[LLVMdev] FYI: Planning to remove ProfileInfo and related passes from LLVM

[Chandler Carruth]

FYI, thanks for all the discussion and feedback!

It sounds like folks are generally OK with the old stuff being cleared out,
so I plan to go ahead and do that. Specific concerns and the strategy for
them being addressed:

- Alastair's GSoC project is moving to the new branch probability
infrastructure and specifically branch weight metadata. It sounds like
nuking the profile stuff won't really even disrupt this work, so no need to
worry there.

- The llvm-prof, profile.pl, related profiling tools may work for some, but
not others. The only user is out-of-tree, and is already regularly broken
by updates. My suggestion would be to not update, and/or contribute
analogous tools for branch weight metadata representation. I'm happy to
give advice or help out here a little if I can. As we're already breaking
these, I don't think we should actually keep them in a half-dead zombie
state. If they're re-written, they should ideally be in C++ and better
tested.

- I'll watch the lists and try to help out anyone impacted by this.


For the record, I'm not just trying to break stuff. i'm looking at deep
changes to the pass manager, and the profiling passes don't always use it
cleanly at the moment. One fewer strange user will make the new design
easier and better. The strangeness appears to have to do with legacy and
lack of maintenance, nothing to do with the nature of profiling passes.


Thanks!
-Chandler


On Tue, Jul 17, 2012 at 11:40 PM, Alastair Murray <
alastairmurray42 at gmail.com> wrote:

> Hi Alok,
>
> On 17/07/12 13:00, #ALOK PRAKASH# wrote:
> > Profile.pl is understandably a very simple script, but it does make
> > it easier to see some preliminary profile results and identity the
> > hot portions of a program which are suitable for hardware
> > acceleration. llvm-prof also helps in the same way.
>
> Ok, great -- using llvm-prof for detecting hot portions is the obvious
> use, but I just wanted to check.
>
> I'll keep llvm-prof in mind when writing the new loader and update
> llvm-prof to use it.  I also don't have an issue with profile.pl so I
> can update it as required, it is tiny after all.  I'm not sure if others
> want it sticking around though.
>
> Regards,
> Alastair.
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