From 2fb075ce580374c7ea01a11b7dee698e8913ef9d Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Sun, 22 Dec 2019 19:58:57 -0600
Subject: [PATCH] Do not dereference and write through a null pointer during
 loop invariant removal.

---
 DAG.pas | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/DAG.pas b/DAG.pas
index e3639f9..791efe2 100644
--- a/DAG.pas
+++ b/DAG.pas
@@ -3255,7 +3255,8 @@ var
    new(dp);
    dp^.last := nil;
    dp^.next := dom;
-   dom^.last := dp;
+   if dom <> nil then
+      dom^.last := dp;
    dom := dp;
    dp^.dfn := dfn;
    end; {AddDominator}