hash.c: aset deduplicates un-tainted string

We revisit [Bug #9188] since st.c is much improved since then,
and benchmarks against so_k_nucleotide seem to indicate little
or no performance change compared to before.

[ruby-core:89555] [Feature #15251]

From: Anmol Chopra <chopraanmol1@gmail.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65371 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 5 insertions, 1 deletions

diff --git a/hash.c b/hash.c
index fc38f2f0ab..3f278e0c03 100644
--- a/hash.c
+++ b/hash.c
@@ -1587,11 +1587,15 @@ VALUE
 rb_hash_key_str(VALUE key)
 {
     VALUE k;
+    int not_tainted = !RB_OBJ_TAINTED(key);
 
-    if (!RB_OBJ_TAINTED(key) &&
+    if (not_tainted &&
 	(k = fstring_existing_str(key)) != Qnil) {
 	return k;
     }
+    else if(not_tainted) {
+        return rb_fstring(key);
+    }
     else {
 	return rb_str_new_frozen(key);
     }