Remove partially_inited flag

Summary:
This was added to prevent GC crashes when scanning uninitialized memory
in partially-constructed APC objects, when PHP callbacks (sprop init)
occurred during apc_fetch.

Since then, we made the GC scanner robust against uninitialized
pointers; TypedValue scanner will do nothing for bogus data types,
and plain pointers are all filtered through PtrMap, just like with
conservative scanning.

Reviewed By: ricklavoie

Differential Revision: D4891114

fbshipit-source-id: b6cb0feb4e8b68ac6e2608a49f7e879e14d0ef84

hphp/runtime/base/apc-object.cpp

@@ -237,18 +237,18 @@ Object APCObject::createObject() const {
   auto const apcProp = persistentProps();
 
   if (m_fast_init) {
-    obj->setPartiallyInited(true);
+    // re-entry is possible while we're executing toLocal() on each
+    // property, so heap inspectors may see partially initid objects
+    // not yet exposed to PHP.
     unsigned i = 0;
     try {
       for (; i < numProps; ++i) {
         new (objProp + i) Variant(apcProp[i]->toLocal());
       }
-      obj->setPartiallyInited(false);
     } catch (...) {
       for (; i < numProps; ++i) {
         new (objProp + i) Variant();
       }
-      obj->setPartiallyInited(false);
       throw;
     }
   } else {

hphp/runtime/base/header-kind.h

@@ -91,8 +91,7 @@ struct HeapObject {
       mutable RefCount m_count;
       HeaderKind m_kind;
       mutable uint8_t m_weak_refed:1;
-      mutable uint8_t m_partially_inited:1;
-      mutable uint8_t m_marks:6;
+      mutable uint8_t m_marks:7;
       mutable uint16_t m_aux16;
     };
     struct {

hphp/runtime/base/heap-scan.h

@@ -188,12 +188,7 @@ inline void c_WaitHandle::scan(type_scan::Scanner& scanner) const {
 
 inline void ObjectData::scan(type_scan::Scanner& scanner) const {
   auto props = propVec();
-  if (m_partially_inited) {
-    // we don't know which properties are initialized yet
-    scanner.conservative(props, m_cls->numDeclProperties() * sizeof(*props));
-  } else {
-    scanner.scan(*props, m_cls->numDeclProperties() * sizeof(*props));
-  }
+  scanner.scan(*props, m_cls->numDeclProperties() * sizeof(*props));
   if (getAttribute(HasDynPropArr)) {
     // nb: dynamic property arrays are in ExecutionContext::dynPropTable,
     // which is not marked as a root. Scan the entry pair, so both the key

hphp/runtime/base/object-data.h

@@ -147,10 +147,6 @@ struct ObjectData : Countable, type_scan::MarkCountable<ObjectData> {
     m_weak_refed = flag;
   }
 
-  inline void setPartiallyInited(bool f) const {
-    m_partially_inited = f;
-  }
-
  public:
 
   /*