[Bug tree-optimization/69249] Array-boundary offending code is silently discarded without warnings

[arnd at linaro dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69249

Arnd Bergmann <arnd at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arnd at linaro dot org

--- Comment #3 from Arnd Bergmann <arnd at linaro dot org> ---
I see the same behavior on incorrect code (off-by-one bug accessing beyond the
array, in my case with a negative index) on Linux kernel code: The following
snippet produces a warning with all versions up to 4.7, but not with 4.8 or
later (latest tried: gcc-8.0.0):

8<----
#define MEDIA_BUS_FMT_YUYV8_2X8                 0x2008
#define MEDIA_BUS_FMT_YVYU8_2X8                 0x2009
#define MEDIA_BUS_FMT_UYVY8_2X8                 0x2006
#define MEDIA_BUS_FMT_VYUY8_2X8                 0x2007

static const unsigned int camif_mbus_formats[4] = {
        MEDIA_BUS_FMT_YUYV8_2X8,
        MEDIA_BUS_FMT_YVYU8_2X8,
        MEDIA_BUS_FMT_UYVY8_2X8,
        MEDIA_BUS_FMT_VYUY8_2X8,
};

int __camif_subdev_try_format(unsigned int code)
{
        int i = sizeof(camif_mbus_formats) / sizeof(camif_mbus_formats[0]);

        while (i-- >= 0)
                if (camif_mbus_formats[i] == code)
                        break;

        return i;
}