Optimize QXmlStreamWriterPrivate::doWriteToDevice(QLatin1StringView)

Use a stack buffer, and perform the recoding from L1 to U8 in chunks.

Solves the L1 case of

Task-number: QTBUG-109284
Pick-to: 6.5
Change-Id: Ia9ac7d8b27fd452d24d9e27f0575f9fc83b6dcbc
Reviewed-by: Mate Barany <mate.barany@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/corelib/serialization/qxmlstream.cpp b/src/corelib/serialization/qxmlstream.cpp
index 48487fd83d..0b5843f032 100644
--- a/src/corelib/serialization/qxmlstream.cpp
+++ b/src/corelib/serialization/qxmlstream.cpp
@@ -3085,10 +3085,14 @@ void QXmlStreamWriterPrivate::doWriteToDevice(QUtf8StringView s)
 
 void QXmlStreamWriterPrivate::doWriteToDevice(QLatin1StringView s)
 {
-    QByteArray utf8(s.size() * 2, Qt::Uninitialized);
-    char *end = QUtf8::convertFromLatin1(utf8.data(), s);
-    utf8.truncate(end - utf8.data());
-    doWriteToDevice(QUtf8StringView{utf8});
+    constexpr qsizetype MaxChunkSize = 512;
+    char buffer [2 * MaxChunkSize];
+    while (!s.isEmpty()) {
+        const qsizetype chunkSize = std::min(s.size(), MaxChunkSize);
+        char *end = QUtf8::convertFromLatin1(buffer, s.first(chunkSize));
+        doWriteToDevice(QUtf8StringView{buffer, end});
+        s = s.sliced(chunkSize);
+    }
 }
 
 /*!