Make async drop code more consistent with regular drop code

Fixes rust-lang#126573

Author: zetanumbers

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -371,7 +371,7 @@ fn exported_symbols_provider_local(
                 }) => {
                     // A little sanity-check
                     debug_assert_eq!(
-                        args.non_erasable_generics(tcx, def_id).skip(1).next(),
+                        args.non_erasable_generics(tcx, def_id).next(),
                         Some(GenericArgKind::Type(ty))
                     );
                     symbols.push((
@@ -422,10 +422,7 @@ fn upstream_monomorphizations_provider(
                 }
                 ExportedSymbol::AsyncDropGlueCtorShim(ty) => {
                     if let Some(async_drop_in_place_fn_def_id) = async_drop_in_place_fn_def_id {
-                        (
-                            async_drop_in_place_fn_def_id,
-                            tcx.mk_args(&[tcx.lifetimes.re_erased.into(), ty.into()]),
-                        )
+                        (async_drop_in_place_fn_def_id, tcx.mk_args(&[ty.into()]))
                     } else {
                         // `drop_in_place` in place does not exist, don't try
                         // to use it.
@@ -480,6 +477,17 @@ fn upstream_drop_glue_for_provider<'tcx>(
     }
 }
 
+fn upstream_async_drop_glue_for_provider<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    args: GenericArgsRef<'tcx>,
+) -> Option<CrateNum> {
+    if let Some(def_id) = tcx.lang_items().async_drop_in_place_fn() {
+        tcx.upstream_monomorphizations_for(def_id).and_then(|monos| monos.get(&args).cloned())
+    } else {
+        None
+    }
+}
+
 fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     !tcx.reachable_set(()).contains(&def_id)
 }
@@ -491,6 +499,7 @@ pub fn provide(providers: &mut Providers) {
     providers.upstream_monomorphizations = upstream_monomorphizations_provider;
     providers.is_unreachable_local_definition = is_unreachable_local_definition_provider;
     providers.upstream_drop_glue_for = upstream_drop_glue_for_provider;
+    providers.upstream_async_drop_glue_for = upstream_async_drop_glue_for_provider;
     providers.wasm_import_module_map = wasm_import_module_map;
     providers.extern_queries.is_reachable_non_generic = is_reachable_non_generic_provider_extern;
     providers.extern_queries.upstream_monomorphizations_for =

compiler/rustc_middle/src/query/mod.rs

@@ -1554,12 +1554,13 @@ rustc_queries! {
         }
     }
 
-    /// The entire set of monomorphizations the local crate can safely link
-    /// to because they are exported from upstream crates. Do not depend on
-    /// this directly, as its value changes anytime a monomorphization gets
-    /// added or removed in any upstream crate. Instead use the narrower
-    /// `upstream_monomorphizations_for`, `upstream_drop_glue_for`, or, even
-    /// better, `Instance::upstream_monomorphization()`.
+    /// The entire set of monomorphizations the local crate can safely
+    /// link to because they are exported from upstream crates. Do
+    /// not depend on this directly, as its value changes anytime
+    /// a monomorphization gets added or removed in any upstream
+    /// crate. Instead use the narrower `upstream_monomorphizations_for`,
+    /// `upstream_drop_glue_for`, `upstream_async_drop_glue_for`, or,
+    /// even better, `Instance::upstream_monomorphization()`.
     query upstream_monomorphizations(_: ()) -> &'tcx DefIdMap<UnordMap<GenericArgsRef<'tcx>, CrateNum>> {
         arena_cache
         desc { "collecting available upstream monomorphizations" }
@@ -1601,6 +1602,26 @@ rustc_queries! {
         desc { "available upstream drop-glue for `{:?}`", args }
     }
 
+    /// Returns the upstream crate that exports async-drop-glue for
+    /// the given type (`args` is expected to be a single-item list
+    /// containing the type one wants async-drop-glue for).
+    ///
+    /// This is a subset of `upstream_monomorphizations_for` in order
+    /// to increase dep-tracking granularity. Otherwise adding or
+    /// removing any type with async-drop-glue in any upstream crate
+    /// would invalidate all functions calling async-drop-glue of an
+    /// upstream type.
+    ///
+    /// You likely want to call `Instance::upstream_monomorphization()`
+    /// instead of invoking this query directly.
+    ///
+    /// NOTE: This query could easily be extended to also support other
+    ///       common functions that have are large set of monomorphizations
+    ///       (like `Clone::clone` for example).
+    query upstream_async_drop_glue_for(args: GenericArgsRef<'tcx>) -> Option<CrateNum> {
+        desc { "available upstream async-drop-glue for `{:?}`", args }
+    }
+
     /// Returns a list of all `extern` blocks of a crate.
     query foreign_modules(_: CrateNum) -> &'tcx FxIndexMap<DefId, ForeignModule> {
         arena_cache

compiler/rustc_middle/src/ty/instance.rs

@@ -219,8 +219,9 @@ impl<'tcx> Instance<'tcx> {
             InstanceKind::Item(def) => tcx
                 .upstream_monomorphizations_for(def)
                 .and_then(|monos| monos.get(&self.args).cloned()),
-            InstanceKind::DropGlue(_, Some(_)) | InstanceKind::AsyncDropGlueCtorShim(_, _) => {
-                tcx.upstream_drop_glue_for(self.args)
+            InstanceKind::DropGlue(_, Some(_)) => tcx.upstream_drop_glue_for(self.args),
+            InstanceKind::AsyncDropGlueCtorShim(_, Some(_)) => {
+                tcx.upstream_async_drop_glue_for(self.args)
             }
             _ => None,
         }
@@ -256,7 +257,7 @@ impl<'tcx> InstanceKind<'tcx> {
         match self {
             ty::InstanceKind::Item(def) => Some(def),
             ty::InstanceKind::DropGlue(def_id, Some(_))
-            | InstanceKind::AsyncDropGlueCtorShim(def_id, _)
+            | InstanceKind::AsyncDropGlueCtorShim(def_id, Some(_))
             | InstanceKind::ThreadLocalShim(def_id) => Some(def_id),
             InstanceKind::VTableShim(..)
             | InstanceKind::ReifyShim(..)
@@ -267,6 +268,7 @@ impl<'tcx> InstanceKind<'tcx> {
             | ty::InstanceKind::ConstructCoroutineInClosureShim { .. }
             | ty::InstanceKind::CoroutineKindShim { .. }
             | InstanceKind::DropGlue(..)
+            | InstanceKind::AsyncDropGlueCtorShim(..)
             | InstanceKind::CloneShim(..)
             | InstanceKind::FnPtrAddrShim(..) => None,
         }
@@ -332,6 +334,26 @@ impl<'tcx> InstanceKind<'tcx> {
                     .map_or_else(|| adt_def.is_enum(), |dtor| tcx.cross_crate_inlinable(dtor.did))
             });
         }
+        if let ty::InstanceKind::AsyncDropGlueCtorShim(.., Some(ty)) = *self {
+            // Async drop glue generally wants to be instantiated at
+            // every codegen unit, but without an #[inline] hint. We
+            // should make this available to normal end-users.
+            if tcx.sess.opts.incremental.is_none() {
+                return true;
+            }
+            // When compiling with incremental, we can generate a *lot* of
+            // codegen units. Including drop glue into all of them has a
+            // considerable compile time cost.
+            //
+            // We include enums without destructors to allow, say, optimizing
+            // drops of `Option::None` before LTO. We also respect the intent of
+            // `#[inline]` on `Drop::drop` implementations.
+            return ty.ty_adt_def().map_or(true, |adt_def| {
+                adt_def
+                    .async_destructor(tcx)
+                    .map_or_else(|| adt_def.is_enum(), |dtor| tcx.cross_crate_inlinable(dtor.ctor))
+            });
+        }
         if let ty::InstanceKind::ThreadLocalShim(..) = *self {
             return false;
         }

compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs

@@ -288,6 +288,7 @@ pub fn transform_instance<'tcx>(
     mut instance: Instance<'tcx>,
     options: TransformTyOptions,
 ) -> Instance<'tcx> {
+    // FIXME: account for async-drop-glue
     if (matches!(instance.def, ty::InstanceKind::Virtual(..))
         && tcx.is_lang_item(instance.def_id(), LangItem::DropInPlace))
         || matches!(instance.def, ty::InstanceKind::DropGlue(..))