Speed up source code reading

Since we always convert the source code of .qml/.js/qmldir files from
utf-8 to utf-16, we always end up copying bytes around. That means
instead of allocating memory on the C++ heap and copying bytes from
kernel space to user space and then a few times through QIODevice
buffers until we reach QString::fromUtf8, we might as well mmap() the
file directly - if possible.

Change-Id: I54c88d4d9f03f9967130d65a7b53cfec93734018
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/qml/qml/qqmltypeloader.cpp b/src/qml/qml/qqmltypeloader.cpp
index 9526615c0d..eedb649ef6 100644
--- a/src/qml/qml/qqmltypeloader.cpp
+++ b/src/qml/qml/qqmltypeloader.cpp
@@ -3086,7 +3086,15 @@ QString QQmlDataBlob::SourceCodeData::readAll(QString *error) const
         return QString();
     }
 
-    QByteArray data(fileInfo.size(), Qt::Uninitialized);
+    const qint64 fileSize = fileInfo.size();
+
+    if (uchar *mappedData = f.map(0, fileSize)) {
+        QString source = QString::fromUtf8(reinterpret_cast<const char *>(mappedData), fileSize);
+        f.unmap(mappedData);
+        return source;
+    }
+
+    QByteArray data(fileSize, Qt::Uninitialized);
     if (f.read(data.data(), data.length()) != data.length()) {
         *error = f.errorString();
         return QString();