[llvm-dev] LLVM AutoFDO status

[Xinliang David Li via llvm-dev]

On Sat, Oct 10, 2015 at 12:09 AM, Eric Christopher <echristo at gmail.com> wrote:
> Hi Dehao,
>
> Do you have any specific bugs for "inaccurate/lost debug info"? I haven't
> seen anything and I'm curious what you might be running into.

Those lost info are mostly due to optimizations (examples include code
introduced by the optimizer, such as those from strength reduction,
runtime condition check etc) -- not that the base debug info
generation has anything wrong..

David

>
> Thanks.
>
> -eric
>
> On Fri, Oct 9, 2015 at 3:08 PM Dehao Chen via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> 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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