Stores to external references don't need write barriers.

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index 7edf2d9f3e0a4148c047da290fbd38c9fb35af9a..91c41110828eaaa17365c84640a63b9fb74ff39c 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -2422,15 +2422,15 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
       instr->NeedsWriteBarrierForMap();
 
   LOperand* obj;
-  if (needs_write_barrier) {
-    obj = is_in_object
-        ? UseRegister(instr->object())
-        : UseTempRegister(instr->object());
-  } else if (is_external_location) {
+  if (is_external_location) {
     ASSERT(!is_in_object);
     ASSERT(!needs_write_barrier);
     ASSERT(!needs_write_barrier_for_map);
     obj = UseRegisterOrConstant(instr->object());
+  } else if (needs_write_barrier) {
+    obj = is_in_object
+        ? UseRegister(instr->object())

[mvstanton, 2013/07/31 13:37:47]

Is this reordering needed?
If so, do you need to make the change for ARM as well as x64 and ia32?

[Benedikt Meurer, 2013/07/31 13:45:39]

Nope.
No, ARM is a regular load/store architecture.

+        : UseTempRegister(instr->object());
   } else {
     obj = needs_write_barrier_for_map
         ? UseRegister(instr->object())