From b0a3cfaf53af5e7e306369d336b9d7e2763e62de Mon Sep 17 00:00:00 2001
From: Ahmad Samir <a.samirh78@gmail.com>
Date: Fri, 5 May 2023 19:17:27 +0300
Subject: [PATCH] QStringList: optimize replaceInStrings

By first checking if the list has any matches before potentially making
it detach.

Change-Id: I7a42c2910ef6efc45033e562573414a3a9ef972e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/text/qstringlist.cpp              | 29 +++++++++++++++++--
 .../text/qstringlist/tst_qstringlist.cpp      | 13 +++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/corelib/text/qstringlist.cpp b/src/corelib/text/qstringlist.cpp
index 5e937b5555..92330c1aa4 100644
--- a/src/corelib/text/qstringlist.cpp
+++ b/src/corelib/text/qstringlist.cpp
@@ -363,7 +363,18 @@ QStringList QtPrivate::QStringList_filter(const QStringList *that, const QRegula
 void QtPrivate::QStringList_replaceInStrings(QStringList *that, QStringView before,
                                              QStringView after, Qt::CaseSensitivity cs)
 {
-    for (qsizetype i = 0; i < that->size(); ++i)
+    // Before potentially detaching "that" list, check if any string contains "before"
+    qsizetype i = -1;
+    for (qsizetype j = 0; j < that->size(); ++j) {
+        if (that->at(j).contains(before, cs)) {
+            i = j;
+            break;
+        }
+    }
+    if (i == -1)
+        return;
+
+    for (; i < that->size(); ++i)
         (*that)[i].replace(before.data(), before.size(), after.data(), after.size(), cs);
 }
 
@@ -391,9 +402,21 @@ void QtPrivate::QStringList_replaceInStrings(QStringList *that, QStringView befo
     \snippet qstringlist/main.cpp 5
     \snippet qstringlist/main.cpp 17
 */
-void QtPrivate::QStringList_replaceInStrings(QStringList *that, const QRegularExpression &re, const QString &after)
+void QtPrivate::QStringList_replaceInStrings(QStringList *that, const QRegularExpression &re,
+                                             const QString &after)
 {
-    for (qsizetype i = 0; i < that->size(); ++i)
+    // Before potentially detaching "that" list, check if any string contains "before"
+    qsizetype i = -1;
+    for (qsizetype j = 0; j < that->size(); ++j) {
+        if (that->at(j).contains(re)) {
+            i = j;
+            break;
+        }
+    }
+    if (i == -1)
+        return;
+
+    for (; i < that->size(); ++i)
         (*that)[i].replace(re, after);
 }
 #endif // QT_CONFIG(regularexpression)
diff --git a/tests/auto/corelib/text/qstringlist/tst_qstringlist.cpp b/tests/auto/corelib/text/qstringlist/tst_qstringlist.cpp
index 3a3cbd5a81..d8a3fb78df 100644
--- a/tests/auto/corelib/text/qstringlist/tst_qstringlist.cpp
+++ b/tests/auto/corelib/text/qstringlist/tst_qstringlist.cpp
@@ -225,6 +225,19 @@ void tst_QStringList::replaceInStrings()
     list13.replaceInStrings( QString("a"), QStringView(QString("o")) );
     list14 << "olpho" << "beto" << "gommo" << "epsilon";
     QCOMPARE( list11, list12 );
+
+    QStringList list{"alpha", "beta", "gamma"};
+    QStringList copy = list;
+    QVERIFY(!copy.isDetached());
+
+    // No matches, no detach
+    copy.replaceInStrings("z", "y");
+    QVERIFY(!copy.isDetached());
+    QCOMPARE(copy, list);
+
+    copy.replaceInStrings("a", "y");
+    QVERIFY(copy.isDetached());
+    QCOMPARE(copy, (QStringList{"ylphy", "bety", "gymmy"}));
 }
 
 void tst_QStringList::contains()