X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;ds=sidebyside;f=Readme.md;h=22d9e00923f006f1711a5d6791fd8ac78ad9d827;hb=3ea8915d4a247b5b3c4cfb3424c230ccd2645b17;hp=230a08191ff5bfdf032f14f6a021adb569d1a233;hpb=52a43e963961d1e78cc8d272044e1d23cada19f0;p=rust.git

diff --git a/Readme.md b/Readme.md
index 230a08191ff..22d9e00923f 100644
--- a/Readme.md
+++ b/Readme.md
@@ -1,48 +1,111 @@
-# Work in progress cranelift codegen backend for rust
+# WIP Cranelift codegen backend for rust
 
-> ⚠⚠⚠ This doesn't do much useful yet ⚠⚠⚠
+> ⚠⚠⚠ Certain kinds of FFI don't work yet. ⚠⚠⚠
 
-## Building
+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).
+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.
+
+## Building and testing
 
 ```bash
 $ git clone https://github.com/bjorn3/rustc_codegen_cranelift.git
 $ cd rustc_codegen_cranelift
-$ ./prepare.sh # downloads and patches sysroot src and installs hyperfine for benchmarking
+$ ./prepare.sh # download and patch sysroot src and install hyperfine for benchmarking
+$ ./build.sh
+```
+
+To run the test suite replace the last command with:
+
+```bash
 $ ./test.sh
 ```
 
+This will implicitly build cg_clif too. Both `build.sh` and `test.sh` accept a `--debug` argument to
+build in debug mode.
+
+Alternatively you can download a pre built version from [GHA]. It is listed in the artifacts section
+of workflow runs. Unfortunately due to GHA restrictions you need to be logged in to access it.
+
+[GHA]: https://github.com/bjorn3/rustc_codegen_cranelift/actions?query=branch%3Amaster+event%3Apush+is%3Asuccess
+
 ## Usage
 
-`$cg_clif_dir` is the directory you cloned this repo into in the following instruction.
+rustc_codegen_cranelift can be used as a near-drop-in replacement for `cargo build` or `cargo run` for existing projects.
+
+Assuming `$cg_clif_dir` is the directory you cloned this repo into and you followed the instructions (`prepare.sh` and `build.sh` or `test.sh`).
+
+### Cargo
+
+In the directory with your project (where you can do the usual `cargo build`), run:
+
+```bash
+$ $cg_clif_dir/build/cargo.sh run
+```
+
+This should build and run your project with rustc_codegen_cranelift instead of the usual LLVM backend.
 
 ### Rustc
 
+> You should prefer using the Cargo method.
+
 ```bash
-$ rustc -Cpanic=abort -Zcodegen-backend=$cg_clif_dir/target/debug/librustc_codegen_cranelift.so my_crate.rs
+$ $cg_clif_dir/build/bin/cg_clif my_crate.rs
 ```
 
-### Cargo
+### Jit mode
+
+In jit mode cg_clif will immediately execute your code without creating an executable file.
+
+> This requires all dependencies to be available as dynamic library.
+> The jit mode will probably need cargo integration to make this possible.
 
 ```bash
-$ RUSTFLAGS="-Cpanic=abort -Zcodegen-backend=$cg_clif_dir/target/debug/librustc_codegen_cranelift.dylib --sysroot $cg_clif_dir/build_sysroot/sysroot" cargo run
+$ $cg_clif_dir/build/cargo.sh jit
 ```
 
-## Not yet supported
+or
 
-* Good non-rust abi support ([scalar pair and vector are passed by-ref](https://github.com/bjorn3/rustc_codegen_cranelift/issues/10))
-* Checked binops ([some missing instructions in cranelift](https://github.com/CraneStation/cranelift/issues/460))
-* Inline assembly ([no cranelift support](https://github.com/CraneStation/cranelift/issues/444))
-* Varargs ([no cranelift support](https://github.com/CraneStation/cranelift/issues/212))
-* libstd (needs varargs and some other stuff) ([tracked here](https://github.com/bjorn3/rustc_codegen_cranelift/issues/146))
-* u128 and i128 ([no cranelift support](https://github.com/CraneStation/cranelift/issues/354))
-* SIMD ([tracked here](https://github.com/bjorn3/rustc_codegen_cranelift/issues/171))
+```bash
+$ $cg_clif_dir/build/bin/cg_clif -Cllvm-args=mode=jit -Cprefer-dynamic my_crate.rs
+```
+
+There is also an experimental lazy jit mode. In this mode functions are only compiled once they are
+first called. It currently does not work with multi-threaded programs. When a not yet compiled
+function is called from another thread than the main thread, you will get an ICE.
 
-## Troubleshooting
+```bash
+$ $cg_clif_dir/build/cargo.sh lazy-jit
+```
 
-### Can't compile
+### Shell
 
-Try updating your nightly compiler. You can try to use an nightly a day or two older if updating rustc doesn't fix it. If you still can't compile it, please fill an issue.
+These are a few functions that allow you to easily run rust code from the shell using cg_clif as jit.
 
-### error[E0463]: can't find crate for `std` while compiling a no_std crate
+```bash
+function jit_naked() {
+    echo "$@" | $cg_clif_dir/build/bin/cg_clif - -Cllvm-args=mode=jit -Cprefer-dynamic
+}
+
+function jit() {
+    jit_naked "fn main() { $@ }"
+}
+
+function jit_calc() {
+    jit 'println!("0x{:x}", ' $@ ');';
+}
+```
+
+## Env vars
+
+[see env_vars.md](docs/env_vars.md)
+
+## Not yet supported
 
-If you use `RUSTFLAGS` to pass `-Zcodegen-backend` to rustc, cargo will compile `build-dependencies` with those flags too. Because this project doesn't support libstd yet, that will result in an error. I don't know of any way to fix this. :(
+* Good non-rust abi support ([several problems](https://github.com/bjorn3/rustc_codegen_cranelift/issues/10))
+* Inline assembly ([no cranelift support](https://github.com/bytecodealliance/wasmtime/issues/1041)
+    * On Linux there is support for invoking an external assembler for `global_asm!` and `asm!`.
+      `llvm_asm!` will remain unimplemented forever. `asm!` doesn't yet support reg classes. You
+      have to specify specific registers instead.
+* SIMD ([tracked here](https://github.com/bjorn3/rustc_codegen_cranelift/issues/171), some basic things work)