Implement lowering of JSLoadContext to machine operators.

src/compiler/js-generic-lowering.cc

Index: src/compiler/js-generic-lowering.cc
diff --git a/src/compiler/js-generic-lowering.cc b/src/compiler/js-generic-lowering.cc
index 5085e9feb9e0ad0563b042e2dae3169de313d385..130d62591c0611d9bfbdab650b4feefaa656492e 100644
--- a/src/compiler/js-generic-lowering.cc
+++ b/src/compiler/js-generic-lowering.cc
@@ -370,9 +370,16 @@ Node* JSGenericLowering::LowerJSInstanceOf(Node* 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;
 }