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-- Netlist cleanup.
-- Copyright (C) 2019 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, see <gnu.org/licenses>.
with Netlists.Utils; use Netlists.Utils;
with Netlists.Gates;
package body Netlists.Cleanup is
-- Return False iff INST has no outputs (and INST is not Id_Free).
-- Return True iff all outputs of INST are unconnected.
-- Return False otherwise.
function Is_Unused_Instance (Inst : Instance) return Boolean
is
Nbr_Outputs : constant Port_Idx := Get_Nbr_Outputs (Inst);
N : Net;
begin
-- An instance without outputs is considered as used.
if Nbr_Outputs = 0 then
return Get_Module (Inst) = Free_Module;
end if;
for Idx in 0 .. Nbr_Outputs - 1 loop
N := Get_Output (Inst, Idx);
if Is_Connected (N) then
-- Connected output.
return False;
end if;
end loop;
-- All outputs are unconnected.
return True;
end Is_Unused_Instance;
-- Move INST on LIST iff INST is unused.
procedure Extract_If_Unused (Inst : Instance; List : in out Instance) is
begin
if Is_Unused_Instance (Inst) then
Extract_Instance (Inst);
Set_Next_Instance (Inst, List);
List := Inst;
end if;
end Extract_If_Unused;
-- TODO: use mark & sweep to remove unused assignments ?
procedure Remove_Unconnected_Instances (M : Module)
is
Inst : Instance;
Next_Inst : Instance;
List : Instance;
begin
-- Extract from instances of M all unconnected instances. Put them
-- in a list.
List := No_Instance;
Inst := Get_First_Instance (M);
-- But keep the self-instance.
Inst := Get_Next_Instance (Inst);
while Inst /= No_Instance loop
Next_Inst := Get_Next_Instance (Inst);
Extract_If_Unused (Inst, List);
Inst := Next_Inst;
end loop;
-- While the list is not empty:
-- extract the first instance of the list.
-- unconnect all inputs of the instance, free the instance.
-- if unconnected an input resulted in an instance without connected
-- output, extract it from M and append it in the list.
while List /= No_Instance loop
Inst := List;
List := Get_Next_Instance (Inst);
declare
Nbr_Inputs : constant Port_Nbr := Get_Nbr_Inputs (Inst);
Inp : Input;
Drv : Net;
Inst2 : Instance;
begin
if Nbr_Inputs > 0 then
for K in 0 .. Nbr_Inputs - 1 loop
Inp := Get_Input (Inst, K);
Drv := Get_Driver (Inp);
if Drv /= No_Net then
-- Disconnect the input.
Disconnect (Inp);
-- Possibly consider the driver as unconnected if was
-- the last input connected.
if Get_First_Sink (Drv) = No_Input then
Inst2 := Get_Net_Parent (Drv);
Extract_If_Unused (Inst2, List);
end if;
end if;
end loop;
end if;
end;
Free_Instance (Inst);
end loop;
end Remove_Unconnected_Instances;
procedure Remove_Output_Gates (M : Module)
is
use Netlists.Gates;
Inst : Instance;
Next_Inst : Instance;
begin
Inst := Get_First_Instance (M);
while Inst /= No_Instance loop
Next_Inst := Get_Next_Instance (Inst);
case Get_Id (Inst) is
when Id_Output
| Id_Ioutput
| Id_Port
| Id_Enable
| Id_Nop =>
declare
Inp : Input;
In_Drv : Net;
O : Net;
begin
Inp := Get_Input (Inst, 0);
In_Drv := Get_Driver (Inp);
O := Get_Output (Inst, 0);
if In_Drv /= No_Net then
-- Only when the output is driven.
Disconnect (Inp);
Redirect_Inputs (O, In_Drv);
else
Disconnect (Get_First_Sink (O));
end if;
if Get_Id (Inst) = Id_Ioutput then
-- Disconnect the initial value.
Disconnect (Get_Input (Inst, 1));
end if;
Remove_Instance (Inst);
end;
when others =>
null;
end case;
Inst := Next_Inst;
end loop;
end Remove_Output_Gates;
procedure Insert_Mark_And_Sweep (Inspect : in out Instance_Tables.Instance;
Inst : Instance) is
begin
if not Get_Mark_Flag (Inst) then
Set_Mark_Flag (Inst, True);
Instance_Tables.Append (Inspect, Inst);
end if;
end Insert_Mark_And_Sweep;
procedure Mark_And_Sweep (M : Module)
is
use Netlists.Gates;
-- Table of new gates to be inspected.
Inspect : Instance_Tables.Instance;
Inst : Instance;
Inp : Input;
begin
Instance_Tables.Init (Inspect, 64);
-- 1. Check instances are not marked.
-- 1.1 Insert assertion gates.
Inst := Get_First_Instance (M);
while Inst /= No_Instance loop
pragma Assert (Get_Mark_Flag (Inst) = False);
case Get_Id (Inst) is
when Id_Assert
| Id_Assume
| Id_Cover
| Id_Assert_Cover =>
Insert_Mark_And_Sweep (Inspect, Inst);
when Id_User_None
| Id_User_Parameters =>
-- Always keep user modules.
Insert_Mark_And_Sweep (Inspect, Inst);
when others =>
null;
end case;
Inst := Get_Next_Instance (Inst);
end loop;
-- 1.2 Insert output drivers.
-- This corresponds to the input of the self instance.
Insert_Mark_And_Sweep (Inspect, Get_Self_Instance (M));
-- 2. While the table is not empty, extract an element and insert
-- all the input drivers.
loop
declare
Idx : Int32;
N : Net;
begin
Idx := Instance_Tables.Last (Inspect);
exit when Idx < Instance_Tables.First;
Inst := Inspect.Table (Idx);
Instance_Tables.Decrement_Last (Inspect);
for I in 1 .. Get_Nbr_Inputs (Inst) loop
N := Get_Input_Net (Inst, I - 1);
if N /= No_Net then
Insert_Mark_And_Sweep (Inspect, Get_Net_Parent (N));
end if;
end loop;
case Get_Id (Inst) is
when Id_Mem_Rd
| Id_Mem_Rd_Sync =>
-- When a memory read port is found, mark the whole
-- memory.
-- FIXME: free unused read ports.
declare
Inp : Input;
begin
loop
N := Get_Output (Inst, 0);
Inp := Get_First_Sink (N);
exit when Inp = No_Input;
pragma Assert (Get_Next_Sink (Inp) = No_Input);
Inst := Get_Input_Parent (Inp);
exit when Get_Mark_Flag (Inst);
Insert_Mark_And_Sweep (Inspect, Inst);
N := Get_Output (Inst, 0);
end loop;
end;
when others =>
null;
end case;
end;
end loop;
-- 3. Remove unused instances; unmark used instances.
Instance_Tables.Free (Inspect);
declare
Next_Inst : Instance;
First_Unused : Instance;
Last_Unused : Instance;
begin
First_Unused := No_Instance;
Last_Unused := No_Instance;
Extract_All_Instances (M, Inst);
-- But keep the self-instance.
pragma Assert (Get_Mark_Flag (Inst));
Set_Mark_Flag (Inst, False);
Next_Inst := Get_Next_Instance (Inst);
Append_Instance (M, Inst);
Inst := Next_Inst;
while Inst /= No_Instance loop
Next_Inst := Get_Next_Instance (Inst);
if Get_Mark_Flag (Inst) then
-- Instance was marked, keept it.
Set_Mark_Flag (Inst, False);
Append_Instance (M, Inst);
else
-- Instance was not marked, disconnect it.
for I in 1 .. Get_Nbr_Inputs (Inst) loop
Inp := Get_Input (Inst, I - 1);
if Get_Driver (Inp) /= No_Net then
-- Disconnect the input.
Disconnect (Inp);
end if;
end loop;
if First_Unused = No_Instance then
First_Unused := Inst;
else
Set_Next_Instance (Last_Unused, Inst);
end if;
Last_Unused := Inst;
end if;
Inst := Next_Inst;
end loop;
-- Free unused instances. This must be done at the end so that
-- their outputs are disconnected.
if First_Unused /= No_Instance then
Set_Next_Instance (Last_Unused, No_Instance);
loop
Inst := First_Unused;
exit when Inst = No_Instance;
First_Unused := Get_Next_Instance (Inst);
Set_Next_Instance (Inst, No_Instance);
Set_Prev_Instance (Inst, No_Instance);
Free_Instance (Inst);
end loop;
end if;
end;
end Mark_And_Sweep;
end Netlists.Cleanup;
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