Be less aggressive in sharing contexts between scopes so that sibling contexts

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 "lib/invocation_mirror.h"
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/class_finalizer.h"
@@ skipping 3767 matching lines @@
   NestedBlock nested_block(owner(), node);
 
   if (num_context_variables > 0) {
     // The local scope declares variables that are captured.
     // Allocate and chain a new context (Except don't chain when at the function
     // entry if the function does not capture any variables from outer scopes).
     Value* allocated_context =
         Bind(new(Z) AllocateContextInstr(node->token_pos(),
                                          num_context_variables));
     { LocalVariable* tmp_var = EnterTempLocalScope(allocated_context);
-      if (HasContextScope() || !is_top_level_sequence) {
+      if (!is_top_level_sequence || HasContextScope()) {
+        ASSERT(is_top_level_sequence ||
+               (nested_block.ContextLevel() ==
+                nested_block.outer()->ContextLevel() + 1));
         Value* tmp_val = Bind(new(Z) LoadLocalInstr(*tmp_var));
         Value* parent_context = Bind(BuildCurrentContext());
         Do(new(Z) StoreInstanceFieldInstr(Context::parent_offset(),
                                           tmp_val,
                                           parent_context,
                                           kEmitStoreBarrier,
                                           Scanner::kNoSourcePos));
       }
       Do(BuildStoreContext(Bind(ExitTempLocalScope(tmp_var))));
     }
@@ skipping 188 matching lines @@
           exit_->LinkTo(preamble_start);
         }
       }
     }
     entry_ = saved_entry;
     exit_ = saved_exit;
   }
 
   if (is_open() &&
       (num_context_variables > 0) &&
-      (HasContextScope() || !is_top_level_sequence)) {
+      (!is_top_level_sequence || HasContextScope())) {
     UnchainContexts(1);
   }
 
   // If this node sequence is labeled, a break out of the sequence will have
   // taken care of unchaining the context.
   if (nested_block.break_target() != NULL) {
     if (is_open()) Goto(nested_block.break_target());
     exit_ = nested_block.break_target();
   }
 }
@@ skipping 360 matching lines @@
   Report::MessageF(Report::kBailout,
                    Script::Handle(function.script()),
                    function.token_pos(),
                    "FlowGraphBuilder Bailout: %s %s",
                    String::Handle(function.name()).ToCString(),
                    reason);
   UNREACHABLE();
 }
 
 }  // namespace dart