Auto merge of #38097 - Mark-Simulacrum:fn-sig-slice, r=eddyb

Refactor ty::FnSig to contain a &'tcx Slice<Ty<'tcx>>

We refactor this in order to achieve the following wins:

 - Decrease the size of `FnSig` (`Vec` + `bool`: 32, `&Slice` + `bool`: 24).
 - Potentially decrease total allocated memory due to arena-allocating `FnSig` inputs/output; since they are allocated in the type list arena, other users of type lists can reuse the same allocation for an equivalent type list.
 - Remove the last part of the type system which needs drop glue (#37965 removed the other remaining part). This makes arenas containing `FnSig` faster to drop (since we don't need to drop a Vec for each one), and makes reusing them without clearing/dropping potentially possible.

r? @eddyb

src/librustc/middle/intrinsicck.rs

@@ -178,8 +178,8 @@ impl<'a, 'gcx, 'tcx> Visitor<'gcx> for ExprVisitor<'a, 'gcx, 'tcx> {
                 let typ = self.infcx.tcx.tables().node_id_to_type(expr.id);
                 match typ.sty {
                     ty::TyFnDef(.., ref bare_fn_ty) if bare_fn_ty.abi == RustIntrinsic => {
-                        let from = bare_fn_ty.sig.0.inputs[0];
-                        let to = bare_fn_ty.sig.0.output;
+                        let from = bare_fn_ty.sig.skip_binder().inputs()[0];
+                        let to = bare_fn_ty.sig.skip_binder().output();
                         self.check_transmute(expr.span, from, to, expr.id);
                     }
                     _ => {

src/librustc/traits/object_safety.rs

@@ -241,12 +241,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         // The `Self` type is erased, so it should not appear in list of
         // arguments or return type apart from the receiver.
         let ref sig = self.item_type(method.def_id).fn_sig();
-        for &input_ty in &sig.0.inputs[1..] {
+        for input_ty in &sig.skip_binder().inputs()[1..] {
             if self.contains_illegal_self_type_reference(trait_def_id, input_ty) {
                 return Some(MethodViolationCode::ReferencesSelf);
             }
         }
-        if self.contains_illegal_self_type_reference(trait_def_id, sig.0.output) {
+        if self.contains_illegal_self_type_reference(trait_def_id, sig.output().skip_binder()) {
             return Some(MethodViolationCode::ReferencesSelf);
         }
 

src/librustc/traits/select.rs

@@ -1368,21 +1368,13 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             ty::TyFnDef(.., &ty::BareFnTy {
                 unsafety: hir::Unsafety::Normal,
                 abi: Abi::Rust,
-                sig: ty::Binder(ty::FnSig {
-                    inputs: _,
-                    output: _,
-                    variadic: false
-                })
+                ref sig,
             }) |
             ty::TyFnPtr(&ty::BareFnTy {
                 unsafety: hir::Unsafety::Normal,
                 abi: Abi::Rust,
-                sig: ty::Binder(ty::FnSig {
-                    inputs: _,
-                    output: _,
-                    variadic: false
-                })
-            }) => {
+                ref sig
+            }) if !sig.variadic() => {
                 candidates.vec.push(FnPointerCandidate);
             }
 

src/librustc/traits/util.rs

@@ -487,14 +487,15 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         -> ty::Binder<(ty::TraitRef<'tcx>, Ty<'tcx>)>
     {
         let arguments_tuple = match tuple_arguments {
-            TupleArgumentsFlag::No => sig.0.inputs[0],
-            TupleArgumentsFlag::Yes => self.intern_tup(&sig.0.inputs[..]),
+            TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
+            TupleArgumentsFlag::Yes =>
+                self.intern_tup(sig.skip_binder().inputs()),
         };
         let trait_ref = ty::TraitRef {
             def_id: fn_trait_def_id,
             substs: self.mk_substs_trait(self_ty, &[arguments_tuple]),
         };
-        ty::Binder((trait_ref, sig.0.output))
+        ty::Binder((trait_ref, sig.skip_binder().output()))
     }
 }
 

src/librustc/ty/context.rs

@@ -1542,6 +1542,17 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
+    pub fn mk_fn_sig<I>(self, inputs: I, output: I::Item, variadic: bool)
+        -> <I::Item as InternIteratorElement<Ty<'tcx>, ty::FnSig<'tcx>>>::Output
+        where I: Iterator,
+              I::Item: InternIteratorElement<Ty<'tcx>, ty::FnSig<'tcx>>
+    {
+        inputs.chain(iter::once(output)).intern_with(|xs| ty::FnSig {
+            inputs_and_output: self.intern_type_list(xs),
+            variadic: variadic
+        })
+    }
+
     pub fn mk_existential_predicates<I: InternAs<[ExistentialPredicate<'tcx>],
                                      &'tcx Slice<ExistentialPredicate<'tcx>>>>(self, iter: I)
                                      -> I::Output {

src/librustc/ty/fast_reject.rs

@@ -81,7 +81,7 @@ pub fn simplify_type<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
             Some(TupleSimplifiedType(tys.len()))
         }
         ty::TyFnDef(.., ref f) | ty::TyFnPtr(ref f) => {
-            Some(FunctionSimplifiedType(f.sig.0.inputs.len()))
+            Some(FunctionSimplifiedType(f.sig.skip_binder().inputs().len()))
         }
         ty::TyProjection(_) | ty::TyParam(_) => {
             if can_simplify_params {

src/librustc/ty/flags.rs

@@ -180,8 +180,8 @@ impl FlagComputation {
     fn add_fn_sig(&mut self, fn_sig: &ty::PolyFnSig) {
         let mut computation = FlagComputation::new();
 
-        computation.add_tys(&fn_sig.0.inputs);
-        computation.add_ty(fn_sig.0.output);
+        computation.add_tys(fn_sig.skip_binder().inputs());
+        computation.add_ty(fn_sig.skip_binder().output());
 
         self.add_bound_computation(&computation);
     }

src/librustc/ty/relate.rs

@@ -18,8 +18,10 @@ use ty::subst::{Kind, Substs};
 use ty::{self, Ty, TyCtxt, TypeFoldable};
 use ty::error::{ExpectedFound, TypeError};
 use std::rc::Rc;
+use std::iter;
 use syntax::abi;
 use hir as ast;
+use rustc_data_structures::accumulate_vec::AccumulateVec;
 
 pub type RelateResult<'tcx, T> = Result<T, TypeError<'tcx>>;
 
@@ -185,32 +187,28 @@ impl<'tcx> Relate<'tcx> for ty::FnSig<'tcx> {
                 expected_found(relation, &a.variadic, &b.variadic)));
         }
 
-        let inputs = relate_arg_vecs(relation,
-                                     &a.inputs,
-                                     &b.inputs)?;
-        let output = relation.relate(&a.output, &b.output)?;
+        if a.inputs().len() != b.inputs().len() {
+            return Err(TypeError::ArgCount);
+        }
 
-        Ok(ty::FnSig {inputs: inputs,
-                      output: output,
-                      variadic: a.variadic})
+        let inputs_and_output = a.inputs().iter().cloned()
+            .zip(b.inputs().iter().cloned())
+            .map(|x| (x, false))
+            .chain(iter::once(((a.output(), b.output()), true)))
+            .map(|((a, b), is_output)| {
+                if is_output {
+                    relation.relate(&a, &b)
+                } else {
+                    relation.relate_with_variance(ty::Contravariant, &a, &b)
+                }
+            }).collect::<Result<AccumulateVec<[_; 8]>, _>>()?;
+        Ok(ty::FnSig {
+            inputs_and_output: relation.tcx().intern_type_list(&inputs_and_output),
+            variadic: a.variadic
+        })
     }
 }
 
-fn relate_arg_vecs<'a, 'gcx, 'tcx, R>(relation: &mut R,
-                                      a_args: &[Ty<'tcx>],
-                                      b_args: &[Ty<'tcx>])
-                                      -> RelateResult<'tcx, Vec<Ty<'tcx>>>
-    where R: TypeRelation<'a, 'gcx, 'tcx>, 'gcx: 'a+'tcx, 'tcx: 'a
-{
-    if a_args.len() != b_args.len() {
-        return Err(TypeError::ArgCount);
-    }
-
-    a_args.iter().zip(b_args)
-          .map(|(a, b)| relation.relate_with_variance(ty::Contravariant, a, b))
-          .collect()
-}
-
 impl<'tcx> Relate<'tcx> for ast::Unsafety {
     fn relate<'a, 'gcx, R>(relation: &mut R,
                            a: &ast::Unsafety,

src/librustc/ty/structural_impls.rs

@@ -232,14 +232,11 @@ impl<'a, 'tcx> Lift<'tcx> for ty::adjustment::AutoBorrow<'a> {
 impl<'a, 'tcx> Lift<'tcx> for ty::FnSig<'a> {
     type Lifted = ty::FnSig<'tcx>;
     fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>) -> Option<Self::Lifted> {
-        tcx.lift(&self.inputs[..]).and_then(|inputs| {
-            tcx.lift(&self.output).map(|output| {
-                ty::FnSig {
-                    inputs: inputs,
-                    output: output,
-                    variadic: self.variadic
-                }
-            })
+        tcx.lift(&self.inputs_and_output).map(|x| {
+            ty::FnSig {
+                inputs_and_output: x,
+                variadic: self.variadic
+            }
         })
     }
 }
@@ -589,17 +586,20 @@ impl<'tcx> TypeFoldable<'tcx> for ty::TypeAndMut<'tcx> {
 
 impl<'tcx> TypeFoldable<'tcx> for ty::FnSig<'tcx> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
-        ty::FnSig { inputs: self.inputs.fold_with(folder),
-                    output: self.output.fold_with(folder),
-                    variadic: self.variadic }
+        let inputs_and_output = self.inputs_and_output.fold_with(folder);
+        ty::FnSig {
+            inputs_and_output: folder.tcx().intern_type_list(&inputs_and_output),
+            variadic: self.variadic,
+        }
     }
 
     fn fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         folder.fold_fn_sig(self)
     }
 
     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
-        self.inputs.visit_with(visitor) || self.output.visit_with(visitor)
+        self.inputs().iter().any(|i| i.visit_with(visitor)) ||
+        self.output().visit_with(visitor)
     }
 }
 

src/librustc/ty/sty.rs

@@ -563,22 +563,31 @@ pub struct ClosureTy<'tcx> {
 /// - `variadic` indicates whether this is a variadic function. (only true for foreign fns)
 #[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub struct FnSig<'tcx> {
-    pub inputs: Vec<Ty<'tcx>>,
-    pub output: Ty<'tcx>,
+    pub inputs_and_output: &'tcx Slice<Ty<'tcx>>,
     pub variadic: bool
 }
 
+impl<'tcx> FnSig<'tcx> {
+    pub fn inputs(&self) -> &[Ty<'tcx>] {
+        &self.inputs_and_output[..self.inputs_and_output.len() - 1]
+    }
+
+    pub fn output(&self) -> Ty<'tcx> {
+        self.inputs_and_output[self.inputs_and_output.len() - 1]
+    }
+}
+
 pub type PolyFnSig<'tcx> = Binder<FnSig<'tcx>>;
 
 impl<'tcx> PolyFnSig<'tcx> {
-    pub fn inputs(&self) -> ty::Binder<Vec<Ty<'tcx>>> {
-        self.map_bound_ref(|fn_sig| fn_sig.inputs.clone())
+    pub fn inputs(&self) -> Binder<&[Ty<'tcx>]> {
+        Binder(self.skip_binder().inputs())
     }
     pub fn input(&self, index: usize) -> ty::Binder<Ty<'tcx>> {
-        self.map_bound_ref(|fn_sig| fn_sig.inputs[index])
+        self.map_bound_ref(|fn_sig| fn_sig.inputs()[index])
     }
     pub fn output(&self) -> ty::Binder<Ty<'tcx>> {
-        self.map_bound_ref(|fn_sig| fn_sig.output.clone())
+        self.map_bound_ref(|fn_sig| fn_sig.output().clone())
     }
     pub fn variadic(&self) -> bool {
         self.skip_binder().variadic
@@ -1243,7 +1252,7 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
     }
 
     // Type accessors for substructures of types
-    pub fn fn_args(&self) -> ty::Binder<Vec<Ty<'tcx>>> {
+    pub fn fn_args(&self) -> ty::Binder<&[Ty<'tcx>]> {
         self.fn_sig().inputs()
     }
 

src/librustc/ty/util.rs

@@ -530,7 +530,7 @@ impl<'a, 'gcx, 'tcx, H: Hasher> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tc
                 self.hash(f.unsafety);
                 self.hash(f.abi);
                 self.hash(f.sig.variadic());
-                self.hash(f.sig.inputs().skip_binder().len());
+                self.hash(f.sig.skip_binder().inputs().len());
             }
             TyDynamic(ref data, ..) => {
                 if let Some(p) = data.principal() {

src/librustc/ty/walk.rs

@@ -126,6 +126,6 @@ fn push_subtypes<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent_ty: Ty<'tcx>) {
 }
 
 fn push_sig_subtypes<'tcx>(stack: &mut TypeWalkerStack<'tcx>, sig: &ty::PolyFnSig<'tcx>) {
-    stack.push(sig.0.output);
-    stack.extend(sig.0.inputs.iter().cloned().rev());
+    stack.push(sig.skip_binder().output());
+    stack.extend(sig.skip_binder().inputs().iter().cloned().rev());
 }

src/librustc/util/ppaux.rs

@@ -595,7 +595,7 @@ impl<'tcx> fmt::Debug for ty::InstantiatedPredicates<'tcx> {
 impl<'tcx> fmt::Display for ty::FnSig<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "fn")?;
-        fn_sig(f, &self.inputs, self.variadic, self.output)
+        fn_sig(f, self.inputs(), self.variadic, self.output())
     }
 }
 
@@ -625,7 +625,7 @@ impl fmt::Debug for ty::RegionVid {
 
 impl<'tcx> fmt::Debug for ty::FnSig<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "({:?}; variadic: {})->{:?}", self.inputs, self.variadic, self.output)
+        write!(f, "({:?}; variadic: {})->{:?}", self.inputs(), self.variadic, self.output())
     }
 }
 

src/librustc_driver/test.rs

@@ -265,15 +265,10 @@ impl<'a, 'gcx, 'tcx> Env<'a, 'gcx, 'tcx> {
     }
 
     pub fn t_fn(&self, input_tys: &[Ty<'tcx>], output_ty: Ty<'tcx>) -> Ty<'tcx> {
-        let input_args = input_tys.iter().cloned().collect();
         self.infcx.tcx.mk_fn_ptr(self.infcx.tcx.mk_bare_fn(ty::BareFnTy {
             unsafety: hir::Unsafety::Normal,
             abi: Abi::Rust,
-            sig: ty::Binder(ty::FnSig {
-                inputs: input_args,
-                output: output_ty,
-                variadic: false,
-            }),
+            sig: ty::Binder(self.infcx.tcx.mk_fn_sig(input_tys.iter().cloned(), output_ty, false)),
         }))
     }
 

src/librustc_lint/builtin.rs

@@ -1084,8 +1084,8 @@ impl LateLintPass for MutableTransmutes {
                 let typ = cx.tcx.tables().node_id_to_type(expr.id);
                 match typ.sty {
                     ty::TyFnDef(.., ref bare_fn) if bare_fn.abi == RustIntrinsic => {
-                        let from = bare_fn.sig.0.inputs[0];
-                        let to = bare_fn.sig.0.output;
+                        let from = bare_fn.sig.skip_binder().inputs()[0];
+                        let to = bare_fn.sig.skip_binder().output();
                         return Some((&from.sty, &to.sty));
                     }
                     _ => (),

src/librustc_lint/types.rs

@@ -603,16 +603,16 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                 }
 
                 let sig = cx.erase_late_bound_regions(&bare_fn.sig);
-                if !sig.output.is_nil() {
-                    let r = self.check_type_for_ffi(cache, sig.output);
+                if !sig.output().is_nil() {
+                    let r = self.check_type_for_ffi(cache, sig.output());
                     match r {
                         FfiSafe => {}
                         _ => {
                             return r;
                         }
                     }
                 }
-                for arg in sig.inputs {
+                for arg in sig.inputs() {
                     let r = self.check_type_for_ffi(cache, arg);
                     match r {
                         FfiSafe => {}
@@ -678,12 +678,12 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         let sig = self.cx.tcx.item_type(def_id).fn_sig();
         let sig = self.cx.tcx.erase_late_bound_regions(&sig);
 
-        for (&input_ty, input_hir) in sig.inputs.iter().zip(&decl.inputs) {
-            self.check_type_for_ffi_and_report_errors(input_hir.ty.span, &input_ty);
+        for (input_ty, input_hir) in sig.inputs().iter().zip(&decl.inputs) {
+            self.check_type_for_ffi_and_report_errors(input_hir.ty.span, input_ty);
         }
 
         if let hir::Return(ref ret_hir) = decl.output {
-            let ret_ty = sig.output;
+            let ret_ty = sig.output();
             if !ret_ty.is_nil() {
                 self.check_type_for_ffi_and_report_errors(ret_hir.span, ret_ty);
             }

src/librustc_mir/build/expr/into.rs

@@ -208,7 +208,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 let diverges = match ty.sty {
                     ty::TyFnDef(_, _, ref f) | ty::TyFnPtr(ref f) => {
                         // FIXME(canndrew): This is_never should probably be an is_uninhabited
-                        f.sig.0.output.is_never()
+                        f.sig.skip_binder().output().is_never()
                     }
                     _ => false
                 };

src/librustc_mir/hair/cx/expr.rs

@@ -247,10 +247,10 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                     span_bug!(expr.span, "method call has late-bound regions")
                 });
 
-                assert_eq!(sig.inputs.len(), 2);
+                assert_eq!(sig.inputs().len(), 2);
 
                 let tupled_args = Expr {
-                    ty: sig.inputs[1],
+                    ty: sig.inputs()[1],
                     temp_lifetime: temp_lifetime,
                     span: expr.span,
                     kind: ExprKind::Tuple {