> On Nov 20, 2017, at 7:36 AM, Wiles, Keith <keith.wi...@intel.com> wrote: > >> On Nov 19, 2017, at 4:16 PM, Aleksey Baulin <aleksey.bau...@gmail.com> wrote: >> >> #ifndef unlikely >> -#define unlikely(x) __builtin_expect((x),0) >> +#define unlikely(x) __builtin_expect(!!(x), 0) > > I have not looked at the generated code, but does this add some extra > instruction now to do the !!(x) ? > >> #endif /* unlikely */ >> >> #endif /* _RTE_BRANCH_PREDICTION_H_ */ >> -- >> 2.7.4 >> > > Regards, > Keith >
With no ‘-O’, you get an extra cmpl instruction with the double negated unlikely() .vs the one without the ‘!!’. The same assembly is generated with ‘-O’ as a compiler switch. Tested on: [jim@blackbox-1 ~]$ uname -a Linux blackbox-1.netgate.com 3.10.0-514.26.2.el7.x86_64 #1 SMP Tue Jul 4 15:04:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux [jim@blackbox-1 ~]$ gcc --version gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11) Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Jim
