Re-add some inline property storage

It turns out that not using any inline property storage
comes at a relatively high price in terms of memory
consumption, as we always need to also create a
memberData for any object.

This avoids the memberData creation in quite a few
cases, as we use the additional padding we have up
to the 32 byte boundary given by the memory manager
to store some property data.

This complicates property access somewhat. To avoid
performance regressions because of this, add specialized
QV4::Lookup functions that optimize for properties that
are inline or in the memberData struct.

Change seems to be performance neutral on v8-bench on
x86_64, but reduces peak memory usage when running the
benchmark by around 20%.

Change-Id: I0127d31a2d6038aaa540c4c4a1156f45ca3b7464
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Robin Burchell <robin.burchell@crimson.no>

3 files changed, 10 insertions, 5 deletions

diff --git a/src/qml/memory/qv4heap_p.h b/src/qml/memory/qv4heap_p.h
index 173c0a3e20..cd0a6d9a81 100644
--- a/src/qml/memory/qv4heap_p.h
+++ b/src/qml/memory/qv4heap_p.h
@@ -72,6 +72,8 @@ namespace QV4 {
 struct VTable
 {
     const VTable * const parent;
+    uint inlinePropertyOffset : 16;
+    uint nInlineProperties : 16;
     uint isExecutionContext : 1;
     uint isString : 1;
     uint isObject : 1;
diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index 7aa8f91503..0a6dfb9170 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -757,12 +757,15 @@ Heap::Base *MemoryManager::allocData(std::size_t size)
     return *m;
 }
 
-Heap::Object *MemoryManager::allocObjectWithMemberData(std::size_t size, uint nMembers)
+Heap::Object *MemoryManager::allocObjectWithMemberData(const QV4::VTable *vtable, uint nMembers)
 {
+    uint size = (vtable->nInlineProperties + vtable->inlinePropertyOffset)*sizeof(Value);
+    Q_ASSERT(!(size % sizeof(HeapItem)));
     Heap::Object *o = static_cast<Heap::Object *>(allocData(size));
 
     // ### Could optimize this and allocate both in one go through the block allocator
-    if (nMembers) {
+    if (nMembers > vtable->nInlineProperties) {
+        nMembers -= vtable->nInlineProperties;
         std::size_t memberSize = align(sizeof(Heap::MemberData) + (nMembers - 1)*sizeof(Value));
 //        qDebug() << "allocating member data for" << o << nMembers << memberSize;
         Heap::Base *m;
diff --git a/src/qml/memory/qv4mm_p.h b/src/qml/memory/qv4mm_p.h
index 00daf8a622..9b4c2cd8df 100644
--- a/src/qml/memory/qv4mm_p.h
+++ b/src/qml/memory/qv4mm_p.h
@@ -231,7 +231,7 @@ public:
     template <typename ObjectType>
     typename ObjectType::Data *allocateObject(InternalClass *ic)
     {
-        Heap::Object *o = allocObjectWithMemberData(align(sizeof(typename ObjectType::Data)), ic->size);
+        Heap::Object *o = allocObjectWithMemberData(ObjectType::staticVTable(), ic->size);
         o->setVtable(ObjectType::staticVTable());
         o->internalClass = ic;
         return static_cast<typename ObjectType::Data *>(o);
@@ -241,7 +241,7 @@ public:
     typename ObjectType::Data *allocateObject()
     {
         InternalClass *ic = ObjectType::defaultInternalClass(engine);
-        Heap::Object *o = allocObjectWithMemberData(align(sizeof(typename ObjectType::Data)), ic->size);
+        Heap::Object *o = allocObjectWithMemberData(ObjectType::staticVTable(), ic->size);
         o->setVtable(ObjectType::staticVTable());
         Object *prototype = ObjectType::defaultPrototype(engine);
         o->internalClass = ic;
@@ -433,7 +433,7 @@ protected:
     /// expects size to be aligned
     Heap::Base *allocString(std::size_t unmanagedSize);
     Heap::Base *allocData(std::size_t size);
-    Heap::Object *allocObjectWithMemberData(std::size_t size, uint nMembers);
+    Heap::Object *allocObjectWithMemberData(const QV4::VTable *vtable, uint nMembers);
 
 #ifdef DETAILED_MM_STATS
     void willAllocate(std::size_t size);