Make non-Module generators only context allocate parameters.

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 <algorithm>
 #include <memory>
 
 #include "src/api.h"
@@ skipping 688 matching lines @@
       bool is_duplicate;
       bool is_rest = false;
       bool is_optional = false;
       auto var =
           scope->DeclareParameter(name, VAR, is_optional, is_rest,
                                   &is_duplicate, ast_value_factory(), beg_pos);
       DCHECK(!is_duplicate);
       var->AllocateTo(VariableLocation::PARAMETER, 0);
 
       PrepareGeneratorVariables();
+      scope->ForceContextAllocation();
       Expression* initial_yield =
           BuildInitialYield(kNoSourcePosition, kGeneratorFunction);
       body->Add(
           factory()->NewExpressionStatement(initial_yield, kNoSourcePosition),
           zone());
 
       ParseModuleItemList(body, &ok);
       ok = ok &&
            module()->Validate(this->scope()->AsModuleScope(),
                               &pending_error_handler_, zone());
@@ skipping 1807 matching lines @@
   if (!this->classifier()
            ->is_valid_formal_parameter_list_without_duplicates()) {
     *duplicate_loc =
         this->classifier()->duplicate_formal_parameter_error().location;
   }
   DCHECK_EQ(parameters->is_simple, parameters->scope->has_simple_parameters());
 }
 
 void Parser::PrepareGeneratorVariables() {
   // For generators, allocating variables in contexts is currently a win because
   // it minimizes the work needed to suspend and resume an activation.  The

[adamk, 2017/05/23 20:20:38]

This first sentence is now obsolete, and should be removed; I think the rest of
the comment stands on its own.

[Jarin, 2017/05/24 05:03:27]

Done.

   // code produced for generators relies on this forced context allocation (it
   // does not restore the frame's parameters upon resume).
-  function_state_->scope()->ForceContextAllocation();
+  function_state_->scope()->ForceContextAllocationForParameters();
 
   // Calling a generator returns a generator object.  That object is stored
   // in a temporary variable, a definition that is used by "yield"
   // expressions.
   function_state_->scope()->DeclareGeneratorObjectVar(
       ast_value_factory()->dot_generator_object_string());
 }
 
 FunctionLiteral* Parser::ParseFunctionLiteral(
     const AstRawString* function_name, Scanner::Location function_name_location,
@@ skipping 2594 matching lines @@
     literal->SetShouldEagerCompile();
   }
 }
 
 #undef CHECK_OK
 #undef CHECK_OK_VOID
 #undef CHECK_FAILED
 
 }  // namespace internal
 }  // namespace v8