From c953e5c41750ec886880cfb2cedb89f2886e5424 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Thu, 16 Dec 2021 10:09:29 +0100
Subject: [PATCH] QByteArray: avoid detach() in a no-op replace()

When the the replacement has the same size as the replacee, but that
size is zero, the whole operation is a no-op, and there's no need to
detach().

[ChangeLog][QtCore][QByteArray] A replace(pos, n, after) call no
longer detach()es when n == after.size() == 0.

Pick-to: 6.3 6.2
Change-Id: I1e8d7c7fb6383f8bfea3212e49fca8a128535564
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 src/corelib/text/qbytearray.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index a03462561f..e339f2fef5 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -2170,9 +2170,10 @@ QByteArray &QByteArray::replace(qsizetype pos, qsizetype len, QByteArrayView aft
     }
     if (len == after.size() && (pos + len <= size())) {
         // same size: in-place replacement possible
-        detach();
-        if (len > 0)
+        if (len > 0) {
+            detach();
             memcpy(d.data() + pos, after.data(), len*sizeof(char));
+        }
         return *this;
     } else {
         // ### optimize me