[llvm-dev] [GSoC'16] Need details on New Transformations and Analyses

Victor Campos via llvm-dev llvm-dev at lists.llvm.org
Tue Mar 22 18:45:39 PDT 2016


Hi Aries,

regarding the person who proposed a range analysis for GSOC some years ago,
it is likely to have been me. I am one of the authors of a range analysis
for LLVM:

https://code.google.com/archive/p/range-analysis/

The analysis is described here:
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6494996&tag=1

It's pretty fast already (less than 2 seconds to run on SPEC's gcc), with
very good precision. I keep it up to date with the newer versions of LLVM,
and eventually we might try to incorporate it into the trunk. Thus we
consider the implementation finished.

One guy in last year's GSOC proposed a floating-point range analysis, but
I'm not sure what happened then. Send me an email in case you need to know
anything about our project.

Good luck!

Victor.

2016-03-22 18:13 GMT-06:00 Philip Reames via llvm-dev <
llvm-dev at lists.llvm.org>:

>
>
> On 03/20/2016 05:38 AM, Aries Gunawan via llvm-dev wrote:
>
> Hi everyone,
>
>
>
> I am very interested in contributing to LLVM project in this year’s GSoC.
> I am new with LLVM, but this is used in the compiler course in my
> university. So, I am thinking to involve in LLVM development to have a
> better knowledge of the system. Currently, I am preparing the proposal.
>
>
>
> One of the project that caught my eyes is “New Transformations and
> Analysis”. Several code transformations and analyses have been introduced
> in the compiler course that I am currently taking. That’s why I am thinking
> to involve in writing some new transformations and code analyses. But the
> list of transformations in the LLVM Open Projects web page seems too brief
> for me and I need more details on those stuffs.
>
>
>
> *Loop Dependence Analysis Infrastructure. *I have looked in the source
> codes repo and I saw that there is a file named “DependenceAnalysis.cpp”.
> So, does that mean this analysis has been implemented?
>
> I believe major progress has been made it, but haven't been following it
> closely.  I'd suggest talking to committers active in this file in the
> recent past to determine what useful work might be left of appropriate
> scope.
>
>
>
> *Value range propagation pass. *There was a discussion about this topic (
> https://groups.google.com/forum/#!topic/llvm-dev/XXqfemtDX74/discussion).
> Someone already proposed to do this pass for several years ago GSoC. But I
> can’t find the progress of the work. If no progress, then does it mean that
> the VRP based on Patterson’s paper need to be implemented although range
> analysis has been implemented?
>
> This is largely stalled.  The key problem is that between LazyValueInfo
> (constant ranges) and SCEV (symbolic ranges in loops), there's fairly
> little profit to be had and range analysis is relatively expensive.  I'd
> strongly discourage you from implementing a traditional range analysis for
> LLVM without deeply understanding the history here.
>
>
>
> *Predictive Commoning. *The presentation side by Arie Tal seems provide
> quite clear explanation and examples of the algorithm. I guess the
> implementation should be straightforward, isn’t it?
>
> The closest I know of to this in tree is LoadLoadElimination.cpp and (in
> some cases) the PRE code inside GVN.cpp.  Building something like this on
> top of SCEV could be quite interesting.  You should definitely talk to Adam
> Nemet (CC'd) about this.
>
>
>
> *Type Inference (aka. Devirtualization) and Value assertions. *
>
> Can I get more details of these topics? Does the type inference mean the
> translation of *auto* keyword or something else? For value assertions,
> “unreachable” intrinsic seems has been implemented cause I can find the
> usage in some of the testcases.
>
> I believe the "value assertions" link may be stale.   If I'm reading that
> correctly, it looks like the motivation for @llvm.assume.
>
>
>
> Finally, for this project, must I propose to do all of these analyses and
> transformations in my GSoC proposal or can I just propose some of them? In
> addition, I am also looking for a mentor for guidance?
>
> If you want further ideas, consider the list I just sent to llvm-dev a few
> moments ago titled "A couple ideas for possible GSoC projects".
>
>
>
> Looking forward for your comments and feedbacks.
>
> Thank you.
>
>
>
>
>
> Best regards,
>
>
>
>
>
> Aries Thio.
>
>
>
>
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