gcc/testsuite/gcc.dg/pr69543.c

/* PR preprocessor/69543 */
/* { dg-do compile } */
/* { dg-options "-O2 -Wuninitialized" } */

# define YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN \
    _Pragma ("GCC diagnostic push") \
    _Pragma ("GCC diagnostic ignored \"-Wuninitialized\"")\
    _Pragma ("GCC diagnostic ignored \"-Wmaybe-uninitialized\"")
# define YY_IGNORE_MAYBE_UNINITIALIZED_END \
    _Pragma ("GCC diagnostic pop")

void test (char yylval)
{
  char *yyvsp;
  YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN
  *++yyvsp = yylval;
  YY_IGNORE_MAYBE_UNINITIALIZED_END
}