From 83183230bfa25071c6d18df457ba3e2fefa3b001 Mon Sep 17 00:00:00 2001
From: Tristan Gingold <tgingold@free.fr>
Date: Tue, 28 Apr 2020 08:17:16 +0200
Subject: synth: improve handling of synchronous memory read.
---
src/synth/netlists-memories.adb | 98 ++++++++++++++++++++++++++++++++++++++---
1 file changed, 92 insertions(+), 6 deletions(-)
diff --git a/src/synth/netlists-memories.adb b/src/synth/netlists-memories.adb
index 31767e09d..c127b940f 100644
--- a/src/synth/netlists-memories.adb
+++ b/src/synth/netlists-memories.adb
@@ -454,12 +454,13 @@ package body Netlists.Memories is
end if;
end Is_Enable_Dff;
- procedure Extract_Extract_Dff
- (Ctxt : Context_Acc;
- Inst : Instance;
- Last_Inst : out Instance;
- Clk : out Net;
- En : out Net)
+ -- If INST is followed by a dff or a dff+enable (with mux2), return the
+ -- dff in LAST_INST, the clock in CLK and the enable in EN.
+ procedure Extract_Extract_Dff (Ctxt : Context_Acc;
+ Inst : Instance;
+ Last_Inst : out Instance;
+ Clk : out Net;
+ En : out Net)
is
Val : constant Net := Get_Output (Inst, 0);
Inp : Input;
@@ -517,6 +518,90 @@ package body Netlists.Memories is
En := No_Net;
end Extract_Extract_Dff;
+ -- If dyn_extract gate EXTRACT is followed by a concat and a dff, then
+ -- swap the dff and the concat. This will allow to merge the dff during
+ -- the build of mem_rd_sync.
+ -- This creates new gates (the dff is replicated) that will be removed.
+ procedure Maybe_Swap_Concat_Dff (Ctxt : Context_Acc; Extract : Instance)
+ is
+ Extr_Out : constant Net := Get_Output (Extract, 0);
+ Concat : Instance;
+ Concat_Out : Net;
+ Dff : Instance;
+ Clk, En : Net;
+ Loc : Location_Type;
+ begin
+ if not Has_One_Connection (Extr_Out) then
+ -- The dyn_extract is connected to more than one gate.
+ return;
+ end if;
+
+ Concat := Get_Input_Parent (Get_First_Sink (Extr_Out));
+ case Get_Id (Concat) is
+ when Concat_Module_Id
+ | Id_Concatn =>
+ null;
+ when others =>
+ -- Not a concat.
+ return;
+ end case;
+
+ Concat_Out := Get_Output (Concat, 0);
+ if not Has_One_Connection (Concat_Out) then
+ -- The concat is connected to more than one gate.
+ return;
+ end if;
+ for I in 1 .. Get_Nbr_Inputs (Concat) loop
+ declare
+ Src : constant Net := Get_Input_Net (Concat, I - 1);
+ begin
+ if Get_Id (Get_Net_Parent (Src)) /= Id_Dyn_Extract then
+ -- A source of concat is not a dyn_extract.
+ return;
+ end if;
+ if not Has_One_Connection (Src) then
+ -- A source of concat drives something else!
+ return;
+ end if;
+ end;
+ end loop;
+
+ Extract_Extract_Dff (Ctxt, Concat, Dff, Clk, En);
+ if Clk = No_Net then
+ return;
+ end if;
+
+ -- Replicate the dff.
+ Loc := Get_Location (Dff);
+ for I in 1 .. Get_Nbr_Inputs (Concat) loop
+ declare
+ Inp : constant Input := Get_Input (Concat, I - 1);
+ Dff2 : Net;
+ Mux : Net;
+ Dff2_Inp : Input;
+ Src : Net;
+ begin
+ Src := Disconnect_And_Get (Inp);
+
+ Dff2 := Build_Dff (Ctxt, Clk, Src);
+ Set_Location (Dff2, Loc);
+ Connect (Inp, Dff2);
+
+ if En /= No_Net then
+ Dff2_Inp := Get_Input (Get_Net_Parent (Dff2), 1);
+ Mux := Build_Mux2 (Ctxt, En, Dff2, Src);
+ Set_Location (Mux, Loc);
+ Disconnect (Dff2_Inp);
+ Connect (Dff2_Inp, Mux);
+ end if;
+ end;
+ end loop;
+
+ -- Reconnect the concat.
+ Redirect_Inputs (Get_Output (Dff, 0), Concat_Out);
+ Remove_Instance (Dff);
+ end Maybe_Swap_Concat_Dff;
+
-- Create a mem_rd/mem_rd_sync from a dyn_extract gate.
-- LAST is the last memory port on the chain.
-- ADDR is the address (from the dyn_extract).
@@ -1460,6 +1545,7 @@ package body Netlists.Memories is
Addr := Get_Driver (Inp2);
Disconnect (Inp2);
Convert_Memidx (Ctxt, Mem_Sz, Addr, Mem_W);
+ Maybe_Swap_Concat_Dff (Ctxt, In_Inst);
Extract_Extract_Dff (Ctxt, In_Inst, Last_Inst, Clk, En);
if Clk /= No_Net and then En = No_Net then
En := Build_Const_UB32 (Ctxt, 1, 1);
--
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