upstream autodiff build instructions

Author: ZuseZ4

Diff for: src/SUMMARY.md

@@ -100,6 +100,7 @@
     - [Search](./rustdoc-internals/search.md)
 	- [The `rustdoc` test suite](./rustdoc-internals/rustdoc-test-suite.md)
 - [Autodiff internals](./autodiff/internals.md)
+    - [Installation](./autodiff/installation.md)
     - [How to debug](./autodiff/debugging.md)
     - [Autodiff flags](./autodiff/flags.md)
     - [Current limitations](./autodiff/limitations.md)

Diff for: src/autodiff/installation.md

@@ -0,0 +1,86 @@
+# Installation
+
+In the near future, `std::autodiff` should become available in nightly builds for users. As a contribute however, you will still need to build rustc from source. Please be aware that the msvc target is not supported at the moment, all other tier 1 targets should work. Please open an issue if you encounter any problems on a supported tier 1 target, or if you succesfully build this project on a tier2/tier3 target.
+
+## Build instructions
+
+First you need to clone and configure the Rust repository:
+```bash
+git clone --depth=1 [email protected]:rust-lang/rust.git
+cd rust
+./configure --enable-llvm-link-shared --enable-llvm-plugins --enable-llvm-enzyme --release-channel=nightly --enable-llvm-assertions --enable-clang --enable-lld --enable-option-checking --enable-ninja --disable-docs
+```
+
+Afterwards you can build rustc using:
+```bash
+./x.py build --stage 1 library
+```
+
+Afterwards rustc toolchain link will allow you to use it through cargo:
+```
+rustup toolchain link enzyme build/host/stage1
+rustup toolchain install nightly # enables -Z unstable-options
+```
+
+You can then run our test cases:
+
+```bash
+./x.py test --stage 1 library tests/ui/autodiff
+./x.py test --stage 1 library tests/codegen/autodiff
+./x.py test --stage 1 library tests/pretty/autodiff*
+```
+
+Autodiff is still experimental, so if you want to use it in your own projects, you will need to add `lto="fat"` to your Cargo.toml 
+and use `RUSTFLAGS="-Zautodiff=Enable" cargo +enzyme` instead of `cargo` or `cargo +nightly`. 
+
+## Compiler Explorer and dist builds
+
+Our compiler explorer instance can be updated to a newer rustc in a similar way. First, prepare a docker instance.
+```bash
+docker run -it ubuntu:22.04
+export CC=clang CXX=clang++
+apt update
+apt install wget vim python3 git curl libssl-dev pkg-config lld ninja-build cmake clang build-essential 
+```
+Then build rustc in a slightly altered way:
+```bash
+git clone --depth=1 https://github.com/EnzymeAD/rust.git
+cd rust
+./configure --enable-llvm-link-shared --enable-llvm-plugins --enable-llvm-enzyme --release-channel=nightly --enable-llvm-assertions --enable-clang --enable-lld --enable-option-checking --enable-ninja --disable-docs
+./x dist
+```
+We then copy the tarball to our host. The dockerid is the newest entry under `docker ps -a`.
+```bash
+docker cp <dockerid>:/rust/build/dist/rust-nightly-x86_64-unknown-linux-gnu.tar.gz rust-nightly-x86_64-unknown-linux-gnu.tar.gz
+```
+Afterwards we can create a new (pre-release) tag on the EnzymeAD/rust repository and make a PR against the EnzymeAD/enzyme-explorer repository to update the tag.
+Remember to ping `tgymnich` on the PR to run his update script.
+
+
+## Build instruction for Enzyme itself
+
+Following the Rust build instruction above will build LLVMEnzyme, LLDEnzyme, and ClangEnzyme along with the Rust compiler.
+We recommend that approach, if you just want to use any of them and have no experience with cmake.
+However, if you prefer to just build Enzyme without Rust, then these instructions might help.
+
+```bash
+git clone --depth=1 [email protected]:llvm/llvm-project.git 
+cd llvm-project
+mkdir build
+cd build
+cmake -G Ninja ../llvm -DLLVM_TARGETS_TO_BUILD="host" -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_ENABLE_RUNTIMES="openmp" -DLLVM_ENABLE_PLUGINS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=.
+ninja
+ninja install
+```
+This gives you a working LLVM build, now we can continue with building Enzyme.
+Leave the `llvm-project` folder, and execute the following commands:
+```bash
+git clone [email protected]:EnzymeAD/Enzyme.git 
+cd Enzyme/enzyme
+mkdir build 
+cd build 
+cmake .. -G Ninja -DLLVM_DIR=<YourLocalPath>/llvm-project/build/lib/cmake/llvm/ -DLLVM_EXTERNAL_LIT=<YourLocalPath>/llvm-project/llvm/utils/lit/lit.py -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=YES -DBUILD_SHARED_LIBS=ON
+ninja
+```
+This will build Enzyme, and you can find it in `Enzyme/enzyme/build/lib/<LLD/Clang/LLVM>Enzyme.so`. (Endings might differ based on your OS).
+