This document is meant to be a sort of "big TODO list" for LLVM. Each project in this document is something that would be useful for LLVM to have, and would also be a great way to get familiar with the system. Some of these projects are small and self-contained, which may be implemented in a couple of days, others are larger. Several of these projects may lead to interesting research projects in their own right. In any case, we welcome all contributions.

If you are thinking about tackling one of these projects, please send a mail to the LLVM Developer's mailing list, so that we know the project is being worked on. Additionally this is a good way to get more information about a specific project or to suggest other projects to add to this page. Another good place to look for ideas is the LLVM bug tracker.

Improvements to the current infrastructure are always very welcome and tend to be fairly straight-forward to implement. Here are some of the key areas that can use improvement...

It would be very useful to port glibc to LLVM. This would allow a variety of interprocedural algorithms to be much more effective in the face of library calls. The most important pieces to port are things like the string library and the stdio related functions... low-level system calls like 'read' should stay unimplemented in LLVM.

The Nightly Tester is a simple perl script (located in utils/NightlyTest.pl) which runs every night to generate a daily report. It could use the following improvements:

1. Regression tests - We should run the regression tests in addition to the program tests...

We are always looking for new testcases and benchmarks for use with LLVM. In particular, it is useful to try compiling your favorite C source code with LLVM. If it doesn't compile, try to figure out why or report it to the llvm-bugs list. If you get the program to compile, it would be extremely useful to convert the build system to be compatible with the LLVM Programs testsuite so that we can check it into CVS and the automated tester can use it to track progress of the compiler.

When testing a code, try running it with a variety of optimizations, and with all the back-ends: CBE, llc, and lli.

1. Add a new conditional move instruction: X = select bool Cond, Y, Z
2. Add support for platform-independent prefetch support. The GCC prefetch project page has a good survey of the prefetching capabilities of a variety of modern processors.

1. Someone needs to look into getting the ranlib tool to index LLVM bytecode files, so that linking in .a files is not hideously slow. They would also then have to implement the reader for this index in gccld.
2. Rework the PassManager to be more flexible
3. Some transformations and analyses only work on reducible flow graphs. It would be nice to have a transformation which could be "required" by these passes which makes irreducible graphs reducible. This can easily be accomplished through code duplication. See Making Graphs Reducible with Controlled Node Splitting and perhaps Nesting of Reducible and Irreducible Loops.

Sometimes creating new things is more fun that improving existing things. These projects tend to be more involved and perhaps require more work, but can also be very rewarding.

We have a strong base for development of both pointer analysis based optimizations as well as pointer analyses themselves. It seems natural to want to take advantage of this...

1. Implement a flow-sensitive context-sensitive alias analysis algorithm
   - Pick one of the somewhat efficient algorithms, but strive for maximum precision
2. Implement a flow-sensitive context-insensitive alias analysis algorithm
   - Just an efficient local algorithm perhaps?
3. Implement an interface to update analyses in response to common code motion transformations
4. Implement alias-analysis-based optimizations:
   • Dead store elimination
   • ...

We now have a unified infrastructure for writing profile-guided transformations, which will work either at offline-compile-time or in the JIT, but we don't have many transformations. We would welcome new profile-guided transformations as well as improvements to the current profiling system.

Ideas for profile guided transformations:

1. Superblock formation (with many optimizations)
2. Loop unrolling/peeling
3. Profile directed inlining
4. Code layout
5. ...

Improvements to the existing support:

1. The current block and edge profiling code that gets inserted is very simple and inefficient. Through the use of control-dependence information, many fewer counters could be inserted into the code. Also, if the execution count of a loop is known to be a compile-time or runtime constant, all of the counters in the loop could be avoided.
2. You could implement one of the "static profiling" algorithms which analyze a piece of code an make educated guesses about the relative execution frequencies of various parts of the code.
3. You could add path profiling support, or adapt the existing LLVM path profiling code to work with the generic profiling interfaces.

1. Implement a Dependence Analysis Infrastructure
   - Design some way to represent and query dep analysis
2. Implement a strength reduction pass
3. Value range propagation pass
4. Implement an unswitching pass
5. Write a loop unroller, with a simple heuristic for when to unroll

1. Implement a global register allocator
2. Implement a better instruction selector
3. Implement support for the "switch" instruction without requiring the lower-switches pass.

1. Write a new frontend for some language (Java? OCaml? Forth?)
2. Write a new backend for a target (IA64? MIPS? MMIX?)