LLVM for LC-3.2

This repository houses a version of LLVM that has a backend for the LC-3.2 architecture. Much of the documentation follows from LLVM. In particular, it would be good to read the original Getting Started Guide and the original Compilation Guide.

Usage

Build Environment

For ease-of-use, a Nix development shell and a docker-compose.yml script are provided.

Building

To build this project, check out the repository and navigate into it. Create a build subdirectory and change into it too. Configure with

$ cmake -G Ninja \
  -DCMAKE_INSTALL_PREFIX=${LLVM_INSTALL_DIR} \
  -DCMAKE_BUILD_TYPE=Debug -DLLVM_ENABLE_ASSERTIONS=ON \
  -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_ENABLE_RUNTIMES="compiler-rt" \
  -DLLVM_TARGETS_TO_BUILD="" -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="LC32" \
  -DLLVM_DEFAULT_TARGET_TRIPLE="lc_3.2-unknown-unknown" \
  -DLLVM_RUNTIME_TARGETS="lc_3.2-unknown-unknown" \
  -DLLVM_BUILTIN_TARGETS="lc_3.2-unknown-unknown" \
  -DBUILTINS_lc_3.2-unknown-unknown_COMPILER_RT_BAREMETAL_BUILD=ON \
  -DBUILTINS_lc_3.2-unknown-unknown_COMPILER_RT_EXCLUDE_PERSONALITY=ON \
  -DBUILTINS_lc_3.2-unknown-unknown_COMPILER_RT_BUILTINS_PASS_FUNCTION_SECTIONS=ON \
  -DBUILTINS_lc_3.2-unknown-unknown_COMPILER_RT_BUILTINS_PASS_DATA_SECTIONS=ON \
  -DBUILTINS_lc_3.2-unknown-unknown_COMPILER_RT_BUILTINS_PASS_G=ON \
  ../llvm/

Make sure to set CMAKE_INSTALL_PREFIX to the installation directory. Also change CMAKE_BUILD_TYPE as needed. If any targets are added to LLVM_RUNTIME_TARGETS or LLVM_BUILTIN_TARGETS, make sure to add the corresponding flags too. Finally, it is recommended to keep assertions ON even when building in Release mode.

During development, one may enable LLVM_OPTIMIZED_TABLEGEN, BUILD_SHARED_LIBS, and LLVM_USE_SPLIT_DWARF to reduce build times. Furthermore, one can build unit tests by enabling LLVM_BUILD_TESTS, though these take a signigicant amount of time to link, and they're not even used at present.

If memory usage is a concern, consider setting LLVM_PARALLEL_LINK_JOBS.

With configuration done, build and install with

$ ninja
$ ninja install

Running

Once this project is installed, let's say to ${LLVM_INSTALL_DIR}, build with the driver program

$ ${LLVM_INSTALL_DIR}/bin/clang --target=lc_3.2 ...

By default, it will try to link libc and libm. Either set -nostdlib or pass --sysroot to point the driver to the libraries. It will also try to link the compiler runtime. Again, either set -nodefaultlibs or pass --sysroot.

The driver does not link with crt0, nor does it have a default linker script. You must supply both.

Options

The LC-3.2 backend has several options and function attributes to affect code generation. The options are listed in llvm/lib/Target/LC32CLOpts.cpp, and they can be passed to llc with the -mllvm option in the driver. The attributes are listed at the very end of clang/include/clang/Basic/Attr.td, and they can be put on a function with the __attribute__ syntax.

Contributing

To contribute, please file an issue or a pull request on this GitHub. Alternatively, email the project maintainers directly.