QTimeZone: don't use QSet, use sorted QList

QSet, as a node-based container, requires one memory allocation per element
inserted. QList, as a contiguous-memory container (at least in the case of
a QByteArray payload), requires one memory allocation per container.

The higher lookup speed might still speak for using QSet, but there are only
two uses of the sets:

1. Checking for existence (or lack thereof) of timezone names.
   For this, first generating a container full of data just to check for
   existence of one item of data is extremely wasteful. The QTZPrivate
   API should be extended to allow said lookup to be performed on the
   native data store instead.

That leaves

2. Returning a sorted(!) list(!) from the public QTimeZone API.
   There is no reason why, during the construction of those sorted
   lists, the data should be held in a set. Instead, the well-known
   technique of first cramming everything into a result container,
   which is subsequently sorted and has its duplicates removed,
   can be used here.

Saves more than 8K of text size on AMD64 stripped release builds.

Change-Id: I71c2298e94e02d55b0c9fb6f7ebeaed79a1fe2db
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/src/corelib/tools/qtimezoneprivate_tz.cpp b/src/corelib/tools/qtimezoneprivate_tz.cpp
index 0d8ae3b47f..29f0e17012 100644
--- a/src/corelib/tools/qtimezoneprivate_tz.cpp
+++ b/src/corelib/tools/qtimezoneprivate_tz.cpp
@@ -41,6 +41,7 @@
 
 #include <qdebug.h>
 
+#include <algorithm>
 
 QT_BEGIN_NAMESPACE
 
@@ -956,20 +957,23 @@ QByteArray QTzTimeZonePrivate::systemTimeZoneId() const
     return ianaId;
 }
 
-QSet<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds() const
+QList<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds() const
 {
-    return tzZones->keys().toSet();
+    QList<QByteArray> result = tzZones->keys();
+    std::sort(result.begin(), result.end());
+    return result;
 }
 
-QSet<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds(QLocale::Country country) const
+QList<QByteArray> QTzTimeZonePrivate::availableTimeZoneIds(QLocale::Country country) const
 {
     // TODO AnyCountry
-    QSet<QByteArray> set;
+    QList<QByteArray> result;
     foreach (const QByteArray &key, tzZones->keys()) {
         if (tzZones->value(key).country == country)
-            set << key;
+            result << key;
     }
-    return set;
+    std::sort(result.begin(), result.end());
+    return result;
 }
 
 QT_END_NAMESPACE