12 releases (6 breaking)
0.6.0 | Aug 5, 2024 |
---|---|
0.5.0 | Feb 10, 2024 |
0.4.1 | May 3, 2023 |
0.3.0 | Jan 21, 2023 |
0.0.0-reserved | Sep 2, 2022 |
#48 in FFI
90KB
1.5K
SLoC
llvm-plugin-rs
This crate gives the ability to safely implement passes for the new LLVM pass manager, by leveraging the strongly typed interface provided by Inkwell.
If you have never developed LLVM passes before, you can take a look at the available examples. They will (hopefully) give you a better idea of how to use this crate.
If you want a deeper understanding of the many concepts surrounding the new LLVM pass manager, you should read the official LLVM documentation.
Usage
When importing this crate in your Cargo.toml
, you will need to specify the LLVM version to use with a corresponding feature flag:
[dependencies]
llvm-plugin = { version = "0.6", features = ["llvm18-0"] }
Supported versions: LLVM 10-18 mapping to a cargo feature flag llvm*-0
where *
corresponds to the LLVM major version.
Getting Started
An LLVM plugin is merely a dylib that is given a PassBuilder by the LLVM tool (e.g. opt, lld)
loading it.
Therefore, you must add the following line in your Cargo.toml
:
[lib]
crate-type = ["cdylib"]
A PassBuilder allows registering callbacks on specific actions being performed by the LLVM tool.
For instance, the --passes
parameter of opt allows specifying a custom pass pipeline to be run on a given IR module. A plugin
could therefore register a callback for parsing an element of the given pipeline (e.g. a pass name), in order to insert a custom
pass to run by opt.
The following code illustrates the idea:
use llvm_plugin::inkwell::module::Module;
use llvm_plugin::{
LlvmModulePass, ModuleAnalysisManager, PassBuilder, PipelineParsing, PreservedAnalyses,
};
// A name and version is required.
#[llvm_plugin::plugin(name = "plugin_name", version = "0.1")]
fn plugin_registrar(builder: &mut PassBuilder) {
// Add a callback to parse a name from the textual representation of
// the pipeline to be run.
builder.add_module_pipeline_parsing_callback(|name, manager| {
if name == "custom-pass" {
// the input pipeline contains the name "custom-pass",
// so we add our custom pass to the pass manager
manager.add_pass(CustomPass);
// we notify the caller that we were able to parse
// the given name
PipelineParsing::Parsed
} else {
// in any other cases, we notify the caller that our
// callback wasn't able to parse the given name
PipelineParsing::NotParsed
}
});
}
struct CustomPass;
impl LlvmModulePass for CustomPass {
fn run_pass(
&self,
module: &mut Module,
manager: &ModuleAnalysisManager
) -> PreservedAnalyses {
// transform the IR
todo!()
}
}
Now, executing this command would run our custom pass on some input module.bc
:
opt --load-pass-plugin=libplugin.so --passes=custom-pass module.bc -disable-output
However, executing this command would not (custom-pass2
cannot be parsed by our plugin):
opt --load-pass-plugin=libplugin.so --passes=custom-pass2 module.bc -disable-output
More callbacks are available, read the documentation for more details.
To learn more about how to sequentially apply more than one pass, read this opt guide.
Linux & MacOS Requirements
Your LLVM toolchain should dynamically link the LLVM library. Fortunately, this is the case for toolchains
distributed on apt
and homebrew
registeries.
Install LLVM-14 with apt
$ apt install llvm-14
Install LLVM-14 with homebrew
$ brew install llvm@14
If you don't use any of these package managers, you can download a compatible LLVM toolchain from
this LLVM fork instead. In this case, don't forget to update your PATH
environment variable with
your LLVM toolchain path, or use the LLVM_SYS_XXX_PREFIX
environment variable to locate your toolchain.
For instance, if your LLVM-14 toolchain is located at ~/llvm
, you should set either of the following:
PATH=$PATH;$HOME/llvm/bin
LLVM_SYS_140_PREFIX=$HOME/llvm
Windows Requirements
The official LLVM toolchain for Windows was not built with plugin support. However, compatible toolchains can be found here.
Don't forget to update your PATH
environment variable with your LLVM toolchain path, or use the LLVM_SYS_XXX_PREFIX
environment variable to locate your toolchain.
For instance, if your LLVM-14 toolchain is located at C:\llvm
, you should set either of the following:
PATH=$PATH;C:\llvm\bin
LLVM_SYS_140_PREFIX=C:\llvm
Compiling Rust/C++ code with custom LLVM plugins
This LLVM fork explains how to do so, and provides LLVM toolchains that will make the process easier.
Missing Features
- Support for loop passes (
Inkwell
doesn't currently provide safe wrappers) - Support for CGSCC passes (
Inkwell
doesn't currently provide safe wrappers) - FFI over the full manager proxy API (only a subset is currently implemented)
- FFI over the full analysis invalidation API (only a subset is currently implemented)
- FFI over builtin LLVM analyses (e.g. dominator tree)
Contributions are very welcome, make sure to check out the Contributing Guide first!
Dependencies
~1.2–2.4MB
~46K SLoC