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Cleanup LLVM multi-threading checks #89808

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Oct 25, 2021
Merged

Cleanup LLVM multi-threading checks #89808

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2 changes: 1 addition & 1 deletion compiler/rustc_codegen_llvm/src/llvm/ffi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1743,7 +1743,7 @@ extern "C" {

pub fn LLVMDisposeMessage(message: *mut c_char);

pub fn LLVMStartMultithreaded() -> Bool;
pub fn LLVMIsMultithreaded() -> Bool;

/// Returns a string describing the last error caused by an LLVMRust* call.
pub fn LLVMRustGetLastError() -> *const c_char;
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20 changes: 5 additions & 15 deletions compiler/rustc_codegen_llvm/src/llvm_util.rs
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Expand Up @@ -17,35 +17,25 @@ use std::path::Path;
use std::ptr;
use std::slice;
use std::str;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Once;

static POISONED: AtomicBool = AtomicBool::new(false);
static INIT: Once = Once::new();

pub(crate) fn init(sess: &Session) {
unsafe {
// Before we touch LLVM, make sure that multithreading is enabled.
if llvm::LLVMIsMultithreaded() != 1 {
bug!("LLVM compiled without support for threads");
}
INIT.call_once(|| {
if llvm::LLVMStartMultithreaded() != 1 {
// use an extra bool to make sure that all future usage of LLVM
// cannot proceed despite the Once not running more than once.
POISONED.store(true, Ordering::SeqCst);
}

configure_llvm(sess);
});

if POISONED.load(Ordering::SeqCst) {
bug!("couldn't enable multi-threaded LLVM");
}
}
}

fn require_inited() {
INIT.call_once(|| bug!("llvm is not initialized"));
if POISONED.load(Ordering::SeqCst) {
bug!("couldn't enable multi-threaded LLVM");
if !INIT.is_completed() {
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This is somewhat more racy than the previous version. Previously call_once would block if the confiugre_llvm from another call to init was already being executed.

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My thinking was that if there is a race, a thread executing require_inited might win and this would indicate a presence of a bug that needs to be fixed regardless.

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Okay, fair.

bug!("LLVM is not initialized");
}
}

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