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Semestral Work

This is the repository that serves as a simple template for semestral work.

Semestral work structure

  • CMakeLists.txt - CMake source file
  • main.hpp - main function definition
  • Lexan.hpp, Lexan.cpp - Lexan related sources
  • Parser.hpp, Parser.cpp - Parser related sources
  • fce.c - grue for write, writeln, read function, it is compiled together with the program
  • samples - directory with samples describing syntax
  • mila - wrapper script for your compiler

Compilation tests and correct output tests for sample files are implemented using ctest and defined in CMakeLists.txt.

Literature

LLVM supplies a set of tutorials which is available here: https://llvm.org/docs/tutorial/

These tutorials are highly recommended and contains everything from lexical analysis up to transforming AST into LLVM IR.

A nice explanation of LLVM IR can be found here: https://mukulrathi.co.uk/create-your-own-programming-language/llvm-ir-cpp-api-tutorial/

Dependencies

LLVM including headers. Bases on your OS distribution, it would be usually packages like: llvm, llvm-dev.

For downloading this repository and building it: git, cmake, clang and zlib1g-dev.

For Ubuntu or Debian based OS use:

sudo apt install llvm llvm-dev clang git cmake zlib1g-dev

For OpenSuse it will be most likely called llvm-devel and libLLVM, search for *llvm* and *LLVM*.

LLVM version

Recommended version is version (9,) 10, 11 or 12 (currently latest). Older version may require changes.

To get the current LLVM version, just call:

clang --version

You should get an output similar to this:

Ubuntu clang version 12.0.0-++rc3-4ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

If you need to change version of LLVM library used modify CMakeLists.txt based on your needs:

# Change this to force specific version of LLVM
# find_package(LLVM "${MAJOR}.${MINOR}" REQUIRED CONFIG)
find_package(LLVM REQUIRED CONFIG)

For example to force LLVM 10:

find_package(LLVM 10 REQUIRED CONFIG)

Building

We use standard CMake toolchain, i.e. for default compilation in Debug mode, use something like:

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Debug

and then build with cmake --build . or make.

Built compiler outputs intermediate code from which llvm can generate a binary.

OS speficic problems with building:

Linux

Known issues

If you by any change encounter yaml-bench error with llvm-9, follow this guide: https://weliveindetail.github.io/blog/post/2019/12/02/apt-llvm-9-dev-yaml-bench.html . Sufficient workaround should be touch /usr/lib/llvm-9/bin/yaml-bench

Mac OS

Known issues

Some standard utilities may be required: getopts and realpath.

Detailed guide

Via brew:

brew install git
brew install cmake
brew install llvm
brew install gnu-getopt

Then you will need to update *rc file of your terminal (.bashrc, .zshrc, ...) with following lines:

# Verify that the version of LLVM is correct!
export LLVM_DIR="/usr/local/Cellar/llvm/10.0.0_1/lib/cmake"
export PATH="/usr/local/opt/gnu-getopt/bin:$PATH"
export PATH="/usr/local/Cellar/llvm/10.0.0_1/bin:$PATH"

If you dont have utility called realpath you will also need to create it, because it is not in brew:

sudo echo '#!/bin/sh                                                                              
realpath() {
  OURPWD="$PWD"
  cd "$(dirname "$1")"
  LINK=$(readlink "$(basename "$1")")
  while [ "$LINK" ]; do
    cd "$(dirname "$LINK")"
    LINK=$(readlink "$(basename "$1")")
  done
  REALPATH="$PWD/$(basename "$1")"
  cd "$OURPWD"
  echo "$REALPATH"
}' > /usr/local/bin/realpath
sudo chmod +x /usr/local/bin/realpath

Or this on new MacOS:

sudo echo '#!/bin/sh    
OURPWD="$PWD"
cd "$(dirname "$1")"
LINK=$(readlink "$(basename "$1")")
while [ "$LINK" ]; do
cd "$(dirname "$LINK")"
LINK=$(readlink "$(basename "$1")")
done
REALPATH="$PWD/$(basename "$1")"
cd "$OURPWD"
echo "$REALPATH"
' > /usr/local/bin/realpath
sudo chmod +x /usr/local/bin/realpath

Windows - WSL 2 guide

WSL containts only version 6 by default, you need to download newer version from: https://apt.llvm.org/

And create file /etc/apt/sources.list.d/llvm.list with appropriate repositories.

If you need to check your system version, use: lsb_release -a.

Start with basic dependencies for LLVM 10, 11 or 12:

sudo apt install clang cmake git llvm-10 llvm-10-dev

sudo apt install clang cmake git llvm-11 llvm-11-dev

sudo apt install clang cmake git llvm-12 llvm-12-dev

You may be missing default clang, clang++ and llc and have version specific binaries only. The best way to solve this is to make appropriate symlinks based on your version:

LLVM_VERSION=10
sudo ln -sf $(which clang-$LLVM_VERSION) /usr/bin/clang
sudo ln -sf $(which clang++-$LLVM_VERSION) /usr/bin/clang++
sudo ln -sf $(which llc-$LLVM_VERSION) /usr/bin/llc

Alternative is to change a compiler used in CMakeLists.txt:

set(CMAKE_C_COMPILER clang-10)
set(CMAKE_CXX_COMPILER clang++-10)

And mila script:

llc-10 "$OutputFileBaseName.ir" -o "$OutputFileBaseName.s" &&
clang-10 "$OutputFileBaseName.s" "${DIR}/fce.c" -o "$OutputFileName"

With that everything should be ready for compilation.

Known issues

If you get issue during linking:

[ 25%] Linking CXX executable mila
/usr/bin/ld: cannot find -lz
clang: error: linker command failed with exit code 1 (use -v to see invocation)

You can solve it by installing zlib1-dev:

sudo apt-get install zlib1g-dev

Running

Do not call binary mila inside build directory directly, use wrapper script mila inside a root directory:

./mila

Details below.

Testing samples

From inside the build directory you can utilize ctest command. The tests are defined as compilation of all example source codes in samples/ directory and in another tests the created executables are run and their output compared with expected output. There is only limited number of such test though, you should definitely create more tests.

Compiling a program

Use supplied script to compile source code into binary.

First you need to create a source file, otherwise compilation will fail:

touch test.mila

Then you can compile it with compiler.

./mila test.mila -o test.out

How does mila wrapper script works?

It runs build/mila on the source code, then llc and clang (with the fce.c file added):

rm -f "$OutputFileBaseName.ir"
> "$OutputFileBaseName.ir" < "$InputFileName" ${DIR}/build/mila &&
rm -f "$OutputFileBaseName.s"
llc "$OutputFileBaseName.ir" -o "$OutputFileBaseName.s" &&
clang "$OutputFileBaseName.s" "${DIR}/fce.c" -o "$OutputFileName"

How should your semestral work behave?

Compiler processes source code supplied on the stdin and produces LLVM ir on its stdout. All errors should be written to the stderr, non zero return code should be return in case of error. No arguments are required, but the mila wrapper is prepared for -v/--verbose, -d/--debug options which can be passed to the compiler. Other arguments can be also added for various purposes.

What template of semestral work does?

Regardless of the source code supplied, all produced binaries gives "Answer to the Ultimate Question of Life, the Universe, and Everything":

42

Generated intermediate code looks like this:

; ModuleID = 'mila'
source_filename = "mila"

declare i32 @writeln(i32)

define i32 @main() {
entry:
  %0 = call i32 @writeln(i32 42)
  ret i32 0
}

You can try this example without mila wrapper as well:

echo 42 | ./build/mila

How to add your own files?

You want to add Tree.hpp and Tree.cpp, change CMakeLists.txt by adding into add_executable:

add_executable(mila main.cpp Lexer.hpp Lexer.cpp Parser.hpp Parser.cpp)

Result:

add_executable(mila main.cpp Lexer.hpp Lexer.cpp Parser.hpp Parser.cpp Tree.hpp Tree.cpp)

How to process input source code?

You want to print number from the source file, change Lexan.hpp:

int Lexer::gettok() {
    m_NumVal = 42;
    return tok_number;
}

Result:

int Lexer::gettok() {
    std::cin >> m_NumVal;
    return tok_number;
}

For processing input getc (ungetc) is recommended. But scanf or std::cin should work as well.