fungt-dialect

MLIR dialect for shader compilation, lowering to SPIR-V for use in OpenGL and, in the future, Vulkan.

Status

Vertex and Fragment execution mode SPIR-V has been proven to round trip correctly through MLIR's SPIR-V dialect, serialize with mlir-translate, validate with spirv-val, and load in OpenGL via GL_ARB_gl_spirv on both Intel and NVIDIA drivers. This was done with hand written spirv.module MLIR, independent of fungt-dialect's own ops. fungt-dialect's own ops and lowering passes do not yet emit Vertex or Fragment modules.

Overview

fungt-dialect defines the ops and lowering passes needed to build shaders in MLIR and compile them to SPIR-V. It currently has no shading specific ops. A shading language needs, at minimum, first class support for samplers, images, varying and uniform storage classes, and interpolation qualifiers, none of which fungt-dialect currently represents. This is the active area of work.

Tools

fungt-opt Optimizer driver. Runs lowering passes on MLIR input.

fungt-parse FunGT IR parser. Reads user friendly .fgt text files and emits MLIR with fungt ops.

fungt-translate SPIR-V serializer. Converts SPIR-V dialect MLIR to binary .spv files.

Shading Pipeline (proof of concept, not yet wired into fungt-dialect)

Hand written spirv.module MLIR, Fragment or Vertex execution mode
        |
   mlir-translate --serialize-spirv --no-implicit-module -o shader.spv
        |
   spirv-val shader.spv
        |
   OpenGL: glShaderBinary + glSpecializeShader (GL_ARB_gl_spirv)

Both the vertex and fragment shaders in a single OpenGL program must be SPIR-V modules together. Mixing a text compiled GLSL shader with a SPIR-V specialized shader in the same program is invalid per the GL_ARB_gl_spirv spec and produces GL_INVALID_OPERATION on link, and was observed to cause a driver level segmentation fault in Mesa's iris driver on Intel Arc hardware before the mixed state was corrected.

There is no surface syntax for shaders yet.

Building

Requires an LLVM/MLIR build. Point CMake at your MLIR install:

mkdir build && cd build
cmake -G Ninja .. \
  -DMLIR_DIR=/path/to/llvm-project/build/lib/cmake/mlir \
  -DLLVM_EXTERNAL_LIT=/path/to/llvm-project/build/bin/llvm-lit
ninja

Prior work

fungt-dialect originally targeted GLCompute execution mode SPIR-V for LLM generated particle physics kernels, loaded via SYCL's kernel_compiler extension. That work has been superseded by the shading language direction above and is no longer the project's purpose.

Part of FunGT

https://github.com/FunGTs/FunGT

License

Apache 2.0 with LLVM Exceptions. See LICENSE for details.