[es8] Prepare explicit tail calls (STC) for staging with implicit tail calls (PTC).

src/parsing/parser.cc

 // Copyright 2012 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.
 
 #include "src/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-rewriter.h"
 #include "src/ast/ast-expression-visitor.h"
@@ skipping 2639 matching lines @@
       return_value = factory()->NewConditional(
           is_undefined, ThisExpression(scope_, factory(), pos),
           is_object_conditional, pos);
     } else {
       ReturnExprScope maybe_allow_tail_calls(
           function_state_, ReturnExprContext::kInsideValidReturnStatement);
       return_value = ParseExpression(true, CHECK_OK);
 
       if (allow_tailcalls() && !is_sloppy(language_mode())) {
         // ES6 14.6.1 Static Semantics: IsInTailPosition
-        Scanner::Location loc(pos, pos + 1);
-        function_state_->AddExpressionInTailPosition(return_value, loc);
+        function_state_->AddImplicitTailCallExpression(return_value);
       }
     }
   }
   ExpectSemicolon(CHECK_OK);
 
   if (is_generator()) {
     return_value = BuildIteratorResult(return_value, true);
   }
 
   result = factory()->NewReturnStatement(return_value, loc.beg_pos);
@@ skipping 310 matching lines @@
     // to the list of return expressions.
     function_state_->tail_call_expressions().Append(
         tail_call_expressions_in_catch_block);
 
     DCHECK(finally_block == NULL);
     DCHECK(catch_scope != NULL && catch_variable != NULL);
     result = factory()->NewTryCatchStatement(try_block, catch_scope,
                                              catch_variable, catch_block, pos);
   } else {
     if (FLAG_harmony_explicit_tailcalls &&
-        !tail_call_expressions_in_catch_block.is_empty()) {
+        tail_call_expressions_in_catch_block.has_explicit_tail_calls()) {
       // TODO(ishell): update chapter number.
       // ES8 XX.YY.ZZ
       ReportMessageAt(tail_call_expressions_in_catch_block.location(),
                       MessageTemplate::kUnexpectedTailCallInCatchBlock);
       *ok = false;
       return NULL;
     }
     DCHECK(finally_block != NULL);
     result = factory()->NewTryFinallyStatement(try_block, finally_block, pos);
   }
@@ skipping 3814 matching lines @@
                         try_block, target);
     final_loop = target;
   }
 
   return final_loop;
 }
 
 
 }  // namespace internal
 }  // namespace v8