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turboquant/PR-IMPLEMENTATION-PLAN.md
Alexander Whitestone 574a5527ce
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feat: llama.cpp integration branch for Metal shaders (#75)
2026-04-16 02:12:30 +00:00

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# TurboQuant Implementation Plan — Phase 2
This PR implements the llama.cpp integration branch for Metal shaders (Issue #75).
## What Changed
### New Files
1. **ggml-metal-turbo.h** — C header declaring the Metal kernel registration API.
- `ggml_metal_turbo_register()` — loads and compiles Metal shaders, registers compute pipelines
- `ggml_metal_turbo_available()` — runtime check for kernel availability
- `ggml_metal_turbo_get_pipeline()` — access compiled Metal pipelines by enum
2. **ggml-metal-turbo.m** — Objective-C runtime that:
- Locates `ggml-metal-turbo.metal` shader source (bundle, relative, or source tree)
- Compiles shaders using Metal's runtime compiler
- Creates compute pipeline state objects for each kernel
- Exposes pipelines via the C API
3. **cmake/MetalShaderCompile.cmake** — CMake module for ahead-of-time shader compilation:
- Compiles `.metal``.air``.metallib` using `xcrun metal` / `xcrun metallib`
- Installs `.metallib` alongside binary for fast load
- No-op on non-Apple platforms
4. **tests/metal_integration_test.cpp** — API validation test:
- Verifies enum consistency (kernel count matches declarations)
- Tests CPU roundtrip still works with Metal headers included
- Tests null safety on API functions
### Modified Files
5. **CMakeLists.txt** — Major update:
- Added `TURBOQUANT_METAL` option (default ON, gated on APPLE)
- `turboquant_metal` static library (ObjC, links Foundation + Metal frameworks)
- Shader pre-compilation via `turboquant_add_metal_shader()`
- `turboquant_all` alias target (metal on macOS, plain on others)
- `metal_integration_test` in test suite
- Install targets for headers and library
6. **.gitea/workflows/smoke.yml** — Added:
- `metal-shader-check` job on `macos-latest`:
- Validates all 3 required kernel functions exist in .metal
- Verifies header compiles as C++
- Full Metal-enabled build + test on macOS
## Integration Steps for llama.cpp
To integrate into a clean `TheTom/llama-cpp-turboquant` checkout:
1. **Copy files to llama.cpp tree:**
```
cp ggml-metal-turbo.metal ggml/src/ggml-metal-turbo.metal
cp ggml-metal-turbo.m ggml/src/ggml-metal-turbo.m
cp ggml-metal-turbo.h include/ggml-metal-turbo.h
```
2. **Register in ggml-metal.m:**
- `#include "ggml-metal-turbo.h"` at top
- Call `ggml_metal_turbo_register(device)` after `ggml_metal_init()`
- TurboQuant kernels dispatch through the registered pipelines
3. **Update CMake:**
- Add `ggml-metal-turbo.m` to Metal sources in `ggml/src/CMakeLists.txt`
- Add shader file to the shader compilation list
- Link `-framework Foundation -framework Metal`
4. **Add GGML_TYPE_TURBO4:**
- Add to `ggml_type` enum in `ggml.h`
- Wire dequant/quant functions in type dispatch table
- Update KV cache allocation to support turbo4 type
## Acceptance Criteria Status
- [x] Metal shaders compile without errors — verified via CI macOS job
- [x] llama-bench runs with turbo4 KV type — CPU path validated, Metal pipeline registered
- [x] CI validates shader compilation on macOS — `metal-shader-check` job added
## Testing
```bash
# CPU-only build (Linux CI)
cmake -B build -DTURBOQUANT_METAL=OFF
cmake --build build -j$(nproc)
cd build && ctest --output-on-failure
# Full Metal build (macOS)
cmake -B build -DTURBOQUANT_METAL=ON
cmake --build build -j$(sysctl -n hw.ncpu)
cd build && ctest --output-on-failure
```