Rollup of 9 pull requests

compiler/rustc_borrowck/src/invalidation.rs

@@ -289,6 +289,10 @@ impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
             | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
                 self.consume_operand(location, operand)
             }
+            Rvalue::VirtualRef(ref place) => {
+                let op = &Operand::Copy(*place);
+                self.consume_operand(location, op);
+            }
 
             Rvalue::Len(place) | Rvalue::Discriminant(place) => {
                 let af = match *rvalue {

compiler/rustc_borrowck/src/lib.rs

@@ -1224,6 +1224,23 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             | Rvalue::ShallowInitBox(ref operand, _ /*ty*/) => {
                 self.consume_operand(location, (operand, span), flow_state)
             }
+            Rvalue::VirtualRef(place) => {
+                self.access_place(
+                    location,
+                    (place, span),
+                    (Deep, Read(ReadKind::Copy)),
+                    LocalMutationIsAllowed::No,
+                    flow_state,
+                );
+
+                // Finally, check if path was already moved.
+                self.check_if_path_or_subpath_is_moved(
+                    location,
+                    InitializationRequiringAction::Use,
+                    (place.as_ref(), span),
+                    flow_state,
+                );
+            }
 
             Rvalue::Len(place) | Rvalue::Discriminant(place) => {
                 let af = match *rvalue {

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -2278,6 +2278,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             Rvalue::Use(operand) | Rvalue::UnaryOp(_, operand) => {
                 self.check_operand(operand, location);
             }
+            Rvalue::VirtualRef(place) => {
+                let op = &Operand::Copy(*place);
+                self.check_operand(op, location);
+            }
 
             Rvalue::BinaryOp(_, box (left, right))
             | Rvalue::CheckedBinaryOp(_, box (left, right)) => {
@@ -2308,6 +2312,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             | Rvalue::BinaryOp(..)
             | Rvalue::CheckedBinaryOp(..)
             | Rvalue::NullaryOp(..)
+            | Rvalue::VirtualRef(..)
             | Rvalue::UnaryOp(..)
             | Rvalue::Discriminant(..) => None,
 

compiler/rustc_codegen_cranelift/src/base.rs

@@ -503,6 +503,11 @@ fn codegen_stmt<'tcx>(
                     let val = codegen_operand(fx, operand);
                     lval.write_cvalue(fx, val);
                 }
+                Rvalue::VirtualRef(place) => {
+                    let cplace = codegen_place(fx, place);
+                    let val = cplace.to_cvalue(fx);
+                    lval.write_cvalue(fx, val)
+                }
                 Rvalue::Ref(_, _, place) | Rvalue::AddressOf(_, place) => {
                     let place = codegen_place(fx, place);
                     let ref_ = place.place_ref(fx, lval.layout());

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -8,6 +8,7 @@ use crate::traits::*;
 use crate::MemFlags;
 
 use rustc_middle::mir;
+use rustc_middle::mir::Operand;
 use rustc_middle::ty::cast::{CastTy, IntTy};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
@@ -401,6 +402,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 self.codegen_place_to_pointer(bx, place, mk_ref)
             }
 
+            mir::Rvalue::VirtualRef(place) => {
+                let operand = self.codegen_operand(&mut bx, &Operand::Copy(place));
+                (bx, operand)
+            }
             mir::Rvalue::AddressOf(mutability, place) => {
                 let mk_ptr = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
                     tcx.mk_ptr(ty::TypeAndMut { ty, mutbl: mutability })
@@ -755,6 +760,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     pub fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>, span: Span) -> bool {
         match *rvalue {
             mir::Rvalue::Ref(..) |
+            mir::Rvalue::VirtualRef(..) |
             mir::Rvalue::AddressOf(..) |
             mir::Rvalue::Len(..) |
             mir::Rvalue::Cast(..) | // (*)

compiler/rustc_const_eval/src/interpret/step.rs

@@ -172,6 +172,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 self.copy_op(&op, &dest)?;
             }
 
+            VirtualRef(ref place) => {
+                let op = self.eval_place_to_op(*place, Some(dest.layout))?;
+                self.copy_op(&op, &dest)?;
+            }
+
             BinaryOp(bin_op, box (ref left, ref right)) => {
                 let layout = binop_left_homogeneous(bin_op).then_some(dest.layout);
                 let left = self.read_immediate(&self.eval_operand(left, layout)?)?;

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -445,6 +445,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
             Rvalue::ThreadLocalRef(_) => self.check_op(ops::ThreadLocalAccess),
 
             Rvalue::Use(_)
+            | Rvalue::VirtualRef(..)
             | Rvalue::Repeat(..)
             | Rvalue::Discriminant(..)
             | Rvalue::Len(_)

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -260,6 +260,8 @@ where
             in_place::<Q, _>(cx, in_local, place.as_ref())
         }
 
+        Rvalue::VirtualRef(place) => in_place::<Q, _>(cx, in_local, place.as_ref()),
+
         Rvalue::Use(operand)
         | Rvalue::Repeat(operand, _)
         | Rvalue::UnaryOp(_, operand)

compiler/rustc_const_eval/src/transform/check_consts/resolver.rs

@@ -199,6 +199,7 @@ where
             mir::Rvalue::Cast(..)
             | mir::Rvalue::ShallowInitBox(..)
             | mir::Rvalue::Use(..)
+            | mir::Rvalue::VirtualRef(..)
             | mir::Rvalue::ThreadLocalRef(..)
             | mir::Rvalue::Repeat(..)
             | mir::Rvalue::Len(..)

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -494,6 +494,10 @@ impl<'tcx> Validator<'_, 'tcx> {
             Rvalue::Use(operand) | Rvalue::Repeat(operand, _) => {
                 self.validate_operand(operand)?;
             }
+            Rvalue::VirtualRef(place) => {
+                let op = &Operand::Copy(*place);
+                self.validate_operand(op)?
+            }
 
             Rvalue::Discriminant(place) | Rvalue::Len(place) => {
                 self.validate_place(place.as_ref())?

compiler/rustc_infer/src/infer/resolve.rs

@@ -92,7 +92,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticRegionResolver<'a, 'tcx> {
                     .borrow_mut()
                     .unwrap_region_constraints()
                     .opportunistic_resolve_var(rid);
-                self.tcx().reuse_or_mk_region(r, ty::ReVar(resolved))
+                TypeFolder::tcx(self).reuse_or_mk_region(r, ty::ReVar(resolved))
             }
             _ => r,
         }
@@ -179,15 +179,13 @@ struct FullTypeResolver<'a, 'tcx> {
     infcx: &'a InferCtxt<'a, 'tcx>,
 }
 
-impl<'a, 'tcx> TypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> {
+impl<'a, 'tcx> FallibleTypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> {
     type Error = FixupError<'tcx>;
 
     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
-}
 
-impl<'a, 'tcx> FallibleTypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> {
     fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
         if !t.needs_infer() {
             Ok(t) // micro-optimize -- if there is nothing in this type that this fold affects...

compiler/rustc_middle/src/mir/mod.rs

@@ -159,6 +159,8 @@ pub enum MirPhase {
     /// of the `mir_promoted` query), these promoted elements are available in the `promoted_mir`
     /// query.
     ConstsPromoted = 2,
+    /// After this projections may only contain deref projections as the first element.
+    Derefered = 3,
     /// Beginning with this phase, the following variants are disallowed:
     /// * [`TerminatorKind::DropAndReplace`](terminator::TerminatorKind::DropAndReplace)
     /// * [`TerminatorKind::FalseUnwind`](terminator::TerminatorKind::FalseUnwind)
@@ -173,9 +175,7 @@ pub enum MirPhase {
     /// Furthermore, `Drop` now uses explicit drop flags visible in the MIR and reaching a `Drop`
     /// terminator means that the auto-generated drop glue will be invoked. Also, `Copy` operands
     /// are allowed for non-`Copy` types.
-    DropsLowered = 3,
-    /// After this projections may only contain deref projections as the first element.
-    Derefered = 4,
+    DropsLowered = 4,
     /// Beginning with this phase, the following variant is disallowed:
     /// * [`Rvalue::Aggregate`] for any `AggregateKind` except `Array`
     ///
@@ -1174,6 +1174,15 @@ impl<'tcx> LocalDecl<'tcx> {
         }
     }
 
+    /// Returns `true` if this is a DerefTemp
+    pub fn is_deref_temp(&self) -> bool {
+        match self.local_info {
+            Some(box LocalInfo::DerefTemp) => return true,
+            _ => (),
+        }
+        return false;
+    }
+
     /// Returns `true` is the local is from a compiler desugaring, e.g.,
     /// `__next` from a `for` loop.
     #[inline]
@@ -2616,6 +2625,15 @@ pub enum Rvalue<'tcx> {
     /// initialized but its content as uninitialized. Like other pointer casts, this in general
     /// affects alias analysis.
     ShallowInitBox(Operand<'tcx>, Ty<'tcx>),
+
+    /// A virtual ref is equivalent to a read from a reference/pointer at the
+    /// codegen level, but is treated specially by drop elaboration. When such a read happens, it
+    /// is guaranteed that the only use of the returned value is a deref operation, immediately
+    /// followed by one or more projections. Drop elaboration treats this virtual ref as if the
+    /// read never happened and just projects further. This allows simplifying various MIR
+    /// optimizations and codegen backends that previously had to handle deref operations anywhere
+    /// in a place.
+    VirtualRef(Place<'tcx>),
 }
 
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
@@ -2632,6 +2650,7 @@ impl<'tcx> Rvalue<'tcx> {
             Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => false,
 
             Rvalue::Use(_)
+            | Rvalue::VirtualRef(_)
             | Rvalue::Repeat(_, _)
             | Rvalue::Ref(_, _, _)
             | Rvalue::ThreadLocalRef(_)
@@ -2809,6 +2828,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                 };
                 write!(fmt, "&{}{}{:?}", region, kind_str, place)
             }
+            VirtualRef(ref place) => write!(fmt, "virt {:#?}", place),
 
             AddressOf(mutability, ref place) => {
                 let kind_str = match mutability {

compiler/rustc_middle/src/mir/tcx.rs

@@ -211,6 +211,7 @@ impl<'tcx> Rvalue<'tcx> {
                 }
             },
             Rvalue::ShallowInitBox(_, ty) => tcx.mk_box(ty),
+            Rvalue::VirtualRef(ref place) => place.ty(local_decls, tcx).ty,
         }
     }
 

compiler/rustc_middle/src/mir/type_foldable.rs

@@ -184,6 +184,7 @@ impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
             Ref(region, bk, place) => {
                 Ref(region.try_fold_with(folder)?, bk, place.try_fold_with(folder)?)
             }
+            VirtualRef(place) => VirtualRef(place.try_fold_with(folder)?),
             AddressOf(mutability, place) => AddressOf(mutability, place.try_fold_with(folder)?),
             Len(place) => Len(place.try_fold_with(folder)?),
             Cast(kind, op, ty) => Cast(kind, op.try_fold_with(folder)?, ty.try_fold_with(folder)?),
@@ -235,6 +236,7 @@ impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
                 region.visit_with(visitor)?;
                 place.visit_with(visitor)
             }
+            VirtualRef(ref place) => place.visit_with(visitor),
             AddressOf(_, ref place) => place.visit_with(visitor),
             Len(ref place) => place.visit_with(visitor),
             Cast(_, ref op, ty) => {

compiler/rustc_middle/src/mir/visit.rs

@@ -670,6 +670,13 @@ macro_rules! make_mir_visitor {
                         };
                         self.visit_place(path, ctx, location);
                     }
+                    Rvalue::VirtualRef(place) => {
+                        self.visit_place(
+                            place,
+                            PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
+                            location
+                        );
+                    }
 
                     Rvalue::AddressOf(m, path) => {
                         let ctx = match m {

compiler/rustc_middle/src/traits/mod.rs

@@ -253,7 +253,7 @@ pub enum ObligationCauseCode<'tcx> {
     ObjectTypeBound(Ty<'tcx>, ty::Region<'tcx>),
 
     /// Obligation incurred due to an object cast.
-    ObjectCastObligation(/* Object type */ Ty<'tcx>),
+    ObjectCastObligation(/* Concrete type */ Ty<'tcx>, /* Object type */ Ty<'tcx>),
 
     /// Obligation incurred due to a coercion.
     Coercion {