[llvm-dev] Profiling with LLVM.

Giorgio Zacharo via llvm-dev llvm-dev at lists.llvm.org
Thu Feb 4 05:51:37 PST 2016

Dear Duncan,

Thank you a lot for your feedback. I have a problem though. The branch
weights counters overflow in some files and thus I get incorrect numbers.
Is there any way to find a workaround for that? Is is supposed to be a
known bug or is it something that needs configuration on my part?

Again, thank you a lot for your reply.

Best Regards,
Georgios Zacharopoulos

2016-02-03 18:23 GMT+01:00 Duncan P. N. Exon Smith <dexonsmith at apple.com>:

> (Ideally you would have sent this to llvm-dev at lists.llvm.org (and
> CC'ed me) so that the answer is there for others to find in the
> archive.  If you have any follow-up questions, please add llvm-dev
> to the CC list.)
> Assuming you already have branch weights, you should use the
> BlockFrequencyInfo analysis to calculate the block frequencies.  At
> the Machine level, there's a MachineBlockFrequencyInfo analysis.
> The frequencies shouldn't be used in isolation, but with reference
> to each other.
> Cheers,
> Duncan
> > On 2016-Feb-03, at 00:43, Giorgio Zacharo <giorgiozacharo at gmail.com>
> wrote:
> >
> > Dear Duncan,
> >
> > My name is Georgios Zacharopoulos and I am a PhD student at University
> of Lugano, in Switzerland. I am currently working on a research project and
> for a part of it I need to use some profiling information generated by
> existing LLVM tools from the latest version of LLVM. In more detail, I am
> trying to map profiling information generated from LLVM (Profiling with
> instrumentation) to IR.
> > (
> http://clang.llvm.org/docs/UsersManual.html#profiling-with-instrumentation
> )
> >
> > Specifically, I want to annotate each Basic Block with its respective
> execution frequency. In order to accomplish that I am using the branch
> weight metadata annotated to conditional branches in the terminator
> instructions of Basic Blocks. These branch weight information as well as
> the entry counter of each function are generated by the already existing
> profiling tools of LLVM.
> >
> > Are you aware of such frequency annotation for each BB already existing?
> Do you know whether this is feasible using the information of the branch
> weights and the entry counters of functions? I want to verify that I am
> doing it in the correct way, but unfortunately I have not come up with a
> clean way to do this. If you could give me any tips regarding that, it
> would be extremely helpful to me.
> >
> > Thank you a lot in advance.
> >
> > --
> > Best Regards,
> > Georgios Zacharopoulos
> >
> > PhD student
> > Faculty of Informatics
> > Università della Svizzera italiana
> > Lugano, Switzerland

Best Regards,
Georgios Zacharopoulos

PhD student
Faculty of Informatics
Università della Svizzera italiana
Lugano, Switzerland
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