Toolchain

The nu+ toolchain is a collection of tools required to compile a nu+ executable application. It is based on the LLVM project leveraging on a custom version of the Clang Frontend and on a from-scratch implementation of the Backend. The toolchain comes with a modified version of LLD, an elf2hex tool to generate nu+ compatible memory images and lastly a custom version of the objdump tool for debug purposes. A custom implementation of the libc libraries is provided.

The toolchain supports the compilation of C-based and OpenCL C kernels.

Building Toolchain on Ubuntu Linux environment

This section shows how to build the nu+ toolchain in an Ubuntu Linux environment. The following steps are still valid in any other Unix-based system despite of package manager related differences.

Required Software

The nu+ toolchain installation relies on the following dependencies:

• Git
• GCC
• CMake
• Python 2.7
• libxml
• Zlib
• Bison
• Flex
• Libedit
• Swig
• ncurses libraries
• Ninja

The following terminal command may be used to install all required software:

$ sudo apt install libxml2-dev git cmake gcc g++ python bison flex zlib1g-dev swig python-dev libedit-dev libncurses5-dev ninja

Building Process

First, you have to obtain the source code from the official repository by typing the following command:

$ git clone https://gitlab.com/catecio/NuPlusLLVM.git <clone_directory>

The repository contains a helper script, setup.sh to make easier the installation process. To build a new implementation of the nu+ toolchain just type:

$ ./setup.sh -n

This command starts the compilation process, installing the toolchain in Release Mode in /usr/local/llvm-nuplus. If a debug version is required, add the -d flag to setup.sh. You can also choose the number of threads for the compilation process, by using the -t=<number_of_threads> parameter.

At the end of the compilation process, libraries are required to be linked to the installation folder:

$ ./setup.sh -l

Now, you can use the toolchain to build your own application.

The nu+ LLVM Structure

The nu+ toolchain relies on the LLVM project providing customized implementation of its libraries to make possible generating nu+ executable kernels.

[Clang] is the compiler frontend for nu+, extended to handle the token-recognition of custom intrinsic functions.

1. A custom version of the Clang frontend
2. A native nu+ backend
3. Some external tools that are used by llvm, i.e. linker, disassembler, etc..

In addition, in order add the nu+ architecture inside llvm, a registration phase was required.

Testing

To test the code generation process, the LLVM testing infrastructure has been used.

The script "run_tests" can be used to run the nu+ testing suite. The main purpose is to perform regression tests, so that it is possible to determine if a change in the back-end has any negative consequence.

The tool used is the "llvm-lit", a python script that parses the test files and executes the testing commands.

The code generation tests are contained in "compiler/test/CodeGen/NuPlus" and cover the main LLVM IR operations. A code generation test file is a collection of functions written in LLVM IR with commands directed to the llvm-lit and FileCheck tools. These commands are written as comments. The main commands used are RUN, CHECK, and CHECK-LABEL.

The RUN line tells lit how to run the test. If there are no RUN lines, lit will issue an error while running a test. The line syntax is similar to a shell’s syntax for pipelines. To examine the output and check if the test has been passed, the FileCheck tool must be used.

The RUN line used for all the tests is:

; RUN: llc -march=nuplus < %s | FileCheck %s

This tells lit to run llc with nu+ architecture as target, to give the output file to the FileCheck tool.

The CHECK_LABEL and the CHECK lines are interpreted by the FileCheck tool. It compares the llc output file with the CHECK_LABEL and CHECK lines. The comparison is done in sequence, although there are directives that let the checking not be performed in sequential order, see [1] for further details.

Libraries

nu+ is provided with different kind of libraries that are contained in the libs/ folder. For more information, check The nu+ libraries.

Makefiles and linker scripts

TODO: completare

Debug and typical errors

For more information about the debug support and some typical errors, check How to debug LLVM.

Compiler Extensions

• OpenCL extension for the nu+ architecture
• OpenMP extension for the nu+ architecture