synth-inference: use the mux output to detect end of walk. Fix #1122

1 files changed, 8 insertions, 1 deletions

diff --git a/src/synth/synth-inference.adb b/src/synth/synth-inference.adb
index 000b34045..728837f17 100644
--- a/src/synth/synth-inference.adb
+++ b/src/synth/synth-inference.adb
@@ -393,6 +393,7 @@ package body Synth.Inference is
       Rst_Val := No_Net;
       Rst := No_Net;
       declare
+         Done : Boolean;
          Mux : Instance;
          Sel : Net;
          Last_Out : Net;
@@ -402,7 +403,11 @@ package body Synth.Inference is
       begin
          Last_Out := O;
 
-         while Is_Connected (Last_Out) loop
+         --  Initially, the final output is not connected.  So walk from the
+         --  clocked mux until reaching the final output.
+         Done := not Is_Connected (Last_Out);
+
+         while not Done loop
             if not Has_One_Connection (Last_Out)
               and then not Is_Const_Net (Last_Out)
             then
@@ -428,6 +433,7 @@ package body Synth.Inference is
             end if;
 
             Last_Out := Get_Output (Mux, 0);
+            Done := not Is_Connected (Last_Out);
 
             if Is_Prev_FF_Value (Mux_Rst_Val, Prev_Val, Off) then
                --  The mux is like an enable.  Like in this example, q2 is not
@@ -466,6 +472,7 @@ package body Synth.Inference is
                   Disconnect (Get_Mux2_I1 (Mux));
                   Disconnect (Get_Mux2_Sel (Mux));
 
+                  --  The output of the mux is now the reset value.
                   Redirect_Inputs (Last_Out, Mux_Rst_Val);
                   Free_Instance (Mux);