Reduce the number of captured variables in async code, by only capturing local

runtime/vm/scopes.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/scopes.h"
 
 #include "vm/object.h"
 #include "vm/stack_frame.h"
 #include "vm/symbols.h"
 
@@ skipping 599 matching lines @@
     LocalScope* owner_scope = new LocalScope(NULL, 0, 0);
     owner_scope->set_context_level(context_scope.ContextLevelAt(i));
     owner_scope->AddVariable(variable);
     outer_scope->AddVariable(variable);  // As alias.
     ASSERT(variable->owner() == owner_scope);
   }
   return outer_scope;
 }
 
 
-void LocalScope::RecursivelyCaptureAllVariables() {
-  for (intptr_t i = 0; i < num_variables(); i++) {
-    if ((VariableAt(i)->name().raw() == Symbols::StackTraceVar().raw()) ||
-        (VariableAt(i)->name().raw() == Symbols::ExceptionVar().raw()) ||
-        (VariableAt(i)->name().raw() == Symbols::SavedTryContextVar().raw())) {
-      // Don't capture those variables because the VM expects them to be on the
-      // stack.
-      continue;
+void LocalScope::CaptureLocalVariables(LocalScope* top_scope) {
+  ASSERT(top_scope->function_level() == function_level());
+  LocalScope* scope = this;
+  while (scope != top_scope->parent()) {
+    for (intptr_t i = 0; i < scope->num_variables(); i++) {
+      LocalVariable* variable = scope->VariableAt(i);
+      if ((variable->name().raw() == Symbols::StackTraceVar().raw()) ||
+          (variable->name().raw() == Symbols::ExceptionVar().raw()) ||
+          (variable->name().raw() == Symbols::SavedTryContextVar().raw())) {
+        // Don't capture those variables because the VM expects them to be on
+        // the stack.
+        continue;
+      }
+      scope->CaptureVariable(variable);
     }
-    CaptureVariable(VariableAt(i));
+    scope = scope->parent();
   }
-  if (sibling() != NULL) { sibling()->RecursivelyCaptureAllVariables(); }
-  if (child() != NULL) { child()->RecursivelyCaptureAllVariables(); }
 }
 
 
 RawContextScope* LocalScope::CreateImplicitClosureScope(const Function& func) {
   static const intptr_t kNumCapturedVars = 1;
 
   // Create a ContextScope with space for kNumCapturedVars descriptors.
   const ContextScope& context_scope =
       ContextScope::Handle(ContextScope::New(kNumCapturedVars, true));
 
@@ skipping 36 matching lines @@
     return fixed_parameter_count - (index() - kParamEndSlotFromFp);
   } else {
     // Shift negative indexes so that the lowest one is 0 (they are still
     // non-positive).
     return fixed_parameter_count - (index() - kFirstLocalSlotFromFp);
   }
 }
 
 
 }  // namespace dart