[turbofan] Relax constraints on apply with arguments optimization.

src/compiler/js-call-reducer.cc

Index: src/compiler/js-call-reducer.cc
diff --git a/src/compiler/js-call-reducer.cc b/src/compiler/js-call-reducer.cc
index a529464cbd1fa51844970fe3ce997456ba0b400c..cd0ba00790bb0ffc23258a9a975cb85249fcca91 100644
--- a/src/compiler/js-call-reducer.cc
+++ b/src/compiler/js-call-reducer.cc
@@ -134,16 +134,25 @@ Reduction JSCallReducer::ReduceFunctionPrototypeApply(Node* node) {
     CreateArgumentsType const type = CreateArgumentsTypeOf(arg_array->op());
     Node* frame_state = NodeProperties::GetFrameStateInput(arg_array);
     FrameStateInfo state_info = OpParameter<FrameStateInfo>(frame_state);
-    int formal_parameter_count;
     int start_index = 0;
-    {
-      Handle<SharedFunctionInfo> shared;
-      if (!state_info.shared_info().ToHandle(&shared)) return NoChange();
-      formal_parameter_count = shared->internal_formal_parameter_count();
-    }
+    // Determine the formal parameter count;
+    Handle<SharedFunctionInfo> shared;
+    if (!state_info.shared_info().ToHandle(&shared)) return NoChange();
+    int formal_parameter_count = shared->internal_formal_parameter_count();
     if (type == CreateArgumentsType::kMappedArguments) {
-      // Mapped arguments (sloppy mode) cannot be handled if they are aliased.
-      if (formal_parameter_count != 0) return NoChange();
+      // Mapped arguments (sloppy mode) that are aliased can only be handled
+      // here if there's no side-effect between the {node} and the {arg_array}.
+      // TODO(turbofan): Further relax this constraint.
+      if (formal_parameter_count != 0) {
+        Node* effect = NodeProperties::GetEffectInput(node);

[danno, 2017/04/04 07:55:11]

Does it make sense to turn this into a predicate? e.g. 

if (NodeProperties::HasWriteEffectBetween(node, arg_array)) return NoChange(); 

[Benedikt Meurer, 2017/04/04 08:02:14]

Given that we might want to relax the constraints here, which would mean looking
closer at the specific operation in effect, this predicate wouldn't be used here
long-/middle-term.

+        while (effect != arg_array) {
+          if (effect->op()->EffectInputCount() != 1 ||
+              !(effect->op()->properties() & Operator::kNoWrite)) {
+            return NoChange();
+          }
+          effect = NodeProperties::GetEffectInput(effect);
+        }
+      }
     } else if (type == CreateArgumentsType::kRestParameter) {
       start_index = formal_parameter_count;
     }