Verilog: use zero_extend_exprt

This replaces two typecasts by zero_extend_exprt.

Author: kroening

src/verilog/aval_bval_encoding.cpp

@@ -470,3 +470,8 @@ exprt aval_bval(const shift_exprt &expr)
   auto x = make_x(expr.type());
   return if_exprt{distance_has_xz, x, combined};
 }
+
+exprt aval_bval(const zero_extend_exprt &expr)
+{
+  abort();
+}

src/verilog/aval_bval_encoding.h

@@ -65,5 +65,7 @@ exprt aval_bval(const verilog_implies_exprt &);
 exprt aval_bval(const typecast_exprt &);
 /// lowering for shifts
 exprt aval_bval(const shift_exprt &);
+/// lowering for zero extension
+exprt aval_bval(const zero_extend_exprt &);
 
 #endif

src/verilog/expr2verilog.cpp

@@ -896,6 +896,25 @@ expr2verilogt::resultt expr2verilogt::convert_explicit_size_cast(
 
 /*******************************************************************\
 
+Function: expr2verilogt::convert_zero_extend
+
+  Inputs:
+
+ Outputs:
+
+ Purpose:
+
+\*******************************************************************/
+
+expr2verilogt::resultt
+expr2verilogt::convert_zero_extend(const zero_extend_exprt &src)
+{
+  // added by the type checker; igore
+  return convert_rec(src.op());
+}
+
+/*******************************************************************\
+
 Function: expr2verilogt::convert_index
 
   Inputs:
@@ -1664,6 +1683,9 @@ expr2verilogt::resultt expr2verilogt::convert_rec(const exprt &src)
   else if(src.id()==ID_typecast)
     return convert_typecast(to_typecast_expr(src));
 
+  else if(src.id() == ID_zero_extend)
+    return convert_zero_extend(to_zero_extend_expr(src));
+
   else if(src.id()==ID_and)
     return convert_binary(
       to_multi_ary_expr(src), "&&", precedence = verilog_precedencet::AND);

src/verilog/expr2verilog_class.h

@@ -117,6 +117,8 @@ class expr2verilogt
 
   resultt convert_typecast(const typecast_exprt &);
 
+  resultt convert_zero_extend(const zero_extend_exprt &);
+
   resultt
   convert_explicit_size_cast(const class verilog_explicit_size_cast_exprt &);
 

src/verilog/verilog_lowering.cpp

@@ -615,6 +615,20 @@ exprt verilog_lowering(exprt expr)
     else
       return expr;
   }
+  else if(expr.id() == ID_zero_extend)
+  {
+    auto &zero_extend = to_zero_extend_expr(expr);
+
+    if(
+      is_four_valued(zero_extend.type()) ||
+      is_four_valued(zero_extend.op().type()))
+    {
+      // encode into aval/bval
+      return aval_bval(zero_extend);
+    }
+    else
+      return expr; // leave as is
+  }
   else
     return expr; // leave as is
 

src/verilog/verilog_typecheck_expr.cpp

@@ -2316,23 +2316,14 @@ Function: zero_extend
 
 static exprt zero_extend(const exprt &expr, const typet &type)
 {
-  auto old_width = expr.type().id() == ID_bool ? 1
-                   : expr.type().id() == ID_integer
-                     ? 32
-                     : to_bitvector_type(expr.type()).get_width();
+  exprt result = expr;
 
-  // first make unsigned
-  typet tmp_type;
+  if(expr.type().id() == ID_bool)
+    result = typecast_exprt{expr, unsignedbv_typet{1}};
+  else if(expr.type().id() == ID_integer)
+    result = typecast_exprt{expr, unsignedbv_typet{32}};
 
-  if(type.id() == ID_unsignedbv)
-    tmp_type = unsignedbv_typet{old_width};
-  else if(type.id() == ID_verilog_unsignedbv)
-    tmp_type = verilog_unsignedbv_typet{old_width};
-  else
-    PRECONDITION(false);
-
-  return typecast_exprt::conditional_cast(
-    typecast_exprt::conditional_cast(expr, tmp_type), type);
+  return zero_extend_exprt{std::move(result), type};
 }
 
 /*******************************************************************\