register_fstring: avoid duping the passed string when possible

If the passed string is frozen, bare and not shared, then there
is no need to duplicate it.

Ref: 4ab69ebbd7cef8539f687e1f948845d076461dc6
Ref: https://bugs.ruby-lang.org/issues/11386

1 files changed, 2 insertions, 1 deletions

diff --git a/string.c b/string.c
index 1a1b9fd6ed..df7e81410a 100644
--- a/string.c
+++ b/string.c
@@ -305,7 +305,8 @@ fstr_update_callback(st_data_t *key, st_data_t *value, st_data_t arg, int existi
 	    OBJ_FREEZE_RAW(str);
 	}
 	else {
-	    str = str_new_frozen(rb_cString, str);
+	    if (!OBJ_FROZEN(str))
+		str = str_new_frozen(rb_cString, str);
 	    if (STR_SHARED_P(str)) { /* str should not be shared */
 		/* shared substring  */
 		str_make_independent(str);