ZJIT: Add dupn support

Author: XrXr

test/ruby/test_zjit.rb

@@ -671,6 +671,15 @@ def test = X
     end
   end
 
+  def test_dupn
+    assert_compiles '[0, 1]', <<~RUBY, insns: [:dupn]
+      def test(array) = (array[0] ||= 0)
+
+      array = [1]
+      [test(array), array.first]
+    RUBY
+  end
+
   def test_send_backtrace
     backtrace = [
       "-e:2:in 'Object#jit_frame1'",

zjit/src/hir.rs

@@ -2349,6 +2349,13 @@ pub fn iseq_to_hir(iseq: *const rb_iseq_t) -> Result<Function, ParseError> {
                 }
                 YARVINSN_pop => { state.stack_pop()?; }
                 YARVINSN_dup => { state.stack_push(state.stack_top()?); }
+                YARVINSN_dupn => {
+                    let n = get_arg(pc, 0).as_usize();
+                    let top = state.stack_top()?;
+                    for _ in 0..n {
+                        state.stack_push(top);
+                    }
+                }
                 YARVINSN_swap => {
                     let right = state.stack_pop()?;
                     let left = state.stack_pop()?;