Adjust sp for `if true or ...`/`if false and ...`

compile.c

@@ -3889,7 +3889,10 @@ compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *co
 	    LABEL *label = NEW_LABEL(nd_line(cond));
 	    CHECK(compile_branch_condition(iseq, ret, cond->nd_1st, label,
 					   else_label));
-	    if (!label->refcnt) break;
+            if (!label->refcnt) {
+                ADD_INSN(ret, nd_line(cond), putnil);
+                break;
+            }
 	    ADD_LABEL(ret, label);
 	    cond = cond->nd_2nd;
 	    goto again;
@@ -3899,7 +3902,10 @@ compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *co
 	    LABEL *label = NEW_LABEL(nd_line(cond));
 	    CHECK(compile_branch_condition(iseq, ret, cond->nd_1st, then_label,
 					   label));
-	    if (!label->refcnt) break;
+            if (!label->refcnt) {
+                ADD_INSN(ret, nd_line(cond), putnil);
+                break;
+            }
 	    ADD_LABEL(ret, label);
 	    cond = cond->nd_2nd;
 	    goto again;

test/ruby/test_syntax.rb

@@ -1514,6 +1514,11 @@ eom
     assert_valid_syntax("tap {a = (break unless true)}")
   end
 
+  def test_tautological_condition
+    assert_valid_syntax("def f() return if false and invalid; nil end")
+    assert_valid_syntax("def f() return unless true or invalid; nil end")
+  end
+
   def test_argument_forwarding
     assert_valid_syntax('def foo(...) bar(...) end')
     assert_valid_syntax('def foo(...) end')