v4: Delay creating the ScopedValue/ScopedProperty in objectLiteral

Creating a ScopedValue/ScopedProperty is not free. It will use the
ExecutionEngine directly to reserve memory from the JS Stack. In
tests/manual/v4/v8-bench.js and bench-allocate-nonretained.js a lot
of objects are created and the arrayValueCount and the
arrayGetterSetterCount are 0. We can delay the creation for a small
gain.

When generating the code we already know the various sizes and
could already call specialized versions of the creation code. The
gain is not so clear though.

Change-Id: Ic99b241f5506457e57611ad4eba143c56be1f657
Reviewed-by: Simon Hausmann <[email protected]>

1 files changed, 19 insertions, 15 deletions

diff --git a/src/qml/jsruntime/qv4runtime.cpp b/src/qml/jsruntime/qv4runtime.cpp
index e44d1a07a6..bd52f0e678 100644
--- a/src/qml/jsruntime/qv4runtime.cpp
+++ b/src/qml/jsruntime/qv4runtime.cpp
@@ -1162,24 +1162,28 @@ ReturnedValue Runtime::objectLiteral(QV4::ExecutionContext *ctx, const QV4::Valu
     for (uint i = 0; i < klass->size; ++i)
         o->memberData[i] = *args++;
 
-    ScopedValue entry(scope);
-    for (int i = 0; i < arrayValueCount; ++i) {
-        uint idx = args->toUInt32();
-        ++args;
-        entry = *args++;
-        o->arraySet(idx, entry);
+    if (arrayValueCount > 0) {
+        ScopedValue entry(scope);
+        for (int i = 0; i < arrayValueCount; ++i) {
+            uint idx = args->toUInt32();
+            ++args;
+            entry = *args++;
+            o->arraySet(idx, entry);
+        }
     }
 
-    ScopedProperty pd(scope);
     uint arrayGetterSetterCount = arrayGetterSetterCountAndFlags & ((1 << 30) - 1);
-    for (uint i = 0; i < arrayGetterSetterCount; ++i) {
-        uint idx = args->toUInt32();
-        ++args;
-        pd->value = *args;
-        ++args;
-        pd->set = *args;
-        ++args;
-        o->arraySet(idx, pd, Attr_Accessor);
+    if (arrayGetterSetterCount > 0) {
+        ScopedProperty pd(scope);
+        for (uint i = 0; i < arrayGetterSetterCount; ++i) {
+            uint idx = args->toUInt32();
+            ++args;
+            pd->value = *args;
+            ++args;
+            pd->set = *args;
+            ++args;
+            o->arraySet(idx, pd, Attr_Accessor);
+        }
     }
 
     return o.asReturnedValue();