Llvm family (1) - Introduction to llvm

LLVM series （1）- LLVM brief introduction

---

If you need to reprint, please indicate the source ：http://blog.csdn.net/itas109
QQ Technology exchange group ：129518033

1. LLVM summary

LLVM A project is a collection of modular and reusable compiler and tool chain technologies .

LLVM It started as a research project at the University of Illinois , The goal is to provide a modern 、 be based on SSA Compilation policy for , It can support static and dynamic compilation of any programming language .

LLVM At first C/C++ To implement objects , It has been supported at present, including ActionScript、Ada、D Language 、Fortran、GLSL、Haskell、Java Bytecode 、Objective-C、Swift、Python、Ruby、Crystal、Rust、Scala as well as C# Other languages .

---

Official website ：https://llvm.org/
Github Address ：https://github.com/llvm/llvm-project/
Open source licenses ：Apache 2.0 License with LLVM exceptions

2. LLVM Introduction to subprojects

2.1 LLVM Core libraries and add ons

LLVM The core library is located in llvm Directory . It is the mainstream CPU Provides libraries for optimizer and code generation , And some tools .
LLVM The core library provides C++ 、C 、Go、Ocaml and Python Such as the interface .

https://llvm.org/docs/

---

Polly The project uses polyhedron model to realize a set of cache local optimization, automatic parallelization and vectorization , For example, using a cache locally optimized loop .

MLIR Subprojects are a new way to build a reusable and extensible compiler infrastructure .MLIR It aims to solve the problem of software fragmentation , Improve the compilation of heterogeneous hardware , Significantly reduce the cost of building domain specific compilers , And help connect existing compilers .

2.2 Clang compiler

Clang The compiler is located at clang Catalog , It's a LLVM Native C/C++/Objective-C compiler .
clang The catalog also contains some tools , Such as clang-format（ Code formatter ）.
clang-tools-extra The catalog also provides some clang Tools for , Such as clang-tidy（ Static code analysis ）.

https://clang.llvm.org/

2.3 LLD The linker

LLD Project is a new linker . Used to link the object file created by the compiler with the runtime library , Form an executable .LLD Linker support ELF、COFF、Mach-O and WebAssembly Format .

https://lld.llvm.org/

2.4 LLDB The debugger

LLDB The debugger is based on LLVM and Clang , Support C、C++ and Objective-C Debugging of , And provide C++ 、lua and Python etc. API Interface .

https://lldb.llvm.org/

2.5 Runtime library

• compiler-rt Provides a programming language independent support library . by AddressSanitizer、 ThreadSanitizer、 MemorySanitizer and DataFlowSanitizer And other dynamic testing tools provide the implementation of runtime library .
• libunwind Provides the basis for DWARF Standard stack expansion help functions . It is mainly used for C++ And so on
  Regular treatment .
• libcxx and libcxxabi yes C++ Implementation of standard library , Include iostreams and STL., Including yes C++11 and C++14 Full support for .
• pstl Provides a parallel version of STL Algorithm .
• libclc yes OpenCL The runtime library of .OpenCL Is the standard of heterogeneous parallel computing , Help to transfer computing tasks to
  GPU On .
• libc Designed to provide a complete C library .
• OpenMP The project provides support for OpenMP API Support for .OpenMP Can help multi-threaded programming .

3. LLVM framework

 Source code  ->   front end (Fontend) ->  Optimizer (Optimizer)  ->  Back end (Backend) ->  Machine code 

front end (Fontend) ： Parse the source code , Error checking and building AST Abstract syntax tree （ Lexical analysis 、 Syntax analysis 、 Semantic analysis ）

Optimizer (Optimizer) ： Various transformations to try to improve the running time of the code

Back end (Backend) ： The code maps to the target instruction set

             +----------------------------+                                                   +----------------------------+
             |                            |                                                   |                            |
             |                            |                                                   |                            |
 C   +------->      C Frontend            +-----+                                        +---->      X86 Backend           +------->  X86
             |                            |     |                                        |    |                            |
             |                            |     |                                        |    |                            |
             +----------------------------+     |                                        |    +----------------------------+
                                                |                                        |
                                                |                                        |
             +----------------------------+     |     +----------------------------+     |    +----------------------------+
             |                            |     |     |                            |     |    |                            |
             |                            |     |     |                            |     |    |                            |
 Go  +------->      Go Frontend           +----------->     Common Optimizer       +---------->      ARM Backend           +------->  ARM
             |                            |     |     |                            |     |    |                            |
             |                            |     |     |                            |     |    |                            |
             +----------------------------+     |     +----------------------------+     |    +----------------------------+
                                                |                                        |
                                                |                                        |
                                                |                                        |
             +----------------------------+     |                                        |    +----------------------------+
             |                            |     |                                        |    |                            |
             |                            |     |                                        |    |                            |
Rust +------->     Rust  Frontend         +-----+                                        +---->      Mips  Backend         +-------->  Mips
             |                            |                                                   |                            |
             |                            |                                                   |                            |
             +----------------------------+                                                   +----------------------------+

---

License

License under CC BY-NC-ND 4.0: A signature - Non commercial use - No derivatives

If you need to reprint, please indicate the source ：http://blog.csdn.net/itas109
QQ Technology exchange group ：129518033

---

Reference:

1. https://llvm.org/
2. http://www.aosabook.org/en/llvm.html
3. https://en.wikipedia.org/wiki/LLVM