llvm dev - Oct 2017 - PGO — opt -instrprof pass programatically?

Hi,

I’m working to add PGO to the IR I’m producing. Currently I’m using opt
-instrprof to expand the llvm.instrprof_increment calls into runtime calls. I’d
like to be able to do this programmatically instead, and avoid calling an
external process.

I gather from what I’ve read online that this is implemented inside of opt and
clang using the InstrProf pass, but, frustratingly, I haven’t been able to track
down how or where it’s invoked, or even defined. I’m aware of a large amount of
the logic in InstrProf.cpp, but that doesn’t have a clear entry point. What I’ve
read online always makes use of opt or clang, but does not show how to run this
pass programatically.

Is this even possible to do cleanly, or are the implementations closely tied to
opt/clang?

If somebody knows of any tutorials or examples of this they could share, that
would be very helpful. Otherwise, direction towards the important locations in
source would be useful.


Thanks in advance,
Connor

On Tue, Oct 31, 2017 at 11:43 AM, Connor Gray via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> I’m working to add PGO to the IR I’m producing. Currently I’m using opt
> -instrprof to expand the llvm.instrprof_increment calls into runtime calls.

The intrinsic call won't be lowered into calls, but into counter update
inline sequence.

> I’d like to be able to do this programmatically instead, and avoid calling
> an external process.
>
Looks like you want to implement the instrumentation lowering.  Why do you
want to do that? Can you just invoke the InstrProfiling (lowering) pass?


>
> I gather from what I’ve read online that this is implemented inside of opt
> and clang using the InstrProf pass, but, frustratingly, I haven’t been able
> to track down how or where it’s invoked, or even defined. I’m aware of a
> large amount of the logic in InstrProf.cpp, but that doesn’t have a clear
> entry point. What I’ve read online always makes use of opt or clang, but
> does not show how to run this pass programatically.
>
> Is this even possible to do cleanly, or are the implementations closely
> tied to opt/clang?
>
> If somebody knows of any tutorials or examples of this they could share,
> that would be very helpful. Otherwise, direction towards the important
> locations in source would be useful.
>
You should look at Transforms/Instrumentation/InstrProfiling.cpp.  The file
named InstrProf.cpp under ProfileData dir defines common APIs for
instr-gen, lowering, and profile reading/writing.

David
>
>
> Thanks in advance,
> Connor
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