Disallow tail calls from async functions and generators

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 5fabd8e25f122b960a3f72a47d400149fded36d4..8fe70b598751621ac3942f3bf4d8d8bc1c135d02 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -2505,7 +2505,7 @@ Statement* Parser::ParseReturnStatement(bool* ok) {
           function_state_, ReturnExprContext::kInsideValidReturnStatement);
       return_value = ParseExpression(true, CHECK_OK);
 
-      if (allow_tailcalls() && !is_sloppy(language_mode())) {
+      if (allow_tailcalls() && !is_sloppy(language_mode()) && !is_resumable()) {
         // ES6 14.6.1 Static Semantics: IsInTailPosition
         function_state_->AddImplicitTailCallExpression(return_value);
       }