src/tools/enzyme/Readme.md

# <img src="https://enzyme.mit.edu/logo.svg" width="75" align=left> The Enzyme High-Performance Automatic Differentiator of LLVM and MLIR


Enzyme is a plugin that performs automatic differentiation (AD) of statically analyzable LLVM and MLIR.

Enzyme can be used by calling `__enzyme_autodiff` on a function to be differentiated as shown below. 
Running the Enzyme transformation pass then replaces the call to `__enzyme_autodiff` with the gradient of its first argument.
```c
double foo(double);

double grad_foo(double x) {
    return __enzyme_autodiff(foo, x);
}
```

Enzyme is highly-efficient and its ability to perform AD on optimized code allows Enzyme to meet or exceed the performance of state-of-the-art AD tools.

<div style="padding:2em">
<img src="https://enzyme.mit.edu/all_top.png" width="500" align=center>
</div>

Detailed information on installing and using Enzyme can be found on our website: [https://enzyme.mit.edu](https://enzyme.mit.edu).

A short example of how to install Enzyme is below:
```
cd /path/to/Enzyme/enzyme
mkdir build && cd build
cmake -G Ninja .. -DLLVM_DIR=/path/to/llvm/lib/cmake/llvm -DLLVM_EXTERNAL_LIT=/path/to/lit/lit.py
ninja
```

Or, install Enzyme using a package manager:

[Homebrew](https://brew.sh)
```
brew install enzyme
```
[Spack](https://spack.io)
```
spack install enzyme
```

To get involved or if you have questions, please join our [mailing list](https://groups.google.com/d/forum/enzyme-dev).

If using this code in an academic setting, please cite the following three papers (first for Enzyme as a whole, second for GPU+optimizations, and third for AD of all other parallel programs (OpenMP, MPI, Julia Tasks, etc.)):
```
@inproceedings{NEURIPS2020_9332c513,
 author = {Moses, William and Churavy, Valentin},
 booktitle = {Advances in Neural Information Processing Systems},
 editor = {H. Larochelle and M. Ranzato and R. Hadsell and M. F. Balcan and H. Lin},
 pages = {12472--12485},
 publisher = {Curran Associates, Inc.},
 title = {Instead of Rewriting Foreign Code for Machine Learning, Automatically Synthesize Fast Gradients},
 url = {https://proceedings.neurips.cc/paper/2020/file/9332c513ef44b682e9347822c2e457ac-Paper.pdf},
 volume = {33},
 year = {2020}
}
@inproceedings{10.1145/3458817.3476165,
author = {Moses, William S. and Churavy, Valentin and Paehler, Ludger and H\"{u}ckelheim, Jan and Narayanan, Sri Hari Krishna and Schanen, Michel and Doerfert, Johannes},
title = {Reverse-Mode Automatic Differentiation and Optimization of GPU Kernels via Enzyme},
year = {2021},
isbn = {9781450384421},
publisher = {Association for Computing Machinery},
address = {New York, NY, USA},
url = {https://doi.org/10.1145/3458817.3476165},
doi = {10.1145/3458817.3476165},
booktitle = {Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis},
articleno = {61},
numpages = {16},
keywords = {CUDA, LLVM, ROCm, HPC, AD, GPU, automatic differentiation},
location = {St. Louis, Missouri},
series = {SC '21}
}
@inproceedings{10.5555/3571885.3571964,
author = {Moses, William S. and Narayanan, Sri Hari Krishna and Paehler, Ludger and Churavy, Valentin and Schanen, Michel and H\"{u}ckelheim, Jan and Doerfert, Johannes and Hovland, Paul},
title = {Scalable Automatic Differentiation of Multiple Parallel Paradigms through Compiler Augmentation},
year = {2022},
isbn = {9784665454445},
publisher = {IEEE Press},
booktitle = {Proceedings of the International Conference on High Performance Computing, Networking, Storage and Analysis},
articleno = {60},
numpages = {18},
keywords = {automatic differentiation, tasks, OpenMP, compiler, Julia, parallel, Enzyme, C++, RAJA, hybrid parallelization, MPI, distributed, LLVM},
location = {Dallas, Texas},
series = {SC '22}
}
```

Both [Julia bindings](https://github.com/EnzymeAD/Enzyme.jl#readme) and [Rust bindings](https://github.com/EnzymeAD/rust#readme) are available for Enzyme.