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

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 5c0fa9106afbcdfe79c78ad2fb92aaa67fc15b4b..3e7f86ff332d098b3179bd5cc1cb643811443379 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -3284,6 +3284,21 @@ void LCodeGen::DoLoadKeyedFixedArray(LLoadKeyed* instr) {
       __ LoadRoot(scratch, Heap::kTheHoleValueRootIndex);
       DeoptimizeIf(eq, instr, Deoptimizer::kHole, result, Operand(scratch));
     }
+  } else if (instr->hydrogen()->hole_mode() == CONVERT_HOLE_TO_UNDEFINED) {
+    DCHECK(instr->hydrogen()->elements_kind() == FAST_HOLEY_ELEMENTS);
+    Label done;
+    __ LoadRoot(scratch, Heap::kTheHoleValueRootIndex);
+    __ Branch(&done, ne, result, Operand(scratch));
+    if (info()->IsStub()) {
+      // A stub can safely convert the hole to undefined only if the array
+      // protector cell contains (Smi) 1. Otherwise it needs to bail out.
+      __ LoadRoot(scratch, Heap::kArrayProtectorRootIndex);

[balazs.kilvady, 2015/04/23 16:24:37]

The result register should be used instead of scratch in LoadRoot like in
src/arm64/lithium-codegen-arm64.cc.

[mvstanton, 2015/04/27 07:57:13]

Done.

+      __ lw(scratch, FieldMemOperand(result, Cell::kValueOffset));
+      DeoptimizeIf(ne, instr, Deoptimizer::kHole, scratch,
+                   Operand(Smi::FromInt(1)));
+    }
+    __ LoadRoot(result, Heap::kUndefinedValueRootIndex);
+    __ bind(&done);
   }
 }