netlists-inference: handle multiple dff with the same clock. Fix #1563

4 files changed, 39 insertions, 5 deletions

diff --git a/src/synth/netlists-gates.ads b/src/synth/netlists-gates.ads
index 4acf9f6b4..c20cddf74 100644
--- a/src/synth/netlists-gates.ads
+++ b/src/synth/netlists-gates.ads
@@ -186,6 +186,8 @@ package Netlists.Gates is
    --  Output:  0: Q
    Id_Iadff : constant Module_Id := 67;
 
+   subtype Dff_Module_Id is Module_Id range Id_Dff .. Id_Iadff;
+
    --  Multi clock dff.  ELSE is the output of the next DFF.
    --  Inputs:  0: CLK
    --           1: D
diff --git a/src/synth/netlists-inference.adb b/src/synth/netlists-inference.adb
index 58df1b556..fe136008a 100644
--- a/src/synth/netlists-inference.adb
+++ b/src/synth/netlists-inference.adb
@@ -334,14 +334,19 @@ package body Netlists.Inference is
    is
       Ndata : Net;
       Res   : Net;
+      Els_Net : Net;
+      Els_Inst : Instance;
    begin
+      Els_Net := Els;
+      pragma Unreferenced (Els);
+
       if Off = 0
         and then Rst = No_Net
         and then not Synth.Flags.Flag_Debug_Nomemory1
         and then Can_Infere_RAM (Data, Prev_Val)
       then
          --  Maybe it is a RAM.
-         Res := Infere_RAM (Ctxt, Data, Els, Clk, Clk_Enable);
+         Res := Infere_RAM (Ctxt, Data, Els_Net, Clk, Clk_Enable);
       else
          if Clk_Enable /= No_Net then
             --  If there is a condition with the clock, that's an enable which
@@ -363,7 +368,17 @@ package body Netlists.Inference is
          if Rst = No_Net then
             --  No async reset
             pragma Assert (Rst_Val = No_Net);
-            if Els = No_Net then
+
+            if Els_Net /= No_Net then
+               Els_Inst := Get_Net_Parent (Els_Net);
+               if Get_Id (Els_Inst) in Dff_Module_Id
+                 and then Same_Clock (Clk, Get_Input_Net (Els_Inst, 0))
+               then
+                  Els_Net := No_Net;
+               end if;
+            end if;
+
+            if Els_Net = No_Net then
                if Init /= No_Net then
                   Res := Build_Idff (Ctxt, Clk, D => Ndata, Init => Init);
                else
@@ -372,13 +387,13 @@ package body Netlists.Inference is
             else
                if Init /= No_Net then
                   Res := Build_Midff (Ctxt, Clk, D => Ndata,
-                                      Els => Els, Init => Init);
+                                      Els => Els_Net, Init => Init);
                else
-                  Res := Build_Mdff (Ctxt, Clk, D => Ndata, Els => Els);
+                  Res := Build_Mdff (Ctxt, Clk, D => Ndata, Els => Els_Net);
                end if;
             end if;
          else
-            if Els /= No_Net then
+            if Els_Net /= No_Net then
                Error_Msg_Synth
                  (Loc, "synchronous code does not expect else part");
             end if;
diff --git a/src/synth/netlists-utils.adb b/src/synth/netlists-utils.adb
index 74df5908c..8463da355 100644
--- a/src/synth/netlists-utils.adb
+++ b/src/synth/netlists-utils.adb
@@ -289,6 +289,19 @@ package body Netlists.Utils is
       end;
    end Same_Net;
 
+   function Same_Clock (L, R : Net) return Boolean
+   is
+      Linst : constant Instance := Get_Net_Parent (L);
+      Rinst : constant Instance := Get_Net_Parent (R);
+   begin
+      if Get_Id (Linst) /= Get_Id (Rinst) then
+         return False;
+      end if;
+      pragma Assert (Get_Id (Linst) in Edge_Module_Id);
+      return Same_Net (Get_Input_Net (Linst, 0),
+                       Get_Input_Net (Rinst, 0));
+   end Same_Clock;
+
    procedure Copy_Attributes (Dest : Instance; Src : Instance)
    is
       Attr : Attribute;
diff --git a/src/synth/netlists-utils.ads b/src/synth/netlists-utils.ads
index 111c6f9f3..c7a76a502 100644
--- a/src/synth/netlists-utils.ads
+++ b/src/synth/netlists-utils.ads
@@ -90,6 +90,10 @@ package Netlists.Utils is
    --  selection of the same net.
    function Same_Net (L, R : Net) return Boolean;
 
+   --  Like Same_Net but for a clock.  L and R must be both the output of
+   --  an edge detector.
+   function Same_Clock (L, R : Net) return Boolean;
+
    --  If N is the output of a signal or isignal, return the driver of the
    --  input.
    function Skip_Signal (N : Net) return Net;