Intern place projection

src/librustc/mir/mod.rs

@@ -15,8 +15,7 @@ use crate::ty::layout::VariantIdx;
 use crate::ty::print::{FmtPrinter, Printer};
 use crate::ty::subst::{Subst, SubstsRef};
 use crate::ty::{
-    self, AdtDef, CanonicalUserTypeAnnotations, Region, Ty, TyCtxt,
-    UserTypeAnnotationIndex,
+    self, AdtDef, CanonicalUserTypeAnnotations, List, Region, Ty, TyCtxt, UserTypeAnnotationIndex,
 };
 
 use polonius_engine::Atom;
@@ -1712,15 +1711,17 @@ impl Debug for Statement<'_> {
 /// A path to a value; something that can be evaluated without
 /// changing or disturbing program state.
 #[derive(
-    Clone, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable, HashStable,
+    Clone, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, HashStable,
 )]
 pub struct Place<'tcx> {
     pub base: PlaceBase<'tcx>,
 
     /// projection out of a place (access a field, deref a pointer, etc)
-    pub projection: Box<[PlaceElem<'tcx>]>,
+    pub projection: &'tcx List<PlaceElem<'tcx>>,
 }
 
+impl<'tcx> rustc_serialize::UseSpecializedDecodable for Place<'tcx> {}
+
 #[derive(
     Clone, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable, HashStable,
 )]
@@ -1848,50 +1849,56 @@ pub struct PlaceRef<'a, 'tcx> {
 }
 
 impl<'tcx> Place<'tcx> {
-    // FIXME change this back to a const when projection is a shared slice.
-    //
-    // pub const RETURN_PLACE: Place<'tcx> = Place {
-    //     base: PlaceBase::Local(RETURN_PLACE),
-    //     projection: &[],
-    // };
+    // FIXME change this to a const fn by also making List::empty a const fn.
     pub fn return_place() -> Place<'tcx> {
         Place {
             base: PlaceBase::Local(RETURN_PLACE),
-            projection: Box::new([]),
+            projection: List::empty(),
         }
     }
 
-    pub fn field(self, f: Field, ty: Ty<'tcx>) -> Place<'tcx> {
-        self.elem(ProjectionElem::Field(f, ty))
+    pub fn field(self, f: Field, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Place<'tcx> {
+        self.elem(ProjectionElem::Field(f, ty), tcx)
     }
 
-    pub fn deref(self) -> Place<'tcx> {
-        self.elem(ProjectionElem::Deref)
+    pub fn deref(self, tcx: TyCtxt<'tcx>) -> Place<'tcx> {
+        self.elem(ProjectionElem::Deref, tcx)
     }
 
-    pub fn downcast(self, adt_def: &'tcx AdtDef, variant_index: VariantIdx) -> Place<'tcx> {
-        self.elem(ProjectionElem::Downcast(
-            Some(adt_def.variants[variant_index].ident.name),
-            variant_index,
-        ))
+    pub fn downcast(
+        self,
+        adt_def: &'tcx AdtDef,
+        variant_index: VariantIdx,
+        tcx: TyCtxt<'tcx>,
+    ) -> Place<'tcx> {
+        self.elem(
+            ProjectionElem::Downcast(
+                Some(adt_def.variants[variant_index].ident.name),
+                variant_index,
+            ),
+            tcx,
+        )
     }
 
-    pub fn downcast_unnamed(self, variant_index: VariantIdx) -> Place<'tcx> {
-        self.elem(ProjectionElem::Downcast(None, variant_index))
+    pub fn downcast_unnamed(self, variant_index: VariantIdx, tcx: TyCtxt<'tcx>) -> Place<'tcx> {
+        self.elem(ProjectionElem::Downcast(None, variant_index), tcx)
     }
 
-    pub fn index(self, index: Local) -> Place<'tcx> {
-        self.elem(ProjectionElem::Index(index))
+    pub fn index(self, index: Local, tcx: TyCtxt<'tcx>) -> Place<'tcx> {
+        self.elem(ProjectionElem::Index(index), tcx)
     }
 
-    pub fn elem(self, elem: PlaceElem<'tcx>) -> Place<'tcx> {
-        // FIXME(spastorino): revisit this again once projection is not a Box<[T]> anymore
-        let mut projection = self.projection.into_vec();
+    /// This method copies `Place`'s projection, add an element and reintern it. Should not be used
+    /// to build a full `Place` it's just a convenient way to grab a projection and modify it in
+    /// flight.
+    // FIXME: It may be a better idea to move all these methods to `PlaceBuilder`
+    pub fn elem(self, elem: PlaceElem<'tcx>, tcx: TyCtxt<'tcx>) -> Place<'tcx> {
+        let mut projection = self.projection.to_vec();
         projection.push(elem);
 
         Place {
             base: self.base,
-            projection: projection.into_boxed_slice(),
+            projection: tcx.intern_place_elems(&projection),
         }
     }
 
@@ -1939,7 +1946,7 @@ impl From<Local> for Place<'_> {
     fn from(local: Local) -> Self {
         Place {
             base: local.into(),
-            projection: Box::new([]),
+            projection: List::empty(),
         }
     }
 }
@@ -3190,6 +3197,17 @@ impl<'tcx> TypeFoldable<'tcx> for PlaceBase<'tcx> {
     }
 }
 
+impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<PlaceElem<'tcx>> {
+    fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
+        let v = self.iter().map(|t| t.fold_with(folder)).collect::<Vec<_>>();
+        folder.tcx().intern_place_elems(&v)
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.iter().any(|t| t.visit_with(visitor))
+    }
+}
+
 impl<'tcx> TypeFoldable<'tcx> for Static<'tcx> {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
         Static {

src/librustc/mir/visit.rs

@@ -784,6 +784,8 @@ macro_rules! make_mir_visitor {
 
 macro_rules! visit_place_fns {
     (mut) => (
+        fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
+
         fn super_place(
             &mut self,
             place: &mut Place<'tcx>,
@@ -793,19 +795,21 @@ macro_rules! visit_place_fns {
             self.visit_place_base(&mut place.base, context, location);
 
             if let Some(new_projection) = self.process_projection(&place.projection) {
-                place.projection = new_projection;
+                place.projection = self.tcx().intern_place_elems(&new_projection);
             }
         }
 
         fn process_projection(
             &mut self,
             projection: &'a [PlaceElem<'tcx>],
-        ) -> Option<Box<[PlaceElem<'tcx>]>> {
+        ) -> Option<Vec<PlaceElem<'tcx>>> {
             let mut projection = Cow::Borrowed(projection);
 
             for i in 0..projection.len() {
                 if let Some(elem) = projection.get(i) {
                     if let Some(elem) = self.process_projection_elem(elem) {
+                        // This converts the borrowed projection into `Cow::Owned(_)` and returns a
+                        // clone of the projection so we can mutate and reintern later.
                         let vec = projection.to_mut();
                         vec[i] = elem;
                     }
@@ -814,7 +818,7 @@ macro_rules! visit_place_fns {
 
             match projection {
                 Cow::Borrowed(_) => None,
-                Cow::Owned(vec) => Some(vec.into_boxed_slice()),
+                Cow::Owned(vec) => Some(vec),
             }
         }
 

src/librustc/ty/codec.rs

@@ -13,9 +13,9 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_serialize::{Decodable, Decoder, Encoder, Encodable, opaque};
 use std::hash::Hash;
 use std::intrinsics;
-use crate::ty::{self, Ty, TyCtxt};
+use crate::ty::{self, List, Ty, TyCtxt};
 use crate::ty::subst::SubstsRef;
-use crate::mir::interpret::Allocation;
+use crate::mir::{self, interpret::Allocation};
 use syntax_pos::Span;
 
 /// The shorthand encoding uses an enum's variant index `usize`
@@ -218,6 +218,18 @@ where
     Ok(tcx.mk_substs((0..len).map(|_| Decodable::decode(decoder)))?)
 }
 
+#[inline]
+pub fn decode_place<D>(decoder: &mut D) -> Result<mir::Place<'tcx>, D::Error>
+where
+    D: TyDecoder<'tcx>,
+{
+    let base: mir::PlaceBase<'tcx> = Decodable::decode(decoder)?;
+    let len = decoder.read_usize()?;
+    let projection: &'tcx List<mir::PlaceElem<'tcx>> =
+        decoder.tcx().mk_place_elems((0..len).map(|_| Decodable::decode(decoder)))?;
+    Ok(mir::Place { base, projection })
+}
+
 #[inline]
 pub fn decode_region<D>(decoder: &mut D) -> Result<ty::Region<'tcx>, D::Error>
 where
@@ -413,6 +425,15 @@ macro_rules! implement_ty_decoder {
                 }
             }
 
+            impl<$($typaram),*> SpecializedDecoder<$crate::mir::Place<'tcx>>
+            for $DecoderName<$($typaram),*> {
+                fn specialized_decode(
+                    &mut self
+                ) -> Result<$crate::mir::Place<'tcx>, Self::Error> {
+                    decode_place(self)
+                }
+            }
+
             impl<$($typaram),*> SpecializedDecoder<ty::Region<'tcx>>
             for $DecoderName<$($typaram),*> {
                 fn specialized_decode(&mut self) -> Result<ty::Region<'tcx>, Self::Error> {

src/librustc/ty/context.rs

@@ -2711,6 +2711,11 @@ impl<'tcx> TyCtxt<'tcx> {
         iter.intern_with(|xs| self.intern_substs(xs))
     }
 
+    pub fn mk_place_elems<I: InternAs<[PlaceElem<'tcx>],
+                          &'tcx List<PlaceElem<'tcx>>>>(self, iter: I) -> I::Output {
+        iter.intern_with(|xs| self.intern_place_elems(xs))
+    }
+
     pub fn mk_substs_trait(self,
                      self_ty: Ty<'tcx>,
                      rest: &[GenericArg<'tcx>])

src/librustc_mir/borrow_check/conflict_errors.rs

@@ -707,10 +707,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             _ => drop_span,
         };
 
+        let root_place_projection = self.infcx.tcx.intern_place_elems(root_place.projection);
+
         if self.access_place_error_reported
             .contains(&(Place {
                 base: root_place.base.clone(),
-                projection: root_place.projection.to_vec().into_boxed_slice(),
+                projection: root_place_projection,
             }, borrow_span))
         {
             debug!(
@@ -723,7 +725,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         self.access_place_error_reported
             .insert((Place {
                 base: root_place.base.clone(),
-                projection: root_place.projection.to_vec().into_boxed_slice(),
+                projection: root_place_projection,
             }, borrow_span));
 
         if let StorageDeadOrDrop::Destructor(dropped_ty) =

src/librustc_mir/borrow_check/nll/renumber.rs

@@ -1,5 +1,5 @@
 use rustc::ty::subst::SubstsRef;
-use rustc::ty::{self, Ty, TypeFoldable};
+use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
 use rustc::mir::{Body, Location, PlaceElem, Promoted};
 use rustc::mir::visit::{MutVisitor, TyContext};
 use rustc::infer::{InferCtxt, NLLRegionVariableOrigin};
@@ -54,6 +54,10 @@ impl<'a, 'tcx> NLLVisitor<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> MutVisitor<'tcx> for NLLVisitor<'a, 'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.infcx.tcx
+    }
+
     fn visit_ty(&mut self, ty: &mut Ty<'tcx>, ty_context: TyContext) {
         debug!("visit_ty(ty={:?}, ty_context={:?})", ty, ty_context);
 

src/librustc_mir/build/expr/as_place.rs

@@ -6,7 +6,7 @@ use crate::build::{BlockAnd, BlockAndExtension, Builder};
 use crate::hair::*;
 use rustc::mir::interpret::{PanicInfo::BoundsCheck};
 use rustc::mir::*;
-use rustc::ty::{CanonicalUserTypeAnnotation, Ty, Variance};
+use rustc::ty::{CanonicalUserTypeAnnotation, Ty, TyCtxt, Variance};
 
 use rustc_index::vec::Idx;
 
@@ -23,10 +23,10 @@ struct PlaceBuilder<'tcx> {
 }
 
 impl PlaceBuilder<'tcx> {
-    fn into_place(self) -> Place<'tcx> {
+    fn into_place(self, tcx: TyCtxt<'tcx>) -> Place<'tcx> {
         Place {
             base: self.base,
-            projection: self.projection.into_boxed_slice(),
+            projection: tcx.intern_place_elems(&self.projection),
         }
     }
 
@@ -73,7 +73,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         M: Mirror<'tcx, Output = Expr<'tcx>>,
     {
         let place_builder = unpack!(block = self.as_place_builder(block, expr));
-        block.and(place_builder.into_place())
+        block.and(place_builder.into_place(self.hir.tcx()))
     }
 
     /// This is used when constructing a compound `Place`, so that we can avoid creating
@@ -96,7 +96,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         M: Mirror<'tcx, Output = Expr<'tcx>>,
     {
         let place_builder = unpack!(block = self.as_read_only_place_builder(block, expr));
-        block.and(place_builder.into_place())
+        block.and(place_builder.into_place(self.hir.tcx()))
     }
 
     /// This is used when constructing a compound `Place`, so that we can avoid creating
@@ -165,7 +165,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     Mutability::Not,
                 ));
 
-                let slice = place_builder.clone().into_place();
+                let slice = place_builder.clone().into_place(this.hir.tcx());
                 // bounds check:
                 let (len, lt) = (
                     this.temp(usize_ty.clone(), expr_span),
@@ -225,7 +225,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         }
                     );
 
-                    let place = place_builder.clone().into_place();
+                    let place = place_builder.clone().into_place(this.hir.tcx());
                     this.cfg.push(
                         block,
                         Statement {

src/librustc_mir/build/expr/as_rvalue.rs

@@ -139,7 +139,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // initialize the box contents:
                 unpack!(
                     block = this.into(
-                        &Place::from(result).deref(),
+                        &Place::from(result).deref(this.hir.tcx()),
                         block, value
                     )
                 );
@@ -296,8 +296,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         .zip(field_types.into_iter())
                         .map(|(n, ty)| match fields_map.get(&n) {
                             Some(v) => v.clone(),
-                            None => this.consume_by_copy_or_move(base.clone().field(n, ty)),
-                        }).collect()
+                            None => this.consume_by_copy_or_move(base.clone().field(
+                                n,
+                                ty,
+                                this.hir.tcx(),
+                            )),
+                        })
+                        .collect()
                 } else {
                     field_names
                         .iter()
@@ -397,8 +402,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             let val_fld = Field::new(0);
             let of_fld = Field::new(1);
 
-            let val = result_value.clone().field(val_fld, ty);
-            let of = result_value.field(of_fld, bool_ty);
+            let val = result_value.clone().field(val_fld, ty, self.hir.tcx());
+            let of = result_value.field(of_fld, bool_ty, self.hir.tcx());
 
             let err = PanicInfo::Overflow(op);
 

src/librustc_mir/build/expr/into.rs

@@ -235,7 +235,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     });
                     let ptr_temp = Place::from(ptr_temp);
                     let block = unpack!(this.into(&ptr_temp, block, ptr));
-                    this.into(&ptr_temp.deref(), block, val)
+                    this.into(&ptr_temp.deref(this.hir.tcx()), block, val)
                 } else {
                     let args: Vec<_> = args
                         .into_iter()