[Bug c/36359] [Regression] compile error in linux-kernel 2.6.26-rc4 with -O2

["mt-ml at gmx dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from mt-ml at gmx dot de  2008-06-08 00:17 -------
I've been able to identify the code where ilog2 is called. If I do not choose
usbcore as a module I get the following error:
drivers/built-in.o: In function `usb_submit_urb':
(.text+0xc247f): undefined reference to `____ilog2_NaN'
make: *** [.tmp_vmlinux1] Fehler 1

Observing that function usb_submit_urb() in drivers/usb/core/urb.c shows the
interesting lines should be:
        case USB_ENDPOINT_XFER_INT:
                /* too small? */
                if (urb->interval <= 0)
                        return -EINVAL;
                /* too big? */
                switch (dev->speed) {
                case USB_SPEED_HIGH:    /* units are microframes */
                        /* NOTE usb handles 2^15 */
                        if (urb->interval > (1024 * 8))
                                urb->interval = 1024 * 8;
                        max = 1024 * 8;
                        break;
                case USB_SPEED_FULL:    /* units are frames/msec */
                case USB_SPEED_LOW:
                        if (xfertype == USB_ENDPOINT_XFER_INT) {
                                if (urb->interval > 255)
                                        return -EINVAL;
                                /* NOTE ohci only handles up to 32 */
                                max = 128;
                        } else {
                                if (urb->interval > 1024)
                                        urb->interval = 1024;
                                /* NOTE usb and ohci handle up to 2^15 */
                                max = 1024;
                        }
                        break;
                default:
                        return -EINVAL;
                }
                /* Round down to a power of 2, no more than max */
                urb->interval = min(max, 1 << ilog2(urb->interval));
        }

As you can see, the argument to ilog2 is urb->interval which can't be zero at
that point IMHO.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36359