Don't MISS if you read the hole from certain FastHoley arrays.

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index d0ca2a847c2a40ba6e309662fcf936f33afe5816..6ff14315517478155584752ad6abcb51f264ae9c 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -2229,14 +2229,21 @@ LInstruction* LChunkBuilder::DoLoadKeyed(HLoadKeyed* instr) {
     result = DefineAsRegister(new(zone()) LLoadKeyed(backing_store, key));
   }
 
-  if ((instr->is_external() || instr->is_fixed_typed_array()) ?

[Jakob Kummerow, 2015/04/23 13:40:00]

Yo dawg, I heard you like conditions, so I put a conditional into your
condition, so you can check a condition while you check a condition...

+1 to cleaning that up! :-)

[mvstanton, 2015/04/27 07:57:12]

:D, yeah I was like wha?

-      // see LCodeGen::DoLoadKeyedExternalArray
-      ((instr->elements_kind() == EXTERNAL_UINT32_ELEMENTS ||
-        instr->elements_kind() == UINT32_ELEMENTS) &&
-       !instr->CheckFlag(HInstruction::kUint32)) :
-      // see LCodeGen::DoLoadKeyedFixedDoubleArray and
-      // LCodeGen::DoLoadKeyedFixedArray
-      instr->RequiresHoleCheck()) {
+  bool needs_environment;

[Jakob Kummerow, 2015/04/23 13:40:00]

We used to have to initialize such variables to keep all compilers happy... not
sure if that's still necessary.

[mvstanton, 2015/04/27 07:57:12]

I'll try to go without it, hopefully it'll work.

+  if (instr->is_external() || instr->is_fixed_typed_array()) {
+    // see LCodeGen::DoLoadKeyedExternalArray
+    needs_environment = (elements_kind == EXTERNAL_UINT32_ELEMENTS ||
+                         elements_kind == UINT32_ELEMENTS) &&
+                        !instr->CheckFlag(HInstruction::kUint32);
+  } else {
+    // see LCodeGen::DoLoadKeyedFixedDoubleArray and
+    // LCodeGen::DoLoadKeyedFixedArray
+    needs_environment =
+        instr->RequiresHoleCheck() ||
+        (instr->hole_mode() == CONVERT_HOLE_TO_UNDEFINED && info()->IsStub());
+  }
+
+  if (needs_environment) {
     result = AssignEnvironment(result);
   }
   return result;