MIPS: Fix write barrier for StoreKeyedFastElements on ARM.

Port r12238 (300f3dac)

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10828216
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12358 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -2592,13 +2592,14 @@ void LCodeGen::DoLoadKeyedFastElement(LLoadKeyedFastElement* instr) {
   Register elements = ToRegister(instr->elements());
   Register result = ToRegister(instr->result());
   Register scratch = scratch0();
+  Register store_base = scratch;
+  int offset = 0;
 
   if (instr->key()->IsConstantOperand()) {
     LConstantOperand* const_operand = LConstantOperand::cast(instr->key());
-    int offset =
-        (ToInteger32(const_operand) + instr->additional_index()) * kPointerSize
-        + FixedArray::kHeaderSize;
-    __ lw(result, FieldMemOperand(elements, offset));
+    offset = FixedArray::OffsetOfElementAt(ToInteger32(const_operand) +
+                                           instr->additional_index());
+    store_base = elements;
   } else {
     Register key = EmitLoadRegister(instr->key(), scratch);
     // Even though the HLoadKeyedFastElement instruction forces the input
@@ -2612,10 +2613,9 @@ void LCodeGen::DoLoadKeyedFastElement(LLoadKeyedFastElement* instr) {
       __ sll(scratch, key, kPointerSizeLog2);
       __ addu(scratch, elements, scratch);
     }
-    uint32_t offset = FixedArray::kHeaderSize +
-        (instr->additional_index() << kPointerSizeLog2);
-    __ lw(result, FieldMemOperand(scratch, offset));
+    offset = FixedArray::OffsetOfElementAt(instr->additional_index());
   }
+  __ lw(result, FieldMemOperand(store_base, offset));
 
   // Check for the hole value.
   if (instr->hydrogen()->RequiresHoleCheck()) {
@@ -3687,15 +3687,16 @@ void LCodeGen::DoStoreKeyedFastElement(LStoreKeyedFastElement* instr) {
   Register elements = ToRegister(instr->object());
   Register key = instr->key()->IsRegister() ? ToRegister(instr->key()) : no_reg;
   Register scratch = scratch0();
+  Register store_base = scratch;
+  int offset = 0;
 
   // Do the store.
   if (instr->key()->IsConstantOperand()) {
     ASSERT(!instr->hydrogen()->NeedsWriteBarrier());
     LConstantOperand* const_operand = LConstantOperand::cast(instr->key());
-    int offset =
-        (ToInteger32(const_operand) + instr->additional_index()) * kPointerSize
-        + FixedArray::kHeaderSize;
-    __ sw(value, FieldMemOperand(elements, offset));
+    offset = FixedArray::OffsetOfElementAt(ToInteger32(const_operand) +
+                                           instr->additional_index());
+    store_base = elements;
   } else {
     // Even though the HLoadKeyedFastElement instruction forces the input
     // representation for the key to be an integer, the input gets replaced
@@ -3708,17 +3709,16 @@ void LCodeGen::DoStoreKeyedFastElement(LStoreKeyedFastElement* instr) {
       __ sll(scratch, key, kPointerSizeLog2);
       __ addu(scratch, elements, scratch);
     }
-    uint32_t offset = FixedArray::kHeaderSize +
-        (instr->additional_index() << kPointerSizeLog2);
-    __ sw(value, FieldMemOperand(scratch, offset));
+    offset = FixedArray::OffsetOfElementAt(instr->additional_index());
   }
+  __ sw(value, FieldMemOperand(store_base, offset));
 
   if (instr->hydrogen()->NeedsWriteBarrier()) {
     HType type = instr->hydrogen()->value()->type();
     SmiCheck check_needed =
         type.IsHeapObject() ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
     // Compute address of modified element and store it into key register.
-    __ Addu(key, scratch, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
+    __ Addu(key, store_base, Operand(offset - kHeapObjectTag));
     __ RecordWrite(elements,
                    key,
                    value,