Fix optimizations on static fields in precompiled code.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, 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_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/compiler.h"
 #include "vm/cpu.h"
@@ skipping 37 matching lines @@
 #if defined(TARGET_ARCH_ARM) || defined(TARGET_ARCH_IA32)
 DEFINE_FLAG(bool, trace_smi_widening, false, "Trace Smi->Int32 widening pass.");
 #endif
 
 DECLARE_FLAG(bool, polymorphic_with_deopt);
 DECLARE_FLAG(bool, source_lines);
 DECLARE_FLAG(bool, trace_cha);
 DECLARE_FLAG(bool, trace_field_guards);
 DECLARE_FLAG(bool, trace_type_check_elimination);
 DECLARE_FLAG(bool, warn_on_javascript_compatibility);
+DECLARE_FLAG(bool, fields_may_be_reset);
 
 // Quick access to the current isolate and zone.
 #define I (isolate())
 #define Z (zone())
 
 static bool ShouldInlineSimd() {
   return FlowGraphCompiler::SupportsUnboxedSimd128();
 }
 
 
@@ skipping 5579 matching lines @@
               DefinitionName(instance()),
               index_constant(),
               ElementSizeMultiplier(element_size()));
         }
     }
     UNREACHABLE();
     return "<?>";
   }
 
   bool IsFinalField() const {
-    return (kind() == kField) && field().is_final();
+    return (kind() == kField)
+        && field().is_final()
+        && (!field().is_static() || !FLAG_fields_may_be_reset);

[srdjan, 2015/12/03 16:57:56]

IMO, the flag does not belong here, the test is for IsFinalField. I suggest
renaming the test method to something like IsImmutableField and add comment what
is going on.

[rmacnak, 2015/12/03 21:09:11]

Ditto.

[Florian Schneider, 2015/12/04 11:36:54]

Done.

   }
 
   intptr_t Hashcode() const {
     return (flags_ * 63 + reinterpret_cast<intptr_t>(instance_)) * 31 +
         FieldHashcode();
   }
 
   bool Equals(const Place* other) const {
     return (flags_ == other->flags_) &&
         (instance_ == other->instance_) &&
@@ skipping 3157 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, *slots);
   }
 }
 
 
 }  // namespace dart