Dear LLVM community,
I am a GSoC student this year working on the project of improving alias analysis in LLVM.
The proposal initially came from a discussion I had with various devs on the mailing list some time ago [1]. The general goal of this project is to make alias analysis (in particular, cfl-aa) “better”, and to be more concrete here is a list of objectives I had in mind:
- Evaluating the current state of cfl-aa, and fix all known bugs.
- Improving the precision of cfl-aa. Although flow sensitivity may not be very helpful for LLVM in its current form, field sensitivity should be something important and I’ll definitely try to add it to cfl-aa. Given the complexity LLVM’s memory model has, my guess is that I may need to spend most of my summer on this task.
- Improving the performance of cfl-aa. (It is fairly efficient in its current form, IMO. Further performance tuning may be needed if more features such as field sensitivity were added.)
- Understanding how various clients interacts with cfl-aa, and exploring various ways to minimize precision/performance losses caused by the interaction.
- If time permits, maybe I can look at scev-aa and try to bring it back to the compilation pipeline.
I know these objectives are not as clear cut as other GSoC projects people used to have, and it is hard to come up with a clear schedule as well as a success metric. Nevertheless even if my contributions may seem fragmented and incremental, I felt that as long as the work is useful to the community, it is going to be the most valuable summer I’ve ever had as a student.
** Current Status **
I’ve submitted a simple patch last week (D19776) to fix a subtle bug in cfl-aa. After applying the patch on r267335 and bootstrap LLVM/clang with cfl-aa enabled on its own as well as behind basic-aa on an x86 machine, I ran test-suite with lit and saw no failed test cases. I didn’t time the tests in any rigorous way, but it didn’t look like cfl-aa add very noticable performance overhead. It may be a good time, I think, to call for people’s help to test cfl-aa on their internal codebase. If everything goes well, we should be able to safely turn on cfl-aa by default soon.
Let me conclude this introduction by saying thank you for accepting my proposal, and in particular I want to thank my mentors George and Hal for the providing me with so much support and guidance. Please let me know if you have any comments or suggestions.
[1]
