Simplify restoring of saved try contexts in async code by passing around the

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/object_store.h"
 #include "vm/parser.h"
 #include "vm/thread.h"
 
@@ skipping 89 matching lines @@
 void AwaitTransformer::VisitLiteralNode(LiteralNode* node) {
   result_ = node;
 }
 
 
 void AwaitTransformer::VisitTypeNode(TypeNode* node) {
   result_ = new(Z) TypeNode(node->token_pos(), node->type());
 }
 
 
-// Restore the currently relevant :saved_try_context_var on the stack
-// from the captured :async_saved_try_ctx_var_<try_index>.
-AstNode* AwaitTransformer::RestoreSavedTryContext(Zone* zone,
-                                                  LocalScope* scope,
-                                                  int16_t try_index) {
-  LocalVariable* saved_try_ctx =
-      scope->LocalLookupVariable(Symbols::SavedTryContextVar());
-  ASSERT((saved_try_ctx != NULL) && !saved_try_ctx->is_captured());
-  const String& async_saved_try_ctx_name = String::ZoneHandle(zone,
-      Symbols::New(String::Handle(zone,
-          String::NewFormatted("%s%d",
-                               Symbols::AsyncSavedTryCtxVarPrefix().ToCString(),
-                               try_index))));
-  LocalVariable* async_saved_try_ctx =
-      scope->LocalLookupVariable(async_saved_try_ctx_name);
-  ASSERT(async_saved_try_ctx != NULL);
-  ASSERT(async_saved_try_ctx->is_captured());
-  return new (zone) StoreLocalNode(
-      Scanner::kNoSourcePos,
-      saved_try_ctx,
-      new (zone) LoadLocalNode(Scanner::kNoSourcePos, async_saved_try_ctx));
-}
-
-
 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 = Future.value(:result_param);
   //   }
   //   AwaitMarker(kNewContinuationState);
   //   :result_param = :result_param.then(:async_op);
@@ skipping 85 matching lines @@
       Scanner::kNoSourcePos,
       async_catch_helper,
       catch_helper_args));
   ReturnNode* continuation_return = new(Z) ReturnNode(Scanner::kNoSourcePos);
   continuation_return->set_return_type(ReturnNode::kContinuationTarget);
   preamble_->Add(continuation_return);
 
   // If this expression is part of a try block, also append the code for
   // restoring the saved try context that lives on the stack and possibly the
   // saved try context of the outer try block.
-  if (node->try_scope() != NULL) {
-    preamble_->Add(RestoreSavedTryContext(Z,
-                                          node->try_scope(),
-                                          node->try_index()));
-    if (node->outer_try_scope() != NULL) {
-      preamble_->Add(RestoreSavedTryContext(Z,
-                                            node->outer_try_scope(),
-                                            node->outer_try_index()));
+  if (node->saved_try_ctx() != NULL) {
+    preamble_->Add(new (Z) StoreLocalNode(
+        Scanner::kNoSourcePos,
+        node->saved_try_ctx(),
+        new (Z) LoadLocalNode(Scanner::kNoSourcePos,
+                              node->async_saved_try_ctx())));
+    if (node->outer_saved_try_ctx() != NULL) {
+      preamble_->Add(new (Z) StoreLocalNode(
+          Scanner::kNoSourcePos,
+          node->outer_saved_try_ctx(),
+          new (Z) LoadLocalNode(Scanner::kNoSourcePos,
+                                node->outer_async_saved_try_ctx())));
     }
   } else {
-    ASSERT(node->outer_try_scope() == NULL);
+    ASSERT(node->outer_saved_try_ctx() == NULL);
   }
 
   LoadLocalNode* load_error_param = new (Z) LoadLocalNode(
       Scanner::kNoSourcePos, error_param);
   LoadLocalNode* load_stack_trace_param = new (Z) LoadLocalNode(
       Scanner::kNoSourcePos, stack_trace_param);
   SequenceNode* error_ne_null_branch = new (Z) SequenceNode(
       Scanner::kNoSourcePos, ChainNewScope(preamble_->scope()));
   error_ne_null_branch->Add(new (Z) ThrowNode(
       Scanner::kNoSourcePos,
@@ skipping 363 matching lines @@
 
 
 void AwaitTransformer::VisitThrowNode(ThrowNode* node) {
   AstNode* new_exception = Transform(node->exception());
   result_ = new(Z) ThrowNode(node->token_pos(),
                              new_exception,
                              node->stacktrace());
 }
 
 }  // namespace dart