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diff --git a/src/synth/netlists-utils.adb b/src/synth/netlists-utils.adb
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+++ b/src/synth/netlists-utils.adb
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+--  Netlist utilities (composed of a few calls).
+--  Copyright (C) 2017 Tristan Gingold
+--
+--  This file is part of GHDL.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 2 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program; if not, write to the Free Software
+--  Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+--  MA 02110-1301, USA.
+
+package body Netlists.Utils is
+   function Get_Nbr_Inputs (Inst : Instance) return Port_Nbr
+   is
+      M : constant Module := Get_Module (Inst);
+   begin
+      if Is_Self_Instance (Inst) then
+         return Get_Nbr_Outputs (M);
+      else
+         return Get_Nbr_Inputs (M);
+      end if;
+   end Get_Nbr_Inputs;
+
+   function Get_Nbr_Outputs (Inst : Instance) return Port_Nbr
+   is
+      M : constant Module := Get_Module (Inst);
+   begin
+      if Is_Self_Instance (Inst) then
+         return Get_Nbr_Inputs (M);
+      else
+         return Get_Nbr_Outputs (M);
+      end if;
+   end Get_Nbr_Outputs;
+
+   function Get_Nbr_Params (Inst : Instance) return Param_Nbr
+   is
+      M : constant Module := Get_Module (Inst);
+   begin
+      return Get_Nbr_Params (M);
+   end Get_Nbr_Params;
+
+   function Get_Param_Desc
+     (Inst : Instance; Param : Param_Idx) return Param_Desc is
+   begin
+      return Get_Param_Desc (Get_Module (Inst), Param);
+   end Get_Param_Desc;
+
+   function Get_Id (Inst : Instance) return Module_Id is
+   begin
+      return Get_Id (Get_Module (Inst));
+   end Get_Id;
+
+   function Get_Input_Name (M : Module; I : Port_Idx) return Sname is
+   begin
+      return Get_Input_Desc (M, I).Name;
+   end Get_Input_Name;
+
+   function Get_Output_Name (M : Module; I : Port_Idx) return Sname is
+   begin
+      return Get_Output_Desc (M, I).Name;
+   end Get_Output_Name;
+
+   function Is_Connected (O : Net) return Boolean is
+   begin
+      return Get_First_Sink (O) /= No_Input;
+   end Is_Connected;
+
+   function Has_One_Connection (O : Net) return Boolean
+   is
+      Inp : Input;
+   begin
+      Inp := Get_First_Sink (O);
+      if Inp = No_Input then
+         --  No connection.
+         return False;
+      end if;
+      Inp := Get_Next_Sink (Inp);
+      return Inp = No_Input;
+   end Has_One_Connection;
+
+   procedure Disconnect_And_Free (I : Input)
+   is
+      I_Net : constant Net := Get_Driver (I);
+      Inst : constant Instance := Get_Net_Parent (I_Net);
+      Nbr_Inputs : Port_Nbr;
+      Nbr_Outputs : Port_Nbr;
+   begin
+      --  First disconnect.
+      Disconnect (I);
+
+      --  Quick check: is output (of I) still used ?
+      if Is_Connected (I_Net) then
+         return;
+      end if;
+
+      --  Check that all outputs are unused.
+      Nbr_Outputs := Get_Nbr_Outputs (Inst);
+      if Nbr_Outputs > 1 then
+         for K in 0 .. Nbr_Outputs - 1 loop
+            if Is_Connected (Get_Output (Inst, K)) then
+               return;
+            end if;
+         end loop;
+      end if;
+
+      --  First disconnect inputs.
+      Nbr_Inputs := Get_Nbr_Inputs (Inst);
+      if Nbr_Inputs > 0 then
+         for K in 0 .. Nbr_Inputs - 1 loop
+            Disconnect_And_Free (Get_Input (Inst, K));
+         end loop;
+      end if;
+
+      --  Free Inst
+      Free_Instance (Inst);
+   end Disconnect_And_Free;
+end Netlists.Utils;