Revert "Introduce Goto instructions to the flow graph."

runtime/vm/flow_graph_builder.cc

 // Copyright (c) 2012, 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/flow_graph_builder.h"
 
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/code_descriptors.h"
 #include "vm/dart_entry.h"
@@ skipping 77 matching lines @@
   } else {
     exit()->set_next(do_instr);
   }
   exit_ = do_instr;
 }
 
 
 void EffectGraphVisitor::AddInstruction(Instruction* instruction) {
   ASSERT(is_open());
   ASSERT(!instruction->IsDefinition());
-  ASSERT(!instruction->IsBlockEntry());
   DeallocateTempIndex(instruction->InputCount());
+  if (instruction->IsDefinition()) {
+    instruction->AsDefinition()->set_temp_index(AllocateTempIndex());
+  }
   if (is_empty()) {
     entry_ = exit_ = instruction;
   } else {
     exit()->set_next(instruction);
     exit_ = instruction;
   }
 }
 
 
-void EffectGraphVisitor::Goto(JoinEntryInstr* join) {
-  ASSERT(is_open());
-  if (is_empty()) {
-    entry_ = new GotoInstr(join);
-  } else {
-    exit()->Goto(join);
-  }
-  exit_ = NULL;
-}
-
-
-// Appends a graph fragment to a block entry instruction.  Returns the entry
-// instruction if the fragment was empty or else the exit of the fragment if
-// it was non-empty (so NULL if the fragment is closed).
-//
-// Note that the fragment is no longer a valid fragment after calling this
-// function -- the fragment is closed at its entry because the entry has a
-// predecessor in the graph.
+// Appends a graph fragment to a block entry instruction and returns the exit
+// of the resulting graph fragment.
 static Instruction* AppendFragment(BlockEntryInstr* entry,
                                    const EffectGraphVisitor& fragment) {
   if (fragment.is_empty()) return entry;
   entry->set_next(fragment.entry());
   return fragment.exit();
 }
 
 
 void EffectGraphVisitor::Join(const TestGraphVisitor& test_fragment,
                               const EffectGraphVisitor& true_fragment,
@@ skipping 18 matching lines @@
   Instruction* false_exit = AppendFragment(false_entry, false_fragment);
 
   // 3. Add a join or select one (or neither) of the arms as exit.
   if (true_exit == NULL) {
     exit_ = false_exit;  // May be NULL.
     if (false_exit != NULL) temp_index_ = false_fragment.temp_index();
   } else if (false_exit == NULL) {
     exit_ = true_exit;
     temp_index_ = true_fragment.temp_index();
   } else {
-    JoinEntryInstr* join = new JoinEntryInstr();
-    true_exit->Goto(join);
-    false_exit->Goto(join);
-    exit_ = join;
+    exit_ = new JoinEntryInstr();
+    true_exit->set_next(exit_);
+    false_exit->set_next(exit_);
     ASSERT(true_fragment.temp_index() == false_fragment.temp_index());
     temp_index_ = true_fragment.temp_index();
   }
 }
 
 
 void EffectGraphVisitor::TieLoop(const TestGraphVisitor& test_fragment,
                                  const EffectGraphVisitor& body_fragment) {
   // We have: a test graph fragment with zero, one, or two available exits;
   // and an effect graph fragment with zero or one available exits.  We want
   // to append the 'while loop' consisting of the test graph fragment as
   // condition and the effect graph fragment as body.
   ASSERT(is_open());
 
   // 1. Connect the body to the test if it is reachable, and if so record
   // its exit (if any).
   TargetEntryInstr* body_entry = new TargetEntryInstr();
   *test_fragment.true_successor_address() = body_entry;
   Instruction* body_exit = AppendFragment(body_entry, body_fragment);
 
   // 2. Connect the test to this graph, including the body if reachable and
   // using a fresh join node if the body is reachable and has an open exit.
   if (body_exit == NULL) {
     Append(test_fragment);
   } else {
     JoinEntryInstr* join = new JoinEntryInstr();
+    AddInstruction(join);
     join->set_next(test_fragment.entry());
-    Goto(join);
-    body_exit->Goto(join);
+    body_exit->set_next(join);
   }
 
   // 3. Set the exit to the graph to be the false successor of the test, a
   // fresh target node
   exit_ = *test_fragment.false_successor_address() = new TargetEntryInstr();
 }
 
 
 Computation* EffectGraphVisitor::BuildStoreLocal(
     const LocalVariable& local, Value* value) {
@@ skipping 720 matching lines @@
   if (node->false_branch() != NULL) node->false_branch()->Visit(&for_false);
   Join(for_test, for_true, for_false);
 }
 
 
 void EffectGraphVisitor::VisitSwitchNode(SwitchNode* node) {
   EffectGraphVisitor switch_body(owner(), temp_index());
   node->body()->Visit(&switch_body);
   Append(switch_body);
   if ((node->label() != NULL) && (node->label()->join_for_break() != NULL)) {
-    if (is_open()) Goto(node->label()->join_for_break());
-    exit_ = node->label()->join_for_break();
+    if (is_open()) {
+      AddInstruction(node->label()->join_for_break());
+    } else {
+      exit_ = node->label()->join_for_break();
+    }
   }
   // No continue label allowed.
   ASSERT((node->label() == NULL) ||
          (node->label()->join_for_continue() == NULL));
 }
 
 
 // A case node contains zero or more case expressions, can contain default
 // and a case statement body.
 // Compose fragment as follows:
@@ skipping 11 matching lines @@
 //   g) case-statements-join
 //   h) [ case-statements ] -> exit-join
 //   i) exit-target -> exit-join
 //   j) exit-join
 //
 // Note: The specification of switch/case is under discussion and may change
 // drastically.
 void EffectGraphVisitor::VisitCaseNode(CaseNode* node) {
   const intptr_t len = node->case_expressions()->length();
   // Create case statements instructions.
+  const bool needs_join_at_statement_entry =
+      (len > 1) || ((len > 0) && (node->contains_default()));
   EffectGraphVisitor for_case_statements(owner(), temp_index());
   // Compute start of statements fragment.
-  JoinEntryInstr* statement_start = NULL;
-  if ((node->label() != NULL) && node->label()->is_continue_target()) {
+  BlockEntryInstr* statement_start = NULL;
+  if ((node->label() != NULL) && (node->label()->is_continue_target())) {
     // Since a labeled jump continue statement occur in a different case node,
     // allocate JoinNode here and use it as statement start.
+    if (node->label()->join_for_continue() == NULL) {
+      node->label()->set_join_for_continue(new JoinEntryInstr());
+    }
     statement_start = node->label()->join_for_continue();
-    if (statement_start == NULL) {
-      statement_start = new JoinEntryInstr();
-      node->label()->set_join_for_continue(statement_start);
-    }
+  } else if (needs_join_at_statement_entry) {
+    statement_start = new JoinEntryInstr();
   } else {
-    statement_start = new JoinEntryInstr();
+    statement_start = new TargetEntryInstr();
   }
+  for_case_statements.AddInstruction(statement_start);
   node->statements()->Visit(&for_case_statements);
-  Instruction* statement_exit =
-      AppendFragment(statement_start, for_case_statements);
   if (is_open() && (len == 0)) {
     ASSERT(node->contains_default());
     // Default only case node.
-    Goto(statement_start);
-    exit_ = statement_exit;
+    Append(for_case_statements);
     return;
   }
 
-  // Generate instructions for all case expressions.
-  TargetEntryInstr** previous_false_address = NULL;
+  // Generate instructions for all case expressions and collect data to
+  // connect them.
+  GrowableArray<TargetEntryInstr**> case_true_addresses;
+  GrowableArray<TargetEntryInstr**> case_false_addresses;
+  GrowableArray<TargetEntryInstr*> case_entries;
   for (intptr_t i = 0; i < len; i++) {
     AstNode* case_expr = node->case_expressions()->NodeAt(i);
     TestGraphVisitor for_case_expression(owner(),
                                          temp_index(),
                                          case_expr->token_pos());
-    case_expr->Visit(&for_case_expression);
     if (i == 0) {
+      case_entries.Add(NULL);  // Not to be used
+      case_expr->Visit(&for_case_expression);
       // Append only the first one, everything else is connected from it.
       Append(for_case_expression);
     } else {
       TargetEntryInstr* case_entry_target = new TargetEntryInstr();
-      AppendFragment(case_entry_target, for_case_expression);
-      *previous_false_address = case_entry_target;
+      case_entries.Add(case_entry_target);
+      for_case_expression.AddInstruction(case_entry_target);
+      case_expr->Visit(&for_case_expression);
     }
-    TargetEntryInstr* true_target = new TargetEntryInstr();
-    *for_case_expression.true_successor_address() = true_target;
-    true_target->Goto(statement_start);
-    previous_false_address = for_case_expression.false_successor_address();
+    case_true_addresses.Add(for_case_expression.true_successor_address());
+    case_false_addresses.Add(for_case_expression.false_successor_address());
   }
 
   // Once a test fragment has been added, this fragment is closed.
   ASSERT(!is_open());
 
-  Instruction* exit_instruction = NULL;
+  // Connect all test cases except the last one.
+  for (intptr_t i = 0; i < (len - 1); i++) {
+    ASSERT(needs_join_at_statement_entry);
+    *case_false_addresses[i] = case_entries[i + 1];
+    TargetEntryInstr* true_target = new TargetEntryInstr();
+    *case_true_addresses[i] = true_target;
+    true_target->set_next(statement_start);
+  }
+
+  BlockEntryInstr* exit_instruction = NULL;
   // Handle last (or only) case: false goes to exit or to statement if this
   // node contains default.
   if (len > 0) {
+    if (statement_start->IsTargetEntry()) {
+      *case_true_addresses[len - 1] = statement_start->AsTargetEntry();
+    } else {
+      TargetEntryInstr* true_target = new TargetEntryInstr();
+      *case_true_addresses[len - 1] = true_target;
+      true_target->set_next(statement_start);
+    }
     TargetEntryInstr* false_target = new TargetEntryInstr();
-    *previous_false_address = false_target;
+    *case_false_addresses[len - 1] = false_target;
     if (node->contains_default()) {
       // True and false go to statement start.
-      false_target->Goto(statement_start);
-      exit_instruction = statement_exit;
+      false_target->set_next(statement_start);
+      if (for_case_statements.is_open()) {
+        exit_instruction = new TargetEntryInstr();
+        for_case_statements.exit()->set_next(exit_instruction);
+      }
     } else {
-      if (statement_exit != NULL) {
-        JoinEntryInstr* join = new JoinEntryInstr();
-        statement_exit->Goto(join);
-        false_target->Goto(join);
-        exit_instruction = join;
+      if (for_case_statements.is_open()) {
+        exit_instruction = new JoinEntryInstr();
+        for_case_statements.exit()->set_next(exit_instruction);
       } else {
-        exit_instruction = false_target;
+        exit_instruction = new TargetEntryInstr();
       }
+      false_target->set_next(exit_instruction);
     }
   } else {
     // A CaseNode without case expressions must contain default.
     ASSERT(node->contains_default());
-    Goto(statement_start);
-    exit_instruction = statement_exit;
+    AddInstruction(statement_start);
   }
 
   ASSERT(!is_open());
   exit_ = exit_instruction;
 }
 
 
 // <Statement> ::= While { label:     SourceLabel
 //                         condition: <Expression>
 //                         body:      <Sequence> }
@@ skipping 13 matching lines @@
   ASSERT(!for_test.is_empty());  // Language spec.
 
   EffectGraphVisitor for_body(owner(), temp_index());
   for_body.Do(
       new CheckStackOverflowComp(node->token_pos(), owner()->try_index()));
   node->body()->Visit(&for_body);
 
   // Labels are set after body traversal.
   SourceLabel* lbl = node->label();
   ASSERT(lbl != NULL);
-  JoinEntryInstr* join = lbl->join_for_continue();
-  if (join != NULL) {
-    Goto(join);
-    exit_ = join;
+  if (lbl->join_for_continue() != NULL) {
+    AddInstruction(lbl->join_for_continue());
   }
   TieLoop(for_test, for_body);
-  join = lbl->join_for_break();
-  if (join != NULL) {
-    Goto(join);
-    exit_ = join;
+  if (lbl->join_for_break() != NULL) {
+    AddInstruction(lbl->join_for_break());
   }
 }
 
 
 // The fragment is composed as follows:
 // a) body-entry-join
 // b) [ body ]
 // c) test-entry (continue-join or body-exit-target)
 // d) [ test-entry ] -> (back-target, loop-exit-target)
 // e) back-target -> (body-entry-join)
 // f) loop-exit-target
 // g) break-join
 void EffectGraphVisitor::VisitDoWhileNode(DoWhileNode* node) {
   // Traverse body first in order to generate continue and break labels.
   EffectGraphVisitor for_body(owner(), temp_index());
   for_body.Do(
       new CheckStackOverflowComp(node->token_pos(), owner()->try_index()));
   node->body()->Visit(&for_body);
 
   TestGraphVisitor for_test(owner(),
                             temp_index(),
                             node->condition()->token_pos());
   node->condition()->Visit(&for_test);
   ASSERT(is_open());
 
   // Tie do-while loop (test is after the body).
   JoinEntryInstr* body_entry_join = new JoinEntryInstr();
-  Goto(body_entry_join);
+  AddInstruction(body_entry_join);
   Instruction* body_exit = AppendFragment(body_entry_join, for_body);
 
-  JoinEntryInstr* join = node->label()->join_for_continue();
-  if ((body_exit != NULL) || (join != NULL)) {
-    if (join == NULL) join = new JoinEntryInstr();
-    join->set_next(for_test.entry());
+  if (for_body.is_open() || (node->label()->join_for_continue() != NULL)) {
+    BlockEntryInstr* test_entry = NULL;
+    if (node->label()->join_for_continue() == NULL) {
+      test_entry = new TargetEntryInstr();
+    } else {
+      test_entry = node->label()->join_for_continue();
+    }
+    test_entry->set_next(for_test.entry());
     if (body_exit != NULL) {
-      body_exit->Goto(join);
+      body_exit->set_next(test_entry);
     }
   }
 
   TargetEntryInstr* back_target_entry = new TargetEntryInstr();
   *for_test.true_successor_address() = back_target_entry;
-  back_target_entry->Goto(body_entry_join);
+  back_target_entry->set_next(body_entry_join);
   TargetEntryInstr* loop_exit_target = new TargetEntryInstr();
   *for_test.false_successor_address() = loop_exit_target;
   if (node->label()->join_for_break() == NULL) {
     exit_ = loop_exit_target;
   } else {
-    loop_exit_target->Goto(node->label()->join_for_break());
+    loop_exit_target->set_next(node->label()->join_for_break());
     exit_ = node->label()->join_for_break();
   }
 }
 
 
 // A ForNode can contain break and continue jumps. 'break' joins to
 // ForNode exit, 'continue' joins at increment entry. The fragment is composed
 // as follows:
 // a) [ initializer ]
 // b) loop-join
 // c) [ test ] -> (body-entry-target, loop-exit-target)
 // d) body-entry-target
 // e) [ body ]
 // f) continue-join (optional)
 // g) [ increment ] -> (loop-join)
 // h) loop-exit-target
 // i) break-join
 void EffectGraphVisitor::VisitForNode(ForNode* node) {
   EffectGraphVisitor for_initializer(owner(), temp_index());
   node->initializer()->Visit(&for_initializer);
   Append(for_initializer);
   ASSERT(is_open());
 
   // Compose body to set any jump labels.
   EffectGraphVisitor for_body(owner(), temp_index());
+  TargetEntryInstr* body_entry = new TargetEntryInstr();
+  for_body.AddInstruction(body_entry);
   for_body.Do(
       new CheckStackOverflowComp(node->token_pos(), owner()->try_index()));
   node->body()->Visit(&for_body);
 
   // Join loop body, increment and compute their end instruction.
   ASSERT(!for_body.is_empty());
   Instruction* loop_increment_end = NULL;
   EffectGraphVisitor for_increment(owner(), temp_index());
-  node->increment()->Visit(&for_increment);
-  JoinEntryInstr* join = node->label()->join_for_continue();
-  if (join != NULL) {
-    // Insert the join between the body and increment.
-    if (for_body.is_open()) for_body.Goto(join);
-    loop_increment_end = AppendFragment(join, for_increment);
-    ASSERT(loop_increment_end != NULL);
-  } else if (for_body.is_open()) {
+  if ((node->label()->join_for_continue() == NULL) && for_body.is_open()) {
     // Do not insert an extra basic block.
+    node->increment()->Visit(&for_increment);
     for_body.Append(for_increment);
     loop_increment_end = for_body.exit();
-    // 'for_body' contains at least the stack check.
+    // 'for_body' contains at least the TargetInstruction 'body_entry'.
+    ASSERT(loop_increment_end != NULL);
+  } else if (node->label()->join_for_continue() != NULL) {
+    // Insert join between body and increment.
+    if (for_body.is_open()) {
+      for_body.exit()->set_next(node->label()->join_for_continue());
+    }
+    for_increment.AddInstruction(node->label()->join_for_continue());
+    node->increment()->Visit(&for_increment);
+    loop_increment_end = for_increment.exit();
     ASSERT(loop_increment_end != NULL);
   } else {
     loop_increment_end = NULL;
+    ASSERT(!for_body.is_open() && node->label()->join_for_continue() == NULL);
   }
 
   // 'loop_increment_end' is NULL only if there is no join for continue and the
   // body is not open, i.e., no backward branch exists.
   if (loop_increment_end != NULL) {
     JoinEntryInstr* loop_start = new JoinEntryInstr();
-    Goto(loop_start);
-    loop_increment_end->Goto(loop_start);
-    exit_ = loop_start;
+    AddInstruction(loop_start);
+    loop_increment_end->set_next(loop_start);
   }
 
   if (node->condition() == NULL) {
     // Endless loop, no test.
-    JoinEntryInstr* body_entry = new JoinEntryInstr();
-    AppendFragment(body_entry, for_body);
-    Goto(body_entry);
-    if (node->label()->join_for_break() != NULL) {
+    Append(for_body);
+    if (node->label()->join_for_break() == NULL) {
+      CloseFragment();
+    } else {
       // Control flow of ForLoop continues into join_for_break.
       exit_ = node->label()->join_for_break();
     }
   } else {
     TargetEntryInstr* loop_exit = new TargetEntryInstr();
     TestGraphVisitor for_test(owner(),
                               temp_index(),
                               node->condition()->token_pos());
     node->condition()->Visit(&for_test);
     Append(for_test);
-    TargetEntryInstr* body_entry = new TargetEntryInstr();
-    AppendFragment(body_entry, for_body);
     *for_test.true_successor_address() = body_entry;
     *for_test.false_successor_address() = loop_exit;
     if (node->label()->join_for_break() == NULL) {
       exit_ = loop_exit;
     } else {
-      loop_exit->Goto(node->label()->join_for_break());
+      loop_exit->set_next(node->label()->join_for_break());
       exit_ = node->label()->join_for_break();
     }
   }
 }
 
 
 void EffectGraphVisitor::VisitJumpNode(JumpNode* node) {
   for (intptr_t i = 0; i < node->inlined_finally_list_length(); i++) {
     EffectGraphVisitor for_effect(owner(), temp_index());
     node->InlinedFinallyNodeAt(i)->Visit(&for_effect);
@@ skipping 22 matching lines @@
       target_context_level = target_scope->context_level();
     }
   }
   ASSERT(target_context_level >= 0);
   intptr_t current_context_level = owner()->context_level();
   ASSERT(current_context_level >= target_context_level);
   while (current_context_level-- > target_context_level) {
     UnchainContext();
   }
 
-  JoinEntryInstr* jump_target = NULL;
+  Instruction* jump_target = NULL;
   if (node->kind() == Token::kBREAK) {
     if (node->label()->join_for_break() == NULL) {
       node->label()->set_join_for_break(new JoinEntryInstr());
     }
     jump_target = node->label()->join_for_break();
   } else {
     if (node->label()->join_for_continue() == NULL) {
       node->label()->set_join_for_continue(new JoinEntryInstr());
     }
     jump_target = node->label()->join_for_continue();
   }
-  Goto(jump_target);
+  AddInstruction(jump_target);
+  CloseFragment();
 }
 
 
 void EffectGraphVisitor::VisitArgumentListNode(ArgumentListNode* node) {
   UNREACHABLE();
 }
 
 
 void EffectGraphVisitor::VisitArrayNode(ArrayNode* node) {
   // Translate the array elements and collect their values.
@@ skipping 802 matching lines @@
     }
   }
 
   // No continue on sequence allowed.
   ASSERT((node->label() == NULL) ||
          (node->label()->join_for_continue() == NULL));
   // If this node sequence is labeled, a break out of the sequence will have
   // taken care of unchaining the context.
   if ((node->label() != NULL) &&
       (node->label()->join_for_break() != NULL)) {
-    if (is_open()) Goto(node->label()->join_for_break());
-    exit_ = node->label()->join_for_break();
+    if (is_open()) {
+      AddInstruction(node->label()->join_for_break());
+    } else {
+      exit_ = node->label()->join_for_break();
+    }
   }
 
   // The outermost function sequence cannot contain a label.
   ASSERT((node->label() == NULL) ||
          (node != owner()->parsed_function().node_sequence()));
   owner()->set_context_level(previous_context_level);
 }
 
 
 void EffectGraphVisitor::VisitCatchClauseNode(CatchClauseNode* node) {
@@ skipping 24 matching lines @@
   // We are done generating code for the try block.
   owner()->set_try_index(old_try_index);
 
   CatchClauseNode* catch_block = node->catch_block();
   if (catch_block != NULL) {
     // Set the corresponding try index for this catch block so
     // that we can set the appropriate handler pc when we generate
     // code for this catch block.
     catch_block->set_try_index(try_index);
     EffectGraphVisitor for_catch_block(owner(), temp_index());
+    TargetEntryInstr* catch_entry = new TargetEntryInstr(try_index);
+    for_catch_block.AddInstruction(catch_entry);
     catch_block->Visit(&for_catch_block);
-    TargetEntryInstr* catch_entry = new TargetEntryInstr(try_index);
     owner()->AddCatchEntry(catch_entry);
     ASSERT(!for_catch_block.is_open());
-    AppendFragment(catch_entry, for_catch_block);
-    if (node->end_catch_label() != NULL) {
-      JoinEntryInstr* join = node->end_catch_label()->join_for_continue();
-      if (join != NULL) {
-        if (is_open()) Goto(join);
-        exit_ = join;
+    if ((node->end_catch_label() != NULL) &&
+        (node->end_catch_label()->join_for_continue() != NULL)) {
+      if (is_open()) {
+        AddInstruction(node->end_catch_label()->join_for_continue());
+      } else {
+        exit_ = node->end_catch_label()->join_for_continue();
       }
     }
   }
 
   // Generate code for the finally block if one exists.
   if ((node->finally_block() != NULL) && is_open()) {
     EffectGraphVisitor for_finally_block(owner(), temp_index());
     node->finally_block()->Visit(&for_finally_block);
     Append(for_finally_block);
   }
@@ skipping 58 matching lines @@
 void FlowGraphBuilder::BuildGraph(bool for_optimized, bool use_ssa) {
   if (FLAG_print_ast) {
     // Print the function ast before IL generation.
     AstPrinter::PrintFunctionNodes(parsed_function());
   }
   // Compilation can be nested, preserve the computation-id.
   const Function& function = parsed_function().function();
   TargetEntryInstr* normal_entry = new TargetEntryInstr();
   graph_entry_ = new GraphEntryInstr(normal_entry);
   EffectGraphVisitor for_effect(this, 0);
+  for_effect.AddInstruction(normal_entry);
   parsed_function().node_sequence()->Visit(&for_effect);
-  AppendFragment(normal_entry, for_effect);
   // Check that the graph is properly terminated.
   ASSERT(!for_effect.is_open());
   GrowableArray<intptr_t> parent;
   GrowableArray<BitVector*> assigned_vars;
   intptr_t variable_count = parsed_function_.function().num_fixed_parameters() +
       parsed_function_.copied_parameter_count() +
       parsed_function_.stack_local_count();
   // Perform a depth-first traversal of the graph to build preorder and
   // postorder block orders.
   graph_entry_->DiscoverBlocks(NULL,  // Entry block predecessor.
@@ skipping 411 matching lines @@
   char* chars = reinterpret_cast<char*>(
       Isolate::Current()->current_zone()->Allocate(len));
   OS::SNPrint(chars, len, kFormat, function_name, reason);
   const Error& error = Error::Handle(
       LanguageError::New(String::Handle(String::New(chars))));
   Isolate::Current()->long_jump_base()->Jump(1, error);
 }
 
 
 }  // namespace dart