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Re: Branch taken rate of Linux kernel compiled with GCC 4.9


Actually GCC does not help reduce branch misprediction rate on modern
X86 processors.
Reducing branch taken rate is more important.
Related discussion: https://gcc.gnu.org/ml/gcc/2014-12/msg00000.html

Yuan

2015-01-13 22:13 GMT+08:00  <Paul_Koning@dell.com>:
> Depending on what the processor hardware can do, the data you need is the branch mispredict rate.  A lot of processors will predict forward branches not taken, reverse branches taken, and I believe GCC optimizes that way.  (Some processors are different: MC68040 predicts all branches taken no matter what direction!)  If the mispredict rate is unreasonably high, then that might indeed suggest missed optimizations.
>
>         paul


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