introduce pointer_offset_exprt

This introduces a class for an expression that is already in use, i.e.,
merely documenting it.

Author: kroening

src/goto-instrument/accelerate/acceleration_utils.cpp

@@ -1057,7 +1057,7 @@ bool acceleration_utilst::assign_array(
   {
     if(idx.id()==ID_pointer_offset)
     {
-      poly.from_expr(to_unary_expr(idx).op());
+      poly.from_expr(to_pointer_offset_expr(idx).pointer());
     }
     else
     {

src/goto-programs/interpreter_evaluate.cpp

@@ -779,13 +779,10 @@ interpretert::mp_vectort interpretert::evaluate(const exprt &expr)
   }
   else if(expr.id()==ID_pointer_offset)
   {
-    if(expr.operands().size()!=1)
-      throw "pointer_offset expects one operand";
-
-    if(to_unary_expr(expr).op().type().id() != ID_pointer)
+    if(to_pointer_offset_expr(expr).op().type().id() != ID_pointer)
       throw "pointer_offset expects a pointer operand";
 
-    mp_vectort result = evaluate(to_unary_expr(expr).op());
+    mp_vectort result = evaluate(to_pointer_offset_expr(expr).op());
 
     if(result.size()==1)
     {

src/pointer-analysis/value_set.cpp

@@ -309,7 +309,7 @@ bool value_sett::eval_pointer_offset(
   if(expr.id()==ID_pointer_offset)
   {
     const object_mapt reference_set =
-      get_value_set(to_unary_expr(expr).op(), ns, true);
+      get_value_set(to_pointer_offset_expr(expr).pointer(), ns, true);
 
     exprt new_expr;
     mp_integer previous_offset=0;

src/solvers/flattening/bv_pointers.cpp

@@ -683,17 +683,18 @@ bvt bv_pointerst::convert_bitvector(const exprt &expr)
   }
   else if(
     expr.id() == ID_pointer_offset &&
-    to_unary_expr(expr).op().type().id() == ID_pointer)
+    to_pointer_offset_expr(expr).pointer().type().id() == ID_pointer)
   {
     std::size_t width=boolbv_width(expr.type());
 
     if(width==0)
       return conversion_failed(expr);
 
-    const exprt &op0 = to_unary_expr(expr).op();
-    const bvt &op0_bv = convert_bv(op0);
+    const exprt &pointer = to_pointer_offset_expr(expr).pointer();
+    const bvt &pointer_bv = convert_bv(pointer);
 
-    bvt offset_bv = offset_literals(op0_bv, to_pointer_type(op0.type()));
+    bvt offset_bv =
+      offset_literals(pointer_bv, to_pointer_type(pointer.type()));
 
     // we do a sign extension to permit negative offsets
     return bv_utils.sign_extension(offset_bv, width);

src/solvers/smt2/smt2_conv.cpp

@@ -1562,7 +1562,7 @@ void smt2_convt::convert_expr(const exprt &expr)
   }
   else if(expr.id()==ID_pointer_offset)
   {
-    const auto &op = to_unary_expr(expr).op();
+    const auto &op = to_pointer_offset_expr(expr).pointer();
 
     DATA_INVARIANT(
       op.type().id() == ID_pointer,

src/util/pointer_expr.h

@@ -873,4 +873,62 @@ to_annotated_pointer_constant_expr(exprt &expr)
   return ret;
 }
 
+/// The offset (in bytes) of a pointer relative to the object
+class pointer_offset_exprt : public unary_exprt
+{
+public:
+  explicit pointer_offset_exprt(exprt pointer, typet type)
+    : unary_exprt(ID_pointer_offset, std::move(pointer), std::move(type))
+  {
+  }
+
+  exprt &pointer()
+  {
+    return op0();
+  }
+
+  const exprt &pointer() const
+  {
+    return op0();
+  }
+};
+
+template <>
+inline bool can_cast_expr<pointer_offset_exprt>(const exprt &base)
+{
+  return base.id() == ID_pointer_offset;
+}
+
+inline void validate_expr(const pointer_offset_exprt &value)
+{
+  validate_operands(value, 1, "pointer_offset must have one operand");
+  DATA_INVARIANT(
+    value.pointer().type().id() == ID_pointer,
+    "pointer_offset must have pointer-typed operand");
+}
+
+/// \brief Cast an exprt to a \ref pointer_offset_exprt
+///
+/// \a expr must be known to be \ref pointer_offset_exprt.
+///
+/// \param expr: Source expression
+/// \return Object of type \ref pointer_offset_exprt
+inline const pointer_offset_exprt &to_pointer_offset_expr(const exprt &expr)
+{
+  PRECONDITION(expr.id() == ID_pointer_offset);
+  const pointer_offset_exprt &ret =
+    static_cast<const pointer_offset_exprt &>(expr);
+  validate_expr(ret);
+  return ret;
+}
+
+/// \copydoc to_pointer_offset_expr(const exprt &)
+inline pointer_offset_exprt &to_pointer_offset_expr(exprt &expr)
+{
+  PRECONDITION(expr.id() == ID_pointer_offset);
+  pointer_offset_exprt &ret = static_cast<pointer_offset_exprt &>(expr);
+  validate_expr(ret);
+  return ret;
+}
+
 #endif // CPROVER_UTIL_POINTER_EXPR_H

src/util/pointer_predicates.cpp

@@ -37,7 +37,7 @@ exprt object_size(const exprt &pointer)
 
 exprt pointer_offset(const exprt &pointer)
 {
-  return unary_exprt(ID_pointer_offset, pointer, signed_size_type());
+  return pointer_offset_exprt(pointer, signed_size_type());
 }
 
 exprt deallocated(const exprt &pointer, const namespacet &ns)

src/util/simplify_expr.cpp

@@ -2483,7 +2483,7 @@ simplify_exprt::resultt<> simplify_exprt::simplify_node(exprt node)
   }
   else if(expr.id()==ID_pointer_offset)
   {
-    r = simplify_pointer_offset(to_unary_expr(expr));
+    r = simplify_pointer_offset(to_pointer_offset_expr(expr));
   }
   else if(expr.id()==ID_extractbit)
   {

src/util/simplify_expr_class.h

@@ -59,6 +59,7 @@ class mult_exprt;
 class namespacet;
 class not_exprt;
 class plus_exprt;
+class pointer_offset_exprt;
 class popcount_exprt;
 class refined_string_exprt;
 class shift_exprt;
@@ -180,7 +181,7 @@ class simplify_exprt
   NODISCARD resultt<> simplify_unary_plus(const unary_plus_exprt &);
   NODISCARD resultt<> simplify_dereference(const dereference_exprt &);
   NODISCARD resultt<> simplify_address_of(const address_of_exprt &);
-  NODISCARD resultt<> simplify_pointer_offset(const unary_exprt &);
+  NODISCARD resultt<> simplify_pointer_offset(const pointer_offset_exprt &);
   NODISCARD resultt<> simplify_bswap(const bswap_exprt &);
   NODISCARD resultt<> simplify_isinf(const unary_exprt &);
   NODISCARD resultt<> simplify_isnan(const unary_exprt &);

src/util/simplify_expr_pointer.cpp

@@ -245,17 +245,17 @@ simplify_exprt::simplify_address_of(const address_of_exprt &expr)
 }
 
 simplify_exprt::resultt<>
-simplify_exprt::simplify_pointer_offset(const unary_exprt &expr)
+simplify_exprt::simplify_pointer_offset(const pointer_offset_exprt &expr)
 {
-  const exprt &ptr = expr.op();
+  const exprt &ptr = expr.pointer();
 
   if(ptr.id()==ID_if && ptr.operands().size()==3)
   {
     if_exprt if_expr=lift_if(expr, 0);
     if_expr.true_case() =
-      simplify_pointer_offset(to_unary_expr(if_expr.true_case()));
+      simplify_pointer_offset(to_pointer_offset_expr(if_expr.true_case()));
     if_expr.false_case() =
-      simplify_pointer_offset(to_unary_expr(if_expr.false_case()));
+      simplify_pointer_offset(to_pointer_offset_expr(if_expr.false_case()));
     return changed(simplify_if(if_expr));
   }
 
@@ -358,8 +358,8 @@ simplify_exprt::simplify_pointer_offset(const unary_exprt &expr)
       return unchanged(expr);
 
     // this might change the type of the pointer!
-    exprt pointer_offset_expr =
-      simplify_pointer_offset(to_unary_expr(pointer_offset(ptr_expr.front())));
+    exprt pointer_offset_expr = simplify_pointer_offset(
+      to_pointer_offset_expr(pointer_offset(ptr_expr.front())));
 
     exprt sum;