From 33693473d4bf6b28bee2d5fe740633d6867c26af Mon Sep 17 00:00:00 2001
From: Sze Howe Koh <szehowe.koh@gmail.com>
Date: Mon, 25 Sep 2017 19:17:02 +0800
Subject: Remove unnecessary copying in QSet::subtract()

Task-number: QTBUG-42810
Change-Id: I5d4793a12b078e34bea034b4500e270d42609de0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/tools/qset.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/corelib/tools/qset.h b/src/corelib/tools/qset.h
index 08b38a08c2..7ded120ab7 100644
--- a/src/corelib/tools/qset.h
+++ b/src/corelib/tools/qset.h
@@ -340,13 +340,14 @@ Q_INLINE_TEMPLATE bool QSet<T>::intersects(const QSet<T> &other) const
 template <class T>
 Q_INLINE_TEMPLATE QSet<T> &QSet<T>::subtract(const QSet<T> &other)
 {
-    QSet<T> copy1(*this);
-    QSet<T> copy2(other);
-    typename QSet<T>::const_iterator i = copy1.constEnd();
-    while (i != copy1.constBegin()) {
-        --i;
-        if (copy2.contains(*i))
+    if (&other == this) {
+        clear();
+    } else {
+        auto i = other.constEnd();
+        while (i != other.constBegin()) {
+            --i;
             remove(*i);
+        }
     }
     return *this;
 }
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