Move Continuation state check to ContCheck opcode

Add ContCheck opcode that moves away responsibility of checking
Continuation status from Cont{Next,Send,Raise} opcodes.

This check needs to run outside of try/catch in next()/send()/raise()
methods and moving it to a separate opcode lets us merge
Cont{Next,Send,Raise} with ContEnter.

hphp/compiler/analysis/emitter.cpp

@@ -7010,13 +7010,17 @@ static void emitContinuationMethod(UnitEmitter& ue, FuncEmitter* fe,
       // translations
       fe->setAttrs(Attr(fe->attrs() | AttrClone));
 
+      // check continuation status; send()/raise() also checks started
+      ue.emitOp(OpContCheck);
+      ue.emitIVA(m == METH_SEND || m == METH_RAISE);
+
+      const Offset ehStart = ue.bcPos();
       static Op mOps[] = {
         OpContNext,
         OpContSend,
         OpContRaise,
       };
       ue.emitOp(mOps[m]);
-      const Offset ehStart = ue.bcPos();
       ue.emitOp(OpContEnter);
       ue.emitOp(OpContStopped);
       ue.emitOp(OpNull);

hphp/doc/bytecode.specification

@@ -3720,24 +3720,28 @@ ContRetC    [C]  ->  []
   which must be a non-static method of the Continuation class. Further attempts
   to iterate it will fail.
 
+ContCheck <check started>    []  ->  []
+
+  Check whether continuation can be iterated. $this must be a Continuation
+  object. If the continuation is finished, already running, or not yet started
+  and <check started> is enabled, an exception will be thrown.
+
 ContNext    []  ->  []
 
-  Prepare continuation for iteration. $this must be a Continuation
-  object. If the continuation is finished or already running, an exception
-  will be thrown.
+  Prepare continuation for iteration. $this must be a Continuation object
+  that passed ContCheck<false> check.
 
 ContSend    []  ->  []
 
-  Prepare continuation to receive a value. $this must be a Continuation
-  object. If the continuation is finished or already running, an exception will
-  be thrown. Otherwise, the value in local 0 is stored in the continuation.
+  Prepare continuation to receive a value. $this must be a Continuation object
+  that passed ContCheck<true> check. The value in local 0 is stored in the 
+  continuation.
 
 ContRaise    []  ->  []
 
   Prepare continuation to receive a thrown exception. $this must be a
-  Continuation object. If the continuation is finished or already running, an
-  exception will be thrown. Otherwise, the exception in local 0 is stored in
-  the continuation.
+  Continuation object that passed ContCheck<true> check. The exception in
+  local 0 is stored in the continuation.
 
 ContValid    []  ->  [C:Bool]
 

hphp/runtime/base/execution_context.h

@@ -492,8 +492,6 @@ private:
 OPCODES
 #undef O
 
-  template<bool raise>
-  void contSendImpl();
   void classExistsImpl(PC& pc, Attr typeAttr);
   void fPushObjMethodImpl(
       Class* cls, StringData* name, ObjectData* obj, int numArgs);

hphp/runtime/vm/bytecode.cpp

@@ -6853,33 +6853,34 @@ inline void OPTBLD_INLINE VMExecutionContext::iopContRetC(PC& pc) {
   m_fp = prevFp;
 }
 
+inline void OPTBLD_INLINE VMExecutionContext::iopContCheck(PC& pc) {
+  NEXT();
+  DECODE_IVA(check_started);
+  c_Continuation* cont = this_continuation(m_fp);
+  if (check_started) {
+    cont->startedCheck();
+  }
+  cont->preNext();
+}
+
 inline void OPTBLD_INLINE VMExecutionContext::iopContNext(PC& pc) {
   NEXT();
   c_Continuation* cont = this_continuation(m_fp);
-  cont->preNext();
   cont->m_received.setNull();
 }
 
-template<bool raise>
-inline void VMExecutionContext::contSendImpl() {
-  c_Continuation* cont = this_continuation(m_fp);
-  cont->startedCheck();
-  cont->preNext();
-  cont->m_received.assignVal(tvAsVariant(frame_local(m_fp, 0)));
-  if (raise) {
-    assert(cont->m_label);
-    --cont->m_label;
-  }
-}
-
 inline void OPTBLD_INLINE VMExecutionContext::iopContSend(PC& pc) {
   NEXT();
-  contSendImpl<false>();
+  c_Continuation* cont = this_continuation(m_fp);
+  cont->m_received.assignVal(tvAsVariant(frame_local(m_fp, 0)));
 }
 
 inline void OPTBLD_INLINE VMExecutionContext::iopContRaise(PC& pc) {
   NEXT();
-  contSendImpl<true>();
+  c_Continuation* cont = this_continuation(m_fp);
+  cont->m_received.assignVal(tvAsVariant(frame_local(m_fp, 0)));
+  assert(cont->m_label);
+  --cont->m_label;
 }
 
 inline void OPTBLD_INLINE VMExecutionContext::iopContValid(PC& pc) {

hphp/runtime/vm/hhbc.h

@@ -552,6 +552,7 @@ enum SetOpOp {
   O(UnpackCont,      NA,               NOV,             TWO(CV,CV), NF) \
   O(PackCont,        ONE(IVA),         ONE(CV),         NOV,        NF) \
   O(ContRetC,        NA,               ONE(CV),         NOV,        CF_TF) \
+  O(ContCheck,       ONE(IVA),         NOV,             NOV,        NF) \
   O(ContNext,        NA,               NOV,             NOV,        NF) \
   O(ContSend,        NA,               NOV,             NOV,        NF) \
   O(ContRaise,       NA,               NOV,             NOV,        NF) \

hphp/runtime/vm/jit/hhbctranslator.cpp

@@ -1155,10 +1155,18 @@ void HhbcTranslator::emitContRetC() {
   emitContExitImpl();
 }
 
+void HhbcTranslator::emitContCheck(bool checkStarted) {
+  assert(curClass());
+  SSATmp* cont = gen(LdThis, m_tb->fp());
+  if (checkStarted) {
+    gen(ContStartedCheck, getExitSlowTrace(), cont);
+  }
+  gen(ContPreNext, getExitSlowTrace(), cont);
+}
+
 void HhbcTranslator::emitContNext() {
   assert(curClass());
   SSATmp* cont = gen(LdThis, m_tb->fp());
-  gen(ContPreNext, getExitSlowTrace(), cont);
   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)));
@@ -1169,8 +1177,6 @@ void HhbcTranslator::emitContNext() {
 void HhbcTranslator::emitContSendImpl(bool raise) {
   assert(curClass());
   SSATmp* cont = gen(LdThis, m_tb->fp());
-  gen(ContStartedCheck, getExitSlowTrace(), cont);
-  gen(ContPreNext, getExitSlowTrace(), cont);
   gen(AssertLoc, Type::Cell, LocalId(0), m_tb->fp());
   auto const newVal = gen(IncRef, ldLoc(0));
   if (RuntimeOption::EvalHHIRGenerateAsserts) {

hphp/runtime/vm/jit/hhbctranslator.h

@@ -380,6 +380,7 @@ struct HhbcTranslator {
   void emitUnpackCont();
   void emitPackCont(int64_t labelId);
   void emitContRetC();
+  void emitContCheck(bool checkStarted);
   void emitContNext();
   void emitContSendImpl(bool raise);
   void emitContSend();

hphp/runtime/vm/jit/irtranslator.cpp

@@ -564,6 +564,10 @@ void Translator::translateContRetC(const NormalizedInstruction& i) {
   HHIR_EMIT(ContRetC);
 }
 
+void Translator::translateContCheck(const NormalizedInstruction& i) {
+  HHIR_EMIT(ContCheck, i.imm[0].u_IVA);
+}
+
 void Translator::translateContNext(const NormalizedInstruction& i) {
   HHIR_EMIT(ContNext);
 }

hphp/runtime/vm/jit/translator-instrs.h

@@ -133,6 +133,7 @@
   CASE(UnpackCont) \
   CASE(PackCont) \
   CASE(ContRetC) \
+  CASE(ContCheck) \
   CASE(ContNext) \
   CASE(ContSend) \
   CASE(ContRaise) \

hphp/runtime/vm/jit/translator.cpp

@@ -1269,6 +1269,7 @@ static const struct {
   { OpUnpackCont,  {Local,            StackTop2,    OutInt64,          2 }},
   { OpPackCont,    {Local|Stack1,     None,         OutNone,          -1 }},
   { OpContRetC,    {Local|Stack1,     None,         OutNone,          -1 }},
+  { OpContCheck,   {None,             None,         OutNone,           0 }},
   { OpContNext,    {None,             None,         OutNone,           0 }},
   { OpContSend,    {Local,            None,         OutNone,           0 }},
   { OpContRaise,   {Local,            None,         OutNone,           0 }},