On Monday 16 November 2015 20:20:38 you wrote: > Arnd, > > Please pull the following branch: > > git://git.linaro.org/people/nicolas.pitre/linux div64 > > This contains those patches I've initially posted here: > > https://lkml.org/lkml/2015/11/2/715 > > Only changes to those posted patches are cosmetic improvements such as > the use of ilog2() replacing the custom __div64_ffs(). Exposure in > linux-next would be a good thing. > > I also included fixes for a couple do_div() misuses that an allyesconfig > build turned up after switching ARM to the generic do_div() code. > Those patches have been posted separately and addressed to relevant > maintainers. They are included here until/unless those maintainers > include those patches in their tree. > > Original cover letter: > > This is a generalization of the optimization I produced for ARM a decade > ago to turn constant divisors into a multiplication by the divisor > reciprocal. Turns out that after all those years gcc is still not > optimizing things on its own for that case. > > This has important performance benefits as discussed in this thread: > > https://lkml.org/lkml/2015/10/28/851 > > This series brings the formerly ARM-only optimization to all 32-bit > architectures using C code by default. The possibility for the actual > multiplication to be implemented in assembly is provided in order to get > optimal code. The ARM version can be used as an example implementation > for other interested architectures to implement. I'm now getting a build regressing with the attached randconfig configuration, when compiling drivers/net/wireless/iwlegacy/common.o: drivers/built-in.o: In function `il_send_rxon_timing': :(.text+0xbbac80): undefined reference to `__aeabi_uldivmod' :(.text+0xbbac9c): undefined reference to `__aeabi_uldivmod' :(.text+0xbbacdc): undefined reference to `__aeabi_uldivmod' :(.text+0xbbadc8): undefined reference to `__aeabi_uldivmod' :(.text+0xbbadf8): undefined reference to `__aeabi_uldivmod' :(.text+0xbbae3c): more undefined references to `__aeabi_uldivmod' follow drivers/built-in.o: In function `il_send_rxon_timing': :(.text+0xbbb11c): undefined reference to `____ilog2_NaN' I've verified that this goes away if I turn off CONFIG_PROFILE_ALL_BRANCHES, and it only shows up with gcc-5.0 through gcc-5.2.1, but not 4.9.3. Aside from those, I have not been able to reduce the failure scenario. Also, I have only tested on ARM32, no idea if this shows up elsewhere. Arnd
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