synth: improve handling of null-range nets.

3 files changed, 35 insertions, 6 deletions

diff --git a/src/synth/synth-expr.adb b/src/synth/synth-expr.adb
index 4d8c1aec2..742274ec4 100644
--- a/src/synth/synth-expr.adb
+++ b/src/synth/synth-expr.adb
@@ -2170,12 +2170,22 @@ package body Synth.Expr is
                end if;
             end;
          when Iir_Kind_Simple_Name
-           | Iir_Kind_Selected_Name
-           | Iir_Kind_Interface_Signal_Declaration --  For PSL.
-           | Iir_Kind_Signal_Declaration   -- For PSL.
-           | Iir_Kind_Implicit_Dereference
-           | Iir_Kind_Dereference =>
-            return Synth_Name (Syn_Inst, Expr);
+            | Iir_Kind_Selected_Name
+            | Iir_Kind_Interface_Signal_Declaration --  For PSL.
+            | Iir_Kind_Signal_Declaration   -- For PSL.
+            | Iir_Kind_Implicit_Dereference
+            | Iir_Kind_Dereference =>
+            declare
+               Res : Valtyp;
+            begin
+               Res := Synth_Name (Syn_Inst, Expr);
+               if Res.Typ.W = 0 and then Res.Val.Kind /= Value_Memory then
+                  --  This is a null object.  As nothing can be done about it,
+                  --  returns 0.
+                  return Create_Value_Memtyp (Create_Memory_Zero (Res.Typ));
+               end if;
+               return Res;
+            end;
          when Iir_Kind_Reference_Name =>
             --  Only used for anonymous signals in internal association.
             return Synth_Expression_With_Type
diff --git a/src/synth/synth-objtypes.adb b/src/synth/synth-objtypes.adb
index 4b9e6ea54..4c615ca7e 100644
--- a/src/synth/synth-objtypes.adb
+++ b/src/synth/synth-objtypes.adb
@@ -770,6 +770,17 @@ package body Synth.Objtypes is
       return (Vtype, Alloc_Memory (Vtype));
    end Create_Memory;
 
+   function Create_Memory_Zero (Vtype : Type_Acc) return Memtyp
+   is
+      Mem : Memory_Ptr;
+   begin
+      Mem := Alloc_Memory (Vtype);
+      for I in 1 .. Vtype.Sz loop
+         Write_U8 (Mem + (I - 1), 0);
+      end loop;
+      return (Vtype, Mem);
+   end Create_Memory_Zero;
+
    function Create_Memory_U8 (Val : Ghdl_U8; Vtype : Type_Acc)
                              return Memtyp
    is
diff --git a/src/synth/synth-objtypes.ads b/src/synth/synth-objtypes.ads
index dfc0f732b..ff456d35f 100644
--- a/src/synth/synth-objtypes.ads
+++ b/src/synth/synth-objtypes.ads
@@ -125,6 +125,10 @@ package Synth.Objtypes is
       Sz : Size_Type;
 
       --  Number of bits (when in a net) for this type.
+      --  Can be zero only if the type has only 0 or 1 value (like a discrete
+      --  type with 1 element, a null vector, or a null array).
+      --  For non synthesizable types (like files or protected type), just
+      --  use 32.
       W : Width;
 
       case Kind is
@@ -292,6 +296,10 @@ package Synth.Objtypes is
    function Alloc_Memory (Vtype : Type_Acc) return Memory_Ptr;
    function Create_Memory (Vtype : Type_Acc) return Memtyp;
 
+   --  Like Create_Memory but initialize to 0.  To be used only for types
+   --  of width 0.
+   function Create_Memory_Zero (Vtype : Type_Acc) return Memtyp;
+
    function Is_Equal (L, R : Memtyp) return Boolean;
 
    procedure Copy_Memory (Dest : Memory_Ptr; Src : Memory_Ptr; Sz : Size_Type);