[turbofan] Optimize string "length" property access based on types.

test/unittests/compiler/js-typed-lowering-unittest.cc

 // Copyright 2014 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/code-factory.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-operator.h"
 #include "src/compiler/js-typed-lowering.h"
 #include "src/compiler/machine-operator.h"
@@ skipping 856 matching lines @@
       EXPECT_THAT(
           r.replacement(),
           IsStoreElement(
               access, IsIntPtrConstant(bit_cast<intptr_t>(&backing_store[0])),
               key, value, effect, control));
     }
   }
 }
 
 
-TEST_F(JSTypedLoweringTest, JSLoadNamedGlobalConstants) {
+// -----------------------------------------------------------------------------
+// JSLoadGlobal
+
+
+TEST_F(JSTypedLoweringTest, JSLoadGlobalConstants) {
   Handle<String> names[] = {
       Handle<String>(isolate()->heap()->undefined_string(), isolate()),
       Handle<String>(isolate()->heap()->infinity_string(), isolate()),
       Handle<String>(isolate()->heap()->nan_string(), isolate())  // --
   };
   Matcher<Node*> matches[] = {
       IsHeapConstant(Unique<HeapObject>::CreateImmovable(
           Handle<HeapObject>(isolate()->heap()->undefined_value(), isolate()))),
       IsNumberConstant(std::numeric_limits<double>::infinity()),
       IsNumberConstant(IsNaN())  // --
@@ skipping 12 matching lines @@
         javascript()->LoadGlobal(name, feedback), global, vector, context,
         EmptyFrameState(), EmptyFrameState(), effect, control));
 
     ASSERT_TRUE(r.Changed());
     EXPECT_THAT(r.replacement(), matches[i]);
   }
 }
 
 
 // -----------------------------------------------------------------------------
+// JSLoadNamed
+
+
+TEST_F(JSTypedLoweringTest, JSLoadNamedStringLength) {
+  VectorSlotPair feedback;
+  Unique<Name> name = Unique<Name>::CreateImmovable(factory()->length_string());
+  Node* const receiver = Parameter(Type::String(), 0);
+  Node* const vector = Parameter(Type::Internal(), 1);
+  Node* const context = UndefinedConstant();
+  Node* const effect = graph()->start();
+  Node* const control = graph()->start();
+  TRACED_FOREACH(LanguageMode, language_mode, kLanguageModes) {
+    Reduction const r = Reduce(
+        graph()->NewNode(javascript()->LoadNamed(name, feedback, language_mode),
+                         receiver, vector, context, EmptyFrameState(),
+                         EmptyFrameState(), effect, control));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_THAT(r.replacement(),
+                IsLoadField(AccessBuilder::ForStringLength(zone()), receiver,
+                            effect, control));
+  }
+}
+
+
+// -----------------------------------------------------------------------------
 // JSLoadDynamicGlobal
 
 
 TEST_F(JSTypedLoweringTest, JSLoadDynamicGlobal) {
   Node* const context = Parameter(Type::Any());
   Node* const vector = UndefinedConstant();
   Node* const frame_state = EmptyFrameState();
   Node* const effect = graph()->start();
   Node* const control = graph()->start();
   Handle<String> name = factory()->object_string();
@@ skipping 176 matching lines @@
   EXPECT_THAT(r.replacement(),
               IsFinish(IsAllocate(IsNumberConstant(Context::SizeFor(
                                       Context::MIN_CONTEXT_SLOTS)),
                                   effect, control),
                        _));
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8