Implement lowering of JSLoadContext to machine operators.

src/compiler/js-generic-lowering.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-stubs.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph-inl.h"
 #include "src/compiler/js-generic-lowering.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node-aux-data-inl.h"
@@ skipping 352 matching lines @@
   CallDescriptor* desc = linkage()->GetStubCallDescriptor(d, 0);
   Node* stub_code = CodeConstant(stub.GetCode());
   PatchInsertInput(node, 0, stub_code);
   PatchOperator(node, common()->Call(desc));
   return node;
 }
 
 
 Node* JSGenericLowering::LowerJSLoadContext(Node* node) {
   ContextAccess access = OpParameter<ContextAccess>(node);
-  PatchInsertInput(node, 1, SmiConstant(access.depth()));
-  PatchInsertInput(node, 2, SmiConstant(access.index()));
-  ReplaceWithRuntimeCall(node, Runtime::kLoadContextRelative, 3);
+  // TODO(mstarzinger): Use simplified operators instead of machine operators
+  // here so that load/store optimization can be applied afterwards.
+  for (int i = 0; i < access.depth(); ++i) {
+    node->ReplaceInput(
+        0, graph()->NewNode(
+               machine()->Load(kMachineTagged),
+               NodeProperties::GetValueInput(node, 0),
+               Int32Constant(Context::SlotOffset(Context::PREVIOUS_INDEX)),
+               NodeProperties::GetEffectInput(node)));
+  }
+  node->ReplaceInput(1, Int32Constant(Context::SlotOffset(access.index())));
+  PatchOperator(node, machine()->Load(kMachineTagged));
   return node;
 }
 
 
 Node* JSGenericLowering::LowerJSStoreContext(Node* node) {
   ContextAccess access = OpParameter<ContextAccess>(node);
   PatchInsertInput(node, 1, SmiConstant(access.depth()));
   PatchInsertInput(node, 2, SmiConstant(access.index()));
   ReplaceWithRuntimeCall(node, Runtime::kStoreContextRelative, 4);
   return node;
@@ skipping 30 matching lines @@
 
 Node* JSGenericLowering::LowerJSCallRuntime(Node* node) {
   Runtime::FunctionId function = OpParameter<Runtime::FunctionId>(node);
   int arity = NodeProperties::GetValueInputCount(node);
   ReplaceWithRuntimeCall(node, function, arity);
   return node;
 }
 }
 }
 }  // namespace v8::internal::compiler