CreateCont opcode optimization - avoid unnecessary reference counting.

Continuation argument values are copied to the continuation object and the locals are unset - in this way we don't need to change the reference coutners.

hphp/runtime/base/tv_helpers.h

@@ -14,14 +14,14 @@
    +----------------------------------------------------------------------+
 */
 
+#ifndef incl_HPHP_TV_HELPERS_H_
+#define incl_HPHP_TV_HELPERS_H_
+
 #ifndef incl_HPHP_INSIDE_HPHP_COMPLEX_TYPES_H_
 #error Directly including 'tv_helpers.h' is prohibited. \
        Include 'complex_types.h' instead.
 #endif
 
-#ifndef incl_HPHP_TV_HELPERS_H_
-#define incl_HPHP_TV_HELPERS_H_
-
 #include "hphp/runtime/base/types.h"
 
 namespace HPHP {
@@ -216,11 +216,17 @@ inline void tvDupRef(RefData* fr, TypedValue* to) {
 }
 
 // Assumes 'fr' is live and 'to' is dead
-// NOTE: this helper does not modify to->_count
-inline void tvDup(const TypedValue* fr, TypedValue* to) {
+// After this operation, 'fr' is dead and 'to' live.
+inline void tvTeleport(const TypedValue* fr, TypedValue* to) {
   assert(tvIsPlausible(fr));
   to->m_data.num = fr->m_data.num;
   to->m_type = fr->m_type;
+}
+
+// Assumes 'fr' is live and 'to' is dead
+// NOTE: this helper does not modify to->_count
+inline void tvDup(const TypedValue* fr, TypedValue* to) {
+  tvTeleport(fr, to);
   tvRefcountedIncRef(to);
 }
 

hphp/runtime/vm/bytecode.cpp

@@ -383,7 +383,7 @@ void VarEnv::detach(ActRec* fp) {
     TypedValue** origLocs =
       !m_restoreLocations.empty()
         ? m_restoreLocations.back()
-        : reinterpret_cast<TypedValue**>(uintptr_t(this) + sizeof(VarEnv));
+          : reinterpret_cast<TypedValue**>(uintptr_t(this) + sizeof(VarEnv));
 
     for (Id i = 0; i < numLocals; i++) {
       m_nvTable->resettle(func->localVarName(i), origLocs[i]);
@@ -6694,7 +6694,10 @@ static inline void setContVar(const Func* genFunc,
                               c_Continuation* cont) {
   Id destId = genFunc->lookupVarId(name);
   if (destId != kInvalidId) {
-    tvDup(src, frame_local(cont->actRec(), destId));
+    // Copy the value of the local to the cont object and set the
+    // local to uninit so that we don't need to change refcounts.
+    tvTeleport(src, frame_local(cont->actRec(), destId));
+    tvWriteUninit(src);
   } else {
     ActRec *contFP = cont->actRec();
     if (!contFP->hasVarEnv()) {

hphp/runtime/vm/jit/hhbctranslator.cpp

@@ -1033,8 +1033,10 @@ void HhbcTranslator::emitCreateCont(Id funNameStrId) {
       // We must generate an AssertLoc because we don't have tracelet
       // guards on the object type in these outer generator functions.
       gen(AssertLoc, Type::Gen, LocalId(i), m_tb->fp());
-      auto const loc = gen(IncRef, ldLoc(i));
-      gen(StMem, contAR, cns(-cellsToBytes(params[i] + 1)), loc);
+      // Copy the value of the local to the cont object and set the
+      // local to uninit so that we don't need to change refcounts.
+      gen(StMem, contAR, cns(-cellsToBytes(params[i] + 1)), ldLoc(i));
+      gen(StLoc, LocalId(i), m_tb->fp(), m_tb->genDefUninit());
     }
     if (fillThis) {
       assert(thisId != kInvalidId);