[LLVMdev] Updated GSoC Proposal

[Chris Lattner]

On Sun, 25 Mar 2007, Tilmann Scheller wrote:
> Thank you very much for the feedback, I tried to address the brought up
> issues in this updated proposal. In case you have any suggestions or
> comments feel free to tell me.

FWIW, you might be interested in this thesis:
http://llvm.org/pubs/2004-05-JoshiMSThesis.html

It has a chapter about turning Alpha machine code into LLVM.

-Chris

> Tilmann
>
>
> * Proposal for Google Summer of Code Project
>
> ** Using LLVM as a backend for QEMU's dynamic binary translation
>
> *** Terms:
> - host   architecture: the architecture of the CPU QEMU is running on
> - target architecture: the architecture of the program which is being
> executed within QEMU
>
>
> *** Abstract:
> The goal of this project is to modify the QEMU dynamic binary translator
> to use components of the LLVM compiler infrastructure to turn it into a
> highly optimizing dynamic binary translator in order to increase the
> performance of QEMU even further. Instead of directly emitting code for
> the host architecture QEMU is running on, the target code is first
> translated to LLVM IR, then a selection of LLVM's optimization functions
> is applied to the IR and as a last step the LLVM JIT is used to generate
> code from the optimized IR for the host architecture. Since the
> translation to LLVM IR, the optimization and the code generation comes
> at a cost of an increased execution time, it's not feasible to apply
> this process to any piece of code, else the execution time would be even
> lower. Especially since on average a program spends 90% of its time
> within 10% of the code it is critical to get these 10% to execute fast,
> for the other 90% of the code parts might only execute once or only a
> few times and the extra time spent to generate the optimized code would
> not pay off. Therefore the idea is to identify the "hotspots" by
> counting how many times a piece of code has been executed, e.g. on basic
> block level, and performing an optimizing translation once a certain
> threshold is hit or falling back to the current binary translation of
> QEMU if not.
> Detailed speed measurements will be performed in order to evaluate the
> efficiency of this approach, especially in comparison to the approach
> currently used by QEMU.
>
>
> *** Benefits:
> QEMU will largely benefit from this project through an expected increase
> in speed, while remaining portable.
> Through this project LLVM will effectively get front ends for all target
> architectures supported by QEMU (at the moment these are x86, ARM,
> SPARC, PowerPC and MIPS). This lays the ground for the application of
> LLVM on binary code which could be e.g. the optimization of binaries
> where no source code is available, the instrumentation of binary code
> (e.g. for performance analysis), program analysis of binary code to
> assist in reverse engineering or static recompilation (depending on the
> instruction set this requires additional runtime code).
> This project is a first step to enhance LLVM to be suitable for static
> or dynamic binary translation and thereby attracting new users for LLVM
> which are interested in this subject.
> It will show the applicability of LLVM in an emulation environment,
> especially in regard to dynamic binary translation. It can also be used
> as a basis to try out concepts like profile-guided optimization or
> static optimization in the context of an emulator.
> Also since the LLVM JIT will be used for the final code generation QEMU
> can be hosted on any architecture targeted by the LLVM JIT (at the
> moment this are x86, x86-64, PowerPC and PowerPC 64), at least
> concerning code generation. Further adjustments to QEMU might be
> necessary though to get QEMU to run on a certain architecture which is
> supported by the LLVM JIT but not by QEMU.
>
>
> *** Deliverables:
> - a version of QEMU with an optimizing dynamic binary translator
> utilizing LLVM components
> - a set of test suites which are created during the development (with at
> least 80% statement coverage)
> - all necessary documentation to understand and be able to maintain the
> software
>
>
> *** Plan:
> The development of the software will be done within the three month
> timeframe of GSoC. Weekly status reports will be given.
>
> Week 1:
>      - get familiar with LLVM and QEMU
>      - write small test programs for certain LLVM components, or even a
> simple prototype
>      - get to know LLVM example programs
> Week 2, 3, 4:
>      - modify QEMU's dynamic binary translator to emit LLVM IR
>      - create tests to verify the translation
> Week 5, 6:
>      - integrate LLVM JIT into QEMU's dynamic binary translator
>      - perform first speed measurements
> Week 7, 8:
>      - integrate LLVM optimizations into QEMU
>      - perform more speed measurements, select useful optimizations
> Week 9, 10:
>      - test the system extensively
>      - write final documentation
> Week 11, 12:
>      - time buffer to deal with unexpected events
>
>
> *** Qualification:
> I'm a graduate student studying Software Engineering at the University
> of Stuttgart in Germany. I have a strong interest in compiler technology
> and see this project as a great opportunity to gain experience in this
> field. I have taken a compiler building class and plan to focus my
> future studies in this area.
> Emulation is another area i'm interested in. I wrote a Game Boy Advance
> emulator in C from scratch and a GP32 emulator based on QEMU (also C).
> While doing this I gained a basic understanding of the QEMU codebase.
> I'm currently involved in a university project which develops a testing
> tool for glass box tests for Java and COBOL, which allows to gather
> certain coverage metrics, and which will be opensourced later this year.
> I have decent experience with C and Java and i'm familiar with C++. Also
> I have a deep understanding of the ARM architecture and I'm familiar
> with x86.
> This project is a big chance for me to give something back to the open
> source community, especially since both LLVM and QEMU can profit from
> this project.
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/