[turbofan] Constant-fold "length" property on strings.

src/compiler/js-native-context-specialization.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/js-native-context-specialization.h"
 
 #include "src/accessors.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
@@ skipping 342 matching lines @@
 
 Reduction JSNativeContextSpecialization::ReduceJSLoadNamed(Node* node) {
   DCHECK_EQ(IrOpcode::kJSLoadNamed, node->opcode());
   NamedAccess const& p = NamedAccessOf(node->op());
   Node* const receiver = NodeProperties::GetValueInput(node, 0);
   Node* const value = jsgraph()->Dead();
 
   // Check if we have a constant receiver.
   HeapObjectMatcher m(receiver);
   if (m.HasValue()) {
-    // Optimize "prototype" property of functions.
     if (m.Value()->IsJSFunction() &&
         p.name().is_identical_to(factory()->prototype_string())) {
+      // Optimize "prototype" property of functions.
       Handle<JSFunction> function = Handle<JSFunction>::cast(m.Value());
       if (function->has_initial_map()) {
         // We need to add a code dependency on the initial map of the
         // {function} in order to be notified about changes to the
         // "prototype" of {function}, so it doesn't make sense to
         // continue unless deoptimization is enabled.
         if (flags() & kDeoptimizationEnabled) {
           Handle<Map> initial_map(function->initial_map(), isolate());
           dependencies()->AssumeInitialMapCantChange(initial_map);
           Handle<Object> prototype(initial_map->prototype(), isolate());
           Node* value = jsgraph()->Constant(prototype);
           ReplaceWithValue(node, value);
           return Replace(value);
         }
       }
+    } else if (m.Value()->IsString() &&
+               p.name().is_identical_to(factory()->length_string())) {
+      // Constant-fold "length" property on constant strings.
+      Handle<String> string = Handle<String>::cast(m.Value());
+      Node* value = jsgraph()->Constant(string->length());
+      ReplaceWithValue(node, value);
+      return Replace(value);
     }
   }
 
   // Extract receiver maps from the LOAD_IC using the LoadICNexus.
   if (!p.feedback().IsValid()) return NoChange();
   LoadICNexus nexus(p.feedback().vector(), p.feedback().slot());
 
   // Try to lower the named access based on the {receiver_maps}.
   return ReduceNamedAccessFromNexus(node, value, nexus, p.name(),
                                     AccessMode::kLoad, p.language_mode());
@@ skipping 1102 matching lines @@
   return jsgraph()->javascript();
 }
 
 SimplifiedOperatorBuilder* JSNativeContextSpecialization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8