dump-c: when removing const-ness, also handle bit fields

We need to remove the const qualifier when the assignment is no longer
performed as part of the declaration. This worked for various types
already, but bit fields had not been considered.

Author: tautschnig

regression/goto-instrument/chain.sh

@@ -38,6 +38,7 @@ elif echo $args | grep -q -- "--dump-c-type-header" ; then
   cat "${name}-mod.gb"
   mv "${name}.gb" "${name}-mod.gb"
 elif echo $args | grep -q -- "--dump-c" ; then
+  cat "${name}-mod.gb"
   mv "${name}-mod.gb" "${name}-mod.c"
 
   if [[ "${is_windows}" == "true" ]]; then

regression/goto-instrument/dump-decl-const/main.c

@@ -0,0 +1,19 @@
+#include <assert.h>
+
+struct S
+{
+  const int x;
+  const int y : 8;
+  const int *const p;
+};
+
+int foo()
+{
+  return 1;
+}
+
+int main()
+{
+  struct S s1 = {foo(), 1, 0};
+  assert(s1.x == 1);
+}

regression/goto-instrument/dump-decl-const/test.desc

@@ -0,0 +1,16 @@
+CORE
+main.c
+--dump-c
+signed int x
+signed int y
+const signed int \*p
+^[[:space:]]*s1 = \(struct S\)\{ .* \};
+^EXIT=0$
+^SIGNAL=0$
+--
+const signed int x
+const signed int y
+const p
+--
+This test demonstrates that the constness of struct members has been removed,
+which is necessary as the initialisation is not performed in the declaration.

src/goto-instrument/goto_program2code.cpp

@@ -1591,6 +1591,8 @@ void goto_program2codet::remove_const(typet &type)
         ++it)
       remove_const(it->type());
   }
+  else if(type.id() == ID_c_bit_field)
+    to_c_bit_field_type(type).subtype().remove(ID_C_constant);
 }
 
 static bool has_labels(const codet &code)