From 47a4727b78c146adc24cbfbeeabc3abf022e14f8 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Mon, 13 Jul 2015 11:02:29 +0200
Subject: [PATCH] intset-union fast paths

* module/language/cps/intset.scm (intset-union): Add fast paths for
  union with empty intset.
---
 module/language/cps/intset.scm | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/module/language/cps/intset.scm b/module/language/cps/intset.scm
index 87956c525..7f8316ea7 100644
--- a/module/language/cps/intset.scm
+++ b/module/language/cps/intset.scm
@@ -508,6 +508,8 @@
   (match (cons a b)
     ((($ <intset> a-min a-shift a-root) . ($ <intset> b-min b-shift b-root))
      (cond
+      ((not b-root) a)
+      ((not a-root) b)
       ((not (= b-shift a-shift))
        ;; Hoist the set with the lowest shift to meet the one with the
        ;; higher shift.