[async-await] (simpler) fix for Return in try/finally in async functions

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/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/builtins/builtins-constructor.h"
 #include "src/code-stubs.h"
@@ skipping 88 matching lines @@
   explicit ControlScope(BytecodeGenerator* generator)
       : generator_(generator), outer_(generator->execution_control()),
         context_(generator->execution_context()) {
     generator_->set_execution_control(this);
   }
   virtual ~ControlScope() { generator_->set_execution_control(outer()); }
 
   void Break(Statement* stmt) { PerformCommand(CMD_BREAK, stmt); }
   void Continue(Statement* stmt) { PerformCommand(CMD_CONTINUE, stmt); }
   void ReturnAccumulator() { PerformCommand(CMD_RETURN, nullptr); }
+  void AsyncReturnAccumulator() { PerformCommand(CMD_ASYNC_RETURN, nullptr); }
   void ReThrowAccumulator() { PerformCommand(CMD_RETHROW, nullptr); }
 
   class DeferredCommands;
 
  protected:
-  enum Command { CMD_BREAK, CMD_CONTINUE, CMD_RETURN, CMD_RETHROW };
+  enum Command {
+    CMD_BREAK,
+    CMD_CONTINUE,
+    CMD_RETURN,
+    CMD_ASYNC_RETURN,
+    CMD_RETHROW
+  };
   void PerformCommand(Command command, Statement* statement);
   virtual bool Execute(Command command, Statement* statement) = 0;
 
   BytecodeGenerator* generator() const { return generator_; }
   ControlScope* outer() const { return outer_; }
   ContextScope* context() const { return context_; }
 
  private:
   BytecodeGenerator* generator_;
   ControlScope* outer_;
@@ skipping 89 matching lines @@
 
  protected:
   bool Execute(Command command, Statement* statement) override {
     switch (command) {
       case CMD_BREAK:  // We should never see break/continue in top-level.
       case CMD_CONTINUE:
         UNREACHABLE();
       case CMD_RETURN:
         generator()->BuildReturn();
         return true;
+      case CMD_ASYNC_RETURN:
+        generator()->BuildAsyncReturn();
+        return true;
       case CMD_RETHROW:
         generator()->BuildReThrow();
         return true;
     }
     return false;
   }
 };
 
 // Scoped class for enabling break inside blocks and switch blocks.
 class BytecodeGenerator::ControlScopeForBreakable final
     : public BytecodeGenerator::ControlScope {
  public:
   ControlScopeForBreakable(BytecodeGenerator* generator,
                            BreakableStatement* statement,
                            BreakableControlFlowBuilder* control_builder)
       : ControlScope(generator),
         statement_(statement),
         control_builder_(control_builder) {}
 
  protected:
   bool Execute(Command command, Statement* statement) override {
     if (statement != statement_) return false;
     switch (command) {
       case CMD_BREAK:
         control_builder_->Break();
         return true;
       case CMD_CONTINUE:
       case CMD_RETURN:
+      case CMD_ASYNC_RETURN:
       case CMD_RETHROW:
         break;
     }
     return false;
   }
 
  private:
   Statement* statement_;
   BreakableControlFlowBuilder* control_builder_;
 };
@@ skipping 17 matching lines @@
   bool Execute(Command command, Statement* statement) override {
     if (statement != statement_) return false;
     switch (command) {
       case CMD_BREAK:
         loop_builder_->Break();
         return true;
       case CMD_CONTINUE:
         loop_builder_->Continue();
         return true;
       case CMD_RETURN:
+      case CMD_ASYNC_RETURN:
       case CMD_RETHROW:
         break;
     }
     return false;
   }
 
  private:
   Statement* statement_;
   LoopBuilder* loop_builder_;
 };
 
 // Scoped class for enabling 'throw' in try-catch constructs.
 class BytecodeGenerator::ControlScopeForTryCatch final
     : public BytecodeGenerator::ControlScope {
  public:
   ControlScopeForTryCatch(BytecodeGenerator* generator,
                           TryCatchBuilder* try_catch_builder)
       : ControlScope(generator) {}
 
  protected:
   bool Execute(Command command, Statement* statement) override {
     switch (command) {
       case CMD_BREAK:
       case CMD_CONTINUE:
       case CMD_RETURN:
+      case CMD_ASYNC_RETURN:
         break;
       case CMD_RETHROW:
         generator()->BuildReThrow();
         return true;
     }
     return false;
   }
 };
 
 // Scoped class for enabling control flow through try-finally constructs.
 class BytecodeGenerator::ControlScopeForTryFinally final
     : public BytecodeGenerator::ControlScope {
  public:
   ControlScopeForTryFinally(BytecodeGenerator* generator,
                             TryFinallyBuilder* try_finally_builder,
                             DeferredCommands* commands)
       : ControlScope(generator),
         try_finally_builder_(try_finally_builder),
         commands_(commands) {}
 
  protected:
   bool Execute(Command command, Statement* statement) override {
     switch (command) {
       case CMD_BREAK:
       case CMD_CONTINUE:
       case CMD_RETURN:
+      case CMD_ASYNC_RETURN:
       case CMD_RETHROW:
         commands_->RecordCommand(command, statement);
         try_finally_builder_->LeaveTry();
         return true;
     }
     return false;
   }
 
  private:
   TryFinallyBuilder* try_finally_builder_;
@@ skipping 701 matching lines @@
 }
 
 void BytecodeGenerator::VisitBreakStatement(BreakStatement* stmt) {
   builder()->SetStatementPosition(stmt);
   execution_control()->Break(stmt->target());
 }
 
 void BytecodeGenerator::VisitReturnStatement(ReturnStatement* stmt) {
   builder()->SetStatementPosition(stmt);
   VisitForAccumulatorValue(stmt->expression());
+
+  if (stmt->is_async_return()) {
+    return execution_control()->AsyncReturnAccumulator();
+  }
+
   execution_control()->ReturnAccumulator();

[rmcilroy, 2017/02/09 23:31:45]

nit - could you make this: 
if (stmt->is_async_return()) {
  execution_control()->AsyncReturnAccumulator();
} else {
  execution_control()->ReturnAccumulator();
}

[caitp, 2017/02/10 01:20:01]

Done

 }
 
 void BytecodeGenerator::VisitWithStatement(WithStatement* stmt) {
   builder()->SetStatementPosition(stmt);
   VisitForAccumulatorValue(stmt->expression());
   BuildNewLocalWithContext(stmt->scope());
   VisitInScope(stmt->statement(), stmt->scope());
 }
 
 void BytecodeGenerator::VisitSwitchStatement(SwitchStatement* stmt) {
@@ skipping 922 matching lines @@
   if (FLAG_trace) {
     RegisterAllocationScope register_scope(this);
     Register result = register_allocator()->NewRegister();
     // Runtime returns {result} value, preserving accumulator.
     builder()->StoreAccumulatorInRegister(result).CallRuntime(
         Runtime::kTraceExit, result);
   }
   builder()->Return();
 }
 
+void BytecodeGenerator::BuildAsyncReturn() {
+  DCHECK(IsAsyncFunction(info()->literal()->kind()));
+  RegisterAllocationScope register_scope(this);
+  RegisterList args = register_allocator()->NewRegisterList(3);
+  Register receiver = args[0];
+  Register promise = args[1];
+  Register return_value = args[2];
+  builder()->StoreAccumulatorInRegister(return_value);
+
+  Variable* var_promise = scope()->promise_var();
+  DCHECK_NOT_NULL(var_promise);
+  BuildVariableLoad(var_promise, FeedbackSlot::Invalid(),
+                    HoleCheckMode::kElided);
+  builder()
+      ->StoreAccumulatorInRegister(promise)
+      .LoadUndefined()
+      .StoreAccumulatorInRegister(receiver)
+      .CallJSRuntime(Context::PROMISE_RESOLVE_INDEX, args)
+      .LoadAccumulatorWithRegister(promise);
+  BuildReturn();
+}
+
 void BytecodeGenerator::BuildReThrow() { builder()->ReThrow(); }
 
 void BytecodeGenerator::BuildAbort(BailoutReason bailout_reason) {
   RegisterAllocationScope register_scope(this);
   Register reason = register_allocator()->NewRegister();
   builder()
       ->LoadLiteral(Smi::FromInt(static_cast<int>(bailout_reason)))
       .StoreAccumulatorInRegister(reason)
       .CallRuntime(Runtime::kAbort, reason);
 }
@@ skipping 1367 matching lines @@
 }
 
 Runtime::FunctionId BytecodeGenerator::StoreKeyedToSuperRuntimeId() {
   return is_strict(language_mode()) ? Runtime::kStoreKeyedToSuper_Strict
                                     : Runtime::kStoreKeyedToSuper_Sloppy;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8