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

src/compiler/js-typed-lowering.cc

Index: src/compiler/js-typed-lowering.cc
diff --git a/src/compiler/js-typed-lowering.cc b/src/compiler/js-typed-lowering.cc
index d7d0f57fc9047bcd9332ff99cffb6da290482a82..2f100e9fcacd4b349c06c8dca0bfa8f562031349 100644
--- a/src/compiler/js-typed-lowering.cc
+++ b/src/compiler/js-typed-lowering.cc
@@ -1507,16 +1507,17 @@ 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())));
@@ -1527,20 +1528,21 @@ 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) {
@@ -1648,10 +1650,10 @@ Reduction JSTypedLowering::ReduceJSConvertReceiver(Node* node) {
     } 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);
@@ -1753,10 +1755,10 @@ Reduction JSTypedLowering::ReduceJSConvertReceiver(Node* node) {
     } 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);
     }
   }