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<html><head><title>Open LLVM Projects</title></head>

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<center><h1><font size=7>Open LLVM Projects</font></h1></center>

<ul>
  <li><a href="#what">What is this?</a>
  <li><a href="#improving">Improving the current system</a>
  <ol>
    <li><a href="#glibc">Port glibc to LLVM</a>
    <li><a href="#NightlyTest">Improving the Nightly Tester</a>
    <li><a href="#programs">Compile programs with the LLVM Compiler</a>
    <li><a href="#llvm_ir">Extend the LLVM intermediate representation</a>
    <li><a href="#misc_imp">Miscellaneous Improvements</a>
  </ol>

  <li><a href="#new">Adding new capabilities to LLVM</a>
  <ol>
    <li><a href="#pointeranalysis">Pointer and Alias Analysis</a>
    <li><a href="#profileguided">Profile Guided Optimization</a>
    <li><a href="#xforms">New Transformations and Analyses</a>
    <li><a href="#x86be">X86 Back-end Improvements</a>
    <li><a href="#misc_new">Miscellaneous Additions</a>
  </ol>
</ul>

<br><br>

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<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
<a name="what">What is this?
</b></font></td></tr></table><ul>
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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.<p>

If you are thinking about tackling one of these projects, please send a mail to
the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
Developer's</a> 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.<p>


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</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
<a name="improving">Improving the current system
</b></font></td></tr></table><ul>
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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...<p>

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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="glibc">Port glibc to LLVM
</b></font></td></tr></table><ul>

It would be very useful to <a
href="http://www.gnu.org/software/libc/porting.html">port</a> <a
href="http://www.gnu.org/software/glibc/">glibc</a> 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 <tt>stdio</tt> related functions... low-level system calls like
'<tt>read</tt>' should stay unimplemented in LLVM.<p>


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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="NightlyTest">Improving the Nightly Tester
</b></font></td></tr></table><ul>

The <a href="/testresults/">Nightly Tester</a> 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:<p>

<ol>
<li>Olden timings - Time the compilation and execution times for the Olden
    benchmark suite, keeping track of these values over time.

<li>Graphs - It would be great to have gnuplot graphs to keep track of how the
    tree is changing over time.  We already gather a several statistics, it
    just necessary to add the script-fu to gnuplotize it.

<li>Regression tests - We should run the regression tests in addition to the
    program tests...
</ol><p>


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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="programs">Compile programs with the LLVM Compiler
</b></font></td></tr></table><ul>

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 <a
href="http://mail.cs.uiuc.edu/pipermail/llvmbugs/">llvm-bugs</a> 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.<p>

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


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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="llvm_ir">Extend the LLVM intermediate representation
</b></font></td></tr></table><ul>

<ol>
<li>Add a new conditional move instruction: <tt>X = select bool Cond, Y, Z</tt>
<li>Add support for platform independent prefetch support.  The GCC <a
    href="http://gcc.gnu.org/projects/prefetch.html">prefetch project</a> page
    has a good survey of the prefetching capabilities of a variety of modern
    processors.
</ol>


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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="misc_imp">Miscellaneous Improvements
</b></font></td></tr></table><ul>

<ol>
<li>Someone needs to look into getting the <tt>ranlib</tt> 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
    <tt>gccld</tt>.<br>

<li>Improve the efficiency of the bytecode loader/writer<br>
<li>Extend the FunctionPassManager to use a ModuleProvider to stream functions
    in on demand.  This would improve the efficiency of the JIT.
<li>Rework the PassManager to be more flexible
<li>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 <a
href="http://citeseer.nj.nec.com/janssen97making.html">Making Graphs Reducible
with Controlled Node Splitting</a> and perhaps <a
href="http://doi.acm.org/10.1145/262004.262005">Nesting of Reducible and
Irreducible Loops</a>.
</ol>


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</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
<a name="new">Adding new capabilities to LLVM
</b></font></td></tr></table><ul>
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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.<p>

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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="pointeranalysis">Pointer and Alias Analysis
</b></font></td></tr></table><ul>

We have a <a href="AliasAnalysis.html">strong base for development</a> of both
pointer analysis based optimizations as well as pointer analyses themselves.  It
seems natural to want to take advantage of this...<p>

<ol>
<li>Implement a flow-sensitive context-sensitive alias analysis algorithm<br>
  - Pick one of the somewhat efficient algorithms, but strive for maximum
    precision
<li>Implement a flow-sensitive context-insensitive alias analysis algorithm<br>
  - Just an efficient local algorithm perhaps?

<li>Implement an interface to update analyses in response to common code motion
    transformations
<li>Implement alias analysis based optimizations:
  <ul>
  <li>Dead store elimination
  </ul>
</ol>

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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="profileguided">Profile Guided Optimization
</b></font></td></tr></table><ul>

We are getting to the point where we really need a unified infrastructure for
profile guided optimizations.  It would be wonderful to be able to write profile
guided transformations which can be performed either at static compile time
(compile time or offline optimization time) or at runtime in a JIT type setup.
The LLVM transformation itself shouldn't need to know how it is being used.<p>

Ideas for profile guided transformations:<p>

<ol>
<li>Superblock formation (with many optimizations)
<li>Loop unrolling/peeling
<li>Profile directed inlining
<li>Code layout
<li>...
</ol><p>


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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="xforms">New Transformations and Analyses
</b></font></td></tr></table><ul>

<ol>
<li>Implement a Dependence Analysis Infrastructure<br>
     - Design some way to represent and query dep analysis
<li>Implement a faster Dominator Set Construction Algorithm<br>
     - A linear time or nearly so algorithm
<li>Implement a strength reduction pass
<li>Value range propagation pass
<li>Implement an unswitching pass
<li>Write a loop unroller, with a simple heuristic for when to unroll
</ol>

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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="x86be">X86 Back-end Improvements
</b></font></td></tr></table><ul>

<ol>
<li>Implement a global register allocator
<li>Implement a better instruction selector
<li>Implement support for the "switch" instruction without requiring the 
    lower-switches pass.
</ol>

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</ul><table width="50%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width=100%>&nbsp; 
<font color="#EEEEFF" size=+1 face="Georgia,Palatino"><b>
<a name="misc_new">Miscellaneous Additions
</b></font></td></tr></table><ul>

<ol>
<li>Write a new frontend for some language (Java? OCaml? Forth?)
<li>Write a new backend for a target (IA64? MIPS? MMIX?)
</ol>


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</ul>
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<hr><font size-1>
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
<br>
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Last modified: Wed Oct  1 16:48:54 CDT 2003
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