[llvm-dev] LLVM AutoFDO status

[Dehao Chen via llvm-dev]

With recent bug fixes and performance tunings, AutoFDO at llvm has reached a
usable state. To evaluate performance, we used
O3/-fprofile-use/-fprofile-sample-use respectively to optimize clang
itself, and measure its speed.

clang built with -fprofile-use is ~20% faster than clang built with O3
clang built with -fprofile-sample-use is ~10% faster than clang built with
O3

AutoFDO can deliver 50% of the FDO speedup to clang. The gap is mainly due
to inaccurate/lost debug info, which is used to represent the profile. I am
still tuning the performance to fill in the gap.

During the meantime, we encourage you to try it out. Bug reports/fixes are
always welcome. For more information about how to generate AutoFDO profile,
please refer to https://github.com/google/autofdo

Cheers,
Dehao
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