urlPrepended.host().isEmpty() || !urlPrepended.path().isEmpty()))
     {
         int dotIndex = trimmedString.indexOf(QLatin1Char('.'));
-        const QString hostscheme = trimmedString.left(dotIndex).toLower();
+        const QStringRef hostscheme = trimmedString.leftRef(dotIndex);
-        if (hostscheme == ftpScheme())
+        if (hostscheme.compare(ftpScheme(), Qt::CaseInsensitive) == 0)
             urlPrepended.setScheme(ftpScheme());
         return adjustFtpPath(urlPrepended);
     }

src/corelib/kernel/qmetaobject.cpp

@@ -2652,15 +2652,16 @@ int QMetaEnum::keysToValue(const char *keys, bool *ok) const
         return -1;
     if (ok != 0)
         *ok = true;
-    QStringList l = QString::fromLatin1(keys).split(QLatin1Char('|'));
+    const QString keysString = QString::fromLatin1(keys);
-    if (l.isEmpty())
+    const QVector<QStringRef> splitKeys = keysString.splitRef(QLatin1Char('|'));
+    if (splitKeys.isEmpty())
         return 0;
-    //#### TODO write proper code, do not use QStringList
+    // ### TODO write proper code: do not allocate memory, so we can go nothrow
     int value = 0;
     int count = mobj->d.data[handle + 2];
     int data = mobj->d.data[handle + 3];
-    for (int li = 0; li < l.size(); ++li) {
+    for (const QStringRef &untrimmed : splitKeys) {
-        QString trimmed = l.at(li).trimmed();
+        const QStringRef trimmed = untrimmed.trimmed();
         QByteArray qualified_key = trimmed.toLatin1();
         const char *key = qualified_key.constData();
         uint scope = 0;

src/corelib/kernel/qtranslator.cpp

@@ -487,7 +487,7 @@ bool QTranslator::load(const QString & filename, const QString & directory,
     }
 
     const QString suffixOrDotQM = suffix.isNull() ? dotQmLiteral() : suffix;
-    QString fname = filename;
+    QStringRef fname(&filename);
     QString realname;
     QString delims;
     delims = search_delimiters.isNull() ? QStringLiteral("_.") : search_delimiters;

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();

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;
                     }
                 }

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 QString group = name();
-        const int slashindex = group.indexOf(QLatin1Char('/'));
+        QStringRef groupRef(&group);
+        const int slashindex = groupRef.indexOf(QLatin1Char('/'));
         if (slashindex != -1)
-            group = group.left(slashindex);
+            groupRef = groupRef.left(slashindex);
-        return group + QLatin1String("-x-generic");
+        return groupRef + QLatin1String("-x-generic");
     }
     return d->genericIconName;
 }

src/corelib/plugin/qlibrary.cpp

@@ -616,12 +616,12 @@ bool QLibrary::isLibrary(const QString &fileName)
     QString completeSuffix = QFileInfo(fileName).completeSuffix();
     if (completeSuffix.isEmpty())
         return false;
-    QStringList suffixes = completeSuffix.split(QLatin1Char('.'));
+    const QVector<QStringRef> suffixes = completeSuffix.splitRef(QLatin1Char('.'));
 # if defined(Q_OS_DARWIN)
 
     // On Mac, libs look like libmylib.1.0.0.dylib
-    const QString lastSuffix = suffixes.at(suffixes.count() - 1);
+    const QStringRef &lastSuffix = suffixes.at(suffixes.count() - 1);
-    const QString firstSuffix = suffixes.at(0);
+    const QStringRef &firstSuffix = suffixes.at(0);
 
     bool valid = (lastSuffix == QLatin1String("dylib")
             || firstSuffix == QLatin1String("so")
@@ -657,7 +657,7 @@ bool QLibrary::isLibrary(const QString &fileName)
     int suffix;
     int suffixPos = -1;
     for (suffix = 0; suffix < validSuffixList.count() && suffixPos == -1; ++suffix)
-        suffixPos = suffixes.indexOf(validSuffixList.at(suffix));
+        suffixPos = suffixes.indexOf(QStringRef(&validSuffixList.at(suffix)));
 
     bool valid = suffixPos != -1;
     for (int i = suffixPos + 1; i < suffixes.count() && valid; ++i)