Provide a tagged allocation top pointer.

src/compiler/memory-optimizer.cc

Index: src/compiler/memory-optimizer.cc
diff --git a/src/compiler/memory-optimizer.cc b/src/compiler/memory-optimizer.cc
index 8c66347a6e1210494f0f8d372f4f468d211e4a92..420494840af90bc129580a6f47eeb65d1f7d926f 100644
--- a/src/compiler/memory-optimizer.cc
+++ b/src/compiler/memory-optimizer.cc
@@ -146,10 +146,7 @@ void MemoryOptimizer::VisitAllocate(Node* node, AllocationState const* state) {
           top_address, jsgraph()->IntPtrConstant(0), top, effect, control);
 
       // Compute the effective inner allocated address.
-      value = graph()->NewNode(
-          machine()->BitcastWordToTagged(),
-          graph()->NewNode(machine()->IntAdd(), state->top(),
-                           jsgraph()->IntPtrConstant(kHeapObjectTag)));
+      value = graph()->NewNode(machine()->BitcastWordToTagged(), state->top());
 
       // Extend the allocation {group}.
       group->Add(value);
@@ -198,8 +195,6 @@ void MemoryOptimizer::VisitAllocate(Node* node, AllocationState const* state) {
         }
         vfalse = efalse = graph()->NewNode(allocate_operator_.get(), target,
                                            size, efalse, if_false);
-        vfalse = graph()->NewNode(machine()->IntSub(), vfalse,
-                                  jsgraph()->IntPtrConstant(kHeapObjectTag));
       }
 
       control = graph()->NewNode(common()->Merge(2), if_true, if_false);
@@ -217,10 +212,7 @@ void MemoryOptimizer::VisitAllocate(Node* node, AllocationState const* state) {
           top_address, jsgraph()->IntPtrConstant(0), top, effect, control);
 
       // Compute the initial object address.
-      value = graph()->NewNode(
-          machine()->BitcastWordToTagged(),
-          graph()->NewNode(machine()->IntAdd(), value,
-                           jsgraph()->IntPtrConstant(kHeapObjectTag)));
+      value = graph()->NewNode(machine()->BitcastWordToTagged(), value);
 
       // Start a new allocation group.
       AllocationGroup* group =
@@ -256,10 +248,7 @@ void MemoryOptimizer::VisitAllocate(Node* node, AllocationState const* state) {
           machine()->Store(StoreRepresentation(
               MachineType::PointerRepresentation(), kNoWriteBarrier)),
           top_address, jsgraph()->IntPtrConstant(0), new_top, etrue, if_true);
-      vtrue = graph()->NewNode(
-          machine()->BitcastWordToTagged(),
-          graph()->NewNode(machine()->IntAdd(), top,
-                           jsgraph()->IntPtrConstant(kHeapObjectTag)));
+      vtrue = graph()->NewNode(machine()->BitcastWordToTagged(), top);
     }
 
     Node* if_false = graph()->NewNode(common()->IfFalse(), branch);