synth: push extract on mux2 for inference. For #1421

3 files changed, 52 insertions, 17 deletions

diff --git a/src/synth/netlists-folds.adb b/src/synth/netlists-folds.adb
index c4138d0cd..411415901 100644
--- a/src/synth/netlists-folds.adb
+++ b/src/synth/netlists-folds.adb
@@ -270,6 +270,34 @@ package body Netlists.Folds is
       end if;
    end Build2_Extract;
 
+   function Build2_Extract_Push
+     (Ctxt : Context_Acc; I : Net; Off, W : Width) return Net
+   is
+      Inst : constant Instance := Get_Net_Parent (I);
+      Res : Net;
+   begin
+      if Off = 0 and then W = Get_Width (I) then
+         return I;
+      end if;
+
+      case Get_Id (Inst) is
+         when Id_Extract =>
+            return Build2_Extract_Push
+              (Ctxt, Get_Input_Net (Inst, 0),
+               Off + Get_Param_Uns32 (Inst, 0), W);
+         when Id_Mux2 =>
+            Res := Build_Mux2
+              (Ctxt,
+               Get_Input_Net (Inst, 0),
+               Build2_Extract_Push (Ctxt, Get_Input_Net (Inst, 1), Off, W),
+               Build2_Extract_Push (Ctxt, Get_Input_Net (Inst, 2), Off, W));
+            Set_Location (Res, Get_Location (Inst));
+            return Res;
+         when others =>
+            return Build_Extract (Ctxt, I, Off, W);
+      end case;
+   end Build2_Extract_Push;
+
    function Build2_Imp (Ctxt : Context_Acc; A, B : Net; Loc : Location_Type)
                        return Net
    is
diff --git a/src/synth/netlists-folds.ads b/src/synth/netlists-folds.ads
index 6c63f49bc..3ee69f41c 100644
--- a/src/synth/netlists-folds.ads
+++ b/src/synth/netlists-folds.ads
@@ -71,6 +71,12 @@ package Netlists.Folds is
    function Build2_Extract
      (Ctxt : Context_Acc; I : Net; Off, W : Width) return Net;
 
+   --  Likewise, but if I is an output of a mux2, build the extract gates
+   --  on the input of the mux2 (recursively).
+   --  The purpose is to keep the control flow of the mux2 tree.
+   function Build2_Extract_Push
+     (Ctxt : Context_Acc; I : Net; Off, W : Width) return Net;
+
    --  Return A -> B  ==  !A || B
    function Build2_Imp (Ctxt : Context_Acc; A, B : Net; Loc : Location_Type)
                        return Net;
diff --git a/src/synth/synth-environment.adb b/src/synth/synth-environment.adb
index 18133594e..7f552f352 100644
--- a/src/synth/synth-environment.adb
+++ b/src/synth/synth-environment.adb
@@ -1036,7 +1036,7 @@ package body Synth.Environment is
 
       --  If no seq assign, return current value.
       if First_Seq = No_Seq_Assign then
-         return Build2_Extract (Ctxt, Wire_Rec.Gate, Off, Wd);
+         return Build2_Extract_Push (Ctxt, Wire_Rec.Gate, Off, Wd);
       end if;
 
       --  If the current value is static, just return it.
@@ -1096,8 +1096,9 @@ package body Synth.Environment is
                         Cur_Wd := Width'Min
                           (Cur_Wd, Pw - (Cur_Off - Pr.Offset));
                         Append
-                          (Vec, Build_Extract (Ctxt, Pr.Value,
-                                               Cur_Off - Pr.Offset, Cur_Wd));
+                          (Vec,
+                           Build2_Extract_Push (Ctxt, Pr.Value,
+                                                Cur_Off - Pr.Offset, Cur_Wd));
                      end if;
                      exit;
                   end if;
@@ -1122,8 +1123,8 @@ package body Synth.Environment is
                      Seq := Get_Assign_Prev (Seq);
                      if Seq = No_Seq_Assign then
                         --  Extract from gate.
-                        Append (Vec, Build_Extract (Ctxt, Wire_Rec.Gate,
-                                                    Cur_Off, Cur_Wd));
+                        Append (Vec, Build2_Extract_Push (Ctxt, Wire_Rec.Gate,
+                                                          Cur_Off, Cur_Wd));
                         exit;
                      end if;
                      if Get_Assign_Is_Static (Seq) then
@@ -1702,9 +1703,9 @@ package body Synth.Environment is
                   --           |----------||
                   --          P.Off        P.Next
                   --  Shrink EL.
-                  P.Value := Build_Extract (Ctxt, P.Value,
-                                            Off => V_Next - P.Offset,
-                                            W => P_Next - V_Next);
+                  P.Value := Build2_Extract_Push (Ctxt, P.Value,
+                                                  Off => V_Next - P.Offset,
+                                                  W => P_Next - V_Next);
                   P.Offset := V_Next;
                   if not Inserted then
                      if Last_El /= No_Partial_Assign then
@@ -1724,9 +1725,9 @@ package body Synth.Environment is
                   --           |----------||
                   --          P.Off        P.Next
                   --  Shrink EL.
-                  P.Value := Build_Extract (Ctxt, P.Value,
-                                            Off => 0,
-                                            W => V.Offset - P.Offset);
+                  P.Value := Build2_Extract_Push (Ctxt, P.Value,
+                                                  Off => 0,
+                                                  W => V.Offset - P.Offset);
                   pragma Assert (not Inserted);
                   V.Next := P.Next;
                   P.Next := Asgn;
@@ -1742,14 +1743,14 @@ package body Synth.Environment is
                   pragma Assert (not Inserted);
                   Partial_Assign_Table.Append
                     ((Next => P.Next,
-                      Value => Build_Extract (Ctxt, P.Value,
-                                              Off => V_Next - P.Offset,
-                                              W => P_Next - V_Next),
+                      Value => Build2_Extract_Push (Ctxt, P.Value,
+                                                    Off => V_Next - P.Offset,
+                                                    W => P_Next - V_Next),
                       Offset => V_Next));
                   V.Next := Partial_Assign_Table.Last;
-                  P.Value := Build_Extract (Ctxt, P.Value,
-                                            Off => 0,
-                                            W => V.Offset - P.Offset);
+                  P.Value := Build2_Extract_Push (Ctxt, P.Value,
+                                                  Off => 0,
+                                                  W => V.Offset - P.Offset);
                   P.Next := Asgn;
                   Inserted := True;
                   --  No more possible overlaps.