Drop AST on a separate thread and prefetch hir_crate

compiler/rustc_data_structures/src/sync.rs

@@ -43,7 +43,7 @@ pub use self::freeze::{FreezeLock, FreezeReadGuard, FreezeWriteGuard};
 pub use self::lock::{Lock, LockGuard, Mode};
 pub use self::mode::{is_dyn_thread_safe, set_dyn_thread_safe_mode};
 pub use self::parallel::{
-    join, par_for_each_in, par_map, parallel_guard, scope, try_par_for_each_in,
+    join, par_for_each_in, par_map, parallel_guard, scope, spawn, try_par_for_each_in,
 };
 pub use self::vec::{AppendOnlyIndexVec, AppendOnlyVec};
 pub use self::worker_local::{Registry, WorkerLocal};

compiler/rustc_data_structures/src/sync/parallel.rs

@@ -93,6 +93,17 @@ macro_rules! parallel {
         };
     }
 
+pub fn spawn(func: impl FnOnce() + DynSend + 'static) {
+    if mode::is_dyn_thread_safe() {
+        let func = FromDyn::from(func);
+        rayon_core::spawn(|| {
+            (func.into_inner())();
+        });
+    } else {
+        func()
+    }
+}
+
 // This function only works when `mode::is_dyn_thread_safe()`.
 pub fn scope<'scope, OP, R>(op: OP) -> R
 where