a1411de9de
Allow loading of llvm plugins on nightly
Based on a discussion in #82734 / with `@wsmoses.`
Mainly moves [this](0149bc4e7e
) behind a -Z flag, so it can only be used on nightly,
as requested by `@nagisa` in https://github.com/rust-lang/rust/issues/82734#issuecomment-835863940
This change allows loading of llvm plugins like Enzyme.
Right now it also requires a shared library LLVM build of rustc for symbol resolution.
```rust
// test.rs
extern { fn __enzyme_autodiff(_: usize, ...) -> f64; }
fn square(x : f64) -> f64 {
return x * x;
}
fn main() {
unsafe {
println!("Hello, world {} {}!", square(3.0), __enzyme_autodiff(square as usize, 3.0));
}
}
```
```
./rustc test.rs -Z llvm-plugins="./LLVMEnzyme-12.so" -C passes="enzyme"
./test
Hello, world 9 6!
```
I will try to figure out how to simplify the usage and get this into stable in a later iteration,
but having this on nightly will already help testing further steps.
The codegen
crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.