Add mistagging-readbarrier to weak cell

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 ff35b8a318fadae93f84339206062442c611afbc..284c06fbdd4b3e9e04f11af0b4224d605e95c8be 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -2962,6 +2962,7 @@ void LCodeGen::DoLoadNamedField(LLoadNamedField* instr) {
   int offset = access.offset();
 
   if (access.IsExternalMemory()) {
+    DCHECK(!access.read_barrier());
     Register result = ToRegister(instr->result());
     MemOperand operand = instr->object()->IsConstantOperand()
         ? MemOperand::StaticVariable(ToExternalReference(
@@ -2973,6 +2974,7 @@ void LCodeGen::DoLoadNamedField(LLoadNamedField* instr) {
 
   Register object = ToRegister(instr->object());
   if (instr->hydrogen()->representation().IsDouble()) {
+    DCHECK(!access.read_barrier());
     XMMRegister result = ToDoubleRegister(instr->result());
     __ movsd(result, FieldOperand(object, offset));
     return;
@@ -2980,9 +2982,26 @@ void LCodeGen::DoLoadNamedField(LLoadNamedField* instr) {
 
   Register result = ToRegister(instr->result());
   if (!access.IsInobject()) {
+    DCHECK(!access.read_barrier());
     __ mov(result, FieldOperand(object, JSObject::kPropertiesOffset));
     object = result;
   }
+  if (access.read_barrier()) {
+    DCHECK(!result.is(object));
+    DCHECK(instr->hydrogen()->representation().IsTagged());
+    __ Load(result, FieldOperand(object, offset), access.representation());
+    Label done;
+    DCHECK_NE(kReadBarrierTag, 0);
+    __ test(result, Immediate(kReadBarrierMask));
+    __ j(zero, &done);
+    __ test(result, Immediate(kSmiTagMask));
+    DCHECK_EQ(kSmiTag, 0);
+    __ j(zero, &done);
+    __ and_(result, Immediate(~kReadBarrierTag));
+    __ mov(FieldOperand(object, offset), result);
+    __ bind(&done);
+    return;
+  }
   __ Load(result, FieldOperand(object, offset), access.representation());
 }