Make exprt::is_zero() support bitfields

Author: chrisr-diffblue

src/util/expr.cpp

@@ -178,7 +178,8 @@ bool exprt::is_zero() const
     }
     else if(type_id==ID_unsignedbv ||
             type_id==ID_signedbv ||
-            type_id==ID_c_bool)
+            type_id==ID_c_bool ||
+            type_id==ID_c_bit_field)
     {
       return constant.value_is_zero_string();
     }

unit/util/expr.cpp

@@ -0,0 +1,37 @@
+/*******************************************************************\
+
+Module: Unit test for expr.h/expr.cpp
+
+Author: Diffblue Ltd
+
+\*******************************************************************/
+
+#include <testing-utils/catch.hpp>
+
+#include <util/expr.h>
+#include <util/std_types.h>
+#include <util/std_expr.h>
+#include <util/arith_tools.h>
+
+
+SCENARIO("bitfield-expr-is-zero", "[core][util][expr]")
+{
+  GIVEN("An exprt representing a bitfield constant of 3")
+  {
+    const exprt bitfield3 = from_integer(mp_integer(3), c_bit_field_typet(signedbv_typet(32), 4));
+
+    THEN("is_zero() should be false")
+    {
+      REQUIRE(!bitfield3.is_zero());
+    }
+  }
+  GIVEN("An exprt representing a bitfield constant of 0")
+  {
+    const exprt bitfield0 = from_integer(mp_integer(0), c_bit_field_typet(signedbv_typet(32), 4));
+
+    THEN("is_zero() should be true")
+    {
+      REQUIRE(bitfield0.is_zero());
+    }
+  }
+}