Need to keep block argument in `mrb_exec_irep`; fix
MODIFY
src/vm.c
src/vm.c
@@ -516,7 +516,7 @@ mrb_exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
}
ci->nregs = p->body.irep->nregs;
if (ci->argc < 0) keep = 3;
- else keep = ci->argc + 1;
+ else keep = ci->argc + 2;
if (ci->nregs < keep) {
stack_extend(mrb, keep);
}

Need to keep block argument in `mrb_exec_irep`; fix #3973