Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 7152ba21cc2af690406d1d209eba6087c6f53dce..a9e6fa6682979154a4b5f26f56ae3412306071e9 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -5716,13 +5716,62 @@ void LCodeGen::DoCheckMapValue(LCheckMapValue* instr) {
 }
 
 
+void LCodeGen::DoDeferredLoadMutableDouble(LLoadFieldByIndex* instr,
+                                           Register result,
+                                           Register object,
+                                           Register index) {
+  PushSafepointRegistersScope scope(this, Safepoint::kWithRegisters);
+  __ Push(object);
+  __ Push(index);
+  __ mov(cp, Operand::Zero());
+  __ CallRuntimeSaveDoubles(Runtime::kLoadMutableDouble);
+  RecordSafepointWithRegisters(
+      instr->pointer_map(), 1, Safepoint::kNoLazyDeopt);
+  __ StoreToSafepointRegisterSlot(r0, result);
+}
+
+
 void LCodeGen::DoLoadFieldByIndex(LLoadFieldByIndex* instr) {
+  class DeferredLoadMutableDouble V8_FINAL : public LDeferredCode {
+   public:
+    DeferredLoadMutableDouble(LCodeGen* codegen,
+                              LLoadFieldByIndex* instr,
+                              Register result,
+                              Register object,
+                              Register index)
+        : LDeferredCode(codegen),
+          instr_(instr),
+          result_(result),
+          object_(object),
+          index_(index) {
+    }
+    virtual void Generate() V8_OVERRIDE {
+      codegen()->DoDeferredLoadMutableDouble(instr_, result_, object_, index_);
+    }
+    virtual LInstruction* instr() V8_OVERRIDE { return instr_; }
+   private:
+    LLoadFieldByIndex* instr_;
+    Register result_;
+    Register object_;
+    Register index_;
+  };
+
   Register object = ToRegister(instr->object());
   Register index = ToRegister(instr->index());
   Register result = ToRegister(instr->result());
   Register scratch = scratch0();
 
+  DeferredLoadMutableDouble* deferred;
+  deferred = new(zone()) DeferredLoadMutableDouble(
+      this, instr, result, object, index);
+
   Label out_of_object, done;
+
+  __ and_(scratch, index, Operand(Smi::FromInt(1)));
+  __ cmp(scratch, Operand::Zero());
+  __ b(ne, deferred->entry());
+  __ mov(index, Operand(index, ASR, 1));
+
   __ cmp(index, Operand::Zero());
   __ b(lt, &out_of_object);
 
@@ -5738,6 +5787,7 @@ void LCodeGen::DoLoadFieldByIndex(LLoadFieldByIndex* instr) {
   __ sub(scratch, result, Operand::PointerOffsetFromSmiKey(index));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
+  __ bind(deferred->exit());
   __ bind(&done);
 }