The document presents an overview of the LLVM compiler framework, including its architecture, features, and various applications across different programming languages and platforms. It highlights LLVM's capabilities such as optimizations and support for multiple architectures, along with its contributions from various companies and ongoing projects. The summary concludes with an invitation to explore LLVM and resources for its integration.

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Where is LLVM being used today?
Tilmann Scheller
Senior LLVM Compiler Engineer
t.scheller@samsung.com
Samsung Open Source Group
Samsung Research UK
FOSDEM 2016
Brussels, Belgium, January 30 – 31, 2016

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Overview
● Introduction
● LLVM Overview
● Projects
● Summary

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Introduction

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What is LLVM?
● Mature, production-quality compiler framework
● Modular architecture
● Heavily optimizing static and dynamic compiler
● Supports all major architectures (x86, ARM, MIPS,
PowerPC, …)
● Powerful link-time optimizations (LTO)
● Permissive license (BSD-like)

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Which companies are contributing?
®

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History
● Started as Chris Lattner's Master's Thesis at UIUC
● LLVM 1.0 released in October 2003
● LLVM 3.8 about to be released
● Today: LLVM + Clang together 2.5 million LOC of C++
code

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LLVM sub-projects
● Clang
C/C++/Objective C frontend and static analyzer
● LLDB
Next generation debugger leveraging the LLVM libraries, e.g. the Clang expression
parser
● lld
Framework for creating linkers, will make Clang independent of the system linker in
the future
● Polly
Polyhedral optimizer for LLVM, e.g. high-level loop optimizations and data-locality
optimizations

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LLVM Overview

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LLVM
● LLVM IR (Intermediate Representation)
● Scalar optimizations
● Interprocedural optimizations
● Auto-vectorizer (BB, Loop and SLP)
● Profile-guided optimizations

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Compiler architecture
C Frontend
C++ Frontend
Fortran Frontend
Optimizer
x86 Backend
ARM Backend
MIPS Backend

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Compilation steps
● Many steps involved in the translation from C source code to machine code:
– Frontend:
● Lexing, Parsing, AST construction
● Translation to LLVM IR
– Middle-end
● Target-independent optimizations (Analyses & Transformations)
– Backend:
●
Translation into a DAG
●
Instruction selection: Pattern matching on the DAG
● Instruction scheduling: Assigning an order of execution
● Register allocation: Trying to reduce memory traffic

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Clang
● Goals:
– Fast compile time
– Low memory usage
– GCC compatibility
– Expressive diagnostics
● Several tools built on top of Clang:
– Clang static analyzer
– clang-format, clang-modernize, clang-tidy

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Projects

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Traditional C/C++ Toolchain
● Apple iOS/OS X SDK
● Android NDK
● Tizen SDK
● Sony PS4 SDK
● Qualcomm Snapdragon LLVM Compiler for Android

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Programming languages
● Swift
● Haskell: GHC, LHC, UHC
● Ruby: Rubinius, RubyMotion
● Python: Pyston
● Common Lisp: Clasp
● D: LDC
● Go: llgo

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Programming languages
● Standard ML: MLton, SML#, Ex-SML
● Rust
● Julia
● Pure
● Ravi

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Language Runtime Systems
● VMKit (unmaintained)
● LLILC - LLVM-based .NET MSIL compiler
● Mono
● OpenJDK

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GPU
● LLVMpipe (software rasterizer)
● CUDA
● GLSL (LunarGLASS)
● AMDGPU open source drivers
● SPIR
● Majority of OpenCL implementations based on
Clang/LLVM

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Web
● PNaCl
● WebKit FTL JIT
● Emscripten
● WebAssembly

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Sanitizers
● AddressSanitizers
● MemorySanitizer
● ThreadSanitizer
● LeakSanitizer
● SAFECode

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Integrated Development Environments
● Xcode
● KDevelop
● CodeLite
● Qt Creator
● Geany

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Source code navigation
● Doxygen
● Woboq Code Browser
● YouCompleteMe - Code completion for Vim
● clang-tags
● clang-ctags
● clang_complete - Code completion for Vim
● rtags - Indexer for C/C++ with Emacs integration

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Out of tree LLVM backends
● RISC-V
● OpenRISC 1000
● VideoCore IV (VPU/QPU)
● LatticeMico32
● AAP

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Binary translation
● llvm-qemu
● Dagger
● McSema
● libcpu
● Fracture
● SkyEye

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Symbolic Execution/Formal Verification
● KLEE
● S2E
● K framework with formal semantics for LLVM IR

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Linux/FreeBSD
● Debian experimenting with Clang as an additional
compiler (94.1% of ~22k packages successfully build with Clang 3.6)
● LLVMLinux
● OpenMandriva Lx
● FreeBSD

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Misc
● Emacs fork using the LLVM JIT for Elisp byte code
execution :)
● Cling - C++ interpreter
● CodeChecker - Web frontend for the Clang static
analyzer
● include-what-you-use
● clang-closure
● Numba

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Summary

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Summary
● Wide range of different projects
● New frontends being written constantly
● Great compiler infrastructure
● Fast C/C++ compiler with expressive diagnostics

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Give it a try!
● Visit llvm.org
● Distributions with Clang/LLVM packages:
– Fedora
– Debian/Ubuntu
– openSUSE
– Arch Linux
– ...and many more

31. Thank you.
31Samsung Open Source Group

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Contact Information:
Tilmann Scheller
t.scheller@samsung.com
Samsung Open Source Group
Samsung Research UK