Helix Compiler

Overview

Compiler Optimization Techniques

An optimising compiler for a subset of the C programming language, targeting ARMv7-A 32 bit hardware. The project is specifically concerned with program optimisation and machine code generation. Clang is utilised as the C frontend, and the GCC ARM (Windows Cross) toolchain is utilised for assembling the output assembly, linking and as a runtime standard library (in whatever capacity it can be used).

Developed as the final year project for a BSc Computer Science degree at Sheffield Hallam University.

Technical

Requirements

External

• C++17 compatible compiler
  • Only currently tested under Visual Studio 2022 (previously VS2019, so that should still work)
• CMake (only tested at latest version, 3.22.1)
• Precompiled LibTooling (Clang) binaries
  • Run tools/BuildLLVM_Release.bat (or tools/BuildLLVM_Debug.bat depending on your configuration of choice) and this should compile all the clang/llvm binaries for you and put them into the right places in the lib/ folder (also will sort out copying any autogenerated headers that are needed).

Building

Compiling the full compiler is currently only possible under Windows, but it is possible to compile HelixCore and HelixCoreTests under linux (supported for generating code coverage information of the core libraries).

Visual Studio 2022

In a terminal, from the project root.

• Ensure all submodules in external/ are cloned (LLVM is pretty big so using --depth=1 to only fetch the latest commit is recommended to keep time/disk space down).

• Build LLVM using by running tools/BuildLLVM_Release.bat (or tools/BuildLLVM_Debug.bat if wanting to compile in Debug mode)

• To generate the project files into a vs2022/ folder cmake -S. -Bvs2022 -G"Visual Studio 2022"

  • If using the Release mode LLVM binaries, make sure to add -DCMAKE_BUILD_TYPE=Release to the above cmake command.

• To build either

  • Open Visual Studio, set HelixCompiler as the startup project and build as normal, or...
  • cmake --build vs2022 --target HelixCompiler to build via CMake from the command line
  • Make sure to build in the same configuration as LLVM was built in, if building from the command line add --configuration Release.

Linux

Pretty much identical to windows, but you don't need to compile LLVM/Clang.

Internal Details

Compiler Internals

Core

• HelixCore - Core compiler libraries, middle/backend of the compiler.
• HelixCoreTests - Unit tests for HelixCore.
• HelixClangFrontend - C compiler frontend, uses clang to parse C and generate IR, passed to HelixCore.
  • Also currently in charge of parsing and managing command line parameters (defined in options.def), this is because the LLVM cl library is currently used to do this. Ultimately this should go in the compiler driver instead, and HelixClangFrontend should just be concerned with converting C -> IR.
• HelixCompiler - The compiler "driver" system, basically has the job of combining Helix*Frontend to generate IR, then HelixCore to convert that to assembly, and finally using external system tools (like GNU Tools/GCC or Clang) to assemble and link the produced assembly into executable machine code.

Tools

• MachineDescription - Tool that parses the S-Exp like machine description files (e.g. src/arm.md and generating C++ that matches those patterns against the IR and produces assembly code)
• Testify - Tool that is the test runner for all the functional/"integration tests" (doesn't handle unit tests yet, but manages the testing of everything else). E.g. is used to run the internal IR tests (defined in testsuite/) and any configured external testsuite (e.g. c-testsuite conformance tests).

Submodules

• llvm-project submodule, required for the clang C frontend.
  • Binaries not produced as part of the build process and the build system expects them in a certain layout in the lib/ folder. tools/BuildLLVM_[Debug|Release].bat will sort all this out automatically.
• spdlog submodule, used for logging (also use is made of the bundled fomatlib).