Allow PseudoHandle casting and easier assignment.

Summary:
`PinnedHermesValue` can now be assigned to from a `PseudoHandle`,
so this allows assignment into registers and such without having
to remember to invalidate the `PseudoHandle` afterwards.

Add `vmcast` and `dyn_vmcast` static functions to `PseudoHandle`
which are analogous to `Handle`.
The use of the latter does require invalidating the initial handle,
so it doesn't really work for assignment in the condition of an `if`
statement directly, but is sufficient for most other use cases.

Reviewed By: tmikov

Differential Revision: D19746814

fbshipit-source-id: 84ed028279c0924b630fad37db728dfa79ca9b96

include/hermes/VM/Handle-inline.h

@@ -10,11 +10,28 @@
 
 #include "hermes/VM/Handle.h"
 
+#include "hermes/VM/Casting.h"
 #include "hermes/VM/HandleRootOwner.h"
 
 namespace hermes {
 namespace vm {
 
+template <typename T>
+template <typename U>
+inline PseudoHandle<T> PseudoHandle<T>::vmcast(PseudoHandle<U> &&other) {
+ auto result = PseudoHandle<T>::create(hermes::vm::vmcast<T>(other.get()));
+ other.invalidate();
+ return result;
+}
+
+template <typename T>
+template <typename U>
+inline PseudoHandle<T> PseudoHandle<T>::dyn_vmcast(PseudoHandle<U> &&other) {
+ auto result = PseudoHandle<T>::create(hermes::vm::dyn_vmcast<T>(other.get()));
+ other.invalidate();
+ return result;
+}
+
 /// Allocate a new handle in the current GCScope
 inline HandleBase::HandleBase(HandleRootOwner *runtime, HermesValue value)
  : handle_(runtime->newHandle(value)) {

include/hermes/VM/Handle.h

@@ -153,6 +153,12 @@ class PseudoHandle {
  static PseudoHandle<T> create(value_type value) {
  return PseudoHandle<T>(value);
  }
+
+ template <typename U>
+ static inline PseudoHandle vmcast(PseudoHandle<U> &&other);
+
+ template <typename U>
+ static inline PseudoHandle dyn_vmcast(PseudoHandle<U> &&other);
 };
 
 /// A HermesValue in the current GCScope which is trackable by the GC and will

include/hermes/VM/HermesValue-inline.h

@@ -9,6 +9,7 @@
 #define HERMES_VM_HERMESVALUE_INLINE_H
 
 #include "hermes/Support/SlowAssert.h"
+#include "hermes/VM/Handle.h"
 #include "hermes/VM/HermesValue.h"
 
 #include "hermes/VM/GC.h"
@@ -21,6 +22,13 @@ void HermesValue::setInGC(HermesValue hv, GC *gc) {
  assert(gc->inGC());
 }
 
+template <typename T>
+inline PinnedHermesValue &PinnedHermesValue::operator=(PseudoHandle<T> &&hv) {
+ setNoBarrier(hv.getHermesValue());
+ hv.invalidate();
+ return *this;
+}
+
 template <typename NeedsBarriers>
 inline void GCHermesValue::set(HermesValue hv, GC *gc) {
  HERMES_SLOW_ASSERT(

include/hermes/VM/HermesValue.h

@@ -99,6 +99,8 @@ namespace hermes {
 namespace vm {
 
 class StringPrimitive;
+template <typename T>
+class PseudoHandle;
 
 template <typename T>
 class PseudoHandle;
@@ -508,6 +510,8 @@ class PinnedHermesValue : public HermesValue {
  setNoBarrier(hv);
  return *this;
  }
+ template <typename T>
+ inline PinnedHermesValue &operator=(PseudoHandle<T> &&hv);
 } HERMES_ATTRIBUTE_WARN_UNUSED_VARIABLES;
 
 // All HermesValues stored in heap object should be of this