Optimize KConfigGroup::exists and similar operations.

Before, these kind of read-only operations did a lot of allocations:

1) allocate a list of all sub groups
2) for the above, also allocate a sub-group match key
3) iterate over sub groups, allocate a list of all keys in there
and then finally check whether that list is non-empty

All of the above is now done without a single allocation, by simply
iterating over the list of entries.

Note: The whole list was iterated even before in allSubGroups. Now
we still do that, but check for non-empty keys in the group or
sub group directly. Much more efficient.

Note2: While at it, allSubGroups is also optimized to not require the
allocation of the subgroup match key.

REVIEW: 118586

forward-port of commit eaffd50adfd7fcbeafadb0248904176808b4499d

1 files changed, 12 insertions, 8 deletions

diff --git a/src/core/kconfig.cpp b/src/core/kconfig.cpp
index 65edefa9..b9319994 100644
--- a/src/core/kconfig.cpp
+++ b/src/core/kconfig.cpp
@@ -302,16 +302,22 @@ QStringList KConfigPrivate::groupList(const QByteArray &group) const
     return groups.toList();
 }
 
+static bool isGroupOrSubGroupMatch(const QByteArray &potentialGroup, const QByteArray &group)
+{
+    if (!potentialGroup.startsWith(group)) {
+      return false;
+    }
+    return potentialGroup.length() == group.length() || potentialGroup[group.length()] == '\x1d';
+}
+
 // List all sub groups, including subsubgroups
 QSet<QByteArray> KConfigPrivate::allSubGroups(const QByteArray &parentGroup) const
 {
     QSet<QByteArray> groups;
-    QByteArray theGroup = parentGroup + '\x1d';
-    groups << parentGroup;
 
     for (KEntryMap::const_iterator entryMapIt = entryMap.begin(); entryMapIt != entryMap.end(); ++entryMapIt) {
         const KEntryKey &key = entryMapIt.key();
-        if (key.mKey.isNull() && key.mGroup.startsWith(theGroup)) {
+        if (key.mKey.isNull() && isGroupOrSubGroupMatch(key.mGroup, parentGroup)) {
             groups << key.mGroup;
         }
     }
@@ -320,12 +326,10 @@ QSet<QByteArray> KConfigPrivate::allSubGroups(const QByteArray &parentGroup) con
 
 bool KConfigPrivate::hasNonDeletedEntries(const QByteArray &group) const
 {
-    const QSet<QByteArray> allGroups = allSubGroups(group);
-
-    Q_FOREACH (const QByteArray &aGroup, allGroups) {
-        // Could be optimized, let's use the slow way for now
+    for (KEntryMap::const_iterator it = entryMap.begin(); it != entryMap.end(); ++it) {
+        const KEntryKey &key = it.key();
         // Check for any non-deleted entry
-        if (!keyListImpl(aGroup).isEmpty()) {
+        if (isGroupOrSubGroupMatch(key.mGroup, group) && !key.mKey.isNull() && !it->bDeleted) {
             return true;
         }
     }