8134758: Final String field values should be trusted as stable
Reviewed-by: kvn, thartmann
--- a/hotspot/src/share/vm/opto/memnode.cpp Wed Aug 26 17:13:59 2015 +0100
+++ b/hotspot/src/share/vm/opto/memnode.cpp Tue Sep 01 19:48:10 2015 +0300
@@ -1677,6 +1677,9 @@
if (klass == env->String_klass() &&
adr->is_AddP() && off != Type::OffsetBot) {
// For constant Strings treat the final fields as compile time constants.
+ // While we can list what field types java.lang.String has, it is more
+ // future-proof to handle all possible field types, anticipating future
+ // changes and experiments in String code.
Node* base = adr->in(AddPNode::Base);
const TypeOopPtr* t = phase->type(base)->isa_oopptr();
if (t != NULL && t->singleton()) {
@@ -1684,14 +1687,13 @@
if (field != NULL && field->is_final()) {
ciObject* string = t->const_oop();
ciConstant constant = string->as_instance()->field_value(field);
- if (constant.basic_type() == T_INT) {
- return TypeInt::make(constant.as_int());
- } else if (constant.basic_type() == T_ARRAY) {
- if (adr->bottom_type()->is_ptr_to_narrowoop()) {
- return TypeNarrowOop::make_from_constant(constant.as_object(), true);
- } else {
- return TypeOopPtr::make_from_constant(constant.as_object(), true);
- }
+ // Type::make_from_constant does not handle narrow oops, so handle it here.
+ // Everything else can use the factory method.
+ if ((constant.basic_type() == T_ARRAY || constant.basic_type() == T_OBJECT)
+ && adr->bottom_type()->is_ptr_to_narrowoop()) {
+ return TypeNarrowOop::make_from_constant(constant.as_object(), true);
+ } else {
+ return Type::make_from_constant(constant, true);
}
}
}