[LLVMdev] GSoC 2009 application

[Chris Lattner]

On Apr 3, 2009, at 12:52 AM, Kshitiz Garg wrote:
> Here is my formal proposal i have submitted in gsoc. Comments invited.
>
This sounds like a very interesting proposal.    Many compilers clone  
loops and use dynamic checks to enforce invariants in one copy of the  
loop.  Is this intended to be similar to that style of approach?

-Chris

>
>   About me:
>
> I am a final semester Dual Degree( B.Tech. M.Tech.) student from  
> Indian Institute of Technology, Kanpur. I was looking forward to  
> participate in this year's GSoC 2009.Starting Fall 2009 i shall be  
> pursuing a Phd in compilers. I am having a good background in  
> compilers. My current masters thesis is aimed at automatic parallel  
> code from c programs target for the Cell Processor using speculative  
> and runtime parallelization techniques. As a part of this I am  
> taking a profile driven approach to figure out the program access  
> paterns to accurately model the same.
>
> Relevant Skills:
>
> I have been using the LLVm system for some time so am somewhat  
> familiar with the system. I have strong C/C++ skills acquired by  
> working on several projects including my thesis. Besides my thesis I  
> have previously taken classes on Compilers, compilers optimizations,  
> parallel programming and multicore architectures. As part of  
> compilers class project I had to implemented a compiler for the  
> Oberon programming language from scratch.
>
> Project Proposal:
>
> Since several people are working on loop static loop dependence  
> analysis, I wish to extend this into the profile driven paradigm.  
> The profile driven approach can be useful in the following cases:-
>
> 1. Rarely occuring dependeccies.
>
> 2. Silent depencecies (harmless dependecies) eg. writing the same  
> value a before.
>
> The program can be profiled to obtain this information. Based on  
> this information the optimiser can selectively exercise the  
> dependecy, making checks in case of a wrong prediction. This will be  
> particularly useful when try to parallelize the code. The profile  
> information can also be used to obtain the actual desnsity of the  
> loop to figure out the best parallelization technique.
>
> For achieving the above I propose to add the following passes to the  
> LLVm System..-
>
> a. A profiling pass to record the timing, access and value  
> information. This shall be a 2 stage pass. Access / Value profiling  
> is costly so shall be applied only on the HOT code regions.
>
> b.A loop transformation pass to use this information to  
> speculatively parallelize the loop. I aim to use the copy or discrad  
> model [1] for speculative paralleliztion.
>
> c.a loop transformation pass to use profile information to performa  
> strip mining and loop peeling.
>
> Maybes:
>
> a. Partial dead code ellimination,partial redundancy ellimination ,  
> conditional branch ellimination [2]
>
> Roadmap:
>
> April 20 - May 23 -- Familiasing with the LLVM system and the  
> cuurent Loop passes implemented., reading the papers and forming a  
> prelimnary coding plan
>
> May 23 - June 7 -- profiling passes coded ,improved and tested.  
> Passes optimised to incorporate statically available information  
> like loop iterations,known aliases nd estimated parallelism
>
> June 7 - June 21 -- Loop transformation pass converting the loop  
> into a speculative one using the copy or dicard model[1].
>
> June 21 - July 7 - Loop peeling and strip mining passes.
>
> July 7 - August 10 -- Maybes + Complete testing and documentation.
>
>
> References:
>
> [1]Copy or Discard execution model for speculative parallelization  
> on multicoresChen Tian   Min Feng   Nagarajan, V.   Gupta, R.   
> Microarchitecture, 2008. MICRO-41. 2008 41st IEEE/ACM International  
> Symposium 330-341
>
> [2]The Compiler Design Handbook Y. N. Srikant, Priti Shankar 143 - 171
>
>
>
> On Fri, Mar 27, 2009 at 6:43 PM, Anton Korobeynikov <anton at korobeynikov.info 
> > wrote:
> Hello, Kshitiz
>
> >    I was interested in taking up the project ideas on adding  
> profile driven
> > optimization passes and improving alias analysis as this would  
> give me a
> > chance to carry forward and improve my current work and also  
> contribute
> > significantly in terms of tangibles.
> This sounds like a great idea. LLVM definitely lacks some
> profile-driven optimizations.
>
> --
> With best regards, Anton Korobeynikov
> Faculty of Mathematics and Mechanics, Saint Petersburg State  
> University
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>
>
>
> -- 
> Kshitiz Garg
> Graduate Student
> Department of Computer Science & Engineering
> IIT Kanpur
> http://home.iitk.ac.in/~kshitizg
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