Fix a bug in qmljs_set_element and improve it's performance

Avoid expensive function calls for setting indexed properties
in the common case. The spec requires us to read the value before
writing it to check whether it's empty. In that case we need to
fall back to the slow implementation that checks the proto chain.

Change-Id: If278ba81f170d35c18135d2f8661459262e7e606
Reviewed-by: Simon Hausmann <[email protected]>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/qml/jsruntime/qv4runtime.cpp b/src/qml/jsruntime/qv4runtime.cpp
index c929b39e6a..a991940c6b 100644
--- a/src/qml/jsruntime/qv4runtime.cpp
+++ b/src/qml/jsruntime/qv4runtime.cpp
@@ -613,10 +613,14 @@ void __qmljs_set_element(ExecutionContext *ctx, const ValueRef object, const Val
 
     uint idx = index->asArrayIndex();
     if (idx < UINT_MAX) {
-        if (o->arrayType() == ArrayData::Simple && idx < o->arrayData->length())
-            o->arrayPut(idx, value);
-        else
-            o->putIndexed(idx, value);
+        if (o->arrayType() == ArrayData::Simple) {
+            SimpleArrayData *s = static_cast<SimpleArrayData *>(o->arrayData);
+            if (s && idx < s->len && !s->data[idx].isEmpty()) {
+                s->data[idx] = value;
+                return;
+            }
+        }
+        o->putIndexed(idx, value);
         return;
     }