Auto merge of #124662 - zetanumbers:needs_async_drop, r=oli-obk

Implement `needs_async_drop` in rustc and optimize async drop glue

This PR expands on #121801 and implements `Ty::needs_async_drop` which works almost exactly the same as `Ty::needs_drop`, which is needed for #123948.

Also made compiler's async drop code to look more like compiler's regular drop code, which enabled me to write an optimization where types which do not use `AsyncDrop` can simply forward async drop glue to `drop_in_place`. This made size of the async block from the [async_drop test](https://github.com/zetanumbers/rust/blob/67980dd6fb11917d23d01a19c2cf4cfc3978aac8/tests/ui/async-await/async-drop.rs) to decrease by 12%.

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 0d089205c1e..e4dcea785d4 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -4,6 +4,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::bug;
 use rustc_middle::query::Providers;
 use rustc_middle::traits::{BuiltinImplSource, CodegenObligationError};
+use rustc_middle::ty::util::AsyncDropGlueMorphology;
 use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, Instance, TyCtxt, TypeVisitableExt};
 use rustc_span::sym;
@@ -59,7 +60,7 @@ fn resolve_instance<'tcx>(
         } else if Some(def_id) == tcx.lang_items().async_drop_in_place_fn() {
             let ty = args.type_at(0);
 
-            if !ty.is_async_destructor_noop(tcx, param_env) {
+            if ty.async_drop_glue_morphology(tcx) != AsyncDropGlueMorphology::Noop {
                 match *ty.kind() {
                     ty::Closure(..)
                     | ty::CoroutineClosure(..)