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Update links to librustc_llvm and rustllvm #1039

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Jan 24, 2021
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Update links to librustc_llvm and rustllvm #1039

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12 changes: 7 additions & 5 deletions src/backend/updating-llvm.md
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Expand Up @@ -98,9 +98,9 @@ through each in detail.
* `./x.py build src/tools/lld` - same for LLD
* `./x.py build` - build the rest of rustc

You'll likely need to update `src/rustllvm/*.cpp` to compile with updated
LLVM bindings. Note that you should use `#ifdef` and such to ensure that the
bindings still compile on older LLVM versions.
You'll likely need to update [`llvm-wrapper/*.cpp`][`llvm-wrapper`] to compile
with updated LLVM bindings. Note that you should use `#ifdef` and such to ensure
that the bindings still compile on older LLVM versions.

Note that `profile = "compiler"` and other defaults set by `x.py setup`
download LLVM from CI instead of building it from source. You should
Expand Down Expand Up @@ -133,18 +133,20 @@ through each in detail.
5. Prepare a PR to `rust-lang/rust`. Work with maintainers of
`rust-lang/llvm-project` to get your commit in a branch of that repository,
and then you can send a PR to `rust-lang/rust`. You'll change at least
`src/llvm-project` and will likely also change `src/rustllvm/*` as well.
`src/llvm-project` and will likely also change [`llvm-wrapper`] as well.

For prior art, previous LLVM updates look like
[#55835](https://github.com/rust-lang/rust/pull/55835)
[#47828](https://github.com/rust-lang/rust/pull/47828)
[#62474](https://github.com/rust-lang/rust/pull/62474)
[#62592](https://github.com/rust-lang/rust/pull/62592). Note that sometimes it's
easiest to land `src/rustllvm/*` compatibility as a PR before actually updating
easiest to land [`llvm-wrapper`] compatibility as a PR before actually updating
`src/llvm-project`. This way while you're working through LLVM issues others
interested in trying out the new LLVM can benefit from work you've done to
update the C++ bindings.

[`llvm-wrapper`]: https://github.com/rust-lang/rust/tree/master/compiler/rustc_llvm/llvm-wrapper

### Caveats and gotchas

Ideally the above instructions are pretty smooth, but here's some caveats to
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11 changes: 5 additions & 6 deletions src/compiler-src.md
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Expand Up @@ -87,16 +87,15 @@ You can see the exact dependencies by reading the `Cargo.toml` for the various
crates, just like a normal Rust crate.

One final thing: [`src/llvm-project`] is a submodule for our fork of LLVM.
During bootstrapping, LLVM is built and the [`src/librustc_llvm`] and
[`src/rustllvm`] crates contain rust wrappers around LLVM (which is written in
C++), so that the compiler can interface with it.
During bootstrapping, LLVM is built and the [`compiler/rustc_llvm`] crate
contains rust wrappers around LLVM (which is written in C++), so that the
compiler can interface with it.

Most of this book is about the compiler, so we won't have any further
explanation of these crates here.

[`src/llvm-project`]: https://github.com/rust-lang/rust/tree/master/src
[`src/librustc_llvm`]: https://github.com/rust-lang/rust/tree/master/src
[`src/rustllvm`]: https://github.com/rust-lang/rust/tree/master/src
[`src/llvm-project`]: https://github.com/rust-lang/rust/tree/master/src/
[`compiler/rustc_llvm`]: https://github.com/rust-lang/rust/tree/master/compiler/rustc_llvm

### Big picture

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