Make map check in NamedStoreHandlerCompiler::GenerateFieldTypeChecks weak.

src/ic/x64/handler-compiler-x64.cc

Index: src/ic/x64/handler-compiler-x64.cc
diff --git a/src/ic/x64/handler-compiler-x64.cc b/src/ic/x64/handler-compiler-x64.cc
index 46fa8cc337139fa0089a14b2c79e7b22a6161ed8..36973ec074ffc0b774d07e0a84e0c0535066227b 100644
--- a/src/ic/x64/handler-compiler-x64.cc
+++ b/src/ic/x64/handler-compiler-x64.cc
@@ -377,12 +377,17 @@ void NamedStoreHandlerCompiler::GenerateConstantCheck(Register map_reg,
 void NamedStoreHandlerCompiler::GenerateFieldTypeChecks(HeapType* field_type,
                                                         Register value_reg,
                                                         Label* miss_label) {
+  Register map_reg = scratch1();
+  Register scratch = scratch2();
+  DCHECK(!value_reg.is(map_reg));
+  DCHECK(!value_reg.is(scratch));
   __ JumpIfSmi(value_reg, miss_label);
   HeapType::Iterator<Map> it = field_type->Classes();
   if (!it.Done()) {
     Label do_store;
+    __ movp(map_reg, FieldOperand(value_reg, HeapObject::kMapOffset));
     while (true) {
-      __ CompareMap(value_reg, it.Current());
+      __ CmpWeakValue(map_reg, Map::WeakCellForMap(it.Current()), scratch);
       it.Advance();
       if (it.Done()) {
         __ j(not_equal, miss_label);