From c23e68d32b8913f35e344844805d1b80f5633ecd Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Mon, 10 Dec 2018 10:23:01 +0900
Subject: Need to clear stack before invoking a block; fix #4181

---
 src/vm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

(limited to 'src/vm.c')

diff --git a/src/vm.c b/src/vm.c
index 84e076ee8..b5249b325 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -667,10 +667,11 @@ eval_under(mrb_state *mrb, mrb_value self, mrb_value blk, struct RClass *c)
     return MRB_PROC_CFUNC(p)(mrb, self);
   }
   nregs = p->body.irep->nregs;
-  mrb_stack_extend(mrb, (nregs < 3) ? 3 : nregs);
+  if (nregs < 3) nregs = 3;
+  mrb_stack_extend(mrb, nregs);
   mrb->c->stack[0] = self;
   mrb->c->stack[1] = self;
-  mrb->c->stack[2] = mrb_nil_value();
+  stack_clear(mrb->c->stack+2, nregs-2);
   ci = cipush(mrb);
   ci->target_class = 0;
   ci->pc = p->body.irep->iseq;
-- 
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