Make String#replace to check equality before modifying flags.
ref
MODIFY
src/string.c
src/string.c
@@ -520,9 +520,9 @@ str_replace(mrb_state *mrb, struct RString *s1, struct RString *s2)
long len;
check_frozen(mrb, s1);
+ if (s1 == s2) return mrb_obj_value(s1);
s1->flags &= ~MRB_STR_NO_UTF;
s1->flags |= s2->flags&MRB_STR_NO_UTF;
- if (s1 == s2) return mrb_obj_value(s1);
len = RSTR_LEN(s2);
if (RSTR_SHARED_P(s1)) {
str_decref(mrb, s1->as.heap.aux.shared);

Make String#replace to check equality before modifying flags.

ref #3588