Fix context level info in for-loops

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/compiler.h"
@@ skipping 2158 matching lines @@
     if (continue_join != NULL) {
       if (for_body.is_open()) for_body.Goto(continue_join);
       Instruction* current = AppendFragment(continue_join, for_increment);
       current->Goto(loop_entry);
     } else {
       for_body.Append(for_increment);
       for_body.Goto(loop_entry);
     }
     Goto(loop_entry);
     exit_ = loop_entry;
+    // Note: the stack overflow check happens on the back branch that jumps
+    // to the increment instruction. The token position for the overflow
+    // check must match the position of the increment expression, so that
+    // the context level (if any) matches the that of the increment
+    // expression.
     AddInstruction(
-        new(Z) CheckStackOverflowInstr(node->token_pos(),
+        new(Z) CheckStackOverflowInstr(node->increment()->token_pos(),
                                        owner()->loop_depth()));
   }
 
   if (node->condition() == NULL) {
     // Endless loop, no test.
     Append(for_body);
     exit_ = nested_loop.break_target();  // May be NULL.
   } else {
     EffectGraphVisitor for_test_preamble(owner());
     if (node->condition_preamble() != NULL) {
@@ skipping 2460 matching lines @@
                    Script::Handle(function.script()),
                    function.token_pos(),
                    Report::AtLocation,
                    "FlowGraphBuilder Bailout: %s %s",
                    String::Handle(function.name()).ToCString(),
                    reason);
   UNREACHABLE();
 }
 
 }  // namespace dart