llvm-ir seeks to provide a Rust-y representation of LLVM IR.
It's based on the idea that an LLVM [Instruction] shouldn't be an opaque
datatype, but rather an enum with variants like [Add], [Call], and
[Store].
Likewise, types like [BasicBlock], [Function], and [Module] should be
Rust structs containing as much information as possible.
Unlike other safe LLVM bindings such as [inkwell], llvm-ir does not rely
on continuous FFI to the LLVM API.
It uses the LLVM API only for its initial parsing step, to pull in all the
data it needs to construct its rich representation of LLVM IR.
Once llvm-ir creates a [Module] data structure by parsing an LLVM file
(using the excellent [llvm-sys] low-level LLVM bindings), it drops the LLVM
FFI objects and makes no further FFI calls.
This allows you to work with the resulting LLVM IR in pure safe Rust.
llvm-ir is intended for consumption of LLVM IR, and not necessarily
production of LLVM IR (yet).
That is, it is aimed at program analysis and related applications which want
to read and analyze LLVM IR.
In the future, perhaps llvm-ir could be able to output its Modules back
into LLVM files, or even send them directly to the LLVM library for compiling.
If this interests you, contributions are welcome!
(Or in the meantime, check out [inkwell] for a different safe interface for
producing LLVM IR.)
But if you're looking for a nice read-oriented representation of LLVM IR for
working in pure Rust, that's exactly what llvm-ir can provide today.
This crate is on crates.io, so you can simply
add it as a dependency in your Cargo.toml:
toml
[dependencies]
llvm-ir = "0.6.0"
Then, the easiest way to get started is to parse some existing LLVM IR into
this crate's data structures.
To do this, you need LLVM bitcode (*.bc) files.
If you currently have C/C++ sources (say, source.c), you can generate
*.bc files with clang's -c and -emit-llvm flags:
bash
clang -c -emit-llvm source.c -o source.bc
Alternately, to compile Rust sources to LLVM bitcode, you can use rustc's
--emit=llvm-bc flag.
In either case, once you have a bitcode file, then you can use llvm-ir's
Module::from_bc_path function:
```rust
use llvm_ir::Module;
use std::path::Path;
let path = Path::new("path/to/my/file.bc"); let module = Module::frombcpath(&path)?; ```
Documentation for llvm-ir can be found here,
or of course you can generate local documentation with cargo doc --open.
The documentation includes links to relevant parts of the LLVM documentation
when appropriate.
Depending on your LLVM version, you may need to use a different version of llvm-ir.
0.6.x) and the
master branch.0.5.x crates.io releases and the 0.5.x branch.
This branch will receive bugfixes if necessary, but no new features or
breaking API changes.0.5.x
branch of llvm-ir, open the llvm-ir Cargo.toml, and change the
llvm-sys dependency version from 90.0 to 80.1.llvm-ir works on stable Rust, and requires Rust 1.36+.
For development or debugging, you may want LLVM text-format (*.ll) files in
addition to *.bc files.
For C/C++ sources, you can generate these by passing -S -emit-llvm to
clang, instead of -c -emit-llvm.
E.g.,
bash
clang -S -emit-llvm source.c -o source.ll
For Rust sources, you can use rustc's --emit=llvm-ir flag.
Additionally, you may want to ensure you are generating LLVM bitcode with
debuginfo; this will ensure that [Instruction]s, [Terminator]s,
[GlobalVariable]s, and [Function]s have valid [DebugLoc]s attached.
(See the [HasDebugLoc] trait.)
You can do this by passing the -g flag to clang, clang++, or rustc
when generating bitcode.
A few features of LLVM IR are not yet represented in llvm-ir's data
structures.
Most notably, llvm-ir recovers debug-location metadata (for mapping back to
source locations), but makes no attempt to recover any other debug metadata.
LLVM files containing metadata can still be parsed in with no problems, but
the resulting Module structures will not contain any of the metadata,
except debug locations.
Work-in-progress on fixing this can be found on the metadata branch of this
repo, but be warned that the metadata branch doesn't even build at the time
of this writing, let alone provide any meaningful functionality for crate
users.
A few other features are missing from llvm-ir's data structures because
getters for them are missing from the LLVM C API and the Rust llvm-sys
crate, only being present in the LLVM C++ API.
These include but are not limited to:
nsw and nuw flags on Add, Sub, Mul, and Shl, and likewise
the exact flag on UDiv, SDiv, LShr, and AShr. The C API has
functionality to set these flags and/or create new instructions specifying
values of these flags, but not to query the values of these flags on existing
instructions.LandingPad instructionBlockAddress constant expressionCallBr terminatorThese issues with the LLVM C API have also been reported as
LLVM bug #42692.
As discussed there, the AtomicRMW opcode getters (which were previously
missing) were added and are available starting with LLVM 10; but the others
remain open problems.
Any contributions to filling these gaps in the C API are greatly appreciated!
llvm-ir is heavily inspired by the [llvm-hs-pure Haskell package].
Most of the data structures in llvm-ir are essentially translations from
Haskell to Rust of the data structures in llvm-hs-pure (with some tweaks).
To a lesser extent, llvm-ir borrows from the larger [llvm-hs Haskell
package] as well.