Emit either mono item of Drop::drop or Drop::pin_drop depending on which was implemented

Author: frank-king

compiler/rustc_mir_transform/src/elaborate_drop.rs

@@ -9,6 +9,7 @@ use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, GenericArg, GenericArgsRef, Ty, TyCtxt, Unnormalized};
 use rustc_middle::{bug, span_bug, traits};
+use rustc_span::symbol::sym;
 use rustc_span::{DUMMY_SP, Spanned, dummy_spanned};
 use tracing::{debug, instrument};
 
@@ -999,22 +1000,51 @@ where
         debug!("destructor_call_block_sync({:?}, {:?})", self, succ);
         let tcx = self.tcx();
         let drop_trait = tcx.require_lang_item(LangItem::Drop, DUMMY_SP);
-        let drop_fn = tcx.associated_item_def_ids(drop_trait)[0];
+        let mut drop_fn = tcx.associated_item_def_ids(drop_trait)[0];
         let ty = self.place_ty(self.place);
 
         let ref_ty = Ty::new_mut_ref(tcx, tcx.lifetimes.re_erased, ty);
         let ref_place = self.new_temp(ref_ty);
         let unit_temp = Place::from(self.new_temp(tcx.types.unit));
 
-        let result = BasicBlockData::new_stmts(
-            vec![self.assign(
-                Place::from(ref_place),
-                Rvalue::Ref(
-                    tcx.lifetimes.re_erased,
-                    BorrowKind::Mut { kind: MutBorrowKind::Default },
-                    self.place,
+        let mut arg_place = ref_place;
+
+        let mut stmts = vec![self.assign(
+            Place::from(ref_place),
+            Rvalue::Ref(
+                tcx.lifetimes.re_erased,
+                BorrowKind::Mut { kind: MutBorrowKind::Default },
+                self.place,
+            ),
+        )];
+
+        // When the type implements `Drop::pin_drop`, we call it directly instead of `Drop::drop`.
+        if let Some(adt) = ty.ty_adt_def()
+            && let Some(dtor) = adt.destructor(tcx)
+            && tcx.item_name(dtor.did) == sym::pin_drop
+        {
+            debug!("call `pin_drop` for {adt:?}");
+            let pin_ref_ty = Ty::new_pinned_ref(tcx, tcx.lifetimes.re_erased, ty, Mutability::Mut);
+            let pin_ref_place = self.new_temp(pin_ref_ty);
+            stmts.push(self.assign(
+                Place::from(pin_ref_place),
+                Rvalue::Aggregate(
+                    Box::new(AggregateKind::Adt(
+                        tcx.require_lang_item(LangItem::Pin, DUMMY_SP),
+                        VariantIdx::ZERO,
+                        tcx.mk_args(&[ref_ty.into()]),
+                        None,
+                        None,
+                    )),
+                    [Operand::Move(Place::from(ref_place))].into(),
                 ),
-            )],
+            ));
+            drop_fn = tcx.associated_item_def_ids(drop_trait)[1];
+            arg_place = pin_ref_place;
+        }
+
+        let result = BasicBlockData::new_stmts(
+            stmts,
             Some(Terminator {
                 kind: TerminatorKind::Call {
                     func: Operand::function_handle(
@@ -1023,7 +1053,7 @@ where
                         [ty.into()],
                         self.source_info.span,
                     ),
-                    args: [Spanned { node: Operand::Move(Place::from(ref_place)), span: DUMMY_SP }]
+                    args: [Spanned { node: Operand::Move(Place::from(arg_place)), span: DUMMY_SP }]
                         .into(),
                     destination: unit_temp,
                     target: Some(succ),

compiler/rustc_monomorphize/src/collector.rs

@@ -1062,6 +1062,15 @@ fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) ->
         tcx.dcx().delayed_bug("attempt to codegen `#[rustc_force_inline]` item");
     }
 
+    // It is not possible to manually call `Drop::drop` and `Drop::pin_drop`, so we can
+    // skip codegen for mentioned associated items of the `Drop` trait, and only codegen
+    // `drop` or `pin_drop` depending on which was implemented.
+    if let Some(trait_id) = tcx.trait_of_assoc(def_id)
+        && tcx.is_lang_item(trait_id, LangItem::Drop)
+    {
+        return false;
+    }
+
     if def_id.is_local() {
         // Local items cannot be referred to locally without monomorphizing them locally.
         return true;

tests/codegen-units/item-collection/drop-glue-eager.rs

@@ -10,7 +10,6 @@ struct StructWithDrop {
 
 impl Drop for StructWithDrop {
     //~ MONO_ITEM fn <StructWithDrop as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <StructWithDrop as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 
@@ -25,7 +24,6 @@ enum EnumWithDrop {
 
 impl Drop for EnumWithDrop {
     //~ MONO_ITEM fn <EnumWithDrop as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <EnumWithDrop as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 
@@ -36,7 +34,6 @@ enum EnumNoDrop {
 // We should be able to monomorphize drops for struct with lifetimes.
 impl<'a> Drop for StructWithDropAndLt<'a> {
     //~ MONO_ITEM fn <StructWithDropAndLt<'_> as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <StructWithDropAndLt<'_> as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 
@@ -55,6 +52,5 @@ struct StructWithLtAndPredicate<'a: 'a> {
 // We should be able to monomorphize drops for struct with lifetimes.
 impl<'a> Drop for StructWithLtAndPredicate<'a> {
     //~ MONO_ITEM fn <StructWithLtAndPredicate<'_> as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <StructWithLtAndPredicate<'_> as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }

tests/codegen-units/item-collection/drop_in_place_intrinsic.rs

@@ -9,7 +9,6 @@ struct StructWithDtor(u32);
 
 impl Drop for StructWithDtor {
     //~ MONO_ITEM fn <StructWithDtor as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <StructWithDtor as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 //~ MONO_ITEM fn start

tests/codegen-units/item-collection/generic-drop-glue.rs

@@ -39,7 +39,6 @@ struct NonGenericWithDrop(#[allow(dead_code)] i32);
 
 impl Drop for NonGenericWithDrop {
     //~ MONO_ITEM fn <NonGenericWithDrop as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <NonGenericWithDrop as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 

tests/codegen-units/item-collection/non-generic-closures.rs

@@ -74,6 +74,5 @@ struct PresentDrop;
 
 impl Drop for PresentDrop {
     //~ MONO_ITEM fn <PresentDrop as std::ops::Drop>::drop @@ non_generic_closures-cgu.0[External]
-    //~ MONO_ITEM fn <PresentDrop as std::ops::Drop>::pin_drop @@ non_generic_closures-cgu.0[External]
     fn drop(&mut self) {}
 }

tests/codegen-units/item-collection/non-generic-drop-glue.rs

@@ -11,7 +11,6 @@ struct StructWithDrop {
 
 impl Drop for StructWithDrop {
     //~ MONO_ITEM fn <StructWithDrop as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <StructWithDrop as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 
@@ -26,7 +25,6 @@ enum EnumWithDrop {
 
 impl Drop for EnumWithDrop {
     //~ MONO_ITEM fn <EnumWithDrop as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <EnumWithDrop as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 

tests/codegen-units/item-collection/pin-drop.rs

@@ -0,0 +1,41 @@
+#![feature(pin_ergonomics)]
+// Ensure that we emit either `Drop::drop` or `Drop::pin_drop` for types that implement `Drop`.
+
+//@ compile-flags:-Clink-dead-code
+//@ compile-flags:--crate-type=lib
+//@ rustc-env:MONO_TEST=1
+
+//~ MONO_ITEM fn std::ptr::drop_glue::<StructWithDrop> - shim(Some(StructWithDrop))
+struct StructWithDrop {
+    x: i32,
+}
+
+impl Drop for StructWithDrop {
+    //~ MONO_ITEM fn <StructWithDrop as std::ops::Drop>::drop
+    fn drop(&mut self) {}
+}
+
+struct StructNoDrop {
+    x: i32,
+}
+
+//~ MONO_ITEM fn std::ptr::drop_glue::<StructWithPinDrop> - shim(Some(StructWithPinDrop))
+struct StructWithPinDrop {
+    x: i32,
+}
+
+impl Drop for StructWithPinDrop {
+    //~ MONO_ITEM fn <StructWithPinDrop as std::ops::Drop>::pin_drop
+    fn pin_drop(&pin mut self) {}
+}
+
+//~ MONO_ITEM fn std::ptr::drop_glue::<StructPinV2WithPinDrop> - shim(Some(StructPinV2WithPinDrop))
+#[pin_v2]
+struct StructPinV2WithPinDrop {
+    x: i32,
+}
+
+impl Drop for StructPinV2WithPinDrop {
+    //~ MONO_ITEM fn <StructPinV2WithPinDrop as std::ops::Drop>::pin_drop
+    fn pin_drop(&pin mut self) {}
+}

tests/codegen-units/item-collection/transitive-drop-glue.rs

@@ -13,7 +13,6 @@ struct Leaf;
 
 impl Drop for Leaf {
     //~ MONO_ITEM fn <Leaf as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <Leaf as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }
 

tests/codegen-units/item-collection/tuple-drop-glue.rs

@@ -9,7 +9,6 @@ struct Dropped;
 
 impl Drop for Dropped {
     //~ MONO_ITEM fn <Dropped as std::ops::Drop>::drop
-    //~ MONO_ITEM fn <Dropped as std::ops::Drop>::pin_drop
     fn drop(&mut self) {}
 }