glass	2017-10-22 09:57:46 +0900 (Sun, 22 Oct 2017)

  New Revision: 60337

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=60337

  Log:
    hash.c: optimize Hash#compare_by_identity
    
    hash.c (rb_hash_compare_by_id): avoid unnecessary allocation of st_table.
    formerly, st_table created in rb_hash_modify() was not used and replaced immediately.

  Modified files:
    trunk/hash.c
Index: hash.c
===================================================================
--- hash.c	(revision 60336)
+++ hash.c	(revision 60337)
@@ -2899,10 +2899,16 @@ rb_hash_compact_bang(VALUE hash) https://github.com/ruby/ruby/blob/trunk/hash.c#L2899
 static VALUE
 rb_hash_compare_by_id(VALUE hash)
 {
+    st_table *identtable;
     if (rb_hash_compare_by_id_p(hash)) return hash;
-    rb_hash_modify(hash);
-    RHASH(hash)->ntbl->type = &identhash;
-    rb_hash_rehash(hash);
+    rb_hash_modify_check(hash);
+
+    identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
+    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)identtable);
+    if (RHASH(hash)->ntbl)
+	st_free_table(RHASH(hash)->ntbl);
+    RHASH(hash)->ntbl = identtable;
+
     return hash;
 }
 

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