mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Rollup merge of #92134 - nico-abram:patch-1, r=michaelwoerister

Browse Source 
Add x86_64-pc-windows-msvc linker-plugin-lto instructions

I had some trouble getting cross language LTO working for this target, in part because the very few links of documentation I could find were linux-centric and because of a few very specific errors I ran into. I'm not sure if this is the correct place to document this, but this is one of the first links I found when looking for documentation so it might be the best place for it.
This commit is contained in:
Matthias Krüger 2022-01-26 23:45:21 +01:00 committed by GitHub
commit e249812597
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 42 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
src/doc/rustc/src/linker-plugin-lto.md
View File

@ -86,6 +86,48 @@ option:
rustc -Clinker-plugin-lto="/path/to/LLVMgold.so" -L. -Copt-level=2 ./main.rs
```
### Usage with clang-cl and x86_64-pc-windows-msvc
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