[turbofan] Specialize loads of the native context.

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 20 matching lines @@
       jsgraph_(jsgraph),
       flags_(flags),
       native_context_(native_context),
       dependencies_(dependencies),
       zone_(zone),
       type_cache_(TypeCache::Get()) {}
 
 
 Reduction JSNativeContextSpecialization::Reduce(Node* node) {
   switch (node->opcode()) {
+    case IrOpcode::kJSLoadContext:
+      return ReduceJSLoadContext(node);
     case IrOpcode::kJSLoadNamed:
       return ReduceJSLoadNamed(node);
     case IrOpcode::kJSStoreNamed:
       return ReduceJSStoreNamed(node);
     case IrOpcode::kJSLoadProperty:
       return ReduceJSLoadProperty(node);
     case IrOpcode::kJSStoreProperty:
       return ReduceJSStoreProperty(node);
     default:
       break;
   }
   return NoChange();
 }
 
+Reduction JSNativeContextSpecialization::ReduceJSLoadContext(Node* node) {
+  DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode());
+  ContextAccess const& access = ContextAccessOf(node->op());
+  Handle<Context> native_context;
+  // Specialize JSLoadContext(NATIVE_CONTEXT_INDEX) to the known native
+  // context (if any), so we can constant-fold those fields, which is
+  // safe, since the NATIVE_CONTEXT_INDEX slot is always immutable.
+  if (access.index() == Context::NATIVE_CONTEXT_INDEX &&
+      GetNativeContext(node).ToHandle(&native_context)) {
+    Node* value = jsgraph()->HeapConstant(native_context);
+    ReplaceWithValue(node, value);
+    return Replace(value);
+  }
+  return NoChange();
+}
 
 Reduction JSNativeContextSpecialization::ReduceNamedAccess(
     Node* node, Node* value, MapHandleList const& receiver_maps,
     Handle<Name> name, AccessMode access_mode, LanguageMode language_mode,
     Node* index) {
   DCHECK(node->opcode() == IrOpcode::kJSLoadNamed ||
          node->opcode() == IrOpcode::kJSStoreNamed ||
          node->opcode() == IrOpcode::kJSLoadProperty ||
          node->opcode() == IrOpcode::kJSStoreProperty);
   Node* receiver = NodeProperties::GetValueInput(node, 0);
@@ skipping 961 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSNativeContextSpecialization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8