QLoggingRegistry: optimize updateRules()

... by not creating three temporary QVectors just to concatenate them.

There's no QVectorBuilder, so what works well with QStrings doesn't
work well at all with QVectors. The chaining of op+ causes three
temporary QVectors to be created and thrown away.

Instead, use clear() (which preserves the vector's capacity these days),
followed by four op+=.

Change-Id: I300bd35544ea41037d28db0f48f210c33c826b85
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/corelib/io/qloggingregistry.cpp b/src/corelib/io/qloggingregistry.cpp
index eaebbc1ffc..b8d1919ee6 100644
--- a/src/corelib/io/qloggingregistry.cpp
+++ b/src/corelib/io/qloggingregistry.cpp
@@ -365,7 +365,12 @@ void QLoggingRegistry::setApiRules(const QString &content)
 */
 void QLoggingRegistry::updateRules()
 {
-    rules = qtConfigRules + configRules + apiRules + envRules;
+    rules.clear();
+    rules.reserve(qtConfigRules.size() + configRules.size() + apiRules.size() + envRules.size()),
+    rules += qtConfigRules;
+    rules += configRules;
+    rules += apiRules;
+    rules += envRules;
 
     for (auto it = categories.keyBegin(), end = categories.keyEnd(); it != end; ++it)
         (*categoryFilter)(*it);