4ee97fc3db
rustc_codegen_llvm: add support for writing summary bitcode Typical uses of ThinLTO don't have any use for this as a standalone file, but distributed ThinLTO uses this to make the linker phase more efficient. With clang you'd do something like `clang -flto=thin -fthin-link-bitcode=foo.indexing.o -c foo.c` and then get both foo.o (full of bitcode) and foo.indexing.o (just the summary or index part of the bitcode). That's then usable by a two-stage linking process that's more friendly to distributed build systems like bazel, which is why I'm working on this area. I talked some to `@teresajohnson` about naming in this area, as things seem to be a little confused between various blog posts and build systems. "bitcode index" and "bitcode summary" tend to be a little too ambiguous, and she tends to use "thin link bitcode" and "minimized bitcode" (which matches the descriptions in LLVM). Since the clang option is thin-link-bitcode, I went with that to try and not add a new spelling in the world. Per `@dtolnay,` you can work around the lack of this by using `lld --thinlto-index-only` to do the indexing on regular .o files of bitcode, but that is a bit wasteful on actions when we already have all the information in rustc and could just write out the matching minimized bitcode. I didn't test that at all in our infrastructure, because by the time I learned that I already had this patch largely written. |
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Readme.md
Cranelift codegen backend for rust
The goal of this project is to create an alternative codegen backend for the rust compiler based on Cranelift. This has the potential to improve compilation times in debug mode. If your project doesn't use any of the things listed under "Not yet supported", it should work fine. If not please open an issue.
Download using Rustup
The Cranelift codegen backend is distributed in nightly builds on Linux and x86_64 macOS. If you want to install it using Rustup, you can do that by running:
$ rustup component add rustc-codegen-cranelift-preview --toolchain nightly
Once it is installed, you can enable it with one of the following approaches:
CARGO_PROFILE_DEV_CODEGEN_BACKEND=cranelift cargo +nightly build -Zcodegen-backendRUSTFLAGS="-Zcodegen-backend=cranelift" cargo +nightly build- Add the following to
.cargo/config.toml:[unstable] codegen-backend = true [profile.dev] codegen-backend = "cranelift" - Add the following to
Cargo.toml:# This line needs to come before anything else in Cargo.toml cargo-features = ["codegen-backend"] [profile.dev] codegen-backend = "cranelift"
Precompiled builds
You can also download a pre-built version from the releases page.
Extract the dist directory in the archive anywhere you want.
If you want to use cargo clif build instead of having to specify the full path to the cargo-clif executable, you can add the bin subdirectory of the extracted dist directory to your PATH.
(tutorial for Windows, and for Linux/MacOS).
Building and testing
If you want to build the backend manually, you can download it from GitHub and build it yourself:
$ git clone https://github.com/rust-lang/rustc_codegen_cranelift
$ cd rustc_codegen_cranelift
$ ./y.sh prepare
$ ./y.sh build
To run the test suite replace the last command with:
$ ./test.sh
For more docs on how to build and test see build_system/usage.txt or the help message of ./y.sh.
Platform support
| OS \ architecture | x86_64 | AArch64 | Riscv64 | s390x (System-Z) |
|---|---|---|---|---|
| Linux | ✅ | ✅ | ✅1 | ✅1 |
| FreeBSD | ✅1 | ❓ | ❓ | ❓ |
| AIX | ❌2 | N/A | N/A | ❌2 |
| Other unixes | ❓ | ❓ | ❓ | ❓ |
| macOS | ✅ | ❌3 | N/A | N/A |
| Windows | ✅1 | ❌ | N/A | N/A |
✅: Fully supported and tested ❓: Maybe supported, not tested ❌: Not supported at all
Not all targets are available as rustup component for nightly. See notes in the platform support matrix.
Usage
rustc_codegen_cranelift can be used as a near-drop-in replacement for cargo build or cargo run for existing projects.
Assuming $cg_clif_dir is the directory you cloned this repo into and you followed the instructions (y.sh prepare and y.sh build or test.sh).
In the directory with your project (where you can do the usual cargo build), run:
$ $cg_clif_dir/dist/cargo-clif build
This will build your project with rustc_codegen_cranelift instead of the usual LLVM backend.
For additional ways to use rustc_codegen_cranelift like the JIT mode see usage.md.
Building and testing with changes in rustc code
See rustc_testing.md.
Not yet supported
- SIMD (tracked here,
std::simdfully works,std::archis partially supported) - Unwinding on panics (no cranelift support,
-Cpanic=abortis enabled by default)
License
Licensed under either of
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be dual licensed as above, without any additional terms or conditions.