[turbofan] Support for typed lowering of "prototype" load from functions.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 19aaaa531474ac599f6f74267c0bc072cfef59c7..74904a3601569966197a9dd2a8477595b6b853c2 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -1262,7 +1262,37 @@ Type* Typer::Visitor::TypeJSLoadProperty(Node* node) {
 }
 
 
-Type* Typer::Visitor::TypeJSLoadNamed(Node* node) { return Type::Any(); }
+Type* Typer::Visitor::TypeJSLoadNamed(Node* node) {
+  Factory* const f = isolate()->factory();
+  Handle<Name> name = NamedAccessOf(node->op()).name();
+  if (name.is_identical_to(f->prototype_string())) {
+    Type* receiver = Operand(node, 0);
+    if (receiver->Is(Type::None())) return Type::None();
+    if (receiver->IsConstant() &&
+        receiver->AsConstant()->Value()->IsJSFunction()) {
+      Handle<JSFunction> function =
+          Handle<JSFunction>::cast(receiver->AsConstant()->Value());
+      if (function->has_prototype()) {
+        // We need to add a code dependency on the initial map of the {function}
+        // in order to be notified about changes to "prototype" of {function},
+        // so we can only infer a constant type if deoptimization is enabled.
+        if (flags() & kDeoptimizationEnabled) {
+          JSFunction::EnsureHasInitialMap(function);
+          Handle<Map> initial_map(function->initial_map(), isolate());
+          dependencies()->AssumeInitialMapCantChange(initial_map);
+          return Type::Constant(handle(initial_map->prototype(), isolate()),
+                                zone());
+        }
+      }
+    } else if (receiver->IsClass() &&
+               receiver->AsClass()->Map()->IsJSFunctionMap()) {
+      Handle<Map> map = receiver->AsClass()->Map();
+      return map->has_non_instance_prototype() ? Type::Primitive(zone())
+                                               : Type::Receiver(zone());
+    }
+  }
+  return Type::Any();
+}
 
 
 Type* Typer::Visitor::TypeJSLoadGlobal(Node* node) { return Type::Any(); }