Select callee entry for inlining even if guard may fail when there's …

…a single candidate

Summary:
When a function argument's type is relaxed (eg, because it's simply loaded from a local) but the callee
guards on a specific type, the JIT would refuse inlining because the argument type was not a subtype
of the guarded type in the callee. This diff relaxes that condition by searching for all entry blocks
where the guards may succeed (ie, if the argument type intersects the callee's guarded type) and,
in case there's only one such block, selecting that one.

Reviewed By: mofarrell

Differential Revision: D15640002

fbshipit-source-id: d6dff01ecbe38bbf60daf0c5c3f2457a710f46a3

hphp/runtime/vm/jit/inlining-decider.cpp

@@ -736,6 +736,8 @@ TransID findTransIDForCallee(const ProfData* profData,
   TransID ret = kInvalidTransID;
   bool hasThisVaries = callee->hasThisVaries() &&
     ctxType.maybe(TObj) && !(ctxType <= TObj);
+  FTRACE(2, "findTransIDForCallee: offset={}  hasThisVaries={}\n",
+         offset, hasThisVaries);
   for (auto const id : idvec) {
     auto const rec = profData->transRec(id);
     if (rec->startBcOff() != offset) continue;
@@ -750,17 +752,16 @@ TransID findTransIDForCallee(const ProfData* profData,
         if (typeloc.location.tag() != LTag::Local) continue;
         auto const locId = typeloc.location.localId();
 
-        if (locId < numArgs && !(argTypes[locId] <= typeloc.type)) {
+        if (locId < numArgs && !(argTypes[locId].maybe(typeloc.type))) {
           return false;
         }
       }
       return true;
     }();
 
     if (!isvalid) continue;
-    if (!hasThisVaries) return id;
-    // The function may be called with or without $this, if we've seen
-    // both, give up.
+    // Found multiple entries that may match the arguments, so don't return
+    // any.
     if (ret != kInvalidTransID) return kInvalidTransID;
     ret = id;
   }
@@ -858,6 +859,7 @@ RegionDescPtr selectCalleeRegion(const irgen::IRGS& irgs,
     }
   }
 
+  FTRACE(2, "selectCalleeRegion: callee = {}\n", callee->fullName()->data());
   std::vector<Type> argTypes;
   for (int i = fca.numArgs - 1; i >= 0; --i) {
     // DataTypeGeneric is used because we're just passing the locals into the
@@ -873,6 +875,7 @@ RegionDescPtr selectCalleeRegion(const irgen::IRGS& irgs,
                    annotationsPtr);
       return nullptr;
     }
+    FTRACE(2, "arg {}: {}\n", i, type);
     argTypes.push_back(type);
   }