Add docs, remove code, change subtyper code

ouz-a · Mark-Simulacrum · commit caab4b7d9455 · 2023-12-04T09:55:14.000-05:00
diff --git a/compiler/rustc_borrowck/src/diagnostics/mod.rs b/compiler/rustc_borrowck/src/diagnostics/mod.rs
@@ -318,13 +318,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             PlaceRef { local, projection: [proj_base @ .., elem] } => match elem {
                 ProjectionElem::Deref
                 | ProjectionElem::Index(..)
-                | ProjectionElem::Subtype(..)
                 | ProjectionElem::ConstantIndex { .. }
                 | ProjectionElem::Subslice { .. } => {
                     PlaceRef { local, projection: proj_base }.ty(self.body, self.infcx.tcx)
                 }
                 ProjectionElem::Downcast(..) => place.ty(self.body, self.infcx.tcx),
-                ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(*ty),
+                ProjectionElem::Subtype(ty) | ProjectionElem::OpaqueCast(ty) => {
+                    PlaceTy::from_ty(*ty)
+                }
                 ProjectionElem::Field(_, field_type) => PlaceTy::from_ty(*field_type),
             },
         };
diff --git a/compiler/rustc_borrowck/src/places_conflict.rs b/compiler/rustc_borrowck/src/places_conflict.rs
@@ -243,13 +243,13 @@ fn place_components_conflict<'tcx>(
                 }
 
                 (ProjectionElem::Deref, _, Deep)
-                | (ProjectionElem::Subtype(_), _, _)
                 | (ProjectionElem::Deref, _, AccessDepth::Drop)
                 | (ProjectionElem::Field { .. }, _, _)
                 | (ProjectionElem::Index { .. }, _, _)
                 | (ProjectionElem::ConstantIndex { .. }, _, _)
                 | (ProjectionElem::Subslice { .. }, _, _)
                 | (ProjectionElem::OpaqueCast { .. }, _, _)
+                | (ProjectionElem::Subtype(_), _, _)
                 | (ProjectionElem::Downcast { .. }, _, _) => {
                     // Recursive case. This can still be disjoint on a
                     // further iteration if this a shallow access and
@@ -360,7 +360,6 @@ fn place_projection_conflict<'tcx>(
         (
             ProjectionElem::Index(..),
             ProjectionElem::Index(..)
-            | ProjectionElem::Subtype(..)
             | ProjectionElem::ConstantIndex { .. }
             | ProjectionElem::Subslice { .. },
         )
@@ -505,12 +504,12 @@ fn place_projection_conflict<'tcx>(
             debug!("place_element_conflict: DISJOINT-OR-EQ-SLICE-SUBSLICES");
             Overlap::EqualOrDisjoint
         }
-        (ProjectionElem::Subtype(_), _) => Overlap::EqualOrDisjoint,
         (
             ProjectionElem::Deref
             | ProjectionElem::Field(..)
             | ProjectionElem::Index(..)
             | ProjectionElem::ConstantIndex { .. }
+            | ProjectionElem::Subtype(_)
             | ProjectionElem::OpaqueCast { .. }
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Downcast(..),
diff --git a/compiler/rustc_borrowck/src/prefixes.rs b/compiler/rustc_borrowck/src/prefixes.rs
@@ -89,7 +89,9 @@ impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {
                             cursor = cursor_base;
                             continue 'cursor;
                         }
-                        ProjectionElem::Subtype(..) => continue 'cursor,
+                        ProjectionElem::Subtype(..) => {
+                            panic!("Subtype projection is not allowed before borrow check")
+                        }
                         ProjectionElem::Deref => {
                             // (handled below)
                         }
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -621,7 +621,6 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                     span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
                 }))
             }
-            ProjectionElem::Subtype(ty) => PlaceTy::from_ty(ty),
             ProjectionElem::Index(i) => {
                 let index_ty = Place::from(i).ty(self.body(), tcx).ty;
                 if index_ty != tcx.types.usize {
@@ -717,6 +716,14 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 }
                 PlaceTy::from_ty(fty)
             }
+            ProjectionElem::Subtype(_) => {
+                let guard = span_mirbug_and_err!(
+                    self,
+                    place,
+                    "ProjectionElem::Subtype shouldn't exist in borrowck"
+                );
+                PlaceTy::from_ty(Ty::new_error(tcx, guard))
+            }
             ProjectionElem::OpaqueCast(ty) => {
                 let ty = self.sanitize_type(place, ty);
                 let ty = self.cx.normalize(ty, location);
diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -872,13 +872,11 @@ pub(crate) fn codegen_place<'tcx>(
 
     for elem in place.projection {
         match elem {
-            PlaceElem::Subtype(_) => {
-                continue;
-            }
             PlaceElem::Deref => {
                 cplace = cplace.place_deref(fx);
             }
             PlaceElem::OpaqueCast(ty) => bug!("encountered OpaqueCast({ty}) in codegen"),
+            PlaceElem::Subtype(ty) => cplace = cplace.place_transmute_type(fx, ty),
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }
diff --git a/compiler/rustc_codegen_cranelift/src/value_and_place.rs b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
@@ -674,6 +674,14 @@ impl<'tcx> CPlace<'tcx> {
         }
     }
 
+    pub(crate) fn place_transmute_type(
+        self,
+        fx: &mut FunctionCx<'_, '_, 'tcx>,
+        ty: Ty<'tcx>,
+    ) -> CPlace<'tcx> {
+        CPlace { inner: self.inner, layout: fx.layout_of(fx.monomorphize(ty)) }
+    }
+
     pub(crate) fn place_field(
         self,
         fx: &mut FunctionCx<'_, '_, 'tcx>,
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
@@ -466,6 +466,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 mir::ProjectionElem::OpaqueCast(ty) => {
                     bug!("encountered OpaqueCast({ty}) in codegen")
                 }
+                mir::ProjectionElem::Subtype(ty) => cg_base.project_type(bx, self.monomorphize(ty)),
                 mir::ProjectionElem::Index(index) => {
                     let index = &mir::Operand::Copy(mir::Place::from(index));
                     let index = self.codegen_operand(bx, index);
@@ -499,7 +500,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     subslice
                 }
                 mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),
-                mir::ProjectionElem::Subtype(_) => continue,
             };
         }
         debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -665,9 +665,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let mut op = self.local_to_op(self.frame(), mir_place.local, layout)?;
         // Using `try_fold` turned out to be bad for performance, hence the loop.
         for elem in mir_place.projection.iter() {
-            if elem.is_subtype() {
-                continue;
-            }
             op = self.project(&op, elem)?
         }
 
diff --git a/compiler/rustc_const_eval/src/interpret/projection.rs b/compiler/rustc_const_eval/src/interpret/projection.rs
@@ -319,6 +319,8 @@ where
             OpaqueCast(ty) => {
                 span_bug!(self.cur_span(), "OpaqueCast({ty}) encountered after borrowck")
             }
+            // We don't want anything happening here, this is here as a dummy.
+            Subtype(_) => base.transmute(base.layout(), self)?,
             Field(field, _) => self.project_field(base, field.index())?,
             Downcast(_, variant) => self.project_downcast(base, variant)?,
             Deref => self.deref_pointer(&base.to_op(self)?)?.into(),
@@ -332,7 +334,6 @@ where
                 self.project_constant_index(base, offset, min_length, from_end)?
             }
             Subslice { from, to, from_end } => self.project_subslice(base, from, to, from_end)?,
-            Subtype(ty) => base.transmute(self.layout_of(ty)?, self)?,
         })
     }
 }
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -16,6 +16,8 @@ use rustc_target::spec::abi::Abi;
 
 use crate::util::is_within_packed;
 
+use crate::util::is_subtype;
+
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 enum EdgeKind {
     Unwind,
@@ -602,35 +604,12 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             return true;
         }
 
-        crate::util::is_subtype(self.tcx, self.param_env, src, dest)
+        return crate::util::is_subtype(self.tcx, self.param_env, src, dest);
     }
 }
 
 impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
     fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
-        match operand {
-            Operand::Copy(place) | Operand::Move(place) => {
-                if let Some(stmt) = self.body.stmt_at(location).left() {
-                    match &stmt.kind {
-                        StatementKind::Assign(box (lval, rvalue)) => {
-                            let place_ty = place.ty(&self.body.local_decls, self.tcx).ty;
-                            let lval_ty = lval.ty(&self.body.local_decls, self.tcx).ty;
-
-                            if !place.is_subtype()
-                                && place_ty != lval_ty
-                                && rvalue.ty(&self.body.local_decls, self.tcx) != lval_ty
-                                && (rvalue.ty(&self.body.local_decls, self.tcx).is_closure()
-                                    != lval_ty.is_closure())
-                            {
-                                self.fail(location, format!("Subtyping is not allowed between types {place_ty:#?} and {lval_ty:#?}"))
-                            }
-                        }
-                        _ => (),
-                    }
-                }
-            }
-            _ => (),
-        }
         // This check is somewhat expensive, so only run it when -Zvalidate-mir is passed.
         if self.tcx.sess.opts.unstable_opts.validate_mir
             && self.mir_phase < MirPhase::Runtime(RuntimePhase::Initial)
@@ -776,6 +755,22 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     }
                 }
             }
+            ProjectionElem::Subtype(ty) => {
+                if !is_subtype(
+                    self.tcx,
+                    self.param_env,
+                    ty,
+                    place_ref.ty(&self.body.local_decls, self.tcx).ty,
+                ) {
+                    self.fail(
+                        location,
+                        format!(
+                            "Failed subtyping {ty:#?} and {:#?}",
+                            place_ref.ty(&self.body.local_decls, self.tcx).ty
+                        ),
+                    )
+                }
+            }
             _ => {}
         }
         self.super_projection_elem(place_ref, elem, context, location);
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
@@ -1103,6 +1103,7 @@ fn pre_fmt_projection(projection: &[PlaceElem<'_>], fmt: &mut Formatter<'_>) ->
     for &elem in projection.iter().rev() {
         match elem {
             ProjectionElem::OpaqueCast(_)
+            | ProjectionElem::Subtype(_)
             | ProjectionElem::Downcast(_, _)
             | ProjectionElem::Field(_, _) => {
                 write!(fmt, "(").unwrap();
@@ -1125,6 +1126,9 @@ fn post_fmt_projection(projection: &[PlaceElem<'_>], fmt: &mut Formatter<'_>) ->
             ProjectionElem::OpaqueCast(ty) => {
                 write!(fmt, " as {ty})")?;
             }
+            ProjectionElem::Subtype(ty) => {
+                write!(fmt, "as {ty})")?;
+            }
             ProjectionElem::Downcast(Some(name), _index) => {
                 write!(fmt, " as {name})")?;
             }
diff --git a/compiler/rustc_middle/src/mir/statement.rs b/compiler/rustc_middle/src/mir/statement.rs
@@ -57,6 +57,7 @@ impl<V, T> ProjectionElem<V, T> {
             Self::Field(_, _)
             | Self::Index(_)
             | Self::OpaqueCast(_)
+            | Self::Subtype(_)
             | Self::ConstantIndex { .. }
             | Self::Subslice { .. }
             | Self::Downcast(_, _) => false,
@@ -70,6 +71,7 @@ impl<V, T> ProjectionElem<V, T> {
             Self::Deref | Self::Index(_) => false,
             Self::Field(_, _)
             | Self::OpaqueCast(_)
+            | Self::Subtype(_)
             | Self::ConstantIndex { .. }
             | Self::Subslice { .. }
             | Self::Downcast(_, _) => true,
@@ -95,6 +97,7 @@ impl<V, T> ProjectionElem<V, T> {
             | Self::Field(_, _) => true,
             Self::ConstantIndex { from_end: true, .. }
             | Self::Index(_)
+            | Self::Subtype(_)
             | Self::OpaqueCast(_)
             | Self::Subslice { .. } => false,
         }
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
@@ -1076,6 +1076,13 @@ pub enum ProjectionElem<V, T> {
     /// requiring an intermediate variable.
     OpaqueCast(T),
 
+    /// A `Subtype(T)` projection is applied to any `StatementKind::Assign` where
+    /// type of lvalue doesn't match type of rvalue, primary goal being making subtyping
+    /// explicit during optimizations and codegen.
+    ///
+    /// This goal is achieved with mir_transform pass `Subtyper`, which runs right after
+    /// borrowchecker, as we only care about subtyping that can affect trait selection and
+    /// `TypeId`.
     Subtype(T),
 }
 
diff --git a/compiler/rustc_middle/src/mir/visit.rs b/compiler/rustc_middle/src/mir/visit.rs
@@ -1109,8 +1109,12 @@ macro_rules! visit_place_fns {
                     self.visit_ty(&mut new_ty, TyContext::Location(location));
                     if ty != new_ty { Some(PlaceElem::OpaqueCast(new_ty)) } else { None }
                 }
+                PlaceElem::Subtype(ty) => {
+                    let mut new_ty = ty;
+                    self.visit_ty(&mut new_ty, TyContext::Location(location));
+                    if ty != new_ty { Some(PlaceElem::Subtype(new_ty)) } else { None }
+                }
                 PlaceElem::Deref
-                | PlaceElem::Subtype { .. }
                 | PlaceElem::ConstantIndex { .. }
                 | PlaceElem::Subslice { .. }
                 | PlaceElem::Downcast(..) => None,
diff --git a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs b/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
@@ -112,9 +112,8 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
         let mut union_path = None;
 
         for (place_ref, elem) in data.rev_lookup.un_derefer.iter_projections(place.as_ref()) {
-            if elem.is_subtype() {
-                continue;
-            }
+            // We don't care creating `MovePath` for `ProjectionElem::Subtype(T)` because it's for debugging/validating
+            // purposes it's movement doesn't affect anything.
             let body = self.builder.body;
             let tcx = self.builder.tcx;
             let place_ty = place_ref.ty(body, tcx).ty;
@@ -233,7 +232,9 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
                 // `OpaqueCast` only transmutes the type, so no moves there and
                 // `Downcast` only changes information about a `Place` without moving
                 // So it's safe to skip these.
-                ProjectionElem::OpaqueCast(_) | ProjectionElem::Downcast(_, _) => (),
+                ProjectionElem::OpaqueCast(_)
+                | ProjectionElem::Subtype(_)
+                | ProjectionElem::Downcast(_, _) => (),
             }
             if union_path.is_none() {
                 // inlined from add_move_path because of a borrowck conflict with the iterator
diff --git a/compiler/rustc_mir_transform/src/add_subtyping_projections.rs b/compiler/rustc_mir_transform/src/add_subtyping_projections.rs
@@ -7,13 +7,13 @@ use rustc_middle::ty::TyCtxt;
 
 pub struct Subtyper;
 
-pub struct SubTypeCheker<'a, 'tcx> {
+pub struct SubTypeChecker<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
     patcher: MirPatch<'tcx>,
     local_decls: &'a IndexVec<Local, LocalDecl<'tcx>>,
 }
 
-impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeCheker<'a, 'tcx> {
+impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeChecker<'a, 'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
@@ -25,28 +25,30 @@ impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeCheker<'a, 'tcx> {
         location: Location,
     ) {
         let place_ty = place.ty(self.local_decls, self.tcx);
-        let rval_ty = rvalue.ty(self.local_decls, self.tcx);
+        let mut rval_ty = rvalue.ty(self.local_decls, self.tcx);
         if place_ty.ty != rval_ty {
+            // Not erasing this causes `Free Regions` errors in validator,
+            // when rval is `ReStatic`.
+            rval_ty = self.tcx.erase_regions_ty(rval_ty);
             let temp = self
                 .patcher
                 .new_temp(rval_ty, self.local_decls[place.as_ref().local].source_info.span);
-            let new_place =
-                Place::from(temp).project_deeper(&[ProjectionElem::Subtype(place_ty.ty)], self.tcx);
+            let new_place = Place::from(temp);
             self.patcher.add_assign(location, new_place, rvalue.clone());
-            let new_rval = Rvalue::Use(Operand::Move(new_place));
-            *rvalue = new_rval;
+            let subtyped =
+                new_place.project_deeper(&[ProjectionElem::Subtype(place_ty.ty)], self.tcx);
+            *rvalue = Rvalue::Use(Operand::Move(subtyped));
         }
     }
 }
 
 pub fn subtype_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let patch = MirPatch::new(body);
-    let mut checker = SubTypeCheker { tcx, patcher: patch, local_decls: &body.local_decls };
+    let mut checker = SubTypeChecker { tcx, patcher: patch, local_decls: &body.local_decls };
 
     for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
         checker.visit_basic_block_data(bb, data);
     }
-
     checker.patcher.apply(body);
 }
 
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
@@ -306,6 +306,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 }
                 ProjectionElem::Downcast(name, index) => ProjectionElem::Downcast(name, index),
                 ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty),
+                ProjectionElem::Subtype(ty) => ProjectionElem::Subtype(ty),
             };
             value = self.insert(Value::Projection(value, proj));
         }
diff --git a/tabula.rs b/tabula.rs
@@ -0,0 +1,14 @@
+// run-pass
+#![deny(drop_bounds)]
+// As a special exemption, `impl Drop` in the return position raises no error.
+// This allows a convenient way to return an unnamed drop guard.
+fn voldemort_type() -> impl Drop {
+    struct Voldemort;
+    impl Drop for Voldemort {
+        fn drop(&mut self) {}
+    }
+    Voldemort
+}
+fn main() {
+    let _ = voldemort_type();
+}
diff --git a/tests/mir-opt/inline/inline_generator.main.Inline.panic-abort.diff b/tests/mir-opt/inline/inline_generator.main.Inline.panic-abort.diff
diff --git a/tests/mir-opt/inline/inline_generator.main.Inline.panic-unwind.diff b/tests/mir-opt/inline/inline_generator.main.Inline.panic-unwind.diff
diff --git a/tests/mir-opt/mir_subtyping.main.Subtyper.diff b/tests/mir-opt/mir_subtyping.main.Subtyper.diff
diff --git a/tests/mir-opt/mir_subtyping.rs b/tests/mir-opt/mir_subtyping.rs
diff --git a/tests/mir-opt/retag.main.SimplifyCfg-elaborate-drops.after.panic-abort.mir b/tests/mir-opt/retag.main.SimplifyCfg-elaborate-drops.after.panic-abort.mir
diff --git a/tests/mir-opt/retag.main.SimplifyCfg-elaborate-drops.after.panic-unwind.mir b/tests/mir-opt/retag.main.SimplifyCfg-elaborate-drops.after.panic-unwind.mir

Original file line number	Diff line number	Diff line change
`@@ -89,7 +89,9 @@ impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {`
`89`	`89`	`cursor = cursor_base;`
`90`	`90`	`continue 'cursor;`
`91`	`91`	`}`
`92`		`- ProjectionElem::Subtype(..) => continue 'cursor,`
	`92`	`+ ProjectionElem::Subtype(..) => {`
	`93`	`+ panic!("Subtype projection is not allowed before borrow check")`
	`94`	`+ }`
`93`	`95`	`ProjectionElem::Deref => {`
`94`	`96`	`// (handled below)`
`95`	`97`	`}`
Original file line number	Diff line number	Diff line change
`@@ -872,13 +872,11 @@ pub(crate) fn codegen_place<'tcx>(`
`872`	`872`
`873`	`873`	`for elem in place.projection {`
`874`	`874`	`match elem {`
`875`		`- PlaceElem::Subtype(_) => {`
`876`		`- continue;`
`877`		`- }`
`878`	`875`	`PlaceElem::Deref => {`
`879`	`876`	`cplace = cplace.place_deref(fx);`
`880`	`877`	`}`
`881`	`878`	`PlaceElem::OpaqueCast(ty) => bug!("encountered OpaqueCast({ty}) in codegen"),`
	`879`	`+ PlaceElem::Subtype(ty) => cplace = cplace.place_transmute_type(fx, ty),`
`882`	`880`	`PlaceElem::Field(field, _ty) => {`
`883`	`881`	`cplace = cplace.place_field(fx, field);`
`884`	`882`	`}`
Original file line number	Diff line number	Diff line change
`@@ -674,6 +674,14 @@ impl<'tcx> CPlace<'tcx> {`
`674`	`674`	`}`
`675`	`675`	`}`
`676`	`676`
	`677`	`+ pub(crate) fn place_transmute_type(`
	`678`	`+ self,`
	`679`	`+ fx: &mut FunctionCx<'_, '_, 'tcx>,`
	`680`	`+ ty: Ty<'tcx>,`
	`681`	`+ ) -> CPlace<'tcx> {`
	`682`	`+ CPlace { inner: self.inner, layout: fx.layout_of(fx.monomorphize(ty)) }`
	`683`	`+ }`
	`684`	`+`
`677`	`685`	`pub(crate) fn place_field(`
`678`	`686`	`self,`
`679`	`687`	`fx: &mut FunctionCx<'_, '_, 'tcx>,`
Original file line number	Diff line number	Diff line change
`@@ -466,6 +466,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {`
`466`	`466`	`mir::ProjectionElem::OpaqueCast(ty) => {`
`467`	`467`	`bug!("encountered OpaqueCast({ty}) in codegen")`
`468`	`468`	`}`
	`469`	`+ mir::ProjectionElem::Subtype(ty) => cg_base.project_type(bx, self.monomorphize(ty)),`
`469`	`470`	`mir::ProjectionElem::Index(index) => {`
`470`	`471`	`let index = &mir::Operand::Copy(mir::Place::from(index));`
`471`	`472`	`let index = self.codegen_operand(bx, index);`
`@@ -499,7 +500,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {`
`499`	`500`	`subslice`
`500`	`501`	`}`
`501`	`502`	`mir::ProjectionElem::Downcast(_, v) => cg_base.project_downcast(bx, v),`
`502`		`- mir::ProjectionElem::Subtype(_) => continue,`
`503`	`503`	`};`
`504`	`504`	`}`
`505`	`505`	`debug!("codegen_place(place={:?}) => {:?}", place_ref, cg_base);`
Original file line number	Diff line number	Diff line change
`@@ -665,9 +665,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {`
`665`	`665`	`let mut op = self.local_to_op(self.frame(), mir_place.local, layout)?;`
`666`	`666`	// Using `try_fold` turned out to be bad for performance, hence the loop.
`667`	`667`	`for elem in mir_place.projection.iter() {`
`668`		`- if elem.is_subtype() {`
`669`		`- continue;`
`670`		`- }`
`671`	`668`	`op = self.project(&op, elem)?`
`672`	`669`	`}`
`673`	`670`
Original file line number	Diff line number	Diff line change
`@@ -319,6 +319,8 @@ where`
`319`	`319`	`OpaqueCast(ty) => {`
`320`	`320`	`span_bug!(self.cur_span(), "OpaqueCast({ty}) encountered after borrowck")`
`321`	`321`	`}`
	`322`	`+ // We don't want anything happening here, this is here as a dummy.`
	`323`	`+ Subtype(_) => base.transmute(base.layout(), self)?,`
`322`	`324`	`Field(field, _) => self.project_field(base, field.index())?,`
`323`	`325`	`Downcast(_, variant) => self.project_downcast(base, variant)?,`
`324`	`326`	`Deref => self.deref_pointer(&base.to_op(self)?)?.into(),`
`@@ -332,7 +334,6 @@ where`
`332`	`334`	`self.project_constant_index(base, offset, min_length, from_end)?`
`333`	`335`	`}`
`334`	`336`	`Subslice { from, to, from_end } => self.project_subslice(base, from, to, from_end)?,`
`335`		`- Subtype(ty) => base.transmute(self.layout_of(ty)?, self)?,`
`336`	`337`	`})`
`337`	`338`	`}`
`338`	`339`	`}`