[compiler] Remove context value input from JSLoadContext and JSStoreContext.

src/compiler/js-typed-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/compiler/js-typed-lowering.h"
 
 #include "src/ast/modules.h"
 #include "src/builtins/builtins-utils.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
@@ skipping 1489 matching lines @@
   node->TrimInputCount(6);
   NodeProperties::ChangeOp(node,
                            common()->Phi(MachineRepresentation::kTagged, 5));
   return Changed(node);
 }
 
 Reduction JSTypedLowering::ReduceJSLoadContext(Node* node) {
   DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode());
   ContextAccess const& access = ContextAccessOf(node->op());
   Node* effect = NodeProperties::GetEffectInput(node);
+  Node* context = NodeProperties::GetContextInput(node);
   Node* control = graph()->start();
   for (size_t i = 0; i < access.depth(); ++i) {
-    Node* previous = effect = graph()->NewNode(
+    context = effect = graph()->NewNode(
         simplified()->LoadField(
             AccessBuilder::ForContextSlot(Context::PREVIOUS_INDEX)),
-        NodeProperties::GetValueInput(node, 0), effect, control);
-    node->ReplaceInput(0, previous);
+        context, effect, control);
   }
+  node->ReplaceInput(0, context);
   node->ReplaceInput(1, effect);
-  node->ReplaceInput(2, control);
+  node->AppendInput(jsgraph()->zone(), control);
   NodeProperties::ChangeOp(
       node,
       simplified()->LoadField(AccessBuilder::ForContextSlot(access.index())));
   return Changed(node);
 }
 
 Reduction JSTypedLowering::ReduceJSStoreContext(Node* node) {
   DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode());
   ContextAccess const& access = ContextAccessOf(node->op());
   Node* effect = NodeProperties::GetEffectInput(node);
+  Node* context = NodeProperties::GetContextInput(node);
   Node* control = graph()->start();
   for (size_t i = 0; i < access.depth(); ++i) {
-    Node* previous = effect = graph()->NewNode(
+    context = effect = graph()->NewNode(
         simplified()->LoadField(
             AccessBuilder::ForContextSlot(Context::PREVIOUS_INDEX)),
-        NodeProperties::GetValueInput(node, 0), effect, control);
-    node->ReplaceInput(0, previous);
+        context, effect, control);
   }
+  node->InsertInput(jsgraph()->zone(), 0, context);

[Michael Starzinger, 2016/11/30 12:43:28]

nit: First inserting and then removing an input is most likely less efficient
then just replacing all inputs. Also I think readability is improved by listing
all new inputs. I was thinking along the lines of ...

node->ReplaceInput(node, 0, context);
node->ReplaceInput(node, 1, value);
node->ReplaceInput(node, 2, effect)

The "effect" is already at the right place, but needs to be updated with the new
effect produced above. The "control" should already be in the right place and
can remain unchanged. The "value" should be loaded at the top of the function
before any mutation.

   node->RemoveInput(2);
   node->ReplaceInput(2, effect);
   NodeProperties::ChangeOp(
       node,
       simplified()->StoreField(AccessBuilder::ForContextSlot(access.index())));
-  return Changed(node);
+  return Changed(node);  // control??

[Michael Starzinger, 2016/11/30 12:43:28]

explanation: The {JSStoreContext} operators are marked as taking one control
input whereas {JSLoadContext} take zero control inputs. Hence the asymmetry
here.

 }
 
 Reduction JSTypedLowering::ReduceJSLoadModule(Node* node) {
   DCHECK_EQ(IrOpcode::kJSLoadModule, node->opcode());
   Node* effect = NodeProperties::GetEffectInput(node);
   Node* control = NodeProperties::GetControlInput(node);
 
   int32_t cell_index = OpParameter<int32_t>(node);
   Node* module = NodeProperties::GetValueInput(node, 0);
 
@@ skipping 87 matching lines @@
       mode == ConvertReceiverMode::kNullOrUndefined) {
     if (context_type->IsHeapConstant()) {
       Handle<JSObject> global_proxy(
           Handle<Context>::cast(context_type->AsHeapConstant()->Value())
               ->global_proxy(),
           isolate());
       receiver = jsgraph()->Constant(global_proxy);
     } else {
       Node* native_context = effect = graph()->NewNode(
           javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true),
-          context, context, effect);
+          context, effect);
       receiver = effect = graph()->NewNode(
           javascript()->LoadContext(0, Context::GLOBAL_PROXY_INDEX, true),
-          native_context, native_context, effect);
+          native_context, effect);
     }
     ReplaceWithValue(node, receiver, effect, control);
     return Replace(receiver);
   }
 
   // If {receiver} cannot be null or undefined we can skip a few checks.
   if (!receiver_type->Maybe(Type::NullOrUndefined()) ||
       mode == ConvertReceiverMode::kNotNullOrUndefined) {
     Node* check = graph()->NewNode(simplified()->ObjectIsReceiver(), receiver);
     Node* branch =
@@ skipping 81 matching lines @@
   {
     if (context_type->IsHeapConstant()) {
       Handle<JSObject> global_proxy(
           Handle<Context>::cast(context_type->AsHeapConstant()->Value())
               ->global_proxy(),
           isolate());
       rglobal = jsgraph()->Constant(global_proxy);
     } else {
       Node* native_context = eglobal = graph()->NewNode(
           javascript()->LoadContext(0, Context::NATIVE_CONTEXT_INDEX, true),
-          context, context, eglobal);
+          context, eglobal);
       rglobal = eglobal = graph()->NewNode(
           javascript()->LoadContext(0, Context::GLOBAL_PROXY_INDEX, true),
-          native_context, native_context, eglobal);
+          native_context, eglobal);
     }
   }
 
   control =
       graph()->NewNode(common()->Merge(3), if_noop, if_convert, if_global);
   effect = graph()->NewNode(common()->EffectPhi(3), enoop, econvert, eglobal,
                             control);
   // Morph the {node} into an appropriate Phi.
   ReplaceWithValue(node, node, effect, control);
   node->ReplaceInput(0, rnoop);
@@ skipping 535 matching lines @@
 }
 
 
 CompilationDependencies* JSTypedLowering::dependencies() const {
   return dependencies_;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8