Auto merge of #32346 - nikomatsakis:no-erased-regions, r=eddyb

Remove `ErasedRegions` from substs

This commit removes the `ErasedRegions` enum from `Substs`. Instead, in trans, we just generate a vector of `ReStatic` of suitable length. The goal is both general cleanup and to help pave the way for a glorious future where erasure is used in type check.

r? @eddyb

One concern: might be nice to do some profiling. Not sure the best way to do that. Perhaps I'll investigate running nrc's test suite locally.

src/librustc/middle/subst.rs

@@ -11,7 +11,6 @@
 // Type substitutions.
 
 pub use self::ParamSpace::*;
-pub use self::RegionSubsts::*;
 
 use middle::cstore;
 use middle::def_id::DefId;
@@ -34,24 +33,15 @@ use syntax::codemap::{Span, DUMMY_SP};
 #[derive(Clone, PartialEq, Eq, Hash)]
 pub struct Substs<'tcx> {
     pub types: VecPerParamSpace<Ty<'tcx>>,
-    pub regions: RegionSubsts,
-}
-
-/// Represents the values to use when substituting lifetime parameters.
-/// If the value is `ErasedRegions`, then this subst is occurring during
-/// trans, and all region parameters will be replaced with `ty::ReStatic`.
-#[derive(Clone, PartialEq, Eq, Hash)]
-pub enum RegionSubsts {
-    ErasedRegions,
-    NonerasedRegions(VecPerParamSpace<ty::Region>)
+    pub regions: VecPerParamSpace<ty::Region>,
 }
 
 impl<'tcx> Substs<'tcx> {
     pub fn new(t: VecPerParamSpace<Ty<'tcx>>,
                r: VecPerParamSpace<ty::Region>)
                -> Substs<'tcx>
     {
-        Substs { types: t, regions: NonerasedRegions(r) }
+        Substs { types: t, regions: r }
     }
 
     pub fn new_type(t: Vec<Ty<'tcx>>,
@@ -71,32 +61,15 @@ impl<'tcx> Substs<'tcx> {
                     VecPerParamSpace::new(r, Vec::new(), Vec::new()))
     }
 
-    pub fn erased(t: VecPerParamSpace<Ty<'tcx>>) -> Substs<'tcx>
-    {
-        Substs { types: t, regions: ErasedRegions }
-    }
-
     pub fn empty() -> Substs<'tcx> {
         Substs {
             types: VecPerParamSpace::empty(),
-            regions: NonerasedRegions(VecPerParamSpace::empty()),
-        }
-    }
-
-    pub fn trans_empty() -> Substs<'tcx> {
-        Substs {
-            types: VecPerParamSpace::empty(),
-            regions: ErasedRegions
+            regions: VecPerParamSpace::empty(),
         }
     }
 
     pub fn is_noop(&self) -> bool {
-        let regions_is_noop = match self.regions {
-            ErasedRegions => false, // may be used to canonicalize
-            NonerasedRegions(ref regions) => regions.is_empty(),
-        };
-
-        regions_is_noop && self.types.is_empty()
+        self.regions.is_empty() && self.types.is_empty()
     }
 
     pub fn type_for_def(&self, ty_param_def: &ty::TypeParameterDef) -> Ty<'tcx> {
@@ -115,26 +88,9 @@ impl<'tcx> Substs<'tcx> {
     }
 
     pub fn erase_regions(self) -> Substs<'tcx> {
-        let Substs { types, regions: _ } = self;
-        Substs { types: types, regions: ErasedRegions }
-    }
-
-    /// Since ErasedRegions are only to be used in trans, most of the compiler can use this method
-    /// to easily access the set of region substitutions.
-    pub fn regions<'a>(&'a self) -> &'a VecPerParamSpace<ty::Region> {
-        match self.regions {
-            ErasedRegions => panic!("Erased regions only expected in trans"),
-            NonerasedRegions(ref r) => r
-        }
-    }
-
-    /// Since ErasedRegions are only to be used in trans, most of the compiler can use this method
-    /// to easily access the set of region substitutions.
-    pub fn mut_regions<'a>(&'a mut self) -> &'a mut VecPerParamSpace<ty::Region> {
-        match self.regions {
-            ErasedRegions => panic!("Erased regions only expected in trans"),
-            NonerasedRegions(ref mut r) => r
-        }
+        let Substs { types, regions } = self;
+        let regions = regions.map(|_| ty::ReStatic);
+        Substs { types: types, regions: regions }
     }
 
     pub fn with_method(self,
@@ -144,7 +100,7 @@ impl<'tcx> Substs<'tcx> {
     {
         let Substs { types, regions } = self;
         let types = types.with_slice(FnSpace, &m_types);
-        let regions = regions.map(|r| r.with_slice(FnSpace, &m_regions));
+        let regions = regions.with_slice(FnSpace, &m_regions);
         Substs { types: types, regions: regions }
     }
 
@@ -154,27 +110,23 @@ impl<'tcx> Substs<'tcx> {
     {
         let Substs { types, regions } = self.clone();
         let types = types.with_slice(FnSpace, meth_substs.types.get_slice(FnSpace));
-        let regions = regions.map(|r| {
-            r.with_slice(FnSpace, meth_substs.regions().get_slice(FnSpace))
-        });
+        let regions = regions.with_slice(FnSpace, meth_substs.regions.get_slice(FnSpace));
         Substs { types: types, regions: regions }
     }
 
     pub fn with_method_from_subst(self, other: &Substs<'tcx>) -> Substs<'tcx> {
         let Substs { types, regions } = self;
         let types = types.with_slice(FnSpace, other.types.get_slice(FnSpace));
-        let regions = regions.map(|r| {
-            r.with_slice(FnSpace, other.regions().get_slice(FnSpace))
-        });
+        let regions = regions.with_slice(FnSpace, other.regions.get_slice(FnSpace));
         Substs { types: types, regions: regions }
     }
 
     /// Creates a trait-ref out of this substs, ignoring the FnSpace substs
     pub fn to_trait_ref(&self, tcx: &TyCtxt<'tcx>, trait_id: DefId)
                         -> ty::TraitRef<'tcx> {
-        let Substs { mut types, regions } = self.clone();
+        let Substs { mut types, mut regions } = self.clone();
         types.truncate(FnSpace, 0);
-        let regions = regions.map(|mut r| { r.truncate(FnSpace, 0); r });
+        regions.truncate(FnSpace, 0);
 
         ty::TraitRef {
             def_id: trait_id,
@@ -212,24 +164,6 @@ impl<'tcx> Decodable for &'tcx Substs<'tcx> {
     }
 }
 
-impl RegionSubsts {
-    pub fn map<F>(self, op: F) -> RegionSubsts where
-        F: FnOnce(VecPerParamSpace<ty::Region>) -> VecPerParamSpace<ty::Region>,
-    {
-        match self {
-            ErasedRegions => ErasedRegions,
-            NonerasedRegions(r) => NonerasedRegions(op(r))
-        }
-    }
-
-    pub fn is_erased(&self) -> bool {
-        match *self {
-            ErasedRegions => true,
-            NonerasedRegions(_) => false,
-        }
-    }
-}
-
 ///////////////////////////////////////////////////////////////////////////
 // ParamSpace
 
@@ -664,26 +598,22 @@ impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
         // the specialized routine `ty::replace_late_regions()`.
         match r {
             ty::ReEarlyBound(data) => {
-                match self.substs.regions {
-                    ErasedRegions => ty::ReStatic,
-                    NonerasedRegions(ref regions) =>
-                        match regions.opt_get(data.space, data.index as usize) {
-                            Some(&r) => {
-                                self.shift_region_through_binders(r)
-                            }
-                            None => {
-                                let span = self.span.unwrap_or(DUMMY_SP);
-                                self.tcx().sess.span_bug(
-                                    span,
-                                    &format!("Type parameter out of range \
-                                              when substituting in region {} (root type={:?}) \
-                                              (space={:?}, index={})",
-                                             data.name,
-                                             self.root_ty,
-                                             data.space,
-                                             data.index));
-                            }
-                        }
+                match self.substs.regions.opt_get(data.space, data.index as usize) {
+                    Some(&r) => {
+                        self.shift_region_through_binders(r)
+                    }
+                    None => {
+                        let span = self.span.unwrap_or(DUMMY_SP);
+                        self.tcx().sess.span_bug(
+                            span,
+                            &format!("Region parameter out of range \
+                                      when substituting in region {} (root type={:?}) \
+                                      (space={:?}, index={})",
+                                     data.name,
+                                     self.root_ty,
+                                     data.space,
+                                     data.index));
+                    }
                 }
             }
             _ => r

src/librustc/middle/traits/specialize/mod.rs

@@ -102,14 +102,6 @@ pub fn translate_substs<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
         specialization_graph::Node::Trait(..) => source_trait_ref.substs.clone(),
     };
 
-    // retain erasure mode
-    // NB: this must happen before inheriting method generics below
-    let target_substs = if source_substs.regions.is_erased() {
-        target_substs.erase_regions()
-    } else {
-        target_substs
-    };
-
     // directly inherent the method generics, since those do not vary across impls
     infcx.tcx.mk_substs(target_substs.with_method_from_subst(source_substs))
 }

src/librustc/middle/ty/flags.rs

@@ -194,13 +194,8 @@ impl FlagComputation {
 
     fn add_substs(&mut self, substs: &subst::Substs) {
         self.add_tys(substs.types.as_slice());
-        match substs.regions {
-            subst::ErasedRegions => {}
-            subst::NonerasedRegions(ref regions) => {
-                for &r in regions {
-                    self.add_region(r);
-                }
-            }
+        for &r in &substs.regions {
+            self.add_region(r);
         }
     }
 

src/librustc/middle/ty/fold.rs

@@ -532,7 +532,7 @@ impl<'tcx> TyCtxt<'tcx> {
             fn fold_substs(&mut self,
                            substs: &subst::Substs<'tcx>)
                            -> subst::Substs<'tcx> {
-                subst::Substs { regions: subst::ErasedRegions,
+                subst::Substs { regions: substs.regions.fold_with(self),
                                 types: substs.types.fold_with(self) }
             }
         }

src/librustc/middle/ty/mod.rs

@@ -2605,7 +2605,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
         Substs {
             types: types,
-            regions: subst::NonerasedRegions(regions)
+            regions: regions,
         }
     }
 

src/librustc/middle/ty/relate.rs

@@ -14,7 +14,7 @@
 //! type equality, etc.
 
 use middle::def_id::DefId;
-use middle::subst::{ErasedRegions, NonerasedRegions, ParamSpace, Substs};
+use middle::subst::{ParamSpace, Substs};
 use middle::ty::{self, Ty, TyCtxt, TypeFoldable};
 use middle::ty::error::{ExpectedFound, TypeError};
 use std::rc::Rc;
@@ -156,23 +156,15 @@ pub fn relate_substs<'a,'tcx:'a,R>(relation: &mut R,
         substs.types.replace(space, tps);
     }
 
-    match (&a_subst.regions, &b_subst.regions) {
-        (&ErasedRegions, _) | (_, &ErasedRegions) => {
-            substs.regions = ErasedRegions;
-        }
-
-        (&NonerasedRegions(ref a), &NonerasedRegions(ref b)) => {
-            for &space in &ParamSpace::all() {
-                let a_regions = a.get_slice(space);
-                let b_regions = b.get_slice(space);
-                let r_variances = variances.map(|v| v.regions.get_slice(space));
-                let regions = relate_region_params(relation,
-                                                   r_variances,
-                                                   a_regions,
-                                                   b_regions)?;
-                substs.mut_regions().replace(space, regions);
-            }
-        }
+    for &space in &ParamSpace::all() {
+        let a_regions = a_subst.regions.get_slice(space);
+        let b_regions = b_subst.regions.get_slice(space);
+        let r_variances = variances.map(|v| v.regions.get_slice(space));
+        let regions = relate_region_params(relation,
+                                           r_variances,
+                                           a_regions,
+                                           b_regions)?;
+        substs.regions.replace(space, regions);
     }
 
     Ok(substs)

src/librustc/middle/ty/structural_impls.rs

@@ -487,14 +487,7 @@ impl<'tcx> TypeFoldable<'tcx> for ty::Region {
 
 impl<'tcx> TypeFoldable<'tcx> for subst::Substs<'tcx> {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
-        let regions = match self.regions {
-            subst::ErasedRegions => subst::ErasedRegions,
-            subst::NonerasedRegions(ref regions) => {
-                subst::NonerasedRegions(regions.fold_with(folder))
-            }
-        };
-
-        subst::Substs { regions: regions,
+        subst::Substs { regions: self.regions.fold_with(folder),
                         types: self.types.fold_with(folder) }
     }
 
@@ -503,10 +496,7 @@ impl<'tcx> TypeFoldable<'tcx> for subst::Substs<'tcx> {
     }
 
     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
-        self.types.visit_with(visitor) || match self.regions {
-            subst::ErasedRegions => false,
-            subst::NonerasedRegions(ref regions) => regions.visit_with(visitor),
-        }
+        self.types.visit_with(visitor) || self.regions.visit_with(visitor)
     }
 }
 

src/librustc/middle/ty/sty.rs

@@ -1204,18 +1204,18 @@ impl<'tcx> TyS<'tcx> {
             TyTrait(ref obj) => {
                 let mut v = vec![obj.bounds.region_bound];
                 v.extend_from_slice(obj.principal.skip_binder()
-                                       .substs.regions().as_slice());
+                                       .substs.regions.as_slice());
                 v
             }
             TyEnum(_, substs) |
             TyStruct(_, substs) => {
-                substs.regions().as_slice().to_vec()
+                substs.regions.as_slice().to_vec()
             }
             TyClosure(_, ref substs) => {
-                substs.func_substs.regions().as_slice().to_vec()
+                substs.func_substs.regions.as_slice().to_vec()
             }
             TyProjection(ref data) => {
-                data.trait_ref.substs.regions().as_slice().to_vec()
+                data.trait_ref.substs.regions.as_slice().to_vec()
             }
             TyFnDef(..) |
             TyFnPtr(_) |