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Diploma

This is an optimizing compiler for the subset of the C99 language producing LLVM assembler. It is my bachelor's diploma work.

There are some examples of compilable code in the directory with tests. All tests can be checked via run_tests script. To do this, one should set the path to the compiler executable via CC_tst variable inside this script. Also, one should change the value of CW39_LLC in this script (see below).

Following optimizations are implemented in this compiler:

  • Memmory to registers conversion, SSA-form creating
  • Tail recursion elimination
  • Functions inlining (manual detection)
  • Dead code elimination
  • Copy propagation and constants folding
  • Algebraic simplifications and common subexpressions elimination
  • Loop invariant code motion
  • Intrisics introduction (special optimization, CTZ only)

Requirements

  • CMake (v3.5)
  • gcc-10 (or equivalent compiler with C++20 support)
  • LLVM (v13.0.1, early versions cannot be compiled with C++20)
  • fmtlib (v8.1)

Following packages are used for code generation. They are optional because all code, that should be generated by them, are already included in this repository.

Building

To build this compiler one should execute following commands, which are common for most CMake projects. Executable binary (cw39) will be placed into the build directory.

mkdir build
cd build
cmake ..
make

By default, all code generators are enabled. But if you don't have such generators installed, the project can be built using already generated source files. To do this, you should call CMake with some of following options:

  • -DCW39_NO_BISON=TRUE to disable flex and bison
  • -DCW39_NO_GPERF=TRUE to disable gperf

For example, cmake command can be executed as shown below.

cmake -DCW39_NO_BISON=TRUE -DCW39_NO_GPERF=TRUE ..

Also, if you have troubles with CMake and generators communication, you can generate source codes manually using this Makefile.

Building using Docker

Docker container can be built using the setup.sh script. After the first usage, this command should be executed if Dockerfile has been changed.

Project can be built using the build.sh script. This script will store the final binary and building files in the docker_build directory created by previous script.

Both scripts don't expect arguments and should be executed from project root (where Dockerfile is located). Optionally, one can specify number of threads used by make in the build script (default is 3).

Usage

cw39 [options] <input_file>

Output options

Option Description
--pproc Preprocessor output
--ast Abstract syntax tree with pseudo graphics
--ir IR in readable text format
--cfg CFG representation in the dot language
--llvm LLVM assembly code
--bc LLVM bitcode (binary output)
--asm Assmbly code (only in Unix-based systems)

Each of listed options can accept optional argument with path to file (e.g. --llvm=./out.ll). In this case output will be written into specified file. If path is empty or -, output will be written into stdout. Without any of these options, compiler will print nothing but errors.

Compilation options

Option Description
-D <macro> Define a macro with optional value
-O <lvl> Set optimization level (0-2, default is 2)
--no-s1 Disable special optimization 1 (intrinsics detector)
--no-s2 Disable special optimization 2 (fixpoints)
--llc-args <args> Specify arguments for llc program

There are following optimization levels:

  • 0: no optimizations
  • 1: most common optimizations (without loops optimizations)
  • 2: all available optimizations

Note, that specifying any llc argument disables default arguments: -O0 -mcpu=native.

There are some llc arguments, that can be interesting:

  • -march=<arch>: specify destination architecture (e.g. x86-64)
  • -mcpu=<cpu>: specify destination CPU (e.g. native, skylake)
  • -O<lvl>: Set LLC optimization level

Other options

Option Description
--times Print elapsed time of each step
--tr-scanner Enable scanner debug mode
--tr-parser Enable parser debug mode
--help Print help page
--version Print compiler version

External programs customization

This compiler uses some external programs via fork-exec calls. This behaviour available only on Unix-based systems and correct working doesn't guarenteed for other ones.

One can specify names for used executables via environment variables listed below.

  • CW39_LLC - name of the llc program from LLVM toolchain (default: llc)

For example:

export CW39_LLC=llc-13
cw39 --asm test.c
# Or
CW39_LLC=llc-13 cw39 --asm test.c

Examples

Print LLVM code into the terminal:

cw39 --llvm test.c

Print LLVM code into the out.ll file:

cw39 --llvm=out.ll test.c

Execute generated code with arguments 1 and 2 immediately (also lli-13 and others can be used):

cw39 --llvm test.c | lli - 1 2

Draw CFG into the graph.svg file:

cw39 --cfg test.c | dot -Tsvg -o graph.svg

Create executable file from assemly code via clang.

cw39 --asm=test.s test.c
clang test.s
# Or
cw39 --asm test.c | clang -x assembler -
# Or
cw39 --llvm test.c | clang -x ir -

Create executable with LLVM optimizations.

cw39 --asm --llc-args="-O3 -mcpu=native" test.c | clang -x assembler -