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<!--#include virtual="header.incl" -->
<div class="www_sectiontitle">Open LLVM Projects</div>
<ul>
<li>Google Summer of Code Ideas & Projects
<ul>
<li>
<a href="#gsoc24">Google Summer of Code 2024</a>
<ul>
<li><b>LLVM Core</b>
<ul>
<li><a href="#remove_ub_tests">Remove undefined behavior from tests</a></li>
<li><a href="#spirv_tablegen">Automatically generate TableGen file for SPIR-V instruction set</a></li>
<li><a href="#bitstream_cas">LLVM bitstream integration with CAS (content-addressable storage)</a></li>
<li><a href="#three_way_comparison">Add 3-way comparison intrinsics</a></li>
<li><a href="#llvm_www">Improve the LLVM.org Website Look and Feel</a></li>
<li><a href="#parameter-tuning">The 1001 thresholds in LLVM</a></li>
</ul>
<li><a href="http://clang.llvm.org/"><b>Clang</b></a>
<ul>
<li><a href="#clang-repl-out-of-process">Out-of-process execution for clang-repl</a></li>
<li><a href="#clang-plugins-windows">Support clang plugins on Windows</a></li>
<li><a href="#clang-on-demand-parsing">On Demand Parsing in Clang</a></li>
<li><a href="#clang-doc-improve-usability">Improve Clang-Doc Usability</a></li>
</ul>
<li><a href="http://lldb.llvm.org/"><b>LLDB</b></a>
<ul>
<li><a href="#rich-disassembler-for-lldb">Rich disassembler for LLDB</a></li>
</ul>
<li><a href="http://openmp.llvm.org/"><b>(OpenMP) Offload</b></a>
<ul>
<li><a href="#gpu-delta-debugging">GPU Delta Debugging</a></li>
<li><a href="#offload-libcxx">Offloading libcxx</a></li>
<li><a href="#gpu-libc">Performance tuning the GPU libc</a></li>
<li><a href="#gpu-first">Improve GPU First Framework</a></li>
</ul>
<li><a href="https://clangir.org"><b>ClangIR</b></a>
<ul>
<li><a href="#clangir-gpu">Compile GPU kernels using ClangIR</a></li>
</ul>
<li><a href="http://libc.llvm.org/"><b>LLVM libc</b></a>
<ul>
<li><a href="#half-precision-libc">Half precision in LLVM libc</a>
</ul>
</ul>
</li>
<li>
<a href="#gsoc23">Google Summer of Code 2023</a>
<ul>
<li>
<b>LLVM Core</b>
<ul>
<li><a href="#llvm_new_jitlink_reopt">Re-optimization using JITLink</a></li>
<li><a href="#llvm_new_jitlink_backends">JITLink new backends</a></li>
<li><a href="#llvm_improving_compile_times">Improving compile times</a></li>
<li><a href="#llvm_addressing_rust_optimization_failures">Addressing Rust optimization failures</a></li>
<li><a href="#llvm_mlgo_latency_model">Better performance models for MLGO training</a></li>
<li><a href="#llvm_mlgo_passes_2023">Machine Learning Guided Ordering of Compiler Optimization Passes</a></li>
<li><a href="#llvm_map_value_to_src_expr">Map LLVM values to corresponding source-level expressions</a></li>
</ul>
</li>
<li><a href="http://clang.llvm.org/"><b>Clang</b></a>
<ul>
<li><a href="#clang-repl-out-of-process">Out-of-process execution for clang-repl</a>
<li><a href="#clang_analyzer_taint_analysis">Improve and Stabilize the Clang Static Analyzer's "Taint Analysis" Checks</a></li>
<li><a href="#clang-repl-autocompletion">Implement autocompletion in clang-repl</a>
<li><a href="#clang-modules-build-daemon">Modules build daemon: build system agnostic support for explicitly built modules</a></li>
<li><a href="#clang-extract-api-categories">ExtractAPI Objective-C categories</a></li>
<li><a href="#clang-extract-api-cpp-support">ExtractAPI C++ Support</a></li>
<li><a href="#clang-extract-api-while-building">ExtractAPI while building</a></li>
<li><a href="#clang-improve-diagnostics2">Improve Clang diagnostics</a></li>
<li><a href="#clang-tutorials-clang-repl">Tutorial development with clang-repl</a></li>
<li><a href="#clang-repl-wasm">Add WebAssembly Support in clang-repl</a></li>
</li>
</ul>
</li>
<li>
<b>LLD</b>
<ul>
<li><a href="#llvm_lld_embedded">LLD Linker Improvements for Embedded Targets</a></li>
</ul>
</li>
<li>
<b>MLIR</b>
<ul>
<li><a href="#llvm_mlir_presburger_opt">Optimizing MLIR’s Presburger library</a></li>
<li><a href="#llvm_mlir_query">Interactively query MLIR IR</a></li>
</ul>
</li>
<li>
<b>Code Coverage</b>
<ul>
<li><a href="#llvm_code_coverage">Support a hierarchical directory structure in generated coverage html reports</a></li>
<li><a href="#llvm_patch_coverage">Patch based test coverage for quick test feedback</a></li>
</ul>
</li>
<li>
<b>ClangIR</b>
<ul>
<li><a href="#clangir">Build and run SingleSource benchmarks using ClangIR</a></li>
</ul>
</li>
<li>
<b><a href="https://enzyme.mit.edu">Enzyme</a></b>
<ul>
<li><a href="#enzyme_tblgen_extension">Move additional Enzyme Rules to Tablegen</a></li>
</ul>
</li>
</ul>
</li>
<li>
<a href="#gsoc22">Google Summer of Code 2022</a>
<ul>
<li>
<b>LLVM Core</b>
<ul>
<li><a href="#llvm_shared_jitlink">Implement a shared-memory based JITLinkMemoryManager for out-of-process JITting</a></li>
<li><a href="#llvm_build_jit_tutorial">Modernize the LLVM "Building A JIT" tutorial series</a></li>
<li><a href="#llvm_jit_new_format">Write JITLink support for a new format/architecture</a></li>
<li><a href="#llvm_instrumentaion_for_compile_time">Instrumentation of Clang/LLVM for Compile Time</a></li>
<li><a href="#llvm_lto_dependency_info">Richer symbol dependency information for LTO</a></li>
<li><a href="#llvm_mlgo_passes">Machine Learning Guided Ordering of Compiler Optimization Passes</a></li>
<li><a href="#llvm_mlgo_loop">Learning Loop Transformation Heuristics</a></li>
<li><a href="#llvm_module_inliner">Evaluate and Expand the Module-Level Inliner</a></li>
<li><a href="#llvm_undef_load">Remove undef: move uninitialized memory to poison</a></li>
<li><a href="#llvm_abi_export">Add ABI/API export annotations to the LLVM build</a></li>
</ul>
</li>
<li><a href="http://clang.llvm.org/"><b>Clang</b></a>
<ul>
<li><a href="#clang-template-instantiation-sugar">Extend clang AST to
provide information for the type as written in template
instantiations</a>
</li>
<li><a href="#clang-sa-structured-bindings">Implement support for
C++17 structured bindings in the Clang Static Analyzer</a>
</li>
<li><a href="#clang-improve-diagnostics">Improve Clang Diagnostics</a>
</li>
</ul>
</li>
<li>
<a href="https://polly.llvm.org"><b>Polly</b></a>
<ul>
<li><a href="#polly_npm">Completely switch to new pass manager</a></li>
</ul>
</li>
<li>
<b><a href="https://enzyme.mit.edu">Enzyme</a></b>
<ul>
<li><a href="#enzyme_tblgen">Move Enzyme Instruction Transformation Rules to Tablegen</a></li>
<li><a href="#enzyme_vector">Vector Reverse-Mode Automatic Differentiation</a></li>
<li><a href="#enzyme_pm">Enable The New Pass Manager</a></li>
</ul>
</li>
</ul>
</li>
<li>
<a href="#gsoc21">Google Summer of Code 2021</a>
<ul>
<li>
<b>LLVM Core</b>
<ul>
<li><a href="#llvm_distributing_lit">Distributed lit testing</a></li>
<li><a href="#llvm_loop_heuristics">Learning Loop Transformation Heuristics</a></li>
<li><a href="#llvm_ir_fuzzing">Fuzzing LLVM-IR Passes</a></li>
<li><a href="#llvm_ir_assume"><tt>llvm.assume</tt> the missing pieces</a></li>
<li><a href="#llvm_shared_jitlink">Implement a shared-memory based JITLinkMemoryManager for out-of-process JITting</a></li>
<li><a href="#llvm_build_jit_tutorial">Modernize the LLVM "Building A JIT" tutorial series</a></li>
<li><a href="#llvm_jit_new_format">Write JITLink support for a new format/architecture</a></li>
<li><a href="#llvm_ir_issues">Fix fundamental issues in LLVM's IR</a></li>
<li><a href="#llvm_utilize_loopnest">Utilize LoopNest Pass</a></li>
</ul>
</li>
<li><a href="http://clang.llvm.org/"><b>Clang</b></a>
<ul>
<li><a href="#clang-template-instantiation-sugar">Extend clang AST to
provide information for the type as written in template
instantiations</a>
</li>
</ul>
</li>
<li>
<b>OpenMP</b>
<ul>
<li><a href="#openmp_gpu_jit">JIT-ing OpenMP GPU kernels transparently</a></li>
</ul>
</li>
<li>
<b>OpenACC</b>
<ul>
<li><a href="#openacc_rt_diagnostics">OpenACC Diagnostics from the OpenMP Runtime</a></li>
</ul>
</li>
<li>
<b><a href="https://polly.llvm.org">Polly</a></b>
<ul>
<li><a href="#polly_isl_bindings">Use official isl C++ bindings</a></li>
</ul>
</li>
<li>
<b><a href="https://enzyme.mit.edu">Enzyme</a></b>
<ul>
<li><a href="#enzyme_blas">Integrate custom derivatives of BLAS, Eigen, and similar routines into Enzyme</a></li>
<li><a href="#enzyme_swift">Integrate Enzyme into Swift to provide high-performance differentiation in Swift</a></li>
<li><a href="#enzyme_fixed">Differentiation of Fixed-Point Arithmetic</a></li>
<li><a href="#enzyme_rust">Integrate Enzyme into Rust to provide high-performance differentiation in Rust</a></li>
</ul>
</li>
<li>
<b>Clang Static Analyzer</b>
<ul>
<li><a href="#static_analyzer_profling">Clang Static Analyzer performance profiling</a></li>
<li><a href="#static_analyzer_constraint_solver">Clang Static Analyzer constraint solver improvements</a></li>
</ul>
</li>
<li>
<b>LLDB</b>
<ul>
<li><a href="#lldb_diagnostics">A structured approach to diagnostics in LLDB</a></li>
</ul>
</li>
</ul>
</li>
<li>
<a href="#gsoc20">Google Summer of Code 2020</a>
<ul>
<li>
<b>LLVM Core</b>
<ul>
<li><a href="#llvm_optimized_debugging">Improve debugging of optimized code</a></li>
<li><a href="#llvm_ipo">Improve inter-procedural analyses and optimizations</a></li>
<li><a href="#llvm_par">Improve parallelism-aware analyses and optimizations</a></li>
<li><a href="#llvm_dbg_invariant">Make LLVM passes debug info invariant</a></li>
<li><a href="#llvm_mergesim">Improve MergeFunctions to incorporate MergeSimilarFunction patches and ThinLTO Support</a></li>
<li><a href="#llvm_dwarf_yaml2obj">Add DWARF support to yaml2obj</a></li>
<li><a href="#llvm_hotcold">Improve hot cold splitting to aggressively outline small blocks</a></li>
<li><a href="#llvm_pass_order">Advanced Heuristics for Ordering Compiler Optimization Passes</a></li>
<li><a href="#llvm_ml_scc">Machine learning and compiler optimizations: using inter-procedural analysis to select optimizations</a></li>
<li><a href="#llvm_postdominators">Add PostDominatorTree in LoopStandardAnalysisResults</a></li>
<li><a href="#llvm_loopnest">Create loop nest pass</a></li>
<li><a href="#llvm_instdump">Instruction properties dumper and checker</a></li>
<li><a href="#llvm_movecode">Unify ways to move code or check if code is safe to be moved</a></li>
</ul>
<li><a href="http://clang.llvm.org/"><b>Clang</b></a>
<ul>
<li><a href="#clang-template-instantiation-sugar">Extend clang AST to
provide information for the type as written in template
instantiations</a>
</li>
<li><a href="#clang-sa-cplusplus-checkers">Find null smart pointer dereferences
with the Static Analyzer</a>
</li>
</ul>
</li>
<li><a href="http://lldb.llvm.org/"><b>LLDB</b></a></li>
<ul>
<li><a href="#lldb-autosuggestions">Support autosuggestions in LLDB's command line</a></li>
<li><a href="#lldb-more-completions">Implement the missing tab completions for LLDB's command line</a></li>
<li><a href="#lldb-reimplement-lldb-cmdline">Reimplement LLDB's command-line commands using the public SB API.</a></li>
<li><a href="#lldb-batch-testing">Add support for batch-testing to the LLDB testsuite.</a></li>
</ul>
<li>
<b>MLIR</b>
<ul>
<li>See the <a href="https://mlir.llvm.org/getting_started/openprojects/">MLIR open project list</a></li>
</ul>
</li>
</ul>
</li>
<li>
<a href="#gsoc19">Google Summer of Code 2019</a>
<ul>
<li>
<b>LLVM Core</b>
<ul>
<li><a href="#debuginfo_codegen_mismatch">Debug Info should have no
effect on codegen</a></li>
<li><a href="#llvm_function_attributes">Improve (function) attribute
inference</a></li>
<li><a href="#improve_binary_utilities">Improve LLVM binary utilities
</a></li>
</ul>
</li>
<li><a href="http://clang.llvm.org/"><b>Clang</b></a>
<ul>
<li><a href="#clang-astimporter-fuzzer">Implement an ASTImporter
fuzzer</a>
</li>
<li><a href="#improve-autocompletion">Improve shell autocompletion
for Clang</a>
</li>
<li><a href="#analyze-llvm">Apply the Clang Static Analyzer to LLVM-based
Projects</a>
</li>
<li><a href="#header-generation">Generate annotated sources based on
LLVM-IR analyses</a>
</li>
</ul>
</li>
</ul>
</li>
<li><a href="#gsoc18">Google Summer of Code 2018</a></li>
<li><a href="#gsoc17">Google Summer of Code 2017</a></li>
</ul>
</li>
<li><a href="#what">What is this?</a></li>
<li><a href="#subprojects">LLVM Subprojects: Clang and more</a></li>
<li><a href="#improving">Improving the current system</a>
<ol>
<li><a href="#target-desc">Factor out target descriptions</a></li>
<li><a href="#code-cleanups">Implementing Code Cleanup bugs</a></li>
<li><a href="#programs">Compile programs with the LLVM Compiler</a></li>
<li><a href="#llvmtest">Add programs to the llvm-test suite</a></li>
<li><a href="#benchmark">Benchmark the LLVM compiler</a></li>
<li><a href="#statistics">Benchmark Statistics and Warning System</a></li>
<li><a href="#coverage">Improving Coverage Reports</a></li>
<li><a href="#misc_imp">Miscellaneous Improvements</a></li>
</ol></li>
<li><a href="#new">Adding new capabilities to LLVM</a>
<ol>
<li><a href="#llvm_ir">Extend the LLVM intermediate representation</a></li>
<li><a href="#pointeranalysis">Pointer and Alias Analysis</a></li>
<li><a href="#profileguided">Profile-Guided Optimization</a></li>
<li><a href="#compaction">Code Compaction</a></li>
<li><a href="#xforms">New Transformations and Analyses</a></li>
<li><a href="#codegen">Code Generator Improvements</a></li>
<li><a href="#misc_new">Miscellaneous Additions</a></li>
</ol></li>
<li><a href="#using">Project using LLVM</a>
<ol>
<li><a href="#machinemodulepass">Add a MachineModulePass</a></li>
<li><a href="#encodeanalysis">Encode Analysis Results in MachineInstr IR</a></li>
<li><a href="#codelayoutjit">Code Layout in the LLVM JIT</a></li>
<li><a href="#fieldlayout">Improved Structure Splitting and Field Reordering</a></li>
<li><a href="#slimmer">Finish the Slimmer Project</a></li>
</ol></li>
</ul>
<div class="doc_author">
<p>Written by the <a href="/">LLVM Team</a></p>
</div>
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<div class="www_sectiontitle">
<a name="gsoc24">Google Summer of Code 2024</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p>
Welcome prospective Google Summer of Code 2024 Students! This document is
your starting point to finding interesting and important projects for LLVM,
Clang, and other related sub-projects. This list of projects is not only
developed for Google Summer of Code, but open projects that really need
developers to work on and are very beneficial for the LLVM community.
</p>
<p>We encourage you to look through this list and see which projects excite
you and match well with your skill set. We also invite proposals not on this
list. More information and discussion about GSoC can be found in
<a href="https://discourse.llvm.org/c/community/gsoc" target="_blank">
discourse
</a>. If you have questions about a particular project please find the
relevant entry in discourse, check previous discussion and ask. If there is
no such entry or you would like to propose an idea please create a new
entry. Feedback from the community is a requirement for your proposal to be
considered and hopefully accepted.
</p>
<p>The LLVM project has participated in Google Summer of Code for several years
and has had some very successful projects. We hope that this year is no
different and look forward to hearing your proposals. For information on how
to submit a proposal, please visit the Google Summer of Code main
<a href="https://summerofcode.withgoogle.com/">website.</a>
</p>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="remove_ub_tests">Remove undefined behavior from tests</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
Many of LLVM's unit tests have been reduced automatically from larger tests.
Previous-generation reduction tools used undef and poison as placeholders
everywhere, as well as introduced undefined behavior (UB).
Tests with UB are not desirable because 1) they are fragile since in the
future the compiler may start optimizing more aggressively and break the
test, and 2) it breaks translation validation tools such as
<a href="https://github.com/AliveToolkit/alive2/">Alive2</a> (since it's
correct to translate a fuction that is always UB into anything).
<br />
The major steps include:
<ol>
<li>Replace known patterns such as branch on undef/poison, memory accesses
with invalid pointers, etc with non-UB patterns.</li>
<li>Use Alive2 to detect further patterns (by searching for tests that are
always UB).</li>
<li>Report any LLVM bug found by Alive2 that is exposed when removing
UB.</li>
</ol>
</p>
<p><b>Expected result:</b>
The majority of LLVM's unit tests will be free of UB.</p>
<p><b>Skills:</b>
Experience with scripting (Python or PHP) is required.
Experience with regular expressions is encouraged.
</p>
<p><b>Project size:</b> Either medium or large.</p>
<p><b>Difficulty:</b> Medium</p>
<p><b>Confirmed Mentor:</b> <a href="https://web.ist.utl.pt/nuno.lopes/">Nuno Lopes</a></p>
<p><b>Discourse:</b>
<a href="https://discourse.llvm.org/t/gsoc-2004-remove-undefined-behavior-from-tests/77236">URL</a>
</p>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="spirv_tablegen">Automatically generate TableGen file for SPIR-V instruction set</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
The existing file that describes the SPIR-V instruction set in LLVM was
manually created and is not always complete or up to date. Whenever new
instructions need to be added to the SPIR-V backend, the file must be
amended. In addition, since it is not created in a systematic way, there are
often slight discrepancies between how an instruction is described in the
SPIR-V spec and how it is declared in the TableGen file. Since SPIR-V
backend developers often use the spec as a reference when developing new
features, having a consistent mapping between the specification and TableGen
records will ease development. This project proposes creating a script
capable of generating a complete TableGen file that describes the SPIR-V
instruction set given the JSON grammar available in the
KhronosGroup/SPIRV-Headers repository, and updating SPIR-V backend code to
use the new definitions. The specific method used for translating the JSON
grammar to TableGen is left up to the discretion of the applicant, however,
it should be checked into the LLVM repository with well-documented
instructions to replicate the translation process so that future maintainers
will be able to regenerate the file when the grammar changes. Note that the
grammar itself should remain out-of-tree in its existing separate
repository.
</p>
<p><b>Expected result:</b>
<ul>
<li>The SPIR-V instruction set's definition in TableGen is replaced with
one that is autogenerated.</li>
<li>A script and documentation are written that support regenerating the
definitions as needed given the JSON grammar of the SPIR-V instruction
set.</li>
<li>Usage of the SPIR-V instruction set in the SPIR-V backend updated to
use the new autogenerated definitions.</li>
</ul>
</p>
<p><b>Skills:</b>
Experience with scripting and an intermediate knowledge of C++. Previous
experience with LLVM/TableGen is a bonus but not required.
</p>
<p><b>Project size:</b> Medium (175 hour)</p>
<p><b>Confirmed Mentors:</b>
<a href="https://github.com/sudonatalie/">Natalie Chouinard</a>,
<a href="https://github.com/keenuts/">Nathan Gauër</a></p>
<p><b>Discourse:</b>
<a href="https://discourse.llvm.org/t/clang-automatically-generate-tablegen-file-for-spir-v-instruction-set/76369">URL</a>
</p>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="bitstream_cas">LLVM bitstream integration with CAS (content-addressable storage)</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
The LLVM bitstream file format is used for serialization of intermediate
compiler artifacts, such as LLVM IR or Clang modules. There are situations
where multiple bitstream files store identical information, and this
duplication leads to increased storage requirements.
<br><br>
This project aims to integrate the LLVM CAS library into the LLVM bitstream
file format. If we factor out the frequently duplicated part of a bitstream
file into a separate CAS object, we can replace all copies with a small
reference to the canonical CAS object, saving storage.
<br><br>
The primary motivating use-case for this project is the dependency scanner
that's powering "implicitly-discovered, explicitly-built" Clang modules.
There are real-world situations where even coarse de-duplication on the
block level could halve the size of the scanning module cache.
</p>
<p><b>Expected result:</b>
There's a way to configure the LLVM bitstream writer/reader to use CAS as
the backing storage.
</p>
<p><b>Skills:</b>
Intermediate knowledge of C++, some familiarity with data serialization, self-motivation.
</p>
<p><b>Project size:</b> Medium or large</p>
<p><b>Confirmed Mentors:</b>
<a href="https://github.com/jansvoboda11/">Jan Svoboda</a>,
<a href="https://github.com/cachemeifyoucan/">Steven Wu</a></p>
<p><b>Discourse:</b>
<a href="https://discourse.llvm.org/t/llvm-bitstream-integration-with-cas-content-addressable-storage/76757">URL</a>
</p>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="three_way_comparison">Add 3-way comparison intrinsics</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
<a href="https://en.wikipedia.org/wiki/Three-way_comparison">3-way comparisons</a>
return the values -1, 0 or 1 depending on whether the values compare lower,
equal or greater. They are exposed in C++ via the spaceship operator
(operator<=>) and in Rust via the PartialOrd and Ord traits.
Currently, such comparisons produce sub-optimal codegen and optimization
results in some cases.
<br/><br/>
The goal of this project is to resolve these optimization issues by
implementing new 3-way comparison intrinsics, as described in
<a href="https://discourse.llvm.org/t/rfc-add-3-way-comparison-intrinsics/76685">[RFC] Add 3-way comparison intrinsics</a>.
The implementation steps are broadly:
<ol>
<li>Add the intrinsics to LLVM IR.</li>
<li>Implement legalization/expansion support in SelectionDAG and
GlobalISel.</li>
<li>Implement optimization support in ConstantFolding, InstSimplify,
InstCombine, CorrelatedValuePropagation, IndVarSimplify,
ConstraintElimination, IPSCCP, and other relevant transforms.</li>
<li> Make use of the intrinsics via InstCombine canonicalization or
direct emission in clang/rustc.</li>
</ol>
Adding new target-independent intrinsics is a good way of becoming familiar with a broad slice of LLVM!
</p>
<p><b>Expected result:</b>
Support for the intrinsics in the backend and the most important
optimization passes. Ideally full integration starting at the frontend.
</p>
<p><b>Skills:</b> Intermediate knowledge of C++ </p>
<p><b>Project size:</b> Medium or large</p>
<p><b>Difficulty:</b> Medium</p>
<p><b>Confirmed Mentors:</b>
<a href="https://github.com/nikic">Nikita Popov</a>,
<a href="https://github.com/dc03">Dhruv Chawla</a></p>
<p><b>Discourse:</b>
<a href="https://discourse.llvm.org/t/llvm-add-3-way-comparison-intrinsics/76807">URL</a>
</p>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="llvm_www">Improve the LLVM.org Website Look and Feel</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
The llvm.org website serves as the central hub for information about the
LLVM project, encompassing project details, current events, and relevant
resources. Over time, the website has evolved organically, prompting the
need for a redesign to enhance its modernity, structure, and ease of
maintenance.
<br/><br/>
The goal of this project is to create a contemporary and coherent static
website that reflects the essence of LLVM.org. This redesign aims to improve
navigation, taxonomy, content discoverability, mobile device support,
accessibility, and overall usability. Given
the critical role of the website in the community, efforts will be made to
engage with community members, seeking consensus on the proposed changes.
</p>
<p><b>Expected result:</b>
A modern, coherent-looking website that attracts new prospect users and
empowers the existing community with better navigation, taxonomy, content
discoverability, and overall usability. Since the website is a critical
infrastructure and most of the community will have an opinion this project
should try to engage with the community building community consensus on the
steps being taken. Suggested approach:
<ul>
<li>Conduct a comprehensive content audit of the existing website.</li>
<li>Select appropriate technologies, preferably static site generators
like Hugo or Jekyll.</li>
<li>Advocate for a separation of data and visualization, utilizing formats
such as YAML and Markdown to facilitate content management without
direct HTML coding.</li>
<li>Present three design mockups for the new website, fostering open
discussions and allowing time for alternative proposals from interested
parties.</li>
<li>Implement the chosen design, incorporating valuable feedback from the
community.</li>
<li>Collaborate with content creators to integrate or update content as
needed.</li>
</ul>
The successful candidate should commit to regular participation in weekly
meetings, deliver presentations, and contribute blog posts as requested.
Additionally, they should demonstrate the ability to navigate the community
process with patience and understanding.
</p>
<p><b>Skills:</b>
Knowledge in the area of web development with static site generators.
Knowledge in html, css, bootstrap, and markdown. Patience and self-motivation.
</p>
<p><b>Difficulty:</b> Hard</p>
<p><b>Project size:</b> Large</p>
<p><b>Confirmed Mentors:</b>
<a href=https://github.com/tlattner>Tanya Lattner</a>,
<a href=https://github.com/vgvassilev>Vassil Vassilev</a>
</p>
<p><b>Discourse:</b>
<a href="https://discourse.llvm.org/t/improve-the-llvm-org-website-look-and-feel/76864">URL</a>
</p>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="clang-repl-out-of-process">Out-of-process execution for clang-repl</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
The Clang compiler is part of the LLVM compiler infrastructure and supports
various languages such as C, C++, ObjC and ObjC++. The design of LLVM and
Clang enables them to be used as libraries, and has led to the creation of
an entire compiler-assisted ecosystem of tools. The relatively friendly
codebase of Clang and advancements in the JIT infrastructure in LLVM further
enable research into different methods for processing C++ by blurring the
boundary between compile time and runtime. Challenges include incremental
compilation and fitting compile/link time optimizations into a more dynamic
environment.
<br /> <br />
Incremental compilation pipelines process code chunk-by-chunk by building an
ever-growing translation unit. Code is then lowered into the LLVM IR and
subsequently run by the LLVM JIT. Such a pipeline allows creation of
efficient interpreters. The interpreter enables interactive exploration and
makes the C++ language more user friendly. Clang-Repl is one example.
<br /> <br />
Clang-Repl uses the Orcv2 JIT infrastructure within the same process. That
design is efficient and easy to implement however it suffers from two
significant drawbacks. First, it cannot be used in devices which do not have
sufficient resources to host the entire infrastructure, such as the arduino
due (see this
<a href="https://compiler-research.org/meetings/#caas_10Mar2022">talk</a>
for more details). Second, crashes in user codes mean that the entire
process crashes, hindering overall reliability and ease of use.
<br /> <br />
This project aims to move Clang-Repl to an out-of-process execution model
in order to address both of these issues.
</p>
<p><b>Expected result:</b>
Implement an out-of-process execution of statements with Clang-Repl;
Demonstrate that Clang-Repl can support some of the ez-clang use-cases;
Research into approaches to restart/continue the session upon crash;
As a stretch goal design a versatile reliability approach for crash recovery;
</p>
<p><b>Skills:</b>
Intermediate knowledge of C++, Understanding of LLVM and the LLVM JIT in particular
</p>
<p><b>Project size:</b>Either medium or large.</p>
<p><b>Difficulty:</b> Medium</p>
<p><b>Confirmed Mentor:</b>
<a href=https://github.com/vgvassilev>Vassil Vassilev</a>,
</p>
<p><b>Discourse:</b> <a href="https://discourse.llvm.org/t/clang-out-of-process-execution-for-clang-repl/68225">URL</a>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="clang-plugins-windows">Support clang plugins on Windows</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
The Clang compiler is part of the LLVM compiler infrastructure and supports
various languages such as C, C++, ObjC and ObjC++. The design of LLVM and
Clang allows the compiler to be extended with plugins[1]. A plugin makes it
possible to run extra user defined actions during a compilation. Plugins
are supported on unix and darwin but not on windows due to some specifics of
the windows platform.
<br /> <br />
This project would expose the participant to a broad cross section of the LLVM codebase. It involves exploring the API surface, classifying the interfaces as being public or private, and annotating that information to the API declarations. It would also expose the participant to details and differences of different platforms as this work is cross-platform (Windows, Linux, Darwin, BSD, etc). The resulting changes would improve LLVM on Linux and Windows while enabling new functionality on Windows.
</p>
<p><b>Expected result:</b>
This project aims to allow make clang -fplugin=windows/plugin.dll work. The
implementation approach should extend the working prototype [3] and extend
the annotation tool [4]. The successful candidate should be prepared to
attend a weekly meeting, make presentations and prepare blog posts upon
request.
</p>
<p><i>Further reading</i><br />
[1] https://clang.llvm.org/docs/ClangPlugins.html
<br />
[2] https://discourse.llvm.org/t/clang-plugins-on-windows
<br />
[3] https://github.com/llvm/llvm-project/pull/67502
<br />
[4] https://github.com/compnerd/ids
</p>
<p><b>Skills:</b>
Intermediate knowledge of C++, Experience with Windows and its compilation
and linking model.
</p>
<p><b>Project size:</b>Either medium or large.</p>
<p><b>Difficulty:</b> Medium</p>
<p><b>Confirmed Mentor:</b>
<a href=https://github.com/vgvassilev>Vassil Vassilev</a>,
<a href=https://github.com/compnerd>Saleem Abdulrasool</a>
</p>
<p><b>Discourse:</b> <a href="https://discourse.llvm.org/t/support-clang-plugins-on-windows/76408">URL</a>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="clang-on-demand-parsing">On Demand Parsing in Clang</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b> Clang, like any C++ compiler, parses a
sequence of characters as they appear, linearly. The linear character
sequence is then turned into tokens and AST before lowering to machine
code. In many cases the end-user code uses a small portion of the C++
entities from the entire translation unit but the user still pays the price
for compiling all of the redundancies.
<br /> <br />
This project proposes to process the heavy compiling C++ entities upon using
them rather than eagerly. This approach is already adopted in Clang’s
CodeGen where it allows Clang to produce code only for what is being
used. On demand compilation is expected to significantly reduce the
compilation peak memory and improve the compile time for translation units
which sparsely use their contents. In addition, that would have a
significant impact on interactive C++ where header inclusion essentially
becomes a no-op and entities will be only parsed on demand.
<br /> <br />
The Cling interpreter implements a very naive but efficient
cross-translation unit lazy compilation optimization which scales across
hundreds of libraries in the field of high-energy physics.
<br /> <br />
<pre>
// A.h
#include <string>
#include <vector>
template <class T, class U = int> struct AStruct {
void doIt() { /*...*/ }
const char* data;
// ...
};
template<class T, class U = AStruct<T>>
inline void freeFunction() { /* ... */ }
inline void doit(unsigned N = 1) { /* ... */ }
// Main.cpp
#include "A.h"
int main() {
doit();
return 0;
}
</pre>
<br /> <br />
This pathological example expands to 37253 lines of code to process. Cling
builds an index (it calls it an autoloading map) where it contains only
forward declarations of these C++ entities. Their size is 3000 lines of
code. The index looks like:
<pre>
// A.h.index
namespace std{inline namespace __1{template <class _Tp, class _Allocator> class __attribute__((annotate("$clingAutoload$vector"))) __attribute__((annotate("$clingAutoload$A.h"))) __vector_base;
}}
...
template <class T, class U = int> struct __attribute__((annotate("$clingAutoload$A.h"))) AStruct;
</pre>
<br /> <br />
Upon requiring the complete type of an entity, Cling includes the relevant
header file to get it. There are several trivial workarounds to deal with
default arguments and default template arguments as they now appear on the
forward declaration and then the definition. You can read more in [1].
<br /> <br />
Although the implementation could not be called a reference implementation,
it shows that the Parser and the Preprocessor of Clang are relatively
stateless and can be used to process character sequences which are not
linear in their nature. In particular namespace-scope definitions are
relatively easy to handle and it is not very difficult to return to
namespace-scope when we lazily parse something. For other contexts such as
local classes we will have lost some essential information such as name
lookup tables for local entities. However, these cases are probably not very
interesting as the lazy parsing granularity is probably worth doing only for
top-level entities.
<br /> <br />
Such implementation can help with already existing issues in the standard
such as CWG2335, under which the delayed portions of classes get parsed
immediately when they're first needed, if that first usage precedes the end
of the class. That should give good motivation to upstream all the
operations needed to return to an enclosing scope and parse something.
<br /> <br />
<b>Implementation approach</b>: Upon seeing a tag definition during parsing
we could create a forward declaration, record the token sequence and mark it
as a lazy definition. Later upon complete type request, we could re-position
the parser to parse the definition body. We already skip some of the
template specializations in a similar way [2, 3].
<br /> <br />
Another approach is every lazy parsed entity to record its token stream and
change the Toks stored on LateParsedDeclarations to optionally refer to a
subsequence of the externally-stored token sequence instead of storing its
own sequence (or maybe change CachedTokens so it can do that
transparently). One of the challenges would be that we currently modify the
cached tokens list to append an "eof" token, but it should be possible to
handle that in a different way.
<br /> <br />
In some cases, a class definition can affect its surrounding context in a
few ways you'll need to be careful about here:
<br /> <br />
1) `struct X` appearing inside the class can introduce the name `X` into the
enclosing context.
<br /> <br />
2) `static inline` declarations can introduce global variables with
non-constant initializers that may have arbitrary side-effects.
<br /> <br />
For point (2), there's a more general problem: parsing any expression can
trigger a template instantiation of a class template that has a static data
member with an initializer that has side-effects. Unlike the above two
cases, I don't think there's any way we can correctly detect and handle such
cases by some simple analysis of the token stream; actual semantic analysis
is required to detect such cases. But perhaps if they happen only in code
that is itself unused, it wouldn't be terrible for Clang to have a language
mode that doesn't guarantee that such instantiations actually happen.
<br /> <br />
Alternative and more efficient implementation could be to make the lookup
tables range based but we do not have even a prototype proving this could be
a feasible approach.
</p>
<p><b>Expected result:</b>
<ul>
<li>Design and implementation of on-demand compilation for non-templated functions</li>
<li>Support non-templated structs and classes</li>
<li>Run performance benchmarks on relevant codebases and prepare report</li>
<li>Prepare a community RFC document</li>
<li>[Stretch goal] Support templates</li>
</ul>
The successful candidate should commit to regular participation in weekly
meetings, deliver presentations, and contribute blog posts as
requested. Additionally, they should demonstrate the ability to navigate the
community process with patience and understanding.
</p>
<p><i>Further reading</i><br/>
[1] https://github.com/root-project/root/blob/master/README/README.CXXMODULES.md#header-parsing-in-root
<br />
[2] https://github.com/llvm/llvm-project/commit/b9fa99649bc99
<br />
[3] https://github.com/llvm/llvm-project/commit/0f192e89405ce
</p>
<p><b>Skills:</b>
Knowledge of C++, Deeper understanding of how Clang works,
knowledge of Clang AST and Preprocessor.
</p>
<p><b>Project size:</b>Large</p>
<p><b>Difficulty:</b> Hard</p>
<p><b>Confirmed Mentor:</b>
<a href=https://github.com/vgvassilev>Vassil Vassilev</a>,
<a href=https://github.com/mizvekov>Matheus Izvekov</a>
</p>
<p><b>Discourse:</b> <a href="https://discourse.llvm.org/t/on-demand-parsing-in-clang/76912">URL</a>
</div>
<!-- *********************************************************************** -->
<div class="www_subsubsection">
<a name="clang-doc-improve-usability">Improve Clang-Doc Usability</a>
</div>
<!-- *********************************************************************** -->
<div class="www_text">
<p><b>Description of the project:</b>
<a href=https://clang.llvm.org/extra/clang-doc.html>Clang-Doc</a> is a
C/C++ documentation generation tool created as an alternative for Doxygen
and built on top of LibTooling. This effort started in 2018 and critical
mass has landed in 2019, but the development has been largely dormant since
then, mostly due to a lack of resources.
<br /> <br />
The tool can currently generate documentation in Markdown and HTML formats,
but the tool has some structural issues, is difficult to use, the generated
documentation has usability issues and is missing several key features:
<ul>
<li>Not all C/C++ constructs are currently handled by the Markdown and
HTML emitter limiting the tool’s usability.</li>
<li>The generated HTML output does not scale with the size of the
codebase making it unusable for larger C/C++ projects.</li>
<li>The implementation does not always use the most efficient or
appropriate data structures which leads to correctness and performance
issues.</li>
<li>There is a lot of duplicated boiler plate code which could be
improved with templates and helpers.</li>
</ul>
</p>
<p><b>Expected result:</b>
The goal of this project is to address the existing shortcomings and
improve the usability of Clang-Doc to the point where it can be used to
generate documentation for large scale projects such as LLVM. The ideal
outcome is that the LLVM project will use Clang-Doc for generating its <a
href=https://llvm.org/doxygen/>reference documentation</a>.
<br /><br />
Successful proposals should focus not only on addressing the existing
limitations, but also draw inspiration for other potential improvements
from other similar tools such as <a href=https://hdoc.io/>hdoc</a>, <a
href=https://github.com/standardese/standardese>standardese</a>, <a
href=https://github.com/chromium/subspace/tree/main/subdoc>subdoc</a> or
<a href=https://cs.opensource.google/fuchsia/fuchsia/+/main:tools/cppdocgen/>cppdocgen</a>.
</p>
<p><b>Skills:</b>
Experience with web technologies (HTML, CSS, JS) and an intermediate
knowledge of C++. Previous experience with Clang/LibTooling is a bonus but
not required.
</p>
<p><b>Project size:</b> Either medium or large.</p>
<p><b>Difficulty:</b> Medium</p>
<p><b>Confirmed Mentor:</b>
<a href=https://github.com/petrhosek>Petr Hosek</a>,
<a href=https://github.com/ilovepi>Paul Kirth</a>
</p>
<p><b>Discourse:</b> <a href=https://discourse.llvm.org/t/improve-clang-doc-usability/76996>URL</a>
</div>
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