https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102849
Bug ID: 102849
Summary: missing warning for unsigned bitfield tests for
negativity
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
GCC warns for less than comparisons of unsigned integers to zero but it fails
to do the same for unsigned bit-fields (likely because they promote to int;
comparisons of unsigned bit-fields larger than int are diagnosed by
-Wtype-limits). Diagnosing both kinds of expressions would be helpful.
$ cat x.c && gcc -S -Wall -Wextra x.c
struct A
{
unsigned i, j: 3;
};
void f (struct A *p)
{
p->i = -1; // missing warning
p->j = -1; // missing warning in C, -Woverflow in C++
}
void g (struct A *p)
{
if (p->i < 0) // -Wtype-limits in both C and C++, folded to false
__builtin_abort ();
}
void h (struct A *p)
{
if (p->j < 0) // missing warning in both C and C++, folded to false
__builtin_abort ();
}
x.c: In function ‘g’:
x.c:14:12: warning: comparison of unsigned expression in ‘< 0’ is always false
[-Wtype-limits]
14 | if (p->i < 0) // -Wtype-limits in both C and C++, folded to
false
| ^
