Verilog: use zero_extend_exprt

This replaces two typecasts by zero_extend_exprt.

Author: kroening

src/verilog/aval_bval_encoding.cpp

@@ -392,3 +392,8 @@ exprt aval_bval(const typecast_exprt &expr)
   auto op_aval_zero = to_bv_type(op_aval.type()).all_zeros_expr();
   return and_exprt{not_exprt{op_has_xz}, notequal_exprt{op_aval, op_aval_zero}};
 }
+
+exprt aval_bval(const zero_extend_exprt &expr)
+{
+  abort();
+}

src/verilog/aval_bval_encoding.h

@@ -9,6 +9,7 @@ Author: Daniel Kroening, dkr@amazon.com
 #ifndef CPROVER_VERILOG_AVAL_BVAL_H
 #define CPROVER_VERILOG_AVAL_BVAL_H
 
+#include <util/bitvector_expr.h>
 #include <util/bitvector_types.h>
 #include <util/mathematical_expr.h>
 
@@ -58,5 +59,7 @@ exprt aval_bval(const verilog_iff_exprt &);
 exprt aval_bval(const verilog_implies_exprt &);
 /// lowering for typecasts
 exprt aval_bval(const typecast_exprt &);
+/// lowering for zero extension
+exprt aval_bval(const zero_extend_exprt &);
 
 #endif

src/verilog/expr2verilog.cpp

@@ -694,6 +694,25 @@ expr2verilogt::convert_typecast(const typecast_exprt &src)
 
 /*******************************************************************\
 
+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:
@@ -1453,6 +1472,9 @@ 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

@@ -107,6 +107,8 @@ class expr2verilogt
 
   resultt convert_typecast(const typecast_exprt &);
 
+  resultt convert_zero_extend(const zero_extend_exprt &);
+
   resultt
   convert_concatenation(const concatenation_exprt &, verilog_precedencet);
 

src/verilog/verilog_lowering.cpp

@@ -366,6 +366,20 @@ exprt verilog_lowering(exprt expr)
       return implies_exprt{lhs_boolean, rhs_boolean};
     }
   }
+  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

@@ -2097,23 +2097,14 @@ 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();
-
-  // first make unsigned
-  typet tmp_type;
-
-  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);
+  exprt result = expr;
+
+  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}};
 
-  return typecast_exprt::conditional_cast(
-    typecast_exprt::conditional_cast(expr, tmp_type), type);
+  return zero_extend_exprt{std::move(result), type};
 }
 
 /*******************************************************************\