Avoid a QVector allocation in QRegularExpressionMatchPrivate

Explicitely pass the number of capturing groups for which the
offsets should be reserved in the capturedOffsets vector,
instead of relying on it adding 1 (for the implicit capturing
group #0).

In case 0 is passed, don't allocate any space for that vector.
This is being used in case of NoMatch match type or failing
match (invalid regexp, out of bounds offset, etc.).

Change-Id: I0ec7646d5bd53e7a7973177100b163a5e5030307
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 10 insertions, 8 deletions

diff --git a/src/corelib/tools/qregularexpression.cpp b/src/corelib/tools/qregularexpression.cpp
index 1585389d22..06c696e1e2 100644
--- a/src/corelib/tools/qregularexpression.cpp
+++ b/src/corelib/tools/qregularexpression.cpp
@@ -842,7 +842,7 @@ struct QRegularExpressionMatchPrivate : QSharedData
                                    const QString &subject,
                                    QRegularExpression::MatchType matchType,
                                    QRegularExpression::MatchOptions matchOptions,
-                                   int capturingCount);
+                                   int capturingCount = 0);
 
     QRegularExpressionMatch nextMatch() const;
 
@@ -1201,25 +1201,25 @@ QRegularExpressionMatchPrivate *QRegularExpressionPrivate::doMatch(const QString
     QRegularExpression re(*const_cast<QRegularExpressionPrivate *>(this));
 
     if (offset < 0 || offset > subject.length())
-        return new QRegularExpressionMatchPrivate(re, subject, matchType, matchOptions, 0);
+        return new QRegularExpressionMatchPrivate(re, subject, matchType, matchOptions);
 
     if (!compiledPattern) {
         qWarning("QRegularExpressionPrivate::doMatch(): called on an invalid QRegularExpression object");
-        return new QRegularExpressionMatchPrivate(re, subject, matchType, matchOptions, 0);
+        return new QRegularExpressionMatchPrivate(re, subject, matchType, matchOptions);
     }
 
     // skip optimizing and doing the actual matching if NoMatch type was requested
     if (matchType == QRegularExpression::NoMatch) {
         QRegularExpressionMatchPrivate *priv = new QRegularExpressionMatchPrivate(re, subject,
-                                                                                  matchType, matchOptions,
-                                                                                  0);
+                                                                                  matchType, matchOptions);
         priv->isValid = true;
         return priv;
     }
 
+    // capturingCount doesn't include the implicit "0" capturing group
     QRegularExpressionMatchPrivate *priv = new QRegularExpressionMatchPrivate(re, subject,
                                                                               matchType, matchOptions,
-                                                                              capturingCount);
+                                                                              capturingCount + 1);
 
     // this is mutex protected
     const pcre16_extra *currentStudyData = const_cast<QRegularExpressionPrivate *>(this)->optimizePattern();
@@ -1328,8 +1328,10 @@ QRegularExpressionMatchPrivate::QRegularExpressionMatchPrivate(const QRegularExp
       hasMatch(false), hasPartialMatch(false), isValid(false)
 {
     Q_ASSERT(capturingCount >= 0);
-    const int captureOffsetsCount = (capturingCount + 1) * 3;
-    capturedOffsets.resize(captureOffsetsCount);
+    if (capturingCount > 0) {
+        const int captureOffsetsCount = capturingCount * 3;
+        capturedOffsets.resize(captureOffsetsCount);
+    }
 }