Clang performance on ppc64le power8

Dear LLVM Developers,

The following are the performance comparisons on some different versions of llvm I used to test my project (running openmp with 2 threads on Power8):

GCC/8.2.0 - host compiler: 17 Seconds
LLVM/12.0.0 - built with gcc/8.2.0: 27 Seconds
LLVM/11.0.0 - Downloaded Pre-built Binaries (PowerPC64LE Red Hat Enterprise Linux): 27 Seconds
LLVM/8.0.1 - Downloaded Pre-built Binaries ( Red Hat Enterprise Linux 7.4 ppc64le ): 17 Seconds

It is surprising to find that the older version of llvm/8.0.1 reaches its performance that is close to gcc/8.2.0, while the newer are almost twice as slower than gcc/8.2.0.
Any idea about these low performances of newer versions?

Best Regards,

Hi Shelton,

Thanks for reporting this…

There were large number of features and bug fixes between V8 and V11,
it is possible that one of them is causing performance degradation…

It would be great if you can open bugs with reduced testcase that can reproduce the problem,
so that we can help have a look. Thanks.


Jinsong Ji (纪金松), PhD.

XL/LLVM on Power Compiler Development