Flame

Flame is a set of C# libraries and tools for reading, analyzing, optimizing, and writing managed code.

It is built around an SSA-based intermediate representation and includes:

  • an IR designed for compiler analysis and transformation
  • optimization passes such as inlining, scalar replacement, value numbering, control-flow simplification, and tail-recursion elimination
  • analysis passes for dominators, liveness, value uses, predecessors, nullability, and more
  • a CIL frontend and backend for translating between .NET IL and Flame IR
  • command-line tools and examples built on top of the core libraries

Documentation:

Repository layout

The main projects live under src/:

  • Flame: core abstractions and type system
  • Flame.Compiler: IR, analyses, and optimization passes
  • Flame.Clr: CIL import/export and CLR-specific support
  • Flame.Ir: IR serialization support
  • Flame.Llvm: LLVM backend pieces
  • ILOpt: CIL optimizer built on Flame
  • IL2LLVM: IL-to-LLVM compilation tool
  • Examples/Brainfuck: Brainfuck-to-CIL compiler example
  • UnitTests: unit tests and tool tests

Tool-oriented test inputs live under tool-tests/.

Requirements

  • .NET SDK 10.x

Build

From the repository root:

$ dotnet restore src/Flame.sln
$ dotnet build src/Flame.sln -c Debug

There is also a small make wrapper in src/Makefile:

$ make -C src debug

Test

The main test entrypoint is the portable suite, which excludes LLVM-dependent tests:

$ dotnet test src/UnitTests/UnitTests.csproj -c Debug --filter "TestCategory!=LLVM"

The make wrapper runs the same suite:

$ make -C src test

The LLVM-specific tests are separate and require LLVM/Clang to be installed:

$ make -C src test-llvm

To run the LLVM tests manually, specify the runtime identifier for your platform and set CLANG_PATH to the Clang executable:

$ CLANG_PATH=clang dotnet test src/UnitTests/UnitTests.csproj -c Debug -r osx-arm64 --filter "TestCategory=LLVM"

Common runtime identifiers are linux-x64, linux-arm64, osx-arm64, win-x64, and win-arm64.

The current tool-tests/IL2LLVM samples use Linux libc.so.6 imports. On non-Linux hosts, the LLVM tool tests skip those samples instead of failing; CI still exercises them on Linux.

Tools

ilopt

ilopt reads a managed assembly, optimizes it, and writes the optimized result back to disk.

Build it with the solution or directly:

$ dotnet build src/ILOpt/ILOpt.csproj -c Debug

Run it with:

$ dotnet src/ILOpt/bin/Debug/net10.0/ilopt.dll input.dll -o output.dll

The supported single-file samples used by the test suite live in tool-tests/ILOpt.

il2llvm

il2llvm compiles managed assemblies to LLVM IR.

$ dotnet publish src/IL2LLVM/IL2LLVM.csproj -c Debug -r osx-arm64 --self-contained false
$ dotnet src/IL2LLVM/bin/Debug/net10.0/osx-arm64/publish/il2llvm.dll input.dll -o output.ll

Continuous integration

GitHub Actions is configured in .github/workflows/ci.yml.

The CI workflow:

  • restores src/Flame.sln
  • builds the solution in Debug
  • runs the portable test suite via dotnet test --filter "TestCategory!=LLVM"
  • runs the LLVM backend test suite via dotnet test -r linux-x64 --filter "TestCategory=LLVM" with CLANG_PATH set to clang-20