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378 lines
15 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>Open LLVM Projects</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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</head>
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<body>
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<div class="doc_title">
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Open LLVM Projects
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</div>
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<ul>
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<li><a href="#what">What is this?</a></li>
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<li><a href="#improving">Improving the current system</a>
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<ol>
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<li><a href="#code-cleanups">Implementing Code Cleanup bugs</a></li>
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<li><a href="#glibc">Port glibc to LLVM</a></li>
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<li><a href="#programs">Compile programs with the LLVM Compiler</a></li>
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<li><a href="#llvm_ir">Extend the LLVM intermediate representation</a></li>
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<li><a href="#misc_imp">Miscellaneous Improvements</a></li>
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</ol></li>
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<li><a href="#new">Adding new capabilities to LLVM</a>
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<ol>
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<li><a href="#newfeaturebugs">Implementing new feature PRs</a></li>
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<li><a href="#pointeranalysis">Pointer and Alias Analysis</a></li>
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<li><a href="#profileguided">Profile-Guided Optimization</a></li>
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<li><a href="#xforms">New Transformations and Analyses</a></li>
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<li><a href="#x86be">X86 Back-end Improvements</a></li>
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<li><a href="#misc_new">Miscellaneous Additions</a></li>
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</ol></li>
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</ul>
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<div class="doc_author">
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<p>Written by the <a href="http://llvm.cs.uiuc.edu/">LLVM Team</a></p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="what">What is this?</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This document is meant to be a sort of "big TODO list" for LLVM. Each
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project in this document is something that would be useful for LLVM to have, and
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would also be a great way to get familiar with the system. Some of these
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projects are small and self-contained, which may be implemented in a couple of
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days, others are larger. Several of these projects may lead to interesting
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research projects in their own right. In any case, we welcome all
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contributions.</p>
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<p>If you are thinking about tackling one of these projects, please send a mail
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to the <a href="http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev">LLVM
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Developer's</a> mailing list, so that we know the project is being worked on.
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Additionally this is a good way to get more information about a specific project
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or to suggest other projects to add to this page.
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</p>
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<p>The projects in this page are open-ended. More specific projects are
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filed as unassigned enhancements in the <a href="http://llvm.cs.uiuc.edu/bugs/">
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LLVM bug tracker</a>. See the <a href="http://llvm.cs.uiuc.edu/bugs/buglist.cgi?keywords_type=allwords&keywords=&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&bug_severity=enhancement&emailassigned_to1=1&emailtype1=substring&email1=unassigned">list of currently outstanding issues</a> if you wish to help improve LLVM.</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="improving">Improving the current system</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>Improvements to the current infrastructure are always very welcome and tend
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to be fairly straight-forward to implement. Here are some of the key areas that
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can use improvement...</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="code-cleanups">Implementing Code Cleanup bugs</a>
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</div>
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<div class="doc_text">
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<p>
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The <a href="http://llvm.cs.uiuc.edu/bugs/">LLVM bug tracker</a> occasionally
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has <a
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href="http://llvm.cs.uiuc.edu/bugs/buglist.cgi?short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr&long_desc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=code-cleanup&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&emailassigned_to1=1&emailtype1=substring&email1=&emailassigned_to2=1&emailreporter2=1&emailcc2=1&emailtype2=substring&email2=&bugidtype=include&bug_id=&votes=&changedin=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&order=Bug+Number&field0-0-0=noop&type0-0-0=noop&value0-0-0=">"code-cleanup" bugs</a> filed in it. Taking one of these and fixing it is a good
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way to get your feet wet in the LLVM code and discover how some of its components
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work.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="glibc">Port glibc to LLVM</a>
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</div>
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<div class="doc_text">
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<p>It would be very useful to <a
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href="http://www.gnu.org/software/libc/manual/html_node/Porting.html">port</a> <a
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href="http://www.gnu.org/software/libc/">glibc</a> to LLVM. This would allow a
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variety of interprocedural algorithms to be much more effective in the face of
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library calls. The most important pieces to port are things like the string
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library and the <tt>stdio</tt> related functions... low-level system calls like
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'<tt>read</tt>' should stay unimplemented in LLVM.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="programs">Compile programs with the LLVM Compiler</a>
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</div>
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<div class="doc_text">
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<p>We are always looking for new testcases and benchmarks for use with LLVM. In
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particular, it is useful to try compiling your favorite C source code with LLVM.
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If it doesn't compile, try to figure out why or report it to the <a
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href="http://mail.cs.uiuc.edu/pipermail/llvmbugs/">llvm-bugs</a> list. If you
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get the program to compile, it would be extremely useful to convert the build
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system to be compatible with the LLVM Programs testsuite so that we can check it
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into CVS and the automated tester can use it to track progress of the
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compiler.</p>
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<p>When testing a code, try running it with a variety of optimizations, and with
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all the back-ends: CBE, llc, and lli.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="llvm_ir">Extend the LLVM intermediate representation</a>
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</div>
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<div class="doc_text">
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<ol>
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<li>Add support for platform-independent prefetch support. The GCC <a
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href="http://gcc.gnu.org/projects/prefetch.html">prefetch project</a> page
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has a good survey of the prefetching capabilities of a variety of modern
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processors.</li>
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</ol>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="misc_imp">Miscellaneous Improvements</a>
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</div>
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<div class="doc_text">
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<ol>
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<li>Someone needs to look into getting the <tt>ranlib</tt> tool to index LLVM
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bytecode files, so that linking in .a files is not hideously slow. They
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would also then have to implement the reader for this index in
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<tt>gccld</tt>.</li>
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<li>Rework the PassManager to be more flexible</li>
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<li>Some transformations and analyses only work on reducible flow graphs. It
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would be nice to have a transformation which could be "required" by these passes
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which makes irreducible graphs reducible. This can easily be accomplished
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through code duplication. See <a
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href="http://citeseer.nj.nec.com/janssen97making.html">Making Graphs Reducible
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with Controlled Node Splitting</a> and perhaps <a
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href="http://doi.acm.org/10.1145/262004.262005">Nesting of Reducible and
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Irreducible Loops</a>.</li>
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</ol>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section">
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<a name="new">Adding new capabilities to LLVM</a>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>Sometimes creating new things is more fun than improving existing things.
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These projects tend to be more involved and perhaps require more work, but can
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also be very rewarding.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="newfeaturebugs">Implementing new feature PRs</a>
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</div>
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<div class="doc_text">
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<p>Many ideas for feature requests are stored in LLVM bugzilla. Just <a
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href="http://llvm.org/bugs/buglist.cgi?short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr&long_desc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=new-feature&bug_status=UNCONFIRMED&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&emailassigned_to1=1&emailtype1=substring&email1=&emailassigned_to2=1&emailreporter2=1&emailcc2=1&emailtype2=substring&email2=&bugidtype=include&bug_id=&votes=&changedin=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&namedcmd=All+PRs&newqueryname=&order=Bug+Number&field0-0-0=noop&type0-0-0=noop&value0-0-0=">search for bugs with a "new-feature" keyword</a>.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="pointeranalysis">Pointer and Alias Analysis</a>
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</div>
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<div class="doc_text">
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<p>We have a <a href="AliasAnalysis.html">strong base for development</a> of
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both pointer analysis based optimizations as well as pointer analyses
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themselves. It seems natural to want to take advantage of this...</p>
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<ol>
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<li>Implement a flow-sensitive context-sensitive alias analysis algorithm<br>
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- Pick one of the somewhat efficient algorithms, but strive for maximum
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precision</li>
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<li>Implement a flow-sensitive context-insensitive alias analysis algorithm<br>
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- Just an efficient local algorithm perhaps?</li>
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<li>Implement alias-analysis-based optimizations:
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<ul>
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<li>...</li>
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</ul></li>
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</ol>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="profileguided">Profile-Guided Optimization</a>
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</div>
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<div class="doc_text">
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<p>We now have a unified infrastructure for writing profile-guided
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transformations, which will work either at offline-compile-time or in the JIT,
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but we don't have many transformations. We would welcome new profile-guided
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transformations as well as improvements to the current profiling system.
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</p>
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<p>Ideas for profile-guided transformations:</p>
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<ol>
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<li>Superblock formation (with many optimizations)</li>
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<li>Loop unrolling/peeling</li>
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<li>Profile directed inlining</li>
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<li>Code layout</li>
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<li>...</li>
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</ol>
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<p>Improvements to the existing support:</p>
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<ol>
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<li>The current block and edge profiling code that gets inserted is very simple
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and inefficient. Through the use of control-dependence information, many fewer
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counters could be inserted into the code. Also, if the execution count of a
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loop is known to be a compile-time or runtime constant, all of the counters in
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the loop could be avoided.</li>
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<li>You could implement one of the "static profiling" algorithms which analyze a
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piece of code an make educated guesses about the relative execution frequencies
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of various parts of the code.</li>
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<li>You could add path profiling support, or adapt the existing LLVM path
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profiling code to work with the generic profiling interfaces.</li>
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</ol>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection">
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<a name="xforms">New Transformations and Analyses</a>
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</div>
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<div class="doc_text">
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<ol>
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<li>Implement <a href="http://www.cs.purdue.edu/homes/vandrutj/">GVN-PRE</a>, a
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powerful and simple Partial Redundancy Elimination algorithm for SSA form</li>
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<li>Implement a Dependence Analysis Infrastructure<br>
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- Design some way to represent and query dep analysis</li>
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<li>Implement a strength reduction pass</li>
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<li>Value range propagation pass</li>
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</ol>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_section">
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<a name="x86be">X86 Back-end Improvements</a>
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</div>
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<div class="doc_text">
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<ol>
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<li>Implement a better instruction selector</li>
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<li>Implement support for the "switch" instruction without requiring the
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lower-switches pass.</li>
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<li>Implement interprocedural register allocation. The CallGraphSCCPass can be
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used to implement a bottom-up analysis that will determine the *actual*
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registers clobbered by a function. Use the pass to fine tune register usage
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in callers based on *actual* registers used by the callee.</li>
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</ol>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_section">
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<a name="misc_new">Miscellaneous Additions</a>
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</div>
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<div class="doc_text">
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<ol>
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<li>Port the <a href="http://www-sop.inria.fr/mimosa/fp/Bigloo/">Bigloo</A>
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Scheme compiler, from Manuel Serrano at INRIA Sophia-Antipolis, to
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output LLVM bytecode. It seems that it can already output .NET
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bytecode, JVM bytecode, and C, so LLVM would ostensibly be another good
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candidate.</li>
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<li>Write a new frontend for C/C++ <b>in</b> C++, giving us the ability to
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directly use LLVM C++ classes from within a compiler rather than use
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C-based wrapper functions a la llvm-gcc. One possible starting point is the <a
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href="http://www.parashift.com/c++-faq-lite/compiler-dependencies.html#faq-37.11">C++
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yacc grammar by Ed Willink</a>.</li>
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<li>Write a new frontend for some other language (Java? OCaml? Forth?)</li>
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<li>Write a new backend for a target (IA64? MIPS? MMIX?)</li>
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<li>Write a disassembler for machine code that would use TableGen to output
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<tt>MachineInstr</tt>s for transformations, optimizations, etc.</li>
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<li>Random test vector generator: Use a C grammar to generate random C code;
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run it through llvm-gcc, then run a random set of passes on it using opt.
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Try to crash opt. When opt crashes, use bugpoint to reduce the test case and
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mail the result to yourself. Repeat ad infinitum.</li>
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<li>Design a simple, recognizable logo.</li>
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<li>Improve the usefulness and utility of the Skeleton target backend:
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<ul>
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<li>Convert the non-functional Skeleton target to become an abstract machine
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target (choose some simple instructions, a register set, etc). This will
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become a much more useful example of a backend since it would be a simple
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but <em>functional</em> backend. Examples of such architectures include MIX,
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MMIX, <a
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href="http://www.cs.cinvestav.mx/SC/prof_personal/adiaz/vhdl/DLX/">DLX</a>,
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or come up with your own!</li>
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<li>Use the new Skeleton backend in the Interpreter: compile LLVM to Skeleton
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target, and then interpret that code instead of LLVM. Performance win would
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be the primary goal, as the number of registers would be a small constant
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instead of unbounded, for example.</li>
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</ul></li>
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</ol>
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</div>
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<!-- *********************************************************************** -->
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<hr>
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<address>
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src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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<a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
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Last modified: $Date$
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</address>
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</html>
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