[interpreter] Don't assume generator functions do an initial yield.

src/interpreter/bytecode-generator.cc

 // Copyright 2015 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/interpreter/bytecode-generator.h"
 
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-flags.h"
@@ skipping 858 matching lines @@
       .JumpIfUndefined(&regular_call);
 
   // This is a resume call. Restore registers and perform state dispatch.
   // (The current context has already been restored by the trampoline.)
   builder()
       ->ResumeGenerator(generator_object)
       .StoreAccumulatorInRegister(generator_state_);
   BuildIndexedJump(generator_state_, 0, generator_resume_points_.size(),
                    generator_resume_points_);
 
-  builder()->Bind(&regular_call);
+  builder()
+      ->Bind(&regular_call)
+      .LoadLiteral(Smi::FromInt(JSGeneratorObject::kGeneratorExecuting))
+      .StoreAccumulatorInRegister(generator_state_);

[Dan Ehrenberg, 2016/08/17 13:44:34]

Looks like you're doing this extra load/store for generators too, not just async
functions, is this right? Seems fine but very slightly suboptimal.

[rmcilroy, 2016/08/17 13:53:40]

+1

   // This is a regular call. Fall through to the ordinary function prologue,
   // after which we will run into the generator object creation and other extra
   // code inserted by the parser.
 }
 
 void BytecodeGenerator::VisitBlock(Block* stmt) {
   // Visit declarations and statements.
   if (stmt->scope() != nullptr && stmt->scope()->NeedsContext()) {
     VisitNewLocalBlockContext(stmt->scope());
     ContextScope scope(this, stmt->scope());
@@ skipping 2532 matching lines @@
   return execution_context()->scope()->language_mode();
 }
 
 int BytecodeGenerator::feedback_index(FeedbackVectorSlot slot) const {
   return TypeFeedbackVector::GetIndex(slot);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8