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Re: AutoFDO profile toolchain is open-sourced


> On Tue, Apr 7, 2015 at 9:45 AM, Ilya Palachev <i.palachev@samsung.com> wrote:
> > In the mentioned README file it is said that " In order to collect this
> > profile, you will need to have an Intel CPU that have last branch record
> > (LBR) support." Is this information obsolete? Chrome Canary builds use
> > AutoFDO for ARMv7l
> > (https://code.google.com/p/chromium/issues/detail?id=434587)
> 
> It does not mean that the profile was recorded on an ARM system: they
> can gather perf.data on x86 and then produce a coverage file that is
> then used in ARM compiles.  I tried it and seems to work well.

I must say I did not even try running AutoFDO myself (so I am happy to hear
it works). My understanding is that you need LBR only to get indirect
call profiling working (i.e. you want to know from where the indirect
function is called).

Depending on your application this may not be the most important thing to
record (either you don't have indirect calls in hot paths or they are handled
resonably by speculative devirtualization)

Some ARMs also has support for tracing jump pairs, right?
Honza
> 
> Sebastian


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