Disallow tail calls from async functions and generators

Tail calls don't make sense from async functions and generators, as
each activation of these functions needs to make a new, distnict,
non-reused generator object. These tail calls are not required per
spec. This patch disables both syntactic and implicit tail calls
in async functions and generators.

R=neis
BUG=v8:5301,chromium:639270

Review-Url: https://codereview.chromium.org/2278413003
Cr-Commit-Position: refs/heads/master@{#38986}

src/parsing/parser-base.h

@@ -2548,6 +2548,7 @@ ParserBase<Impl>::ParseTailCallExpression(ExpressionClassifier* classifier,
   CheckNoTailCallExpressions(classifier, CHECK_OK);
 
   Scanner::Location loc(pos, scanner()->location().end_pos);
+
   if (!expression->IsCall()) {
     Scanner::Location sub_loc(sub_expression_pos, loc.end_pos);
     impl()->ReportMessageAt(sub_loc,
@@ -2567,6 +2568,12 @@ ParserBase<Impl>::ParseTailCallExpression(ExpressionClassifier* classifier,
     *ok = false;
     return impl()->EmptyExpression();
   }
+  if (is_resumable()) {
+    Scanner::Location sub_loc(sub_expression_pos, loc.end_pos);
+    impl()->ReportMessageAt(sub_loc, MessageTemplate::kUnexpectedTailCall);
+    *ok = false;
+    return impl()->EmptyExpression();
+  }
   ReturnExprContext return_expr_context =
       function_state_->return_expr_context();
   if (return_expr_context != ReturnExprContext::kInsideValidReturnStatement) {

src/parsing/parser.cc

@@ -2369,7 +2369,7 @@ 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);
       }

test/message/syntactic-tail-call-generator.js

+// Copyright 2016 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.
+
+// Flags: --harmony-explicit-tailcalls
+
+function f() {
+  return 1;
+}
+
+function* g() {
+  'use strict';
+  return continue f();
+}

test/message/syntactic-tail-call-generator.out

+*%(basename)s:13: SyntaxError: Tail call expression is not allowed here
+  return continue f();
+                  ^^^
+SyntaxError: Tail call expression is not allowed here 

test/mjsunit/es8/syntactic-tail-call-parsing.js

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // Flags: --allow-natives-syntax --harmony-explicit-tailcalls
-// Flags: --harmony-do-expressions
+// Flags: --harmony-do-expressions --harmony-async-await
 "use strict";
 
 var SyntaxErrorTests = [
@@ -128,7 +128,10 @@ var SyntaxErrorTests = [
         err: `                    ^^^^^^^^^^^^^^`,
       },
       { src: `()=>{ function* G() { yield continue foo(); } }`,
-        err: `                            ^^^^^^^^^^^^^^`,
+        err: `                                     ^^^^^`,
+      },
+      { src: `()=>{ function* G() { return continue foo(); } }`,
+        err: `                                      ^^^^^`,
       },
       { src: `()=>{ (1, 2, 3, continue f() ) => {} }`,
         err: `                ^^^^^^^^^^^^`,
@@ -235,6 +238,9 @@ var SyntaxErrorTests = [
       { src: `class A extends continue f () {}; }`,
         err: `                ^^^^^^^^^^^^^`,
       },
+      { src: `async() => continue foo()`,
+        err: `                    ^^^^^`,
+      },
     ],
   },
   { msg: "Tail call expression in try block",
@@ -311,7 +317,6 @@ var NoErrorTests = [
   `()=>{ return a || continue f() ; }`,
   `()=>{ return a && continue f() ; }`,
   `()=>{ return a , continue f() ; }`,
-  `()=>{ function* G() { return continue foo(); } }`,
   `()=>{ class A { foo() { return continue super.f() ; } } }`,
   `()=>{ function B() { return continue new.target() ; } }`,
   `()=>{ return continue do { x ? foo() : bar() ; }() }`,

test/mjsunit/regress/regress-639270.js

+// Copyright 2016 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.
+
+// Flags: --allow-natives-syntax --es-staging --ignition-staging --turbo
+
+"use strict";
+
+var g = (async () => { return JSON.stringify() });
+
+g();
+g();
+%OptimizeFunctionOnNextCall(g);
+g();