Auto merge of #121909 - Zoxc:drop-ast-task, r=petrochenkov

Drop AST on a separate thread and prefetch `hir_crate`

This drop AST on a separate thread and prefetches `hir_crate`.

A `spawn` function is added to the `parallel` module which spawn some work on the Rayon thread pool.

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 66d2a79b93a..aad63f4edcf 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -900,6 +900,12 @@ fn run_required_analyses(tcx: TyCtxt<'_>) {
     // is not defined. So we need to cfg it out.
     #[cfg(all(not(doc), debug_assertions))]
     rustc_passes::hir_id_validator::check_crate(tcx);
+
+    // Prefetch this to prevent multiple threads from blocking on it later.
+    // This is needed since the `hir_id_validator::check_crate` call above is not guaranteed
+    // to use `hir_crate`.
+    tcx.ensure_done().hir_crate(());
+
     let sess = tcx.sess;
     sess.time("misc_checking_1", || {
         parallel!(