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>

8 files changed, 25 insertions, 19 deletions

diff --git a/src/corelib/io/qdir.cpp b/src/corelib/io/qdir.cpp
index af07b52cdb..8197ea63e7 100644
--- a/src/corelib/io/qdir.cpp
+++ b/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);
-    for (int i = 0; i < ret.count(); ++i)
-        ret[i] = ret[i].trimmed();
+    const QVector<QStringRef> split = nameFilter.splitRef(sep);
+    QStringList ret;
+    ret.reserve(split.size());
+    for (const auto &e : split)
+        ret.append(e.trimmed().toString());
     return ret;
 }
 
diff --git a/src/corelib/io/qfilesystemengine.cpp b/src/corelib/io/qfilesystemengine.cpp
index fd8f251ccb..febfdbb9d4 100644
--- a/src/corelib/io/qfilesystemengine.cpp
+++ b/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;
diff --git a/src/corelib/io/qfilesystemengine_unix.cpp b/src/corelib/io/qfilesystemengine_unix.cpp
index eebe5f1f94..6aaaa4c05a 100644
--- a/src/corelib/io/qfilesystemengine_unix.cpp
+++ b/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('/'))) {
-                ret.prepend(link.filePath().left(link.filePath().lastIndexOf(QLatin1Char('/')))
+            const QString linkFilePath = link.filePath();
+            if (linkFilePath.startsWith(QLatin1Char('/'))) {
+                ret.prepend(linkFilePath.leftRef(linkFilePath.lastIndexOf(QLatin1Char('/')))
                             + QLatin1Char('/'));
             } else {
                 ret.prepend(QDir::currentPath() + QLatin1Char('/'));
diff --git a/src/corelib/io/qfilesystemengine_win.cpp b/src/corelib/io/qfilesystemengine_win.cpp
index 8375dc9b1b..abf346a717 100644
--- a/src/corelib/io/qfilesystemengine_win.cpp
+++ b/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);
-            if (chunk.length() == 2 && chunk.at(0).isLetter() && chunk.at(1) == QLatin1Char(':'))
+            const QStringRef chunkRef = dirName.leftRef(slash);
+            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))
diff --git a/src/corelib/io/qfilesystemiterator_win.cpp b/src/corelib/io/qfilesystemiterator_win.cpp
index 9e40a41b4c..2ce7bd7a4b 100644
--- a/src/corelib/io/qfilesystemiterator_win.cpp
+++ b/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())
diff --git a/src/corelib/io/qresource.cpp b/src/corelib/io/qresource.cpp
index 96957ac11d..7fe3753da4 100644
--- a/src/corelib/io/qresource.cpp
+++ b/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();
diff --git a/src/corelib/io/qstandardpaths_unix.cpp b/src/corelib/io/qstandardpaths_unix.cpp
index bcbc9664ef..0561e5833f 100644
--- a/src/corelib/io/qstandardpaths_unix.cpp
+++ b/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;
diff --git a/src/corelib/io/qurl.cpp b/src/corelib/io/qurl.cpp
index 40fc492d91..e20a98fbf1 100644
--- a/src/corelib/io/qurl.cpp
+++ b/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();
-        if (hostscheme == ftpScheme())
+        const QStringRef hostscheme = trimmedString.leftRef(dotIndex);
+        if (hostscheme.compare(ftpScheme(), Qt::CaseInsensitive) == 0)
             urlPrepended.setScheme(ftpScheme());
         return adjustFtpPath(urlPrepended);
     }