[turbofan] Introduce a dedicated Array type.

src/compiler/js-builtin-reducer.cc

Index: src/compiler/js-builtin-reducer.cc
diff --git a/src/compiler/js-builtin-reducer.cc b/src/compiler/js-builtin-reducer.cc
index a1c83ce1b639b733205909e760f79e672e49b081..f812a2cf0483d7fdd7745998132dc5a23475fc00 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -733,11 +733,23 @@ Reduction JSBuiltinReducer::ReduceArrayIsArray(Node* node) {
     return Replace(value);
   }
   Node* value = NodeProperties::GetValueInput(node, 2);
+  Type* value_type = NodeProperties::GetType(value);
   Node* context = NodeProperties::GetContextInput(node);
   Node* frame_state = NodeProperties::GetFrameStateInput(node);
   Node* effect = NodeProperties::GetEffectInput(node);
   Node* control = NodeProperties::GetControlInput(node);
 
+  // Constant-fold based on {value} type.
+  if (value_type->Is(Type::Array())) {
+    Node* value = jsgraph()->TrueConstant();
+    ReplaceWithValue(node, value);
+    return Replace(value);
+  } else if (!value_type->Maybe(Type::ArrayOrProxy())) {
+    Node* value = jsgraph()->FalseConstant();
+    ReplaceWithValue(node, value);
+    return Replace(value);
+  }
+
   int count = 0;
   Node* values[5];
   Node* effects[5];