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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/108483] gcc warns about suspicious constructs for unevaluted
 ?: operand
Date: Sat, 21 Jan 2023 12:17:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108483

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
If it needs to be used in constant expression and you want warnings for the
non-void * cases with pointers, not arrays and errors for use of void *
pointers except for NULL, then maybe:
typedef __SIZE_TYPE__ size_t;
typedef __UINTPTR_TYPE__ uintptr_t;
#define NULL ((void *) 0)
#define ARRAY_SIZE_MAYBENULL(x) _Generic((x), void*: (size_t) (uintptr_t)
((char (*) [__builtin_constant_p (x) && (x) =3D=3D 0 ? 1 : _Generic((x), vo=
id*: -1,
default: 1)]) 0), default: \
  sizeof(x)/sizeof(_Generic((x), void*: (x), default:*(x))))

int a[10];
int *q;
void *r;
int p[] =3D {
ARRAY_SIZE_MAYBENULL (a),
ARRAY_SIZE_MAYBENULL (NULL),
ARRAY_SIZE_MAYBENULL ((const void *) 0),
ARRAY_SIZE_MAYBENULL ((volatile void *) 0),
ARRAY_SIZE_MAYBENULL ((void *restrict) 0),
ARRAY_SIZE_MAYBENULL ((const volatile void *) 0),
ARRAY_SIZE_MAYBENULL (q),
ARRAY_SIZE_MAYBENULL (r),
ARRAY_SIZE_MAYBENULL ((void *) (uintptr_t) 0x1234abc)
};

This warns -Wsizeof-pointer-div on the const void *, volatile void *, const
volatile void * and q cases and errors on the last 2.
clang seems to also emit those 4 -Wsizeof-pointer-div warnings, but doesn't
emit any errors nor warnings on the last 2.=