Fix write barrier for StoreKeyedFastElements on ARM

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 d915c7d247bb9d13248840f43ae841e2be4ddd8b..a0da25c2b1d561a4203556d46f02b5be4d8e933c 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -2781,13 +2781,14 @@ 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;
-    __ ldr(result, FieldMemOperand(elements, offset));
+    offset = FixedArray::OffsetOfElementAt(ToInteger32(const_operand) +
+                                           instr->additional_index());
+    store_base = elements;
   } else {
     Register key = EmitLoadRegister(instr->key(), scratch0());
     // Even though the HLoadKeyedFastElement instruction forces the input
@@ -2800,10 +2801,9 @@ void LCodeGen::DoLoadKeyedFastElement(LLoadKeyedFastElement* instr) {
     } else {
       __ add(scratch, elements, Operand(key, LSL, kPointerSizeLog2));
     }
-    uint32_t offset = FixedArray::kHeaderSize +
-        (instr->additional_index() << kPointerSizeLog2);
-    __ ldr(result, FieldMemOperand(scratch, offset));
+    offset = FixedArray::OffsetOfElementAt(instr->additional_index());
   }
+  __ ldr(result, FieldMemOperand(store_base, offset));
 
   // Check for the hole value.
   if (instr->hydrogen()->RequiresHoleCheck()) {
@@ -3849,15 +3849,16 @@ 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;
-    __ str(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
@@ -3869,17 +3870,16 @@ void LCodeGen::DoStoreKeyedFastElement(LStoreKeyedFastElement* instr) {
     } else {
       __ add(scratch, elements, Operand(key, LSL, kPointerSizeLog2));
     }
-    uint32_t offset = FixedArray::kHeaderSize +
-        (instr->additional_index() << kPointerSizeLog2);
-    __ str(value, FieldMemOperand(scratch, offset));
+    offset = FixedArray::OffsetOfElementAt(instr->additional_index());
   }
+  __ str(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.
-    __ add(key, scratch, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
+    __ add(key, store_base, Operand(offset - kHeapObjectTag));
     __ RecordWrite(elements,
                    key,
                    value,