LuisaCompute Rust Workspace

src/rust/ — legacy IR implementation, compiler passes, CPU/Remote backends. Integrates with C++ via FFI (cbindgen headers + static libs).

Workspace Structure

src/rust/
├── Cargo.toml                         # workspace root
├── luisa_compute_api_types/           # shared C++/Rust FFI types (staticlib+rlib)
├── luisa_compute_ir/                  # core IR data structures & transforms (rlib)
├── luisa_compute_ir_staticlib/        # static lib wrapper for C++ linking (staticlib)
│                                     # produces library luisa_compute_ir_static
├── luisa_compute_ir_v2/               # IR v2 C API bindings (libloading)
├── luisa_compute_cpu_kernel_defs/     # CPU kernel runtime types
├── luisa_compute_backend/             # Backend trait definitions
└── luisa_compute_backend_impl/        # CPU + Remote backends (cdylib)

Dependency Graph

luisa_compute_api_types
  ├── luisa_compute_ir
  │     ├── luisa_compute_ir_staticlib  (lib name: luisa_compute_ir_static)
  │     ├── luisa_compute_ir_v2
  │     └── luisa_compute_backend
  │           └── luisa_compute_backend_impl
  ├── luisa_compute_backend
  └── luisa_compute_cpu_kernel_defs
        └── luisa_compute_backend_impl

luisa_compute_backend_impl also depends directly on luisa_compute_ir_v2 and the four crates above.

Crate Responsibilities

luisa_compute_api_types

FFI types shared between C++ and Rust. Build script uses cbindgen → api_types.hpp/api_types.h.

• Resource handles: Buffer, Texture, Stream, Device, Shader, Accel, Mesh, Curve, ProceduralPrimitive, BindlessArray, Event, Swapchain, IrModule, NodeRef
• Commands: BufferUploadCommand, ShaderDispatchCommand, AccelBuildCommand, MeshBuildCommand, CurveBuildCommand, ProceduralPrimitiveBuildCommand, BindlessArrayUpdateCommand, etc.
• Pixel formats: PixelStorage (28 variants incl. BC compression), PixelFormat
• Ray tracing: AccelOption, AccelBuildModification, CurveBasis
• DeviceInterface / LibInterface (vtable of function pointers), denoiser extension types, pinned-memory extension

luisa_compute_ir

Core IR (rlib). Key deps: half, serde, bincode, indexmap, parking_lot, smallvec, bitflags, plus luisa_compute_api_types.

Data structures (src/ir.rs):

pub enum Type {
    Void,
    UserData,
    Primitive(Primitive),
    Vector(VectorType),
    Matrix(MatrixType),
    Struct(StructType),
    Array(ArrayType),
    Opaque(CBoxedSlice<u8>),
}

pub enum Primitive {
    Bool, Int8, Int16, Int32, Int64,
    Uint8, Uint16, Uint32, Uint64,
    Float16, Float32, Float64,
}

pub struct Node {
    pub type_: CArc<Type>,
    pub next: NodeRef,
    pub prev: NodeRef,
    pub instruction: CArc<Instruction>,
}
// NodeRef is a pool-index handle: pub struct NodeRef(pub usize)

pub enum Instruction {
    Buffer, Bindless, Texture2D, Texture3D, Accel, Shared, Uniform,
    Local { init: NodeRef },
    Argument { by_value: bool },
    UserData(CArc<UserData>),
    Const(Const),
    Update { var: NodeRef, value: NodeRef },
    Call(Func, CBoxedSlice<NodeRef>),
    Phi(CBoxedSlice<PhiIncoming>),
    Return(NodeRef),
    Loop { body: Pooled<BasicBlock>, cond: NodeRef },
    GenericLoop { prepare, cond, body, update: Pooled<BasicBlock> },
    Break, Continue,
    If { cond, true_branch, false_branch: Pooled<BasicBlock> },
    Switch { value, default, cases: CBoxedSlice<SwitchCase> },
    AdScope { body, forward, n_forward_grads },
    RayQuery { ray_query, on_triangle_hit, on_procedural_hit },
    Print { fmt: CBoxedSlice<u8>, args: CBoxedSlice<NodeRef> },
    AdDetach(Pooled<BasicBlock>),
    Comment(CBoxedSlice<u8>),
    Invalid,
}

pub struct Module {
    pub kind: ModuleKind,        // Block | Function | Kernel
    pub entry: Pooled<BasicBlock>,
    pub flags: ModuleFlags,      // REQUIRES_REV_AD_TRANSFORM, REQUIRES_FWD_AD_TRANSFORM
    pub curve_basis_set: CurveBasisSet,
    pub pools: CArc<ModulePools>,
}

Func enum: ~180 builtins — math (Add, Mul, Sin, Cos, Exp, Log, Sqrt), vector/matrix (Cross, Dot, Determinant, Inverse, Transpose), memory (BufferRead/Write, Texture2dRead), atomic (AtomicExchange, AtomicFetchAdd), warp (WarpActiveSum, WarpPrefixSum), ray tracing (RayTracingTraceClosest, RayQueryCommitTriangle), AD (RequiresGradient, Backward, PropagateGrad, OutputGrad), indirect dispatch, raster discard, shader execution reorder, etc.

Memory: CArc<T> (atomic refcount), CBox<T> / CBoxedSlice<T> (C-compat boxes), Pool<T> (chunked pool), ModulePools (separate pools for nodes/blocks).

luisa_compute_ir_staticlib / luisa_compute_ir_v2

• Staticlib: re-exports luisa_compute_ir symbols so C++ can link the static library luisa_compute_ir_static (crate folder name ≠ lib name).
• IR v2: libloading-based Rust wrapper around the IR v2 C API. Loaded via lc_ir_v2_binding_table and consumed by luisa_compute_backend_impl through IrV2BindingTable.

luisa_compute_cpu_kernel_defs

Runtime types passed to CPU kernels: KernelFnArgs, KernelFnArg, BufferView, Texture, BindlessArray, Accel, Ray, Hit/TriangleHit/ProceduralHit/CommittedHit/HitType, RayQuery, CpuCustomOp, Aabb, Mat4.

luisa_compute_backend

• Backend trait (20+ methods) implemented by concrete backends.
• Context loads the C++ luisa-api shared library (luisa-api.dll / libluisa-api.so / libluisa-api.dylib) that exports luisa_compute_lib_interface().
• ProxyBackend dynamic-dispatches through the C DeviceInterface vtable.

luisa_compute_backend_impl

Concrete backend cdylib. Features: cpu (enables embree_sys), remote (stub).

• Exports luisa_compute_lib_interface() and luisa_compute_set_ir_v2_binding(...).
• CPU (cpu/): RustBackend with Rayon thread pool, warp size = 1.
  • shader.rs — kernel compilation orchestration & cache.
  • codegen/cpp.rs, codegen/cpp_v2.rs — IR → C++ source.
  • llvm.rs — loads libLLVM at runtime, parses bitcode, runs LLJIT.
  • accel.rs — Embree ray tracing.
  • stream.rs, texture.rs, resource.rs.
• Remote: network-distributed backend placeholder.

C-Compatible Pointers (src/ffi.rs)

pub struct CArc<T> { inner: *mut CArcSharedBlock<T> }
pub struct CArcSharedBlock<T> {
    pub(crate) ptr: *mut T,
    ref_count: AtomicUsize,
    destructor: extern "C" fn(*mut CArcSharedBlock<T>),
}

pub struct CBox<T> {
    ptr: *mut T,
    destructor: unsafe extern "C" fn(*mut T),
}

pub struct CBoxedSlice<T> {
    ptr: *mut T,
    len: usize,
    destructor: Option<unsafe extern "C" fn(*mut T, usize)>,
}

pub struct CSlice<'a, T> { ptr: *const T, len: usize, phantom: PhantomData<&'a T> }
pub struct CSliceMut<'a, T> { ptr: *mut T, len: usize, phantom: PhantomData<&'a T> }

All are #[repr(C)] and designed for zero-cost crossing with C++.

Transforms (src/transform/)

Transform	Purpose	Pipeline name
ssa::ToSSA	Local/Update → SSA with Phi nodes	ssa
autodiff::Autodiff	Reverse-mode AD	autodiff
fwd_autodiff::FwdAutodiff	Forward-mode AD	(used by transform_auto only)
dce::Dce	Dead code elimination	(struct exists; not registered in pipeline)
inliner::inline_callable	Function inlining helper	(utility, not pipeline-registered)
canonicalize_control_flow::CanonicalizeControlFlow	Normalize control flow	canonicalize_control_flow
ref2ret::Ref2Ret	Reference returns → value returns	ref2ret
reg2mem::Reg2Mem	Register → memory conversion	reg2mem

TransformPipeline is created from C++ via:

luisa_compute_ir_transform_pipeline_new() -> *mut TransformPipeline
luisa_compute_ir_transform_pipeline_add_transform(pipeline, name)
luisa_compute_ir_transform_pipeline_transform(pipeline, module) -> Module
luisa_compute_ir_transform_pipeline_destroy(pipeline)
luisa_compute_ir_transform_auto(module) -> Module

Autodiff (autodiff.rs)

Reverse-mode: forward sweep marks gradient-requiring nodes, backward sweep accumulates via chain rule. Supports arithmetic, vector (dot, cross, length, normalize), matrix (matmul, determinant, inverse, transpose), math (exp, log, sin, cos, sqrt, pow, trig), selection (min, max, select, clamp).

SSA (ssa.rs)

Promotes Local→SSA values, tracks current value in stored map, inserts Phi at merge points (if/else, loops), supports GetElementPtr → ExtractElement/InsertElement.

DCE (dce.rs)

UseDef analysis, removes pure nodes with no side effects, preserves memory ops and control flow.

CPU Backend

• Thread Pool: Rayon parallel.
• Warp Size: 1 (scalar).
• Shader Pipeline: IR → C++ source → clang++ -emit-llvm → .bc bitcode → libLLVM C API (LLJIT) → native code.
• Codegen: cpu/codegen/cpp.rs / cpp_v2.rs.
• Ray Tracing: Embree integration (accel.rs).
• Resources: BufferImpl (aligned host memory), TextureImpl (mipmapped), BindlessArrayImpl, AccelImpl (Embree scene).
• Swapchain: CPU backend optionally loads a platform helper DLL (luisa-backend-cpu.dll / .so) exposing luisa_compute_create_cpu_swapchain etc.

FFI Integration

Header Generation

cbindgen in build.rs:

• luisa_compute_ir → include/luisa/rust/ir.hpp
• luisa_compute_api_types → include/luisa/rust/api_types.hpp (C++) and include/luisa/rust/api_types.h (C)
• luisa_compute_cpu_kernel_defs → cpu_kernel_defs.h (only when LC_RS_GENERATE_BINDINGS=1)

Key FFI Functions

// IR transform pipeline
luisa_compute_ir_transform_pipeline_new() -> *mut TransformPipeline
luisa_compute_ir_transform_pipeline_add_transform(pipeline, name)
luisa_compute_ir_transform_pipeline_transform(pipeline, module) -> Module
luisa_compute_ir_transform_pipeline_destroy(pipeline)
luisa_compute_ir_transform_auto(module) -> Module

// Backend loader interface
luisa_compute_lib_interface() -> LibInterface
luisa_compute_set_ir_v2_binding(table: *const IrV2BindingTable)

Conventions

• All FFI types are #[repr(C)].
• Handle types are newtype wrappers around u64 (e.g., pub struct Buffer(pub u64)).
• Callbacks use extern "C" fn pointers; DeviceInterface/LibInterface are fn-pointer vtable structs.
• Static libs for C++ linking: luisa_compute_api_types, luisa_compute_ir_static.
• Shared backend lib: luisa_compute_backend_impl (exports luisa_compute_lib_interface).

CMake Integration

File: src/rust/CMakeLists.txt.

Custom commands invoke cargo build:

• Profile: dev in Debug, release in Release.
• Features: controlled by CMake options LUISA_COMPUTE_ENABLE_CPU (cpu) and LUISA_COMPUTE_ENABLE_REMOTE (remote); passed as --no-default-features --features <list>.
• CARGO_TARGET_DIR is redirected to the CMake binary dir.

Targets produced:

• luisa_compute_rust_build — builds all Rust artifacts.
• luisa-compute-rust-meta (INTERFACE) — links the static Rust libs + Windows system libs.
• luisa_compute_backend_impl (INTERFACE) — links the shared Rust backend.

Platform handling:

• Windows: copies .dll, .lib, .pdb.
• macOS: install_name_tool for rpath/id.
• Linux: patchelf --set-rpath $ORIGIN.

Embree (CPU only):

• CMake forwards LUISA_COMPUTE_EMBREE_ZIP_PATH or the EMBREE_ZIP_FILE/EMBREE_ZIP_PATH environment variables to the Rust build.
• The Rust embree_sys build script downloads/builds Embree and copies shared libraries to the output directory.

XMake Integration

src/rust/xmake.lua defines target lc-rust with the build_cargo rule. It sets LC_RS_DO_NOT_GENERATE_BINDINGS=1 before building to skip cbindgen header generation.

Common Workflows

Running Rust checks

cd src/rust

# Check default workspace (no backend features)
cargo check

# Check with CPU and remote features
# CPU requires the Embree dependency to be available.
cargo check -p luisa_compute_backend_impl --features cpu,remote

# Run tests
cargo test

# Formatting & lints
cargo fmt --check
cargo clippy --workspace -- -D warnings

Adding a transform

1. Create luisa_compute_ir/src/transform/my_transform.rs.
2. Implement the Transform trait (fn transform(&self, module: ir::Module) -> ir::Module).
3. pub mod my_transform; in luisa_compute_ir/src/transform/mod.rs.
4. If it should be pipeline-selectable from C++, add a match arm in luisa_compute_ir_transform_pipeline_add_transform.

Exposing a new FFI function

1. Add #[no_mangle] pub extern "C" fn luisa_compute_ir_... in the appropriate crate (usually luisa_compute_ir or luisa_compute_backend_impl).
2. Ensure argument/return types are #[repr(C)].
3. Rebuild; cbindgen will emit the declaration into ir.hpp / api_types.hpp.

Debugging cbindgen output

• Set LC_RS_DO_NOT_GENERATE_BINDINGS=1 to skip header generation and speed up cargo check.
• Force regeneration by unsetting it and running cargo build for luisa_compute_ir or luisa_compute_api_types.
• Verify output under include/luisa/rust/.

Key Design Decisions

1. Intrusive linked-list IR with pool allocation for cache efficiency.
2. Global type registry with structural equality (context.rs).
3. CArc/CBox/CBoxedSlice custom smart pointers with C-compatible destructor callbacks.
4. Pipeline-based transforms: modular passes (SSA, autodiff, DCE).
5. CPU JIT: C++ source → LLVM bitcode → runtime-loaded libLLVM / LLJIT.
6. Bidirectional FFI: cbindgen (Rust → C++) + staticlib (C++ → Rust) + cdylib backend loader.