Add support for untagged LoadField, StoreField, LoadElement, and StoreElement simplfied operators. …

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index 44eed8fddfd64d417c749b94e50f58ea82dd50cd..486d470e4fee571625b8118b03cd8e799b011fa3 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -193,9 +193,10 @@ void SimplifiedLowering::DoChangeBitToBool(Node* node, Node* effect,
 
 
 static WriteBarrierKind ComputeWriteBarrierKind(
-    MachineRepresentation representation, Type* type) {
+    bool base_is_tagged, MachineRepresentation representation, Type* type) {
   // TODO(turbofan): skip write barriers for Smis, etc.
-  if (representation == kMachineTagged) {
+  if (base_is_tagged && representation == kMachineTagged) {
+    // Write barriers are only for writes into heap objects (i.e. tagged base).
     return kFullWriteBarrier;
   }
   return kNoWriteBarrier;
@@ -205,19 +206,19 @@ static WriteBarrierKind ComputeWriteBarrierKind(
 void SimplifiedLowering::DoLoadField(Node* node, Node* effect, Node* control) {
   const FieldAccess& access = FieldAccessOf(node->op());
   node->set_op(machine_.Load(access.representation));
-  Node* offset =
-      graph()->NewNode(common()->Int32Constant(access.offset - kHeapObjectTag));
+  int tag = access.base_is_tagged ? kHeapObjectTag : 0;
+  Node* offset = graph()->NewNode(common()->Int32Constant(access.offset - tag));
   node->InsertInput(zone(), 1, offset);
 }
 
 
 void SimplifiedLowering::DoStoreField(Node* node, Node* effect, Node* control) {
   const FieldAccess& access = FieldAccessOf(node->op());
-  WriteBarrierKind kind =
-      ComputeWriteBarrierKind(access.representation, access.type);
+  WriteBarrierKind kind = ComputeWriteBarrierKind(
+      access.base_is_tagged, access.representation, access.type);
   node->set_op(machine_.Store(access.representation, kind));
-  Node* offset =
-      graph()->NewNode(common()->Int32Constant(access.offset - kHeapObjectTag));
+  int tag = access.base_is_tagged ? kHeapObjectTag : 0;
+  Node* offset = graph()->NewNode(common()->Int32Constant(access.offset - tag));
   node->InsertInput(zone(), 1, offset);
 }
 
@@ -251,7 +252,8 @@ Node* SimplifiedLowering::ComputeIndex(const ElementAccess& access,
         machine()->Int32Mul(),
         graph()->NewNode(common()->Int32Constant(element_size)), index);
   }
-  int fixed_offset = access.header_size - kHeapObjectTag;
+  int tag = access.base_is_tagged ? kHeapObjectTag : 0;
+  int fixed_offset = access.header_size - tag;
   if (fixed_offset == 0) return index;
   return graph()->NewNode(
       machine()->Int32Add(),
@@ -270,8 +272,8 @@ void SimplifiedLowering::DoLoadElement(Node* node, Node* effect,
 void SimplifiedLowering::DoStoreElement(Node* node, Node* effect,
                                         Node* control) {
   const ElementAccess& access = ElementAccessOf(node->op());
-  WriteBarrierKind kind =
-      ComputeWriteBarrierKind(access.representation, access.type);
+  WriteBarrierKind kind = ComputeWriteBarrierKind(
+      access.base_is_tagged, access.representation, access.type);
   node->set_op(machine_.Store(access.representation, kind));
   node->ReplaceInput(1, ComputeIndex(access, node->InputAt(1)));
 }