From c2f7e242b048ae2691681d62b099ecf9634d6407 Mon Sep 17 00:00:00 2001
From: Tristan Gingold <tgingold@free.fr>
Date: Sat, 11 Jan 2020 07:43:03 +0100
Subject: synth-cleanup: avoid a crash on undriven output.  Fix #1078

---
 src/synth/netlists-cleanup.adb | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

(limited to 'src/synth/netlists-cleanup.adb')

diff --git a/src/synth/netlists-cleanup.adb b/src/synth/netlists-cleanup.adb
index 4d2cc40a9..f7342add9 100644
--- a/src/synth/netlists-cleanup.adb
+++ b/src/synth/netlists-cleanup.adb
@@ -129,9 +129,11 @@ package body Netlists.Cleanup is
          if Get_Id (Inst) = Id_Output then
             Inp := Get_Input (Inst, 0);
             O := Get_Driver (Inp);
-            Disconnect (Inp);
-
-            Redirect_Inputs (Get_Output (Inst, 0), O);
+            if O /= No_Net then
+               --  Only when the output is driven.
+               Disconnect (Inp);
+               Redirect_Inputs (Get_Output (Inst, 0), O);
+            end if;
             Remove_Instance (Inst);
          end if;
 
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