Don't need to guard MBase

Summary: After D8337098, we no longer need to guard on `MBase`.

Reviewed By: ricklavoie

Differential Revision: D50544898

fbshipit-source-id: 11ee112b513f0ea35eb4894dfb81d34710def845

hphp/runtime/vm/jit/region-tracelet.cpp

@@ -123,20 +123,17 @@ SBInvOffset curSpOffset(const Env& env) {
 }
 
 /*
- * Check if the current predicted type for the location in ii is specific
- * enough for what the current opcode wants. If not, return false.
+ * Check if the input has a known datatype or whether we need
+ * to insert a guard.
  */
-bool consumeInput(Env& env, const InputInfo& input) {
-  if (input.dontGuard) return true;
+bool needGuardForInput(Env& env, const InputInfo& input) {
+  if (input.dontGuard) return false;
   auto const type = irgen::provenType(env.irgs, input.loc);
 
-  if (!type.isKnownDataType()) {
-    // Trying to consume a value without a precise enough type.
-    FTRACE(1, "selectTracelet: {} tried to consume {}, type {}\n",
-           env.inst.toString(), show(input.loc), type.toString());
-    return false;
-  }
+  if (type.isKnownDataType()) return false;
 
+  FTRACE(1, "selectTracelet: {} input {}, needs a guard due to unknown type {}\n",
+         env.inst.toString(), show(input.loc), type.toString());
   return true;
 }
 
@@ -242,9 +239,8 @@ bool prepareInstruction(Env& env) {
     addGuardIfUntracked(Location::Stack{sbInvOff});
   }
 
-  // Check all the inputs for unknown values.
   for (auto const& input : inputInfos) {
-    if (!consumeInput(env, input)) {
+    if (needGuardForInput(env, input)) {
       FTRACE(2, "Stopping tracelet consuming {} input {}\n",
              opcodeToName(env.inst.op()), show(input.loc));
       return false;

hphp/runtime/vm/jit/translator.cpp

@@ -467,8 +467,7 @@ const InstrInfo& getInstrInfo(Op op) {
 namespace {
 int64_t countOperands(uint64_t mask) {
   const uint64_t ignore = Local | Iter | DontGuardStack1 |
-    DontGuardAny | This | MBase | StackI | StackI2 | MKey | LocalRange |
-    DontGuardBase;
+    DontGuardAny | This | MBase | StackI | StackI2 | MKey | LocalRange;
   mask &= ~ignore;
 
   static const uint64_t counts[][2] = {
@@ -837,12 +836,8 @@ InputInfoVec getInputs(const NormalizedInstruction& ni, SBInvOffset bcSPOff) {
         break;
     }
   }
-  if (flags & MBase) {
-    inputs.emplace_back(Location::MBase{});
-    if (flags & DontGuardBase) {
-      inputs.back().dontGuard = true;
-    }
-  }
+
+  if (flags & MBase) inputs.emplace_back(Location::MBase{});
 
   SKTRACE(1, sk, "stack args: virtual sfo now %d\n", stackOff.offset);
   TRACE(1, "%s\n", Trace::prettyNode("Inputs", inputs).c_str());