Add map-based read barrier to WeakCell

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 1c8d075dcb8713e8ff40ccc3cf3de3bf8b8d6d77..6be247bef781ca63b6903467f1b40e1197bdf666 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -2193,10 +2193,17 @@ LInstruction* LChunkBuilder::DoStoreContextSlot(HStoreContextSlot* instr) {
 
 
 LInstruction* LChunkBuilder::DoLoadNamedField(HLoadNamedField* instr) {
-  LOperand* obj = (instr->access().IsExternalMemory() &&
-                   instr->access().offset() == 0)
-      ? UseRegisterOrConstantAtStart(instr->object())
-      : UseRegisterAtStart(instr->object());
+  LOperand* obj;
+  if (instr->access().read_barrier()) {
+    DCHECK(!instr->access().IsExternalMemory());
+    obj = UseRegister(instr->object());
+  } else {
+    // With no read barrier we can have the same register for the object and
+    // the field.
+    obj = (instr->access().IsExternalMemory() && instr->access().offset() == 0)
+              ? UseRegisterOrConstantAtStart(instr->object())
+              : UseRegisterAtStart(instr->object());
+  }
   return DefineAsRegister(new(zone()) LLoadNamedField(obj));
 }