llvm dev - Mar 2021 - [RFC] BOLT: A Framework for Binary Analysis, Transformation, and Optimization

On Wed, Mar 10, 2021 at 7:29 PM Rafael Auler via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> We finished rebasing BOLT on top of the LLVM monorepo and we verified that
> the new BOLT is performing as expected. To make BOLT work, we have a few
> changes to LLVM libs, which we will submit for review (first changes are
> already up: D97531 <https://reviews.llvm.org/D97531>, D97830, D97899,
> D97898, D97891, D97830).
>
> The plan for the initial BOLT commit is to include all its parts under a
> single directory, either /bolt or /llvm/tools/llvm-bolt. Once complete,
> this approach will allow people to directly contribute to the project and
> start using BOLT as part of LLVM. After this phase, we would like to start
> working with the community to break BOLT into separate components that will
> make it easier to build new tools based on the BOLT technology. As
> suggested by Propeller folks, we will split the disassembler component from
> the rest and make it possible to perform optimizations on low-level binary
> IR, which will likely have a serializable form.
>
> It's still unclear, though, the proper location of BOLT in the
monorepo.
> In our rebased branch, we are currently in a /bolt top-level folder in the
> monorepo, but are also considering /llvm/tools/llvm-bolt.
>
> We are trying to work out the pros and cons of living in these locations
> and would appreciate community input. From our understanding, living under
> the /bolt top-level folder would give BOLT the following advantages:
>
> - More independence to build a test infrastructure for BOLT. We could make
> check-bolt depend on LLD, for instance, if we need to build binaries on the
> fly to test BOLT features. Generating test inputs is a big problem for us,
> since we can't add real-world test binaries into the LLVM repo (which
are
> awkward to track in the repo and also use a lot of space).
> - We would share a similarity with other large projects such as flang and
> lld in location: these projects have their own top-level folder too.
> - It would make more sense to live in a top-level folder because we intend
> to support building multiple tools (llvm-bolt, llvm-boltdiff, perf2bolt,
> merge-fdata). Living under llvm/tools is typically reserved for simpler
> single-binary projects.
>
> Living in /llvm/tools/llvm-bolt, on the other hand, is perhaps more
> aligned with a longer-term goal of migrating BOLT to live as a lib under
> /llvm/lib and has the following advantages:
>
> - Piggybacking on the LLVM release process, BOLT is released along with
> other llvm tools
> - Piggybacking on buildbots being configured to build llvm tools, the
> project is more robust and well tested
> - BOLT was originally developed to live under tools, and the project was
> named llvm-bolt to reflect that
> - Being closer to LLVM will allow BOLT to migrate functionality more
> easily to llvm/lib
>
In general lllvm/tools are supposed to be entry points that exercises the
LLVM Libraries. I'd be concerned about adding a tool/bolt that contains
more than that (i.e. the entire implementation of the framework, instead of
having it live in libraries). But it seems like you intend this as a step
towards this? Is there a well defined plan to get there?

Is it difficult / overly involved to split things like the disassembler and
other components in libraries that can live in `llvm/lib/...` and use them
from tools/bolt/? Can this be done ahead of time and upstream these
libraries first ahead of bolt itself?

Thanks,

-- 
Mehdi


>
> Any thoughts on this?
>
>
>
>
>
> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of
Rafael
> Auler via llvm-dev <llvm-dev at lists.llvm.org>
> *Date: *Tuesday, January 26, 2021 at 4:54 PM
> *To: *Andrey Bokhanko <andreybokhanko at gmail.com>, llvm-dev <
> llvm-dev at lists.llvm.org>, Maksim Panchenko <maks at fb.com>
> *Subject: *Re: [llvm-dev] [RFC] BOLT: A Framework for Binary Analysis,
> Transformation, and Optimization
>
> Hi Andrey,
>
>
>
> We appreciate your interest and we look forward to collaborating. We are
> currently rebasing BOLT on top of LLVM trunk. Since it’s been a while since
> the last rebase, this is a bit of an involved task and we need to work
> through a rather lengthy list of conflicts. After we finish this and make
> sure BOLT works on the new repo, we plan to publish the list of commits and
> the merging diff so the community can evaluate a project merge proposal
> that works.
>
>
>
> Regarding the project organization, remember BOLT was created before llvm
> monorepo. To address this, we are currently going for a similar approach to
> the one used by flang, re-editing all of our history on top of a new folder
> structure (root repo /bolt, similar to /flang), but trying to keep old
> commits mostly intact so we preserve project history -- I’m happy to change
> this to whatever makes more sense to the community. The least intrusive way
> to do this that I found was the flang merge approach. Now, because the
> project is not so small, we need a starting point that works in LLVM trunk,
> everything self-contained in /bolt with as few diffs as possible in /llvm,
> and then from there possibly work on evolving the project to other
> suggested organization (such as breaking up BOLT in a lib in llvm/lib). But
> first we wanted to start with the rebase that we knew would take some time.
>
>
>
> That’s the gist of the current direction, thanks for pinging!
>
>
>
> -Rafael
>
>
>
> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of
Andrey
> Bokhanko via llvm-dev <llvm-dev at lists.llvm.org>
> *Date: *Tuesday, January 26, 2021 at 2:31 AM
> *To: *llvm-dev <llvm-dev at lists.llvm.org>, Maksim Panchenko
<maks at fb.com>
> *Subject: *Re: [llvm-dev] [RFC] BOLT: A Framework for Binary Analysis,
> Transformation, and Optimization
>
> One more thing (to clarify my interest): my team is working on Golang
> support in BOLT, and we're keen to open-source our developments
> (pending approvals from the higher-ups). It's much more preferable for
> us to contribute our code to LLVM project.
>
> On Tue, Jan 26, 2021 at 1:26 PM Andrey Bokhanko
> <andreybokhanko at gmail.com> wrote:
> >
> > Hi Maksim,
> >
> > Any updates on adding BOLT to LLVM?
> >
> > If you need any help / support, feel free to ask. The World is waiting
> > for BOLT! :-)
> >
> > Yours,
> > Andrey
> > ==> > Director
> > Advanced Software Technology Lab
> > Huawei
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20210311/400cc668/attachment.html>

Hi Mehdi and David,

Indeed, we share similar concerns. We do intend to move functionality of BOLT to
live as a library, but the timeline is unclear. In fact, most of BOLT could live
in a library already, it’s just a matter of moving some files into separate
components. Instead of the files living in tools/llvm-bolt, most could just be
moved under lib/something, and we already have a llvm-bolt.cpp file that
instantiates the driver that coordinates the binary rewriting process, which is
the entry point of BOLT as a library. People could already leverage this to use
BOLT in different ways (for example, I wrote some time ago a different utility
that runs the driver for two different binaries and compares the two – this was
named boltdiff later).

My main reason for committing the project as a whole first, in the same way as
flang did, though, (as a project merged into the monorepo), is because BOLT is
already opensource for a while, and it is a 6-year old project with about 800
commits and 50K lines of code and we know we have people who forked the project
and would like to contribute to it. If I commit into LLVM a different BOLT (not
just rebased), then I (a) break or make it hard for any work on top of it from
other contributors, (b) lose the original history or make it harder to preserve
it.  That’s why I was going for a more smoother transition. I, as a developer,
put value in the ability to blame and to understand why things were built a
certain way, and not bringing BOLT’s history (in the same way as flang did)
would mean we and the community loses a lot of context on the decisions of the
project. And I guess that’s also the rationale for a monorepo, to have multiple
projects merged together.

Because of that, I initially put bolt under /bolt, following flang’s model of
merging the history so every developer has the right context. But the original
location was under llvm/tools.

From: Mehdi AMINI <joker.eph at gmail.com>
Date: Thursday, March 11, 2021 at 1:32 PM
To: Rafael Auler <rafaelauler at fb.com>
Cc: Andrey Bokhanko <andreybokhanko at gmail.com>, llvm-dev <llvm-dev
at lists.llvm.org>, Maksim Panchenko <maks at fb.com>
Subject: Re: [llvm-dev] [RFC] BOLT: A Framework for Binary Analysis,
Transformation, and Optimization


On Wed, Mar 10, 2021 at 7:29 PM Rafael Auler via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hi,

We finished rebasing BOLT on top of the LLVM monorepo and we verified that the
new BOLT is performing as expected. To make BOLT work, we have a few changes to
LLVM libs, which we will submit for review (first changes are already up:
D97531<https://reviews.llvm.org/D97531>, D97830, D97899, D97898, D97891,
D97830).

The plan for the initial BOLT commit is to include all its parts under a single
directory, either /bolt or /llvm/tools/llvm-bolt. Once complete, this approach
will allow people to directly contribute to the project and start using BOLT as
part of LLVM. After this phase, we would like to start working with the
community to break BOLT into separate components that will make it easier to
build new tools based on the BOLT technology. As suggested by Propeller folks,
we will split the disassembler component from the rest and make it possible to
perform optimizations on low-level binary IR, which will likely have a
serializable form.

It's still unclear, though, the proper location of BOLT in the monorepo. In
our rebased branch, we are currently in a /bolt top-level folder in the
monorepo, but are also considering /llvm/tools/llvm-bolt.

We are trying to work out the pros and cons of living in these locations and
would appreciate community input. From our understanding, living under the /bolt
top-level folder would give BOLT the following advantages:

- More independence to build a test infrastructure for BOLT. We could make
check-bolt depend on LLD, for instance, if we need to build binaries on the fly
to test BOLT features. Generating test inputs is a big problem for us, since we
can't add real-world test binaries into the LLVM repo (which are awkward to
track in the repo and also use a lot of space).
- We would share a similarity with other large projects such as flang and lld in
location: these projects have their own top-level folder too.
- It would make more sense to live in a top-level folder because we intend to
support building multiple tools (llvm-bolt, llvm-boltdiff, perf2bolt,
merge-fdata). Living under llvm/tools is typically reserved for simpler
single-binary projects.

Living in /llvm/tools/llvm-bolt, on the other hand, is perhaps more aligned with
a longer-term goal of migrating BOLT to live as a lib under /llvm/lib and has
the following advantages:

- Piggybacking on the LLVM release process, BOLT is released along with other
llvm tools
- Piggybacking on buildbots being configured to build llvm tools, the project is
more robust and well tested
- BOLT was originally developed to live under tools, and the project was named
llvm-bolt to reflect that
- Being closer to LLVM will allow BOLT to migrate functionality more easily to
llvm/lib

In general lllvm/tools are supposed to be entry points that exercises the LLVM
Libraries. I'd be concerned about adding a tool/bolt that contains more than
that (i.e. the entire implementation of the framework, instead of having it live
in libraries). But it seems like you intend this as a step towards this? Is
there a well defined plan to get there?

Is it difficult / overly involved to split things like the disassembler and
other components in libraries that can live in `llvm/lib/...` and use them from
tools/bolt/? Can this be done ahead of time and upstream these libraries first
ahead of bolt itself?

Thanks,

--
Mehdi



Any thoughts on this?


From: llvm-dev <llvm-dev-bounces at lists.llvm.org<mailto:llvm-dev-bounces
at lists.llvm.org>> on behalf of Rafael Auler via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Date: Tuesday, January 26, 2021 at 4:54 PM
To: Andrey Bokhanko <andreybokhanko at gmail.com<mailto:andreybokhanko at
gmail.com>>, llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at
lists.llvm.org>>, Maksim Panchenko <maks at fb.com<mailto:maks at
fb.com>>
Subject: Re: [llvm-dev] [RFC] BOLT: A Framework for Binary Analysis,
Transformation, and Optimization
Hi Andrey,

We appreciate your interest and we look forward to collaborating. We are
currently rebasing BOLT on top of LLVM trunk. Since it’s been a while since the
last rebase, this is a bit of an involved task and we need to work through a
rather lengthy list of conflicts. After we finish this and make sure BOLT works
on the new repo, we plan to publish the list of commits and the merging diff so
the community can evaluate a project merge proposal that works.

Regarding the project organization, remember BOLT was created before llvm
monorepo. To address this, we are currently going for a similar approach to the
one used by flang, re-editing all of our history on top of a new folder
structure (root repo /bolt, similar to /flang), but trying to keep old commits
mostly intact so we preserve project history -- I’m happy to change this to
whatever makes more sense to the community. The least intrusive way to do this
that I found was the flang merge approach. Now, because the project is not so
small, we need a starting point that works in LLVM trunk, everything
self-contained in /bolt with as few diffs as possible in /llvm, and then from
there possibly work on evolving the project to other suggested organization
(such as breaking up BOLT in a lib in llvm/lib). But first we wanted to start
with the rebase that we knew would take some time.

That’s the gist of the current direction, thanks for pinging!

-Rafael

From: llvm-dev <llvm-dev-bounces at lists.llvm.org<mailto:llvm-dev-bounces
at lists.llvm.org>> on behalf of Andrey Bokhanko via llvm-dev <llvm-dev
at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Date: Tuesday, January 26, 2021 at 2:31 AM
To: llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at
lists.llvm.org>>, Maksim Panchenko <maks at fb.com<mailto:maks at
fb.com>>
Subject: Re: [llvm-dev] [RFC] BOLT: A Framework for Binary Analysis,
Transformation, and Optimization
One more thing (to clarify my interest): my team is working on Golang
support in BOLT, and we're keen to open-source our developments
(pending approvals from the higher-ups). It's much more preferable for
us to contribute our code to LLVM project.

On Tue, Jan 26, 2021 at 1:26 PM Andrey Bokhanko
<andreybokhanko at gmail.com<mailto:andreybokhanko at gmail.com>>
wrote:
>
> Hi Maksim,
>
> Any updates on adding BOLT to LLVM?
>
> If you need any help / support, feel free to ask. The World is waiting
> for BOLT! :-)
>
> Yours,
> Andrey
> ==> Director
> Advanced Software Technology Lab
> Huawei
_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20210312/d46ddbc5/attachment.html>