From 42cf2a2617ffd0d563fcd46c5aa5409007e211de Mon Sep 17 00:00:00 2001
From: David Faure <david.faure@kdab.com>
Date: Fri, 29 Apr 2022 11:29:19 +0200
Subject: [PATCH] QWidgetTextControl: don't clear() a new empty document

Before: 0.063 msecs per iteration
After: 0.054 msecs per iteration

clear() takes time because:
1) QTextDocumentLayout::documentChanged() => doLayout() => layoutFrame()
2) QTextDocumentPrivate::init() => insertBlock() => finishEdit() =>
   QTextDocumentLayout::documentChanged() => layoutStep() => ... => doLayout() again

Pick-to: 6.3 6.2
Change-Id: I7a13164d06a1ed77226f2b9d7d12e69ce5b31dfe
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
---
 src/widgets/widgets/qwidgettextcontrol.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/widgets/widgets/qwidgettextcontrol.cpp b/src/widgets/widgets/qwidgettextcontrol.cpp
index ad8e79f4e2..e73975f9e2 100644
--- a/src/widgets/widgets/qwidgettextcontrol.cpp
+++ b/src/widgets/widgets/qwidgettextcontrol.cpp
@@ -412,11 +412,11 @@ void QWidgetTextControlPrivate::setContent(Qt::TextFormat format, const QString
     if (!doc) {
         if (document) {
             doc = document;
-            clearDocument = false;
         } else {
             palette = QApplication::palette("QWidgetTextControl");
             doc = new QTextDocument(q);
         }
+        clearDocument = false;
         _q_documentLayoutChanged();
         cursor = QTextCursor(doc);