From 4bb12b30a53326ac6e3177bc4016317181dd7f7e Mon Sep 17 00:00:00 2001
From: Tristan Gingold <tgingold@free.fr>
Date: Wed, 22 Apr 2020 08:15:48 +0200
Subject: netlists: infere tri gate.

---
 src/synth/netlists-inference.adb | 26 ++++++++++++++++++++++++++
 src/synth/netlists-utils.adb     | 14 ++++++++++++++
 src/synth/netlists-utils.ads     |  4 ++++
 3 files changed, 44 insertions(+)

(limited to 'src')

diff --git a/src/synth/netlists-inference.adb b/src/synth/netlists-inference.adb
index 1155a6047..8b053855e 100644
--- a/src/synth/netlists-inference.adb
+++ b/src/synth/netlists-inference.adb
@@ -812,6 +812,32 @@ package body Netlists.Inference is
          return Val;
       end if;
 
+      --  Infere tri-buf.
+      First_Mux := Get_Net_Parent (Val);
+      if Get_Id (First_Mux) = Id_Mux2 then
+         declare
+            Nsel, N0, N1 : Net;
+         begin
+            --  Check for VAL <= SEL ? N1 : 'Z'
+            if Get_Id (Get_Input_Instance (First_Mux, 1)) = Id_Const_Z then
+               --  Disconnect the mux.
+               Nsel := Disconnect_And_Get (First_Mux, 0);
+               N0 := Disconnect_And_Get (First_Mux, 1);
+               N1 := Disconnect_And_Get (First_Mux, 2);
+               --  Build the tri buf.
+               Res := Build_Tri (Ctxt, Nsel, N1);
+               --  Remove the 'Z' (shouldn't be connected).
+               Remove_Instance (Get_Net_Parent (N0));
+               --  Copy location.
+               Copy_Location (Res, First_Mux);
+               --  Redirect tri output.
+               Redirect_Inputs (Get_Output (First_Mux, 0), Res);
+               Remove_Instance (First_Mux);
+               return Res;
+            end if;
+         end;
+      end if;
+
       Find_Longest_Loop (Val, Prev_Val, Last_Mux, Len);
       if Len <= 0 then
          --  No logical loop or self assignment.
diff --git a/src/synth/netlists-utils.adb b/src/synth/netlists-utils.adb
index bf33cb13e..fa1494820 100644
--- a/src/synth/netlists-utils.adb
+++ b/src/synth/netlists-utils.adb
@@ -237,6 +237,20 @@ package body Netlists.Utils is
       return Inp = No_Input;
    end Has_One_Connection;
 
+   function Disconnect_And_Get (I : Input) return Net
+   is
+      N : Net;
+   begin
+      N := Get_Driver (I);
+      Disconnect (I);
+      return N;
+   end Disconnect_And_Get;
+
+   function Disconnect_And_Get (Inst : Instance; I : Port_Idx) return Net is
+   begin
+      return Disconnect_And_Get (Get_Input (Inst, I));
+   end Disconnect_And_Get;
+
    procedure Disconnect_And_Free (I : Input)
    is
       I_Net : constant Net := Get_Driver (I);
diff --git a/src/synth/netlists-utils.ads b/src/synth/netlists-utils.ads
index e4981b38a..aeeb5cc78 100644
--- a/src/synth/netlists-utils.ads
+++ b/src/synth/netlists-utils.ads
@@ -85,6 +85,10 @@ package Netlists.Utils is
    --  disconnect and free it.
    procedure Disconnect_And_Free (I : Input);
 
+   --  Disconnect an input and return the previous driver.
+   function Disconnect_And_Get (I : Input) return Net;
+   function Disconnect_And_Get (Inst : Instance; I : Port_Idx) return Net;
+
    --  Return true IFF L and R is the same net.
    --  Either because L = R (obvious case) or because both are the same
    --  selection of the same net.
-- 
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