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Use SyncOnceCell in get_codegen_backend

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This reduces the amount of unsafe code in get_codegen_backend
This commit is contained in:
bjorn3 2021-05-29 15:23:57 +02:00
parent 1870f9b05f
commit d96446c53c
1 changed files with 9 additions and 11 deletions
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20
compiler/rustc_interface/src/util.rs
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@ -32,7 +32,7 @@ use std::ops::DerefMut;
use std::panic;
use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex, Once};
use std::sync::{Arc, Mutex};
use std::thread;
use tracing::info;
@ -251,29 +251,27 @@ pub fn get_codegen_backend(
maybe_sysroot: &Option<PathBuf>,
backend_name: Option<&str>,
) -> Box<dyn CodegenBackend> {
static INIT: Once = Once::new();
static LOAD: SyncOnceCell<unsafe fn() -> Box<dyn CodegenBackend>> = SyncOnceCell::new();
static mut LOAD: fn() -> Box<dyn CodegenBackend> = || unreachable!();
INIT.call_once(|| {
let load = LOAD.get_or_init(|| {
#[cfg(feature = "llvm")]
const DEFAULT_CODEGEN_BACKEND: &str = "llvm";
#[cfg(not(feature = "llvm"))]
const DEFAULT_CODEGEN_BACKEND: &str = "cranelift";
let backend = match backend_name.unwrap_or(DEFAULT_CODEGEN_BACKEND) {
match backend_name.unwrap_or(DEFAULT_CODEGEN_BACKEND) {
filename if filename.contains('.') => load_backend_from_dylib(filename.as_ref()),
#[cfg(feature = "llvm")]
"llvm" => rustc_codegen_llvm::LlvmCodegenBackend::new,
backend_name => get_codegen_sysroot(maybe_sysroot, backend_name),
};
unsafe {
LOAD = backend;
}
});
unsafe { LOAD() }
// SAFETY: In case of a builtin codegen backend this is safe. In case of an external codegen
// backend we hope that the backend links against the same rustc_driver version. If this is not
// the case, we get UB.
unsafe { load() }
}
// This is used for rustdoc, but it uses similar machinery to codegen backend