[turbofan] Restore basic write barrier elimination.

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 15ff8bfeb727842c6ea0c336ea23468eaadd9d09..c7e59198b10f805765991ec5320adce8b792eda0 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -452,6 +452,33 @@ enum AllocationAlignment {
   kSimd128Unaligned
 };
 
+// Supported write barrier modes.
+enum WriteBarrierKind : uint8_t {

[Michael Starzinger, 2016/05/02 17:20:37]

nit: Does this have to be global or can we put it into simplified-operator.h
instead?

[Benedikt Meurer, 2016/05/03 09:05:14]

We need it for both machine and simplified operators.

+  kNoWriteBarrier,
+  kMapWriteBarrier,
+  kPointerWriteBarrier,
+  kFullWriteBarrier
+};
+
+inline size_t hash_value(WriteBarrierKind kind) {
+  return static_cast<uint8_t>(kind);
+}
+
+inline std::ostream& operator<<(std::ostream& os, WriteBarrierKind kind) {
+  switch (kind) {
+    case kNoWriteBarrier:
+      return os << "NoWriteBarrier";
+    case kMapWriteBarrier:
+      return os << "MapWriteBarrier";
+    case kPointerWriteBarrier:
+      return os << "PointerWriteBarrier";
+    case kFullWriteBarrier:
+      return os << "FullWriteBarrier";
+  }
+  UNREACHABLE();
+  return os;
+}
+
 // A flag that indicates whether objects should be pretenured when
 // allocated (allocated directly into the old generation) or not
 // (allocated in the young generation if the object size and type