roc/BUILDING_FROM_SOURCE.md
2020-04-08 06:41:53 -04:00

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# Building the Roc compiler from source
## Installing LLVM
To build the compiler, you need a particular version of LLVM installed on your system.
To see which version of LLVM you need, take a look at `Cargo.toml`, in particular the `branch` section of the `inkwell` dependency. It should have something like `llvmX-Y` where X and Y are the major and minor revisions of LLVM you need.
For Ubuntu, I used the `Automatic installation script` at [apt.llvm.org](https://apt.llvm.org) - but there are plenty of alternative options at http://releases.llvm.org/download.html
## Use LLD for the linker
Using [`lld` for Rust's linker](https://github.com/rust-lang/rust/issues/39915#issuecomment-538049306)
makes build times a lot faster, and I highly recommend it.
Create `~/.config/cargo` and add this to it:
```
[build]
# Link with lld, per https://github.com/rust-lang/rust/issues/39915#issuecomment-538049306
# Use target-cpu=native, per https://deterministic.space/high-performance-rust.html
rustflags = ["-C", "link-arg=-fuse-ld=lld", "-C", "target-cpu=native"]
```
Then install `lld` version 9 (e.g. with `$ sudo apt-get install lld-9`)
and add make sure there's a `ld.lld` executable on your `PATH` which
is symlinked to `lld-9`.
That's it! Enjoy the faster builds.