Ubsan build of GCC 6.0 fails with: cp/search.c:1011:41: error: 'otype' may be used uninitialized in this function

[Martin Sebor]

On 09/09/2015 12:36 PM, Toon Moene wrote:
> See:
>
> https://gcc.gnu.org/ml/gcc-testresults/2015-09/msg00699.html
>
> Full error message:
>
> /home/toon/compilers/trunk/gcc/cp/search.c: In function 'int
> accessible_p(tree, tree, bool)':
> /home/toon/compilers/trunk/gcc/cp/search.c:1011:41: error: 'otype' may
> be used uninitialized in this function [-Werror=maybe-uninitialized]
>     dfs_accessible_data d = { decl, otype };
>                                           ^
> Any ideas ?

It looks as though GCC assumes that TYPE can be null even though
it can't (if it was, TYPE_P (type) would then dereference a null
pointer). As a workaround until this is fixed, initializing OTYPE
with type instead of in the else block should get rid of the error.

Here's a small test case that reproduces the bogus warning:

cat t.c && /build/gcc-trunk/gcc/xg++ -B /build/gcc-trunk/gcc 
-Wmaybe-uninitialized -O2 -c -fsanitize=undefined t.c
struct S { struct S *next; int i; };

int foo (struct S *s) {
     int i;

     if (s->i) {
         struct S *p;
         for (p = s; p; p = p->next)
             i = p->i;
     }
     else
         i = 0;

     return i;
}
t.c: In function ‘int foo(S*)’:
t.c:14:12: warning: ‘i’ may be used uninitialized in this function 
[-Wmaybe-uninitialized]
      return i;
             ^

Martin