V4: change string flattening to be iterative and use a worklist.

And not recursive, because that might blow out of stack space.

Task-number: QTBUG-39520
Change-Id: Id961d4af03a543d3efa173f976626cf2dae4f483
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

2 files changed, 18 insertions, 10 deletions

diff --git a/src/qml/jsruntime/qv4string.cpp b/src/qml/jsruntime/qv4string.cpp
index 123d1648c2..86995e48f9 100644
--- a/src/qml/jsruntime/qv4string.cpp
+++ b/src/qml/jsruntime/qv4string.cpp
@@ -332,23 +332,31 @@ void String::Data::simplifyString() const
     int l = length();
     QString result(l, Qt::Uninitialized);
     QChar *ch = const_cast<QChar *>(result.constData());
-    recursiveAppend(ch);
+    append(this, ch);
     text = result.data_ptr();
     text->ref.ref();
     identifier = 0;
     largestSubLength = 0;
 }
 
-QChar *String::Data::recursiveAppend(QChar *ch) const
+void String::Data::append(const String::Data *data, QChar *ch)
 {
-    if (largestSubLength) {
-        ch = left->d()->recursiveAppend(ch);
-        ch = right->d()->recursiveAppend(ch);
-    } else {
-        memcpy(ch, text->data(), text->size*sizeof(QChar));
-        ch += text->size;
+    std::vector<const String::Data *> worklist;
+    worklist.reserve(32);
+    worklist.push_back(data);
+
+    while (!worklist.empty()) {
+        const String::Data *item = worklist.back();
+        worklist.pop_back();
+
+        if (item->largestSubLength) {
+            worklist.push_back(item->right->d());
+            worklist.push_back(item->left->d());
+        } else {
+            memcpy(ch, item->text->data(), item->text->size * sizeof(QChar));
+            ch += item->text->size;
+        }
     }
-    return ch;
 }
 
 
diff --git a/src/qml/jsruntime/qv4string_p.h b/src/qml/jsruntime/qv4string_p.h
index f9d3cd1cc0..082f296f48 100644
--- a/src/qml/jsruntime/qv4string_p.h
+++ b/src/qml/jsruntime/qv4string_p.h
@@ -79,7 +79,7 @@ struct Q_QML_PRIVATE_EXPORT String : public Managed {
         mutable uint largestSubLength;
         uint len;
     private:
-        QChar *recursiveAppend(QChar *ch) const;
+        static void append(const Data *data, QChar *ch);
     };
     // ### FIXME: Should this be a V4_OBJECT
     V4_OBJECT(QV4::Managed)