Build failure with v4.9-rc1 and GCC trunk -- compiler weirdness

On 19 October 2016 at 16:56, Markus Trippelsdorf [off-list ref] wrote:

On 2016.10.19 at 08:55 -0700, Linus Torvalds wrote:

quoted

On Wed, Oct 19, 2016 at 8:37 AM, Markus Trippelsdorf
[off-list ref] wrote:

quoted

This is a gcc bug, see:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785

Well, in the meantime we apparently have to live with it. Unless Will
is using some unreleased gcc version that nobody else is using and we
can just ignore it?

Yes, he is using gcc-7 that is unreleased. (It will be released April
next year.)

order_base_2() is still broken though, given that it is documented as

 * The first few values calculated by this routine:
 *  ob2(0) = 0
 *  ob2(1) = 0
 *  ob2(2) = 1
 *  ob2(3) = 2
 *  ob2(4) = 2
 *  ob2(5) = 3

whereas order_base_2(0) actually ends up invoking
roundup_pow_of_two(0), which is documented as being undefined.