[llvm-dev] [GSoC] Prospective student for Unify ways to move code or check if code is safe to be moved

Whitney T Tsang via llvm-dev llvm-dev at lists.llvm.org
Mon Mar 30 17:36:55 PDT 2020

Thanks Rithik, your proposal meet my expectations.
Good luck.
Whitney Tsang

From:	RITHIK SHARMA <rithiksh02 at gmail.com>
To:	Whitney T Tsang <whitneyt at ca.ibm.com>
Cc:	bmahjour at ca.ibm.com, etiotto at gmail.com, llvm-dev
            <llvm-dev at lists.llvm.org>, Stefanos Baziotis
            <stefanos.baziotis at gmail.com>
Date:	2020/03/30 04:49 PM
Subject:	[EXTERNAL] Re: [llvm-dev] [GSoC] Prospective student for Unify
            ways to move code or check if code is safe to be moved

Thanks Whitney,

It was really very helpful! I've drafted a proposal [1] with my best
efforts, I hope it does justice to your expectations. Looking forward to
any feedback or suggestions.


Many thanks,

On Sat, 28 Mar 2020 at 03:40, Whitney T Tsang <whitneyt at ca.ibm.com> wrote:
  Hi Rithik,

  CodeMoverUtils is not aimed for only loop transformations, it can be used
  by any transformation which want to move code or check if code is safe to
  be moved.
  It can currently do both hoist and sink but require control flow
  equivalent between the original location and the intended to be moved
  I would like to keep the API decoupled from loop, so other transformation
  can use it.
  In this project we want to limit the scope to loop transformations due to
  the time constraint, but we should keep in mind that it should be usable
  for any kind of transformations.

  My expectations for the proposal should contains
  1. the problem we want to solve
  2. expected end result
  - how many percentage of the loop transformations do you think can be
  changed to use the unified API at the end of the project?
  3. roadmap + timeline
  a. identified all loop transformations which require code motion
  b. identified all existing code mover utilities
  c. understand the difference (some maybe more conservative, but does it
  really need to be)
  d. improve CodeMoverUtils to accommodate different users
  e. change existing loop transformations to use the improved
  CodeMoverUtils (should do with (d) at the same time).

  Note: finding transformations that use code motion is part of the
  project, so no need to include every opportunity in the proposal.

  Hope this help.

  Whitney Tsang

  Inactive hide details for RITHIK SHARMA ---2020/03/27 03:08:47 PM---Hello
  Whitney, I spent some good time going through the exaRITHIK SHARMA
  ---2020/03/27 03:08:47 PM---Hello Whitney, I spent some good time going
  through the exact implementation of a few loop

  From: RITHIK SHARMA <rithiksh02 at gmail.com>
  To: whitneyt at ca.ibm.com
  Cc: etiotto at gmail.com, Stefanos Baziotis <stefanos.baziotis at gmail.com>,
  llvm-dev <llvm-dev at lists.llvm.org>, bmahjour at ca.ibm.com
  Date: 2020/03/27 03:08 PM
  Subject: [EXTERNAL] Re: [llvm-dev] [GSoC] Prospective student for Unify
  ways to move code or check if code is safe to be moved

  Hello Whitney,

  I spent some good time going through the exact implementation of a few
  loop transformation passes in llvm and for others, I tried to quickly get
  an idea of what is going inside them with respect to the implementation
  in llvm.

  I also went through the CodeMoverUtils [1], I really appreciate the
  effort of keeping it generic and decoupled from loop though being derived
  from loop and aimed to be used for loop transformation. I also analyzed
  Loop Fuse pass [2] as a reference as it already uses CodeMoverUtils which
  helped me to concrete my understanding of the vision behind the
  unification of code motion checks.

  LICM [3] does hoisting [4] as well as sinking [5]. I thought about
  extending the already available isSafeToMoveBefore [6] for hoisting the
  code from loop body to the pre-header. In my opinion, hosting and sinking
  are the basic code motions, exposing them in a robust and flexible way
  will also help other transformations (maybe other non-loop

  I also saw that Loop Sink pass [7] uses the same checks [8] from LICM and
  also found another code hoisting opportunity in Loop Rotation pass where
  we once hoist to the pre-header [9]. I also analyzed passes like Loop
  Unswitch [10] in the hope for some code motion opportunities but it seems
  the passes which are expected to run after LICM are void of them (may not
  be true for all). I limited myself to the loop passes in Transform/Scalar
  and I'm planning to take a look into other loop passes as well.

  Having said that, my concern right now is the proposal whose deadline is
  approaching in 4 days, I would like to get a small feedback before the
  deadline. I am aiming to prepare a draft by Monday morning (PST) so then
  I may have a short window to incorporate the feedback. I also have two
  coursework assignment deadlines end of this week which is also demanding
  some of my effort other than attending the lectures.

  I'll be glad to hear about your expectations for the proposal. I'm
  planning to somehow meet them and will also continue to look into loop
  passes for more code motion checks after the proposal deadline. Does this
  look good to you? In my proposal can I focus on the findings that I'm
  able to do before the deadline and keep some buffer for things that I may
  find later as identifying all the existing ways for code motion in loop
  transformations is a big portion of the proposed project.












  On Tue, 24 Mar 2020 at 23:30, Stefanos Baziotis <
  stefanos.baziotis at gmail.com> wrote:
        Np, good luck! :)

        - Stefanos

        Στις Τρί, 24 Μαρ 2020 στις 8:55 μ.μ., ο/η RITHIK SHARMA <
        rithiksh02 at gmail.com> έγραψε:
        Many thanks, Stefanos! I really appreciate your help :) I heard
        from Whitney.


        On Tue, 24 Mar 2020 at 23:08, Stefanos Baziotis <
        stefanos.baziotis at gmail.com> wrote:
              Hi Rithik,

              I CC'd the 2 other mentors and hopefully you'll get answer.
              Sorry, but I don't know of any other way to help. :/
              You may also try to contact them privately.


              Στις Τρί, 24 Μαρ 2020 στις 7:35 μ.μ., ο/η RITHIK SHARMA via
              llvm-dev <llvm-dev at lists.llvm.org> έγραψε:
              I'm bit concern about the approaching deadline next week,
              some pointers will be really appreciated and will be very
              helpful to me.

              Best regards,
              Rithik Sharma

              On Sun, 22 Mar 2020 at 01:24, RITHIK SHARMA <
              rithiksh02 at gmail.com> wrote:

                    I am an undergrad from India. This summer I'm
                    interested in working on unifying the code motion
                    checks as a GSoC intern with LLVM. I started reading
                    about classical data flow analysis since few months, I
                    see this as a great opportunity to start contributing
                    to LLVM. The idea of unifying all the code motion
                    checks into one place seems very rational and
                    interesting to me. As in the project description LICM
                    was mentioned, I have a basic idea about it and I spent
                    some time to go through its implementation in LLVM. It
                    makes a lot of sense to me to keep all code motion
                    checks at one place, say an analysis pass, I also
                    looked into GVN hoist & sink passes as they also have
                    some code motion logic. I'll start drafting the
                    proposal after your initial feedback/suggestions. I'm
                    really very excited to work on this.

                    Best Regards,
                    Rithik Sharma
              LLVM Developers mailing list
              llvm-dev at lists.llvm.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200330/f476b7a2/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: graycol.gif
Type: image/gif
Size: 105 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200330/f476b7a2/attachment-0001.gif>

More information about the llvm-dev mailing list