Xposit RISC-V custom extension for posit arithmetic

This repository contains the LLVM compilation support for posit arithmetic that can be used together with the PERCIVAL posit RISC-V core available here: https://github.com/artecs-group/PERCIVAL

Publication

The Xposit extension was introduced in the following paper, if you use it in your academic work you can cite us:

@article{mallasen2022PERCIVAL,
  title = {PERCIVAL: Open-Source Posit RISC-V Core With Quire Capability},
  author = {Mallasén, David and Murillo, Raul and Del Barrio, Alberto A. and Botella, Guillermo and Piñuel, Luis and Prieto-Matias, Manuel},
  year = {2022},
  journal = {IEEE Transactions on Emerging Topics in Computing},
  volume = {10},
  number = {3},
  pages = {1241-1252},
  issn = {2168-6750},
  doi = {10.1109/TETC.2022.3187199}
}

Getting started

As well as this repository, you will need the RISC-V gcc toolchain.

Install some pre-requisites:

sudo apt install \
  binutils build-essential libtool texinfo \
  gzip zip unzip patchutils curl git \
  make cmake ninja-build automake bison flex gperf \
  grep sed gawk python bc \
  zlib1g-dev libexpat1-dev libmpc-dev \
  libglib2.0-dev libfdt-dev libpixman-1-dev

Install the RISC-V gcc toolchain following the instructions in https://github.com/riscv-collab/riscv-gnu-toolchain for newlib multilib. When you are done, you should have a riscv64-unknown-elf-gcc compiler. Remember to add the bin directory to your path.
Clone, build, and install this repository to a llvm-riscv directory.

mkdir llvm-riscv && cd llvm-riscv
mkdir _install
export PATH=`pwd`/_install/bin:$PATH
git clone https://github.com/artecs-group/llvm-xposit.git
cd llvm-xposit
ln -s ../../clang llvm/tools || true
mkdir _build && cd _build

When building LLVM with the next command, change the path to the riscv64-unknown-elf in your system installed at step 1.

cmake -G Ninja \
        -DCMAKE_BUILD_TYPE="Debug" \
        -DBUILD_SHARED_LIBS=True \
        -DLLVM_USE_SPLIT_DWARF=True \
        -DCMAKE_INSTALL_PREFIX="../../_install" \
        -DLLVM_OPTIMIZED_TABLEGEN=True \
        -DLLVM_BUILD_TESTS=True \
        -DDEFAULT_SYSROOT="/path/to/riscv64-unknown-elf" \
        -DLLVM_DEFAULT_TARGET_TRIPLE="riscv64-unknown-elf" \
        -DLLVM_TARGETS_TO_BUILD="RISCV" \
        -DLLVM_ENABLE_PROJECTS=clang \
        ../llvm
cmake --build . --target install -j`nproc`

Compile a test application. For example the posit_testsuite_llvm.c of PERCIVAL.

clang --target=riscv64 -march=rv64gcxposit posit_testsuite_llvm.c -c -o posit_testsuite_llvm.o
riscv64-unknown-elf-gcc posit_testsuite_llvm.o -o posit_testsuite_llvm.elf

Acknowledgments

This work was supported in part by the 2020 Leonardo Grant for Researchers and Cultural Creators, from BBVA Foundation under Grant PR2003_20/01, and in part by the Spanish MINECO, the EU(FEDER), and Comunidad de Madrid under Grants RTI2018-093684-B-I00 and S2018/TCS-4423.

The LLVM Compiler Infrastructure

This directory and its sub-directories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

The README briefly describes how to get started with building LLVM. For more information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.

Getting Started with the LLVM System

Taken from https://llvm.org/docs/GettingStarted.html.

Overview

Welcome to the LLVM project!

The LLVM project has multiple components. The core of the project is itself called "LLVM". This contains all of the tools, libraries, and header files needed to process intermediate representations and convert them into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer. It also contains basic regression tests.

C-like languages use the Clang front end. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.

Other components include: the libc++ C++ standard library, the LLD linker, and more.

Getting the Source Code and Building LLVM

The LLVM Getting Started documentation may be out of date. The Clang Getting Started page might have more accurate information.

This is an example work-flow and configuration to get and build the LLVM source:

Checkout LLVM (including related sub-projects like Clang):
- git clone https://github.com/llvm/llvm-project.git
- Or, on windows, git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git
Configure and build LLVM and Clang:
- cd llvm-project
- cmake -S llvm -B build -G <generator> [options]
  
  Some common build system generators are:
  - Ninja --- for generating Ninja build files. Most llvm developers use Ninja.
  - Unix Makefiles --- for generating make-compatible parallel makefiles.
  - Visual Studio --- for generating Visual Studio projects and solutions.
  - Xcode --- for generating Xcode projects.
  Some common options:
  - -DLLVM_ENABLE_PROJECTS='...' --- semicolon-separated list of the LLVM sub-projects you'd like to additionally build. Can include any of: clang, clang-tools-extra, compiler-rt,cross-project-tests, flang, libc, libclc, libcxx, libcxxabi, libunwind, lld, lldb, mlir, openmp, polly, or pstl.
    
    For example, to build LLVM, Clang, libcxx, and libcxxabi, use -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi".
  - -DCMAKE_INSTALL_PREFIX=directory --- Specify for directory the full path name of where you want the LLVM tools and libraries to be installed (default /usr/local).
  - -DCMAKE_BUILD_TYPE=type --- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
  - -DLLVM_ENABLE_ASSERTIONS=On --- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).
- cmake --build build [-- [options] <target>] or your build system specified above directly.
  - The default target (i.e. ninja or make) will build all of LLVM.
  - The check-all target (i.e. ninja check-all) will run the regression tests to ensure everything is in working order.
  - CMake will generate targets for each tool and library, and most LLVM sub-projects generate their own check-<project> target.
  - Running a serial build will be slow. To improve speed, try running a parallel build. That's done by default in Ninja; for make, use the option -j NNN, where NNN is the number of parallel jobs, e.g. the number of CPUs you have.
- For more information see CMake

Consult the Getting Started with LLVM page for detailed information on configuring and compiling LLVM. You can visit Directory Layout to learn about the layout of the source code tree.

artecs-group / llvm-xposit