Introduce await

runtime/vm/ast_transformer.cc

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/ast_transformer.h"
+
+#include "vm/parser.h"
+
+namespace dart {
+
+// Quick access to the locally defined isolate() method.
+#define I (isolate())
+
+// Nodes that are unreachable from already parsed expressions.
+#define FOR_EACH_UNREACHABLE_NODE(V)                                           \
+  V(Case)                                                                      \
+  V(CatchClause)                                                               \
+  V(CloneContext)                                                              \
+  V(ClosureCall)                                                               \
+  V(DoWhile)                                                                   \
+  V(If)                                                                        \
+  V(InlinedFinally)                                                            \
+  V(For)                                                                       \
+  V(Jump)                                                                      \
+  V(LoadInstanceField)                                                         \
+  V(NativeBody)                                                                \
+  V(Primary)                                                                   \
+  V(Return)                                                                    \
+  V(Sequence)                                                                  \
+  V(StoreInstanceField)                                                        \
+  V(Switch)                                                                    \
+  V(TryCatch)                                                                  \
+  V(While)
+
+#define DEFINE_UNREACHABLE(BaseName)                                           \
+void AwaitTransformer::Visit##BaseName##Node(BaseName##Node* node) {           \
+  UNREACHABLE();                                                               \
+}
+
+FOR_EACH_UNREACHABLE_NODE(DEFINE_UNREACHABLE)
+#undef DEFINE_UNREACHABLE
+
+
+void AwaitTransformer::Transform(AstNode* expr) {

[hausner, 2014/08/15 18:09:31]

Why not return the result_ field as a function result? See comment below.

[Michael Lippautz (Google), 2014/08/18 18:39:30]

Done.

I also adjusted the parser to take this return value and got rid of the Result()
getter.

+  expr->Visit(this);
+}
+
+
+LocalVariable* AwaitTransformer::EnsureCurrentTempVar() {
+  const char* await_temp_prefix = ":await_temp_var_";
+  const String& cnt_str = String::ZoneHandle(I,
+      String::NewFormatted(
+          "%s%" Pd "", await_temp_prefix, temp_cnt_));
+  const String& symbol = String::ZoneHandle(I, Symbols::New(cnt_str));
+  ASSERT(!symbol.IsNull());
+  LocalVariable* await_tmp =
+      parsed_function_->await_temps_scope()->LookupVariable(symbol, false);
+  if (await_tmp == NULL) {
+    await_tmp = new(I) LocalVariable(
+        Scanner::kNoSourcePos,
+        symbol,
+        Type::ZoneHandle(I, Type::DynamicType()));
+    parsed_function_->await_temps_scope()->AddVariable(await_tmp);
+  }
+  return await_tmp;
+}
+
+
+LocalVariable* AwaitTransformer::AddToPreambleNewTempVar(AstNode* node) {
+  LocalVariable* tmp_var = EnsureCurrentTempVar();
+  preamble_->Add(new(I) StoreLocalNode(Scanner::kNoSourcePos, tmp_var, node));
+  NextTempVar();
+  return tmp_var;
+}
+
+
+void AwaitTransformer::VisitLiteralNode(LiteralNode* node) {
+  result_ = node;
+}
+
+
+void AwaitTransformer::VisitTypeNode(TypeNode* node) {
+  result_ = new(I) TypeNode(node->token_pos(), node->type());
+}
+
+
+
+void AwaitTransformer::VisitAwaitNode(AwaitNode* node) {
+  // Await transformation:
+  //
+  //   :await_temp_var_X = <expr>;
+  //   :result_param = :await_temp_var_X;
+  //   if (:result_param is Future) {
+  //     // :result_param.then(:async_op);
+  //   }
+  //   :await_temp_var_(X+1) = :result_param;
+
+  LocalVariable* async_op = preamble_->scope()->LookupVariable(
+      Symbols::AsyncOperation(), false);
+  ASSERT(async_op != NULL);
+  LocalVariable* result_param = preamble_->scope()->LookupVariable(
+      Symbols::AsyncOperationParam(), false);
+  ASSERT(result_param != NULL);
+
+  node->expr()->Visit(this);
+  preamble_->Add(new(I) StoreLocalNode(Scanner::kNoSourcePos,
+                                        result_param,
+                                        result_));
+  LoadLocalNode* load_result_param = new(I) LoadLocalNode(
+      Scanner::kNoSourcePos, result_param);
+  SequenceNode* is_future_branch = new(I) SequenceNode(
+      Scanner::kNoSourcePos, preamble_->scope());
+  ArgumentListNode* args = new(I) ArgumentListNode(Scanner::kNoSourcePos);
+  args->Add(new(I) LoadLocalNode(Scanner::kNoSourcePos, async_op));
+  // TODO(mlippautz): Once continuations are supported, just call .then().
+  // is_future_branch->Add(new(I) InstanceCallNode(
+  // Scanner::kNoSourcePos, load_result_param, Symbols::FutureThen(), args));
+  //
+  // For now, throw an exception.
+  const String& exception = String::ZoneHandle(
+      I, String::New("awaitable futures not yet supported", Heap::kOld));
+  is_future_branch->Add(new(I) ThrowNode(
+      Scanner::kNoSourcePos,
+      new(I) LiteralNode(
+          Scanner::kNoSourcePos,
+          String::ZoneHandle(I, Symbols::New(exception))),
+      NULL));
+  const Class& cls = Class::ZoneHandle(
+      I, library_.LookupClass(Symbols::Future()));
+  const AbstractType& future_type = AbstractType::ZoneHandle(I,
+      cls.RareType());
+  ASSERT(!future_type.IsNull());
+  TypeNode* future_type_node = new(I) TypeNode(
+      Scanner::kNoSourcePos, future_type);
+  IfNode* is_future_if = new(I) IfNode(
+      Scanner::kNoSourcePos,
+      new(I) ComparisonNode(Scanner::kNoSourcePos,
+                             Token::kIS,
+                             load_result_param,
+                             future_type_node),
+      is_future_branch,
+      NULL);
+  preamble_->Add(is_future_if);
+
+  // TODO(mlippautz): Join for await needs to happen here.
+
+  LocalVariable* result = AddToPreambleNewTempVar(new(I) LoadLocalNode(
+      Scanner::kNoSourcePos, result_param));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+// Transforms boolean expressions into a sequence of evaluatons that only lazily
+// evaluate subexpressions.
+//
+// Example:
+//
+//   (a || b) only evaluates b if a is true

[hausner, 2014/08/15 18:09:31]

only evaluates b if a is *false*

[Michael Lippautz (Google), 2014/08/18 18:39:30]

Done.

+//
+// Transformation (roughly):
+//
+//   t_1 = a;
+//   if (t_1) {

[hausner, 2014/08/15 18:09:31]

!t_1

[Michael Lippautz (Google), 2014/08/18 18:39:30]

Done.

+//     t_2 = b;
+//   }
+//   t_3 = t_1 || t_2;  // Compiler takes care that lazy evaluation takes place
+//                         on this level.
+AstNode* AwaitTransformer::LazyTransform(const Token::Kind logical_op,
+                                         AstNode* new_left,
+                                         AstNode* right) {
+  ASSERT(logical_op == Token::kAND || logical_op == Token::kOR);
+  AstNode* result = NULL;
+  const Token::Kind compare_logical_op = (logical_op == Token::kAND) ?
+      Token::kEQ : Token::kNE;
+  SequenceNode* eval = new(I) SequenceNode(
+      Scanner::kNoSourcePos, preamble_->scope());
+  SequenceNode* saved_preamble = preamble_;
+  preamble_ = eval;
+  right->Visit(this);
+  result = result_;
+  preamble_ = saved_preamble;
+  IfNode* right_body = new(I) IfNode(
+      Scanner::kNoSourcePos,
+      new(I) ComparisonNode(
+          Scanner::kNoSourcePos,
+          compare_logical_op,
+          new_left,
+          new(I) LiteralNode(Scanner::kNoSourcePos, Bool::True())),
+      eval,
+      NULL);
+  preamble_->Add(right_body);
+  return result;
+}
+
+
+void AwaitTransformer::VisitBinaryOpNode(BinaryOpNode* node) {
+  node->left()->Visit(this);
+  AstNode* new_left = result_;
+  AstNode* new_right = NULL;
+  // Preserve lazy evaluaton.
+  if ((node->kind() == Token::kAND) || (node->kind() == Token::kOR)) {
+    new_right = LazyTransform(node->kind(), new_left, node->right());
+  } else {
+    node->right()->Visit(this);
+    new_right = result_;

[hausner, 2014/08/15 18:09:31]

Would it not make sense to group these two statements into a convenience
function?

AwaitTransformer::Transform(AstNode* n) {
  n->Visit(this);
  return result_;
}

Then the two statements above become new_right = Transform(node->right());

[Michael Lippautz (Google), 2014/08/18 18:39:30]

Done.

+  }
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) BinaryOpNode(node->token_pos(),
+                           node->kind(),
+                           new_left,
+                           new_right));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitBinaryOpWithMask32Node(
+    BinaryOpWithMask32Node* node) {
+  node->left()->Visit(this);
+  AstNode* new_left = result_;
+  AstNode* new_right = NULL;
+  // Preserve lazy evaluaton.
+  if ((node->kind() == Token::kAND) || (node->kind() == Token::kOR)) {
+    new_right = LazyTransform(node->kind(), new_left, node->right());
+  } else {
+    node->right()->Visit(this);
+    new_right = result_;
+  }
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) BinaryOpWithMask32Node(node->token_pos(),
+                                     node->kind(),
+                                     new_left,
+                                     new_right,
+                                     node->mask32()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitComparisonNode(ComparisonNode* node) {
+  node->left()->Visit(this);
+  AstNode* new_left = result_;
+  node->right()->Visit(this);
+  AstNode* new_right = result_;
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) ComparisonNode(node->token_pos(),
+                             node->kind(),
+                             new_left,
+                             new_right));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitUnaryOpNode(UnaryOpNode* node) {
+  node->operand()->Visit(this);
+  AstNode* new_operand = result_;
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) UnaryOpNode(node->token_pos(),
+                          node->kind(),
+                          new_operand));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+// ::= (<condition>) ? <true-branch> : <false-branch>
+//
+void AwaitTransformer::VisitConditionalExprNode(ConditionalExprNode* node) {
+  node->condition()->Visit(this);
+  AstNode* new_condition = result_;
+  SequenceNode* new_true = new(I) SequenceNode(
+      Scanner::kNoSourcePos, preamble_->scope());
+  SequenceNode* saved_preamble = preamble_;
+  preamble_ = new_true;
+  node->true_expr()->Visit(this);
+  AstNode* new_true_result = result_;
+  SequenceNode* new_false = new(I) SequenceNode(
+      Scanner::kNoSourcePos, preamble_->scope());
+  preamble_ = new_false;
+  node->false_expr()->Visit(this);
+  AstNode* new_false_result = result_;
+  preamble_ = saved_preamble;
+  IfNode* new_if = new(I) IfNode(Scanner::kNoSourcePos,
+                                  new_condition,
+                                  new_true,
+                                  new_false);
+  preamble_->Add(new_if);
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) ConditionalExprNode(Scanner::kNoSourcePos,
+                                  new_condition,
+                                  new_true_result,
+                                  new_false_result));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitArgumentListNode(ArgumentListNode* node) {
+  ArgumentListNode* new_args = new(I) ArgumentListNode(node->token_pos());
+  for (intptr_t i = 0; i < node->length(); i++) {
+    node->NodeAt(i)->Visit(this);
+    new_args->Add(result_);
+  }
+  result_ = new_args;
+}
+
+
+void AwaitTransformer::VisitArrayNode(ArrayNode* node) {
+  GrowableArray<AstNode*> new_elements;
+  for (intptr_t i = 0; i < node->length(); i++) {
+    node->ElementAt(i)->Visit(this);
+    new_elements.Add(result_);
+  }
+  result_ = new(I) ArrayNode(node->token_pos(), node->type(), new_elements);
+}
+
+
+void AwaitTransformer::VisitStringInterpolateNode(StringInterpolateNode* node) {
+  node->value()->Visit(this);
+  ArrayNode* new_value = result_->AsArrayNode();
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StringInterpolateNode(node->token_pos(),
+                                    new_value));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitClosureNode(ClosureNode* node) {
+  AstNode* new_receiver = node->receiver();
+  if (new_receiver != NULL) {
+    new_receiver->Visit(this);
+    new_receiver = result_;
+  }
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) ClosureNode(node->token_pos(),
+                          node->function(),
+                          new_receiver,
+                          node->scope()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitInstanceCallNode(InstanceCallNode* node) {
+  node->receiver()->Visit(this);
+  AstNode* new_receiver = result_;
+  node->arguments()->Visit(this);
+  ArgumentListNode* new_args = result_->AsArgumentListNode();
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) InstanceCallNode(node->token_pos(),
+                               new_receiver,
+                               node->function_name(),
+                               new_args));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitStaticCallNode(StaticCallNode* node) {
+  node->arguments()->Visit(this);
+  ArgumentListNode* new_args = result_->AsArgumentListNode();
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StaticCallNode(node->token_pos(),
+                             node->function(),
+                             new_args));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitConstructorCallNode(ConstructorCallNode* node) {
+  node->arguments()->Visit(this);
+  ArgumentListNode* new_args = result_->AsArgumentListNode();
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) ConstructorCallNode(node->token_pos(),
+                                  node->type_arguments(),
+                                  node->constructor(),
+                                  new_args));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitInstanceGetterNode(InstanceGetterNode* node) {
+  node->receiver()->Visit(this);
+  AstNode* new_receiver = result_;
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) InstanceGetterNode(node->token_pos(),
+                                 new_receiver,
+                                 node->field_name()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitInstanceSetterNode(InstanceSetterNode* node) {
+  AstNode* new_receiver = node->receiver();
+  if (new_receiver != NULL) {
+    new_receiver->Visit(this);
+    new_receiver = result_;
+  }
+
+  node->value()->Visit(this);
+  AstNode* new_value = result_;
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) InstanceSetterNode(node->token_pos(),
+                                 new_receiver,
+                                 node->field_name(),
+                                 new_value));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitStaticGetterNode(StaticGetterNode* node) {
+  AstNode* new_receiver = node->receiver();
+  if (new_receiver != NULL) {
+    new_receiver->Visit(this);
+    new_receiver = result_;
+  }
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StaticGetterNode(node->token_pos(),
+                               new_receiver,
+                               node->is_super_getter(),
+                               node->cls(),
+                               node->field_name()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitStaticSetterNode(StaticSetterNode* node) {
+  AstNode* new_receiver = node->receiver();
+  if (new_receiver != NULL) {
+    new_receiver->Visit(this);
+    new_receiver = result_;
+  }
+  node->value()->Visit(this);
+  AstNode* new_value = result_;
+
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StaticSetterNode(node->token_pos(),
+                               new_receiver,
+                               node->cls(),
+                               node->field_name(),
+                               new_value));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitLoadLocalNode(LoadLocalNode* node) {
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) LoadLocalNode(node->token_pos(), &node->local()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitStoreLocalNode(StoreLocalNode* node) {
+  node->value()->Visit(this);
+  AstNode* new_value = result_;
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StoreLocalNode(node->token_pos(),
+                             &node->local(),
+                             new_value));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitLoadStaticFieldNode(LoadStaticFieldNode* node) {
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) LoadStaticFieldNode(node->token_pos(),
+                                  node->field()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitStoreStaticFieldNode(StoreStaticFieldNode* node) {
+  node->value()->Visit(this);
+  AstNode* new_value = result_;
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StoreStaticFieldNode(node->token_pos(),
+                                   node->field(),
+                                   new_value));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitLoadIndexedNode(LoadIndexedNode* node) {
+  node->array()->Visit(this);
+  AstNode* new_array = result_;
+  node->index_expr()->Visit(this);
+  AstNode* new_index = result_;
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) LoadIndexedNode(node->token_pos(),
+                              new_array,
+                              new_index,
+                              node->super_class()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitStoreIndexedNode(StoreIndexedNode* node) {
+  node->array()->Visit(this);
+  AstNode* new_array = result_;
+  node->index_expr()->Visit(this);
+  AstNode* new_index = result_;
+  node->value()->Visit(this);
+  AstNode* new_value = result_;
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) StoreIndexedNode(node->token_pos(),
+                               new_array,
+                               new_index,
+                               new_value,
+                               node->super_class()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitAssignableNode(AssignableNode* node) {
+  node->expr()->Visit(this);
+  AstNode* new_expr = result_;
+  LocalVariable* result = AddToPreambleNewTempVar(
+      new(I) AssignableNode(node->token_pos(),
+                             new_expr,
+                             node->type(),
+                             node->dst_name()));
+  result_ = new(I) LoadLocalNode(Scanner::kNoSourcePos, result);
+}
+
+
+void AwaitTransformer::VisitLetNode(LetNode* node) {
+  // TODO(mlippautz): Check initializers and their temps.
+  LetNode* result = new(I) LetNode(node->token_pos());
+  for (intptr_t i = 0; i < node->nodes().length(); i++) {
+    node->nodes()[i]->Visit(this);
+    result->AddNode(result_);
+  }
+  result_ = result;
+}
+
+
+void AwaitTransformer::VisitThrowNode(ThrowNode* node) {
+  // TODO(mlippautz): Check if relevant.
+  node->exception()->Visit(this);
+  AstNode* new_exception = result_;
+  node->stacktrace()->Visit(this);
+  AstNode* new_stacktrace = result_;
+  result_ = new(I) ThrowNode(node->token_pos(),
+                              new_exception,
+                              new_stacktrace);
+}
+
+}  // namespace dart