Fix LoadFieldByIndex to take mutable heap-numbers into account.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 0dbe3da13d3f1b4f59bfd2b1f31a1fbaf84c6eaa..af76f0332e0974d27f048cb96923bf809ff2b1bc 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -6325,11 +6325,56 @@ void LCodeGen::DoCheckMapValue(LCheckMapValue* instr) {
 }
 
 
+void LCodeGen::DoDeferredLoadMutableDouble(LLoadFieldByIndex* instr,
+                                           Register object,
+                                           Register index) {
+  PushSafepointRegistersScope scope(this);
+  __ push(object);
+  __ push(index);
+  __ xor_(esi, esi);
+  __ CallRuntimeSaveDoubles(Runtime::kLoadMutableDouble);
+  RecordSafepointWithRegisters(
+      instr->pointer_map(), 1, Safepoint::kNoLazyDeopt);
+  __ StoreToSafepointRegisterSlot(object, eax);
+}
+
+
 void LCodeGen::DoLoadFieldByIndex(LLoadFieldByIndex* instr) {
+  class DeferredLoadMutableDouble V8_FINAL : public LDeferredCode {
+   public:
+    DeferredLoadMutableDouble(LCodeGen* codegen,
+                              LLoadFieldByIndex* instr,
+                              Register object,
+                              Register index,
+                              const X87Stack& x87_stack)
+        : LDeferredCode(codegen, x87_stack),
+          instr_(instr),
+          object_(object),
+          index_(index) {
+    }
+    virtual void Generate() V8_OVERRIDE {
+      codegen()->DoDeferredLoadMutableDouble(instr_, object_, index_);
+    }
+    virtual LInstruction* instr() V8_OVERRIDE { return instr_; }
+   private:
+    LLoadFieldByIndex* instr_;
+    Register object_;
+    Register index_;
+  };
+
   Register object = ToRegister(instr->object());
   Register index = ToRegister(instr->index());
 
+  DeferredLoadMutableDouble* deferred;
+  deferred = new(zone()) DeferredLoadMutableDouble(
+      this, instr, object, index, x87_stack_);
+
   Label out_of_object, done;
+  __ test(index, Immediate(Smi::FromInt(1)));
+  __ j(not_zero, deferred->entry());
+
+  __ sar(index, 1);
+
   __ cmp(index, Immediate(0));
   __ j(less, &out_of_object, Label::kNear);
   __ mov(object, FieldOperand(object,
@@ -6346,6 +6391,7 @@ void LCodeGen::DoLoadFieldByIndex(LLoadFieldByIndex* instr) {
                               index,
                               times_half_pointer_size,
                               FixedArray::kHeaderSize - kPointerSize));
+  __ bind(deferred->exit());
   __ bind(&done);
 }