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);
+  for (int i = 0; i < access.depth(); ++i) {

[titzer, 2014/07/31 11:02:16]

Please leave a TODO here because I think we want to lower this to
SimplifiedOperators first so that we have a little more information for GVN and
load/store elimination.

[Michael Starzinger, 2014/07/31 11:18:32]

Done.

+    node->ReplaceInput(
+        0, graph()->NewNode(
+               machine()->Load(machine()->word()),

[titzer, 2014/07/31 11:02:16]

You need kMachineTagged here, otherwise the register allocator won't track it as
a pointer.

[Michael Starzinger, 2014/07/31 11:18:32]

Done. Nice catch.

+               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(machine()->word()));
   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