El Wed, Apr 04, 2018 at 10:33:19PM +0200 Arnd Bergmann ha dit: > On Wed, Apr 4, 2018 at 9:17 PM, Matthias Kaehlcke <m...@chromium.org> wrote: > > El Wed, Apr 04, 2018 at 11:30:07AM +0200 Peter Zijlstra ha dit: > > > >> On Tue, Apr 03, 2018 at 11:06:58AM -0700, Matthias Kaehlcke wrote: > >> > >> > Yes, Chrome OS R67 (currently dev, soon beta) will ship a kernel built > >> > with Clang for multiple x86 Chromebooks. > >> > >> But there are still _known_ miscompilations.... > > > > Our compiler team is looking into this (missing option > > -fno-delete-null-pointer-checks) > > Do you know if anyone is looking into __builtin_constant_p() > optimization as well? We have a lot of uses of this gcc feature > in the kernel, and if I remember correctly, clang implements > this by basically always returning false for the cases we > are interested in. > > In most cases, this is used to implement a fast-path for a helper > function, so not doing it the same way as gcc just results in > slower execution, but I assume we also have code that behaves > differently on clang compared to gcc because of this.
I think I didn't come (knowingly) across that one yet. Could you point me to an instance that could be used as an example in a bug report?