Avoid hash allocation for empty ruby2_keywords flagged keyword hash

If the method being called does not have a keyword splat parameter,
there is no point in allocating the hash, because the hash will
be unused (as empty keyword hashes are ignored).

1 files changed, 3 insertions, 1 deletions

diff --git a/vm_args.c b/vm_args.c
index 1a78e96776..1db62dc7e2 100644
--- a/vm_args.c
+++ b/vm_args.c
@@ -684,7 +684,9 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
             if (RB_TYPE_P(rest_last, T_HASH) && FL_TEST_RAW(rest_last, RHASH_PASS_AS_KEYWORDS)) {
                 // def f(**kw); a = [..., kw]; g(*a)
                 splat_flagged_keyword_hash = rest_last;
-                rest_last = rb_hash_dup(rest_last);
+                if (!RHASH_EMPTY_P(rest_last) || (ISEQ_BODY(iseq)->param.flags.has_kwrest)) {
+                    rest_last = rb_hash_dup(rest_last);
+                }
                 kw_flag |= VM_CALL_KW_SPLAT | VM_CALL_KW_SPLAT_MUT;
 
                 // Unset rest_dupped set by anon_rest as we may need to modify splat in this case