In background compilation make a copy of Field in order to freeze its state

runtime/vm/ast.cc

Index: runtime/vm/ast.cc
diff --git a/runtime/vm/ast.cc b/runtime/vm/ast.cc
index d1cd87779af320925fe9863d43ecfbf023ceef59..2e9cce9ea795fa70e2e3764647e4ac70feaa297c 100644
--- a/runtime/vm/ast.cc
+++ b/runtime/vm/ast.cc
@@ -37,6 +37,17 @@ FOR_EACH_NODE(DEFINE_NAME_FUNCTION)
 #undef DEFINE_NAME_FUNCTION
 
 
+const Field* AstNode::MayCloneField(const Field& value) {
+  if (Compiler::IsBackgroundCompilation() ||
+      FLAG_force_clone_compiler_objects) {
+    return value.CloneFromOriginal();

[siva, 2016/02/25 23:38:32]

Why not create the zone handle here instead of having CloneFromOriginal return a
pointer to a handle. In Object.h we have kept a pattern of returning raw
pointers and taking in arguments as handles.

  return &Field::ZoneHandle(value.CloneFromOriginal());

[srdjan, 2016/02/26 00:40:42]

OK, always returning RawField* instead of Field* in object.h.

+  } else {
+    ASSERT(value.IsZoneHandle());
+    return &value;
+  }
+}
+
+

[siva, 2016/02/25 23:38:32]

Add 
const Field* AstNode::OriginalAsHandle(const Field& value) const {
  return OriginalAsHandle(Thread::Current()->zone(), value);
}
const Field* AstNode::OriginalAsHandle(Zone* zone, const Field& value) const {
  return &Field::ZoneHandle(zone, value.Original());
}

[srdjan, 2016/02/26 00:40:42]

It feels wrong to put that shared functionality in ASTNode, especially since it
cannot be used in the frequent intermediate_language_xxx.cc case. Removing
OriginalAsHandle

 // A visitor class to collect all the nodes (including children) into an
 // array.
 class AstNodeCollector : public AstNodeVisitor {
@@ -582,7 +593,8 @@ AstNode* LoadStaticFieldNode::MakeAssignmentNode(AstNode* rhs) {
         AbstractType::ZoneHandle(field().type()),
         String::ZoneHandle(field().name()));
   }
-  return new StoreStaticFieldNode(token_pos(), field(), rhs);
+  return new StoreStaticFieldNode(
+      token_pos(), *field().OriginalAsHandle(), rhs);

[siva, 2016/02/25 23:38:32]

token_pos(), *OriginalAsHandle(field(), rhs);

[srdjan, 2016/02/26 00:40:42]

Resolved using Field::ZoneHandle

 }