From fc1f68e9df9fb41e3c9d279366b8b95f5c8cc9ca Mon Sep 17 00:00:00 2001
From: Tristan Gingold <tgingold@free.fr>
Date: Fri, 24 Apr 2020 06:39:13 +0200
Subject: synth-environment: add an optimization.  Fix #1258

This optimization is important for the control wires to avoid false paths.
---
 src/synth/synth-environment.adb | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'src')

diff --git a/src/synth/synth-environment.adb b/src/synth/synth-environment.adb
index f11c3f274..03acc2478 100644
--- a/src/synth/synth-environment.adb
+++ b/src/synth/synth-environment.adb
@@ -1285,6 +1285,10 @@ package body Synth.Environment is
                      N (0), Get_Driver (Get_Mux2_I1 (N1_Inst)));
                end if;
             end;
+         elsif N (0) = N (1) then
+            --  Minor optimization: no need to add a mux if both sides are
+            --  equal.  But this is important for the control wires.
+            Res := N (0);
          else
             Res := Build_Mux2 (Ctxt, Sel, N (0), N (1));
          end if;
-- 
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