Eager execution of async function.

Currently, a call to an async function returns a (Continuation)WaitHandle
object but the excution of the function body doesn't start before await
(or join()) on the WaitHandle is called. This changes it to start the
execution immediately and the control is returned to the caller only
after it's blocked.

Differential Revision: D946914

hphp/runtime/vm/bytecode.cpp

@@ -6651,6 +6651,38 @@ inline void OPTBLD_INLINE VMExecutionContext::iopCreateCont(PC& pc) {
   ret->m_data.pobj = cont;
 }
 
+inline void OPTBLD_INLINE VMExecutionContext::iopCreateAsync(PC& pc) {
+  NEXT();
+  DECODE_LITSTR(genName);
+  DECODE_IVA(label);
+  DECODE_IVA(iters);
+
+  const Func* origFunc = m_fp->m_func;
+  const Func* genFunc = origFunc->getGeneratorBody(genName);
+  assert(genFunc != nullptr);
+
+  c_Continuation* cont = origFunc->isMethod()
+    ? createContMeth(origFunc, genFunc, m_fp->getThisOrClass())
+    : createContFunc(origFunc, genFunc);
+
+  // TODO: we should check that the value on top of the stack is indeed
+  // a WaitHandle and fatal if not. Also, if it is a wait handle, assert
+  // that it is not finished.
+  cont->t_update(label, tvAsCVarRef(m_stack.topTV()));
+  m_stack.popTV();
+
+  fillContinuationVars(m_fp, origFunc, cont->actRec(), genFunc);
+
+  // copy the state of all the iterators at once
+  memcpy(frame_iter(cont->actRec(), iters-1),
+         frame_iter(m_fp, iters-1),
+         iters * sizeof(Iter));
+
+  TypedValue* ret = m_stack.allocTV();
+  ret->m_type = KindOfObject;
+  ret->m_data.pobj = cont;
+}
+
 static inline c_Continuation* this_continuation(const ActRec* fp) {
   ObjectData* obj = fp->getThis();
   assert(obj->instanceof(c_Continuation::s_cls));