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Remove "Skipping LLVM build" section #1030

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Jan 20, 2021
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Remove "Skipping LLVM build" section #1030

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9 changes: 9 additions & 0 deletions src/backend/updating-llvm.md
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Expand Up @@ -100,6 +100,15 @@ through each in detail.
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
disable this temporarily to make sure your changes are being used, by setting
```toml
[llvm]
download-ci-llvm = false
```
in config.toml

4. Test for regressions across other platforms. LLVM often has at least one bug
for non-tier-1 architectures, so it's good to do some more testing before
sending this to bors! If you're low on resources you can send the PR as-is
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34 changes: 0 additions & 34 deletions src/building/suggested.md
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Expand Up @@ -201,37 +201,3 @@ git worktree add -b my-feature ../rust2 master

You can then use that rust2 folder as a separate workspace for modifying
and building `rustc`!

## Skipping LLVM Build

By default, LLVM is built from source, and that takes significant amount of
time. One way to avoid that is to add this to `config.toml`:

```toml
[llvm]
download-ci-llvm = true
```

Downloading LLVM from CI is still experimental though, and might not be
available on all platforms. Otherwise, we'd make it a default!

Another alternative is to use LLVM already installed on your computer. This is
specified in the `target` section of `config.toml`:

```toml
[target.x86_64-unknown-linux-gnu]
llvm-config = "/path/to/llvm/llvm-7.0.1/bin/llvm-config"
```

We have observed the following paths before, which may be different from your system:

- `/usr/bin/llvm-config-8`
- `/usr/lib/llvm-8/bin/llvm-config`

Note that you need to have the LLVM `FileCheck` tool installed, which is used
for codegen tests. This tool is normally built with LLVM, but if you use your
own preinstalled LLVM, you will need to provide `FileCheck` in some other way.
On Debian-based systems, you can install the `llvm-N-tools` package (where `N`
is the LLVM version number, e.g. `llvm-8-tools`). Alternately, you can specify
the path to `FileCheck` with the `llvm-filecheck` config item in `config.toml`
or you can disable codegen test with the `codegen-tests` item in `config.toml`.
Comment on lines -218 to -237
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@camelid camelid Jan 21, 2021 •
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@jyn514 Was this supposed to be removed?

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Yes, using system llvm is no longer recommended. There's a short section on it in config.toml.example, I don't think it needs its own section in the guide.