Do not hold unnecessary reference to sent value

Continuaton::send()/raise() are holding reference to the sent value
while the next iteration is being executed. Do not hold this reference
and teleport values instead.

hphp/runtime/vm/bytecode.cpp

@@ -6820,9 +6820,8 @@ inline void OPTBLD_INLINE VMExecutionContext::iopUnpackCont(PC& pc) {
   c_Continuation* cont = frame_continuation(m_fp);
 
   // Return the received value
-  TypedValue* recv_to = m_stack.allocTV();
   TypedValue* recv_fr = cont->m_received.asTypedValue();
-  memcpy(recv_to, recv_fr, sizeof(TypedValue));
+  tvTeleport(recv_fr, m_stack.allocTV());
   tvWriteNull(recv_fr);
 
   // Return the label in a stack cell
@@ -6866,19 +6865,21 @@ inline void OPTBLD_INLINE VMExecutionContext::iopContCheck(PC& pc) {
 inline void OPTBLD_INLINE VMExecutionContext::iopContNext(PC& pc) {
   NEXT();
   c_Continuation* cont = this_continuation(m_fp);
-  cont->m_received.setNull();
+  tvWriteNull(cont->m_received.asTypedValue());
 }
 
 inline void OPTBLD_INLINE VMExecutionContext::iopContSend(PC& pc) {
   NEXT();
   c_Continuation* cont = this_continuation(m_fp);
-  cont->m_received.assignVal(tvAsVariant(frame_local(m_fp, 0)));
+  tvTeleport(frame_local(m_fp, 0), cont->m_received.asTypedValue());
+  tvWriteUninit(frame_local(m_fp, 0));
 }
 
 inline void OPTBLD_INLINE VMExecutionContext::iopContRaise(PC& pc) {
   NEXT();
   c_Continuation* cont = this_continuation(m_fp);
-  cont->m_received.assignVal(tvAsVariant(frame_local(m_fp, 0)));
+  tvTeleport(frame_local(m_fp, 0), cont->m_received.asTypedValue());
+  tvWriteUninit(frame_local(m_fp, 0));
   assert(cont->m_label);
   --cont->m_label;
 }

hphp/runtime/vm/jit/hhbctranslator.cpp

@@ -1177,14 +1177,14 @@ void HhbcTranslator::emitContNext() {
 void HhbcTranslator::emitContSendImpl(bool raise) {
   assert(curClass());
   SSATmp* cont = gen(LdThis, m_tb->fp());
-  gen(AssertLoc, Type::Cell, LocalId(0), m_tb->fp());
-  auto const newVal = gen(IncRef, ldLoc(0));
   if (RuntimeOption::EvalHHIRGenerateAsserts) {
     // We're guaranteed to have a Null in m_received at this point
     auto const oldVal = gen(LdProp, Type::Cell, cont, cns(CONTOFF(m_received)));
     gen(DbgAssertType, Type::InitNull, oldVal);
   }
-  gen(StProp, cont, cns(CONTOFF(m_received)), newVal);
+  gen(AssertLoc, Type::Cell, LocalId(0), m_tb->fp());
+  gen(StProp, cont, cns(CONTOFF(m_received)), ldLoc(0));
+  gen(StLoc, LocalId(0), m_tb->fp(), m_tb->genDefUninit());
   if (raise) {
     SSATmp* label = gen(LdRaw, Type::Int, cont, cns(RawMemSlot::ContLabel));
     label = gen(OpSub, label, cns(1));

hphp/test/slow/yield/2183.php.expect

@@ -1,9 +1,10 @@
 in __destruct()
+object(Evil)#2 (0) {
+}
+in __destruct()
 NULL
 in __destruct()
-NULL
-in __destruct()
-object(Evil)#4 (0) {
+object(Evil)#3 (0) {
 }
 Caught: Continuation is already running
 in __destruct()