108 lines
3.3 KiB
Markdown
108 lines
3.3 KiB
Markdown
# Cranelift codegen backend for rust
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The goal of this project is to create an alternative codegen backend for the rust compiler based on [Cranelift](https://github.com/bytecodealliance/wasmtime/blob/main/cranelift).
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This has the potential to improve compilation times in debug mode.
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If your project doesn't use any of the things listed under "Not yet supported", it should work fine.
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If not please open an issue.
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## Building and testing
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```bash
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$ git clone https://github.com/bjorn3/rustc_codegen_cranelift.git
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$ cd rustc_codegen_cranelift
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$ ./prepare.sh # download and patch sysroot src and install hyperfine for benchmarking
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$ ./build.sh
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```
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To run the test suite replace the last command with:
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```bash
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$ ./test.sh
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```
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This will implicitly build cg_clif too. Both `build.sh` and `test.sh` accept a `--debug` argument to
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build in debug mode.
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Alternatively you can download a pre built version from [GHA]. It is listed in the artifacts section
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of workflow runs. Unfortunately due to GHA restrictions you need to be logged in to access it.
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[GHA]: https://github.com/bjorn3/rustc_codegen_cranelift/actions?query=branch%3Amaster+event%3Apush+is%3Asuccess
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## Usage
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rustc_codegen_cranelift can be used as a near-drop-in replacement for `cargo build` or `cargo run` for existing projects.
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Assuming `$cg_clif_dir` is the directory you cloned this repo into and you followed the instructions (`prepare.sh` and `build.sh` or `test.sh`).
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### Cargo
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In the directory with your project (where you can do the usual `cargo build`), run:
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```bash
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$ $cg_clif_dir/build/cargo.sh run
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```
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This should build and run your project with rustc_codegen_cranelift instead of the usual LLVM backend.
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### Rustc
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> You should prefer using the Cargo method.
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```bash
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$ $cg_clif_dir/build/bin/cg_clif my_crate.rs
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```
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### Jit mode
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In jit mode cg_clif will immediately execute your code without creating an executable file.
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> This requires all dependencies to be available as dynamic library.
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> The jit mode will probably need cargo integration to make this possible.
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```bash
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$ $cg_clif_dir/build/cargo.sh jit
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```
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or
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```bash
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$ $cg_clif_dir/build/bin/cg_clif -Cllvm-args=mode=jit -Cprefer-dynamic my_crate.rs
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```
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There is also an experimental lazy jit mode. In this mode functions are only compiled once they are
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first called. It currently does not work with multi-threaded programs. When a not yet compiled
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function is called from another thread than the main thread, you will get an ICE.
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```bash
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$ $cg_clif_dir/build/cargo.sh lazy-jit
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```
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### Shell
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These are a few functions that allow you to easily run rust code from the shell using cg_clif as jit.
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```bash
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function jit_naked() {
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echo "$@" | $cg_clif_dir/build/bin/cg_clif - -Cllvm-args=mode=jit -Cprefer-dynamic
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}
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function jit() {
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jit_naked "fn main() { $@ }"
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}
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function jit_calc() {
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jit 'println!("0x{:x}", ' $@ ');';
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}
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```
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## Env vars
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[see env_vars.md](docs/env_vars.md)
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## Not yet supported
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* Inline assembly ([no cranelift support](https://github.com/bytecodealliance/wasmtime/issues/1041))
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* On Linux there is support for invoking an external assembler for `global_asm!` and `asm!`.
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`llvm_asm!` will remain unimplemented forever. `asm!` doesn't yet support reg classes. You
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have to specify specific registers instead.
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* SIMD ([tracked here](https://github.com/bjorn3/rustc_codegen_cranelift/issues/171), some basic things work)
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