Reland of [turbofan] Restore basic write barrier elimination.

src/compiler/simplified-operator.h

Index: src/compiler/simplified-operator.h
diff --git a/src/compiler/simplified-operator.h b/src/compiler/simplified-operator.h
index 0828441c1d6001bed01aa425d1a7a73ef491d7af..389e6c4ae53cf96ebf69279fe50e4d9761a1bdbc 100644
--- a/src/compiler/simplified-operator.h
+++ b/src/compiler/simplified-operator.h
@@ -25,8 +25,9 @@
 class Operator;
 struct SimplifiedOperatorGlobalCache;
 
-
-enum BaseTaggedness { kUntaggedBase, kTaggedBase };
+enum BaseTaggedness : uint8_t { kUntaggedBase, kTaggedBase };
+
+size_t hash_value(BaseTaggedness);
 
 std::ostream& operator<<(std::ostream&, BaseTaggedness);
 
@@ -63,6 +64,7 @@
   MaybeHandle<Name> name;         // debugging only.
   Type* type;                     // type of the field.
   MachineType machine_type;       // machine type of the field.
+  WriteBarrierKind write_barrier_kind;  // write barrier hint.
 
   int tag() const { return base_is_tagged == kTaggedBase ? kHeapObjectTag : 0; }
 };
@@ -86,6 +88,7 @@
   int header_size;                // size of the header, without tag.
   Type* type;                     // type of the element.
   MachineType machine_type;       // machine type of the element.
+  WriteBarrierKind write_barrier_kind;  // write barrier hint.
 
   int tag() const { return base_is_tagged == kTaggedBase ? kHeapObjectTag : 0; }
 };