Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Add x86_64-pc-windows-msvc linker-plugin-lto instructions #92134

Merged
merged 4 commits into from
Jan 27, 2022
+42 −0
Merged

Add x86_64-pc-windows-msvc linker-plugin-lto instructions #92134

Changes from 3 commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
7430a55
Add x86_64-pc-windows-msvc linker-plugin-lto instructions
nico-abram Dec 20, 2021
55b6108
Update linker-plugin-lto.md
nico-abram Dec 20, 2021
032c545
Update linker-plugin-lto.md
nico-abram Dec 20, 2021
b75cb95
Update src/doc/rustc/src/linker-plugin-lto.md
nico-abram Jan 25, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 42 additions & 0 deletions src/doc/rustc/src/linker-plugin-lto.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,48 @@ option:
rustc -Clinker-plugin-lto="/path/to/LLVMgold.so" -L. -Copt-level=2 ./main.rs
```

### Usage with clang-cl and --target x86_64-pc-windows-msvc
nico-abram marked this conversation as resolved.
Show resolved Hide resolved

Cross language LTO can be used with the x86_64-pc-windows-msvc target, but this requires using the
clang-cl compiler instead of the MSVC cl.exe included with Visual Studio Build Tools, and linking
with lld-link. Both clang-cl and lld-link can be downloaded from [LLVM's download page](https://releases.llvm.org/download.html).
Note that most crates in the ecosystem are likely to assume you are using cl.exe if using this target
and that some things, like for example vcpkg, [don't work very well with clang-cl](https://github.com/microsoft/vcpkg/issues/2087).

You will want to make sure your rust major LLVM version matches your installed LLVM tooling version,
otherwise it is likely you will get linker errors:

```bat
rustc -V --verbose
clang-cl --version
```

If you are compiling any proc-macros, you will get this error:

```bash
error: Linker plugin based LTO is not supported together with `-C prefer-dynamic` when
targeting Windows-like targets
```

This is fixed if you explicitly set the target, for example
`cargo build --target x86_64-pc-windows-msvc`
Without an explicit --target the flags will be passed to all compiler invocations (including build
scripts and proc macros), see [cargo docs on rustflags](https://doc.rust-lang.org/cargo/reference/config.html#buildrustflags)

If you have dependencies using the `cc` crate, you will need to set these
environment variables:
```bat
set CC=clang-cl
set CXX=clang-cl
set CFLAGS=/clang:-flto=thin /clang:-fuse-ld=lld-link
set CXXFLAGS=/clang:-flto=thin /clang:-fuse-ld=lld-link
REM Needed because msvc's lib.exe crashes on LLVM LTO .obj files
set AR=llvm-lib
```

If you are specifying lld-link as your linker by setting `linker = "lld-link.exe"` in your cargo config,
you may run into issues with some crates that compile code with separate cargo invocations. You should be
able to get around this problem by setting `-Clinker=lld-link` in RUSTFLAGS

## Toolchain Compatibility

Expand Down