Track usage of "this" and "arguments" in Scope

src/scopes.cc

Index: src/scopes.cc
diff --git a/src/scopes.cc b/src/scopes.cc
index de364a5b489050408dd04a32c308054566ae9fec..fd803b3e5281ed02abb692b7fa3d4bed94e94390 100644
--- a/src/scopes.cc
+++ b/src/scopes.cc
@@ -160,12 +160,16 @@ void Scope::SetDefaults(ScopeType scope_type,
   scope_inside_with_ = false;
   scope_contains_with_ = false;
   scope_calls_eval_ = false;
+  scope_uses_this_ = false;
+  scope_uses_arguments_ = false;
   asm_module_ = false;
   asm_function_ = outer_scope != NULL && outer_scope->asm_module_;
   // Inherit the strict mode from the parent scope.
   strict_mode_ = outer_scope != NULL ? outer_scope->strict_mode_ : SLOPPY;
   outer_scope_calls_sloppy_eval_ = false;
   inner_scope_calls_eval_ = false;
+  inner_scope_uses_this_ = false;
+  inner_scope_uses_arguments_ = false;
   force_eager_compilation_ = false;
   force_context_allocation_ = (outer_scope != NULL && !is_function_scope())
       ? outer_scope->has_forced_context_allocation() : false;
@@ -779,6 +783,7 @@ static const char* Header(ScopeType scope_type) {
     case CATCH_SCOPE: return "catch";
     case BLOCK_SCOPE: return "block";
     case WITH_SCOPE: return "with";
+    case ARROW_SCOPE: return "arrow";
   }
   UNREACHABLE();
   return NULL;
@@ -885,6 +890,12 @@ void Scope::Print(int n) {
   if (scope_inside_with_) Indent(n1, "// scope inside 'with'\n");
   if (scope_contains_with_) Indent(n1, "// scope contains 'with'\n");
   if (scope_calls_eval_) Indent(n1, "// scope calls 'eval'\n");
+  if (scope_uses_this_) Indent(n1, "// scope uses 'this'\n");
+  if (scope_uses_arguments_) Indent(n1, "// scope uses 'arguments'\n");
+  if (inner_scope_uses_this_) Indent(n1, "// inner scope uses 'this'\n");
+  if (inner_scope_uses_arguments_) {
+    Indent(n1, "// inner scope uses 'arguments'\n");
+  }
   if (outer_scope_calls_sloppy_eval_) {
     Indent(n1, "// outer scope calls 'eval' in sloppy context\n");
   }
@@ -1166,6 +1177,17 @@ void Scope::PropagateScopeInfo(bool outer_scope_calls_sloppy_eval ) {
     if (inner->scope_calls_eval_ || inner->inner_scope_calls_eval_) {
       inner_scope_calls_eval_ = true;
     }
+    // If the inner scope is an arrow function, propagate the flags tracking
+    // usage of this/arguments, but do not propagate them out from normal
+    // functions.
+    if (!inner->is_function_scope() || inner->is_arrow_scope()) {
+      if (inner->scope_uses_this_ || inner->inner_scope_uses_this_) {
+        inner_scope_uses_this_ = true;
+      }
+      if (inner->scope_uses_arguments_ || inner->inner_scope_uses_arguments_) {
+        inner_scope_uses_arguments_ = true;
+      }
+    }
     if (inner->force_eager_compilation_) {
       force_eager_compilation_ = true;
     }