is_invalid_pointer is now defined as a bi-implication

The previous encoding of is_invalid_pointer is an implication,
which means that constraints that a pointer is not an invalid
pointer have no meaning.

This commit changes the encoding to be a bi-implication, using
the numerical range of the valid pointers.

Author: kroening

regression/cbmc-primitives/r_w_ok_bug/test.desc

@@ -1,10 +1,7 @@
 CORE
 main.c
 --pointer-check --no-simplify --no-propagation
-^\[main.pointer_dereference.\d+\] line 8 dereference failure: pointer outside object bounds in \*p1: FAILURE$
-^\*\* 1 of \d+ failed
-^VERIFICATION FAILED$
-^EXIT=10$
+^VERIFICATION SUCCESSFUL$
+^EXIT=0$
 ^SIGNAL=0$
 --
-^warning: ignoring

regression/cbmc-primitives/r_w_ok_inconsistent_integer/test-no-cp.desc

@@ -1,11 +1,10 @@
-FUTURE
+CORE
 main.c
 --pointer-check --no-simplify --no-propagation
 ^EXIT=0$
 ^SIGNAL=0$
 ^VERIFICATION SUCCESSFUL$
 --
-^warning: ignoring
 --
 Tests that an inconsistent assumption involving a pointer initialized to an
 integer address not pointing to memory and __CPROVER_r_ok() can be detected via

regression/cbmc-primitives/r_w_ok_inconsistent_integer/test.desc

@@ -1,11 +1,10 @@
-FUTURE
+CORE
 main.c
 --pointer-check
 ^EXIT=0$
 ^SIGNAL=0$
 ^VERIFICATION SUCCESSFUL$
 --
-^warning: ignoring
 --
 Tests that an inconsistent assumption involving a pointer initialized to an
 integer address not pointing to memory and __CPROVER_r_ok() can be detected via

regression/cbmc-primitives/r_w_ok_inconsistent_nondet/test-no-cp.desc

@@ -1,11 +1,10 @@
-FUTURE
+CORE
 main.c
 --pointer-check --no-simplify --no-propagation
 ^EXIT=0$
 ^SIGNAL=0$
 ^VERIFICATION SUCCESSFUL$
 --
-^warning: ignoring
 --
 Tests that an inconsistent assumption involving a nondet pointer and
 __CPROVER_r_ok() can be detected via assert(0). We use --no-simplify and

regression/cbmc-primitives/r_w_ok_inconsistent_nondet/test.desc

@@ -1,11 +1,10 @@
-FUTURE
+CORE
 main.c
 --pointer-check
 ^EXIT=0$
 ^SIGNAL=0$
 ^VERIFICATION SUCCESSFUL$
 --
-^warning: ignoring
 --
 Tests that an inconsistent assumption involving a nondet pointer and
 __CPROVER_r_ok() can be detected via assert(0).

regression/cbmc-primitives/same-object-01/main.c

@@ -4,10 +4,10 @@
 void main()
 {
   char *p = malloc(1);
-  assert(__CPROVER_POINTER_OBJECT(p) == 2);
+  assert(__CPROVER_POINTER_OBJECT(p) == 1);
 
   assert(
-    __CPROVER_same_object(p, (char *)((size_t)2 << (sizeof(char *) * 8 - 8))));
+    __CPROVER_same_object(p, (char *)((size_t)1 << (sizeof(char *) * 8 - 8))));
   assert(
-    !__CPROVER_same_object(p, (char *)((size_t)3 << (sizeof(char *) * 8 - 8))));
+    !__CPROVER_same_object(p, (char *)((size_t)2 << (sizeof(char *) * 8 - 8))));
 }

src/solvers/flattening/bv_pointers.cpp

@@ -119,37 +119,7 @@ literalt bv_pointerst::convert_rest(const exprt &expr)
 
   const exprt::operandst &operands=expr.operands();
 
-  if(expr.id() == ID_is_invalid_pointer)
-  {
-    if(operands.size()==1 &&
-       operands[0].type().id()==ID_pointer)
-    {
-      const bvt &bv=convert_bv(operands[0]);
-
-      if(!bv.empty())
-      {
-        const pointer_typet &type = to_pointer_type(operands[0].type());
-        bvt object_bv = object_literals(bv, type);
-
-        bvt invalid_bv = object_literals(
-          encode(pointer_logic.get_invalid_object(), type), type);
-
-        const std::size_t object_bits =
-          bv_pointers_width.get_object_width(type);
-
-        bvt equal_invalid_bv;
-        equal_invalid_bv.reserve(object_bits);
-
-        for(std::size_t i=0; i<object_bits; i++)
-        {
-          equal_invalid_bv.push_back(prop.lequal(object_bv[i], invalid_bv[i]));
-        }
-
-        return prop.land(equal_invalid_bv);
-      }
-    }
-  }
-  else if(expr.id() == ID_is_dynamic_object)
+  if(expr.id() == ID_is_dynamic_object || expr.id() == ID_is_invalid_pointer)
   {
     if(operands.size()==1 &&
        operands[0].type().id()==ID_pointer)
@@ -910,6 +880,28 @@ void bv_pointerst::do_postponed(
       prop.l_set_to_true(prop.limplies(l1, l2));
     }
   }
+  else if(postponed.expr.id() == ID_is_invalid_pointer)
+  {
+    const auto &type =
+      to_pointer_type(to_unary_expr(postponed.expr).op().type());
+    const auto &objects = pointer_logic.objects;
+
+    // only compare object part
+    bvt bv = object_literals(encode(objects.size(), type), type);
+
+    bvt saved_bv = object_literals(postponed.op, type);
+
+    POSTCONDITION(bv.size() == saved_bv.size());
+    PRECONDITION(postponed.bv.size() == 1);
+
+    // the pointer is invalid iff the object number is greater or
+    // equal objects.size()
+    literalt l1 = bv_utils.lt_or_le(
+      true, bv, saved_bv, bv_utilst::representationt::UNSIGNED);
+    literalt l2 = postponed.bv.front();
+
+    prop.l_set_to_true(prop.lequal(l1, l2));
+  }
   else if(postponed.expr.id()==ID_object_size)
   {
     const auto &type =

src/solvers/flattening/pointer_logic.cpp

@@ -160,9 +160,6 @@ pointer_logict::pointer_logict(const namespacet &_ns):ns(_ns)
   // add NULL
   null_object=objects.number(exprt(ID_NULL));
   CHECK_RETURN(null_object == 0);
-
-  // add INVALID
-  invalid_object=objects.number(exprt("INVALID"));
 }
 
 pointer_logict::~pointer_logict()

src/solvers/flattening/pointer_logic.h

@@ -60,12 +60,6 @@ class pointer_logict
     return null_object;
   }
 
-  /// \return number of INVALID object
-  std::size_t get_invalid_object() const
-  {
-    return invalid_object;
-  }
-
   bool is_dynamic_object(const exprt &expr) const;
 
   void get_dynamic_objects(std::vector<std::size_t> &objects) const;

src/solvers/smt2/smt2_conv.cpp

@@ -270,6 +270,7 @@ void smt2_convt::define_object_size(
 
 decision_proceduret::resultt smt2_convt::dec_solve()
 {
+  post_process();
   write_footer();
   out.flush();
   return decision_proceduret::resultt::D_ERROR;
@@ -1615,14 +1616,14 @@ void smt2_convt::convert_expr(const exprt &expr)
   }
   else if(expr.id() == ID_is_invalid_pointer)
   {
+    // we don't know the number of objects until conversion
+    // is finished
     const auto &op = to_unary_expr(expr).op();
     std::size_t pointer_width = boolbv_width(op.type());
-    out << "(= ((_ extract "
-        << pointer_width-1 << " "
-        << pointer_width-config.bv_encoding.object_bits << ") ";
+    out << "(bvuge ((_ extract " << pointer_width - 1 << " "
+        << pointer_width - config.bv_encoding.object_bits << ") ";
     convert_expr(op);
-    out << ") (_ bv" << pointer_logic.get_invalid_object()
-        << " " << config.bv_encoding.object_bits << "))";
+    out << ") number-of-objects)";
   }
   else if(expr.id()==ID_string_constant)
   {
@@ -2133,6 +2134,17 @@ void smt2_convt::convert_expr(const exprt &expr)
       expr.id_string());
 }
 
+void smt2_convt::post_process()
+{
+  // we now know how many objects there are
+  if(number_of_objects_declared)
+  {
+    out << "; fix number of objects\n";
+    out << "(assert (= number-of-objects (_ bv" << pointer_logic.objects.size()
+        << ' ' << config.bv_encoding.object_bits << ")))\n";
+  }
+}
+
 void smt2_convt::convert_typecast(const typecast_exprt &expr)
 {
   const exprt &src = expr.op();
@@ -4723,6 +4735,17 @@ void smt2_convt::find_symbols(const exprt &expr)
       defined_expressions[expr]=id;
     }
   }
+  else if(expr.id() == ID_is_invalid_pointer)
+  {
+    if(!number_of_objects_declared)
+    {
+      out << "; the following is for is_invalid_pointer\n";
+      out << "(declare-fun number-of-objects () ";
+      out << "(_ bv " << config.bv_encoding.object_bits << ')';
+      out << ")\n";
+      number_of_objects_declared = true;
+    }
+  }
   else if(expr.id() == ID_object_size)
   {
     const exprt &op = to_unary_expr(expr).op();