Initial support for length guards on final fields.

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/code_descriptors.h"
@@ skipping 2920 matching lines @@
   Value* store_value = for_value.value();
   if (FLAG_enable_type_checks) {
     const AbstractType& type = AbstractType::ZoneHandle(node->field().type());
     const String& dst_name = String::ZoneHandle(node->field().name());
     store_value = BuildAssignableValue(node->value()->token_pos(),
                                        store_value,
                                        type,
                                        dst_name);
   }
 
+  if (!node->field().is_final()) {
+    // For now, disable list length guarding on non-final fields by specifying
+    // that the field doesn't have a length. See issue #12485.
+    node->field().set_guarded_list_length(Field::kNoLength);
+  }
+
   store_value = Bind(BuildStoreExprTemp(store_value));
   GuardFieldInstr* guard =
       new GuardFieldInstr(store_value,
                           node->field(),
                           Isolate::Current()->GetNextDeoptId());
   AddInstruction(guard);
 
   store_value = Bind(BuildLoadExprTemp());
   StoreInstanceFieldInstr* store =
       new StoreInstanceFieldInstr(node->field(),
@@ skipping 719 matching lines @@
   intptr_t len = OS::SNPrint(NULL, 0, kFormat, function_name, reason) + 1;
   char* chars = Isolate::Current()->current_zone()->Alloc<char>(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