Auto merge of #67899 - Marwes:view, r=<try>

perf: Avoid re-interning types in outlives checking

In profiling `intern_ty` is a very hot function (9% in the test I used). While there does not seem to be a way to reduce the cost of calling we can avoid the call in some cases.

In outlives checking `ParamTy` and `ProjectionTy` are extracted from the `Ty` value that contains them only to later be passed as an argument to `intern_ty` again later. This seems to be happening a lot in my test with `intern_ty` called from outlives is at ~6%.

Since all `ParamTy` and `ProjectionTy` are already stored in a `Ty` I had an idea to pass around a `View` type which provides direct access to the specific, inner type without losing the original `Ty` pointer. While the current implementation does so with some unsafe to let the branch be elided on `Deref`, it could be done entirely in safe code as well, either by accepting the (predictable) branch in `Deref` or by storing the inner type in `View` as well as the `Ty`. But considering that the unsafe is trivial to prove and the call sites seem quite hot I opted to show the unsafe approach first.

Based on #67840 (since it touches the same file/lines)

Commits without #67840 https://github.com/rust-lang/rust/pull/67899/files/77ddc3540e52be4b5bd75cf082c621392acaf81b..b55bab206096c27533120921f6b0c273f115e34a

src/librustc/infer/lexical_region_resolve/mod.rs

@@ -602,7 +602,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
                 continue;
             }
 
-            let verify_kind_ty = verify.kind.to_ty(self.tcx());
+            let verify_kind_ty = verify.kind.as_ty();
             if self.bound_is_met(&verify.bound, var_data, verify_kind_ty, sub) {
                 continue;
             }

src/librustc/infer/outlives/obligations.rs

@@ -321,7 +321,7 @@ where
         &mut self,
         origin: infer::SubregionOrigin<'tcx>,
         region: ty::Region<'tcx>,
-        param_ty: ty::ParamTy,
+        param_ty: ty::View<'tcx, ty::ParamTy>,
     ) {
         debug!(
             "param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
@@ -337,7 +337,7 @@ where
         &mut self,
         origin: infer::SubregionOrigin<'tcx>,
         region: ty::Region<'tcx>,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        projection_ty: ty::View<'tcx, ty::ProjectionTy<'tcx>>,
     ) {
         debug!(
             "projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
@@ -376,8 +376,8 @@ where
         // #55756) in cases where you have e.g., `<T as Foo<'a>>::Item:
         // 'a` in the environment but `trait Foo<'b> { type Item: 'b
         // }` in the trait definition.
-        approx_env_bounds.retain(|bound| match bound.0.kind {
-            ty::Projection(projection_ty) => self
+        approx_env_bounds.retain(|bound| match bound.0.into() {
+            ty::view::Projection(projection_ty) => self
                 .verify_bound
                 .projection_declared_bounds_from_trait(projection_ty)
                 .all(|r| r != bound.1),

src/librustc/infer/outlives/verify.rs

@@ -2,7 +2,7 @@ use crate::infer::outlives::env::RegionBoundPairs;
 use crate::infer::{GenericKind, VerifyBound};
 use crate::traits;
 use crate::ty::subst::{InternalSubsts, Subst};
-use crate::ty::{self, Ty, TyCtxt};
+use crate::ty::{self, Ty, TyCtxt, View};
 use rustc_data_structures::captures::Captures;
 use rustc_hir::def_id::DefId;
 
@@ -39,22 +39,20 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     }
 
     fn type_bound(&self, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
-        match ty.kind {
-            ty::Param(p) => self.param_bound(p),
-            ty::Projection(data) => self.projection_bound(data),
+        match ty.into() {
+            ty::view::Param(p) => self.param_bound(p),
+            ty::view::Projection(data) => self.projection_bound(data),
             _ => self.recursive_type_bound(ty),
         }
     }
 
-    fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> {
+    fn param_bound(&self, param_ty: View<'tcx, ty::ParamTy>) -> VerifyBound<'tcx> {
         debug!("param_bound(param_ty={:?})", param_ty);
 
         // Start with anything like `T: 'a` we can scrape from the
         // environment
-        let param_bounds = self
-            .declared_generic_bounds_from_env(GenericKind::Param(param_ty))
-            .into_iter()
-            .map(|outlives| outlives.1);
+        let param_bounds =
+            self.declared_generic_bounds_from_env(param_ty).into_iter().map(|outlives| outlives.1);
 
         // Add in the default bound of fn body that applies to all in
         // scope type parameters:
@@ -78,9 +76,9 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// this list.
     pub fn projection_approx_declared_bounds_from_env(
         &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        projection_ty: ty::View<'tcx, ty::ProjectionTy<'tcx>>,
     ) -> Vec<ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>> {
-        let projection_ty = GenericKind::Projection(projection_ty).to_ty(self.tcx);
+        let projection_ty = projection_ty.as_ty();
         let erased_projection_ty = self.tcx.erase_regions(&projection_ty);
         self.declared_generic_bounds_from_env_with_compare_fn(|ty| {
             if let ty::Projection(..) = ty.kind {
@@ -97,16 +95,18 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// exact match.
     pub fn projection_declared_bounds_from_trait(
         &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        projection_ty: ty::View<'tcx, ty::ProjectionTy<'tcx>>,
     ) -> impl Iterator<Item = ty::Region<'tcx>> + 'cx + Captures<'tcx> {
         self.declared_projection_bounds_from_trait(projection_ty)
     }
 
-    pub fn projection_bound(&self, projection_ty: ty::ProjectionTy<'tcx>) -> VerifyBound<'tcx> {
+    pub fn projection_bound(
+        &self,
+        projection_ty: ty::View<'tcx, ty::ProjectionTy<'tcx>>,
+    ) -> VerifyBound<'tcx> {
         debug!("projection_bound(projection_ty={:?})", projection_ty);
 
-        let projection_ty_as_ty =
-            self.tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs);
+        let projection_ty_as_ty = projection_ty.as_ty();
 
         // Search the env for where clauses like `P: 'a`.
         let env_bounds = self
@@ -161,18 +161,16 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// bounds, but all the bounds it returns can be relied upon.
     fn declared_generic_bounds_from_env(
         &self,
-        generic: GenericKind<'tcx>,
+        generic: View<'tcx, ty::ParamTy>,
     ) -> Vec<ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>> {
-        let generic_ty = generic.to_ty(self.tcx);
+        let generic_ty = generic.as_ty();
         self.declared_generic_bounds_from_env_with_compare_fn(|ty| ty == generic_ty)
     }
 
     fn declared_generic_bounds_from_env_with_compare_fn(
         &self,
         compare_ty: impl Fn(Ty<'tcx>) -> bool,
     ) -> Vec<ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>> {
-        let tcx = self.tcx;
-
         // To start, collect bounds from user environment. Note that
         // parameter environments are already elaborated, so we don't
         // have to worry about that. Comparing using `==` is a bit
@@ -198,7 +196,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
                 "declared_generic_bounds_from_env_with_compare_fn: region_bound_pair = {:?}",
                 (r, p)
             );
-            let p_ty = p.to_ty(tcx);
+            let p_ty = p.as_ty();
             compare_ty(p_ty).then_some(ty::OutlivesPredicate(p_ty, r))
         });
 
@@ -227,7 +225,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// `region_bounds_declared_on_associated_item`.
     fn declared_projection_bounds_from_trait(
         &self,
-        projection_ty: ty::ProjectionTy<'tcx>,
+        projection_ty: ty::View<'tcx, ty::ProjectionTy<'tcx>>,
     ) -> impl Iterator<Item = ty::Region<'tcx>> + 'cx + Captures<'tcx> {
         debug!("projection_bounds(projection_ty={:?})", projection_ty);
         let tcx = self.tcx;

src/librustc/infer/region_constraints/mod.rs

@@ -184,8 +184,8 @@ pub struct Verify<'tcx> {
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, TypeFoldable)]
 pub enum GenericKind<'tcx> {
-    Param(ty::ParamTy),
-    Projection(ty::ProjectionTy<'tcx>),
+    Param(ty::View<'tcx, ty::ParamTy>),
+    Projection(ty::View<'tcx, ty::ProjectionTy<'tcx>>),
 }
 
 /// Describes the things that some `GenericKind` value `G` is known to
@@ -875,10 +875,10 @@ impl<'tcx> fmt::Display for GenericKind<'tcx> {
 }
 
 impl<'tcx> GenericKind<'tcx> {
-    pub fn to_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+    pub fn as_ty(&self) -> Ty<'tcx> {
         match *self {
-            GenericKind::Param(ref p) => p.to_ty(tcx),
-            GenericKind::Projection(ref p) => tcx.mk_projection(p.item_def_id, p.substs),
+            GenericKind::Param(ref p) => p.as_ty(),
+            GenericKind::Projection(ref p) => p.as_ty(),
         }
     }
 }

src/librustc/traits/query/outlives_bounds.rs

@@ -20,8 +20,8 @@ use std::mem;
 #[derive(Clone, Debug, TypeFoldable, Lift)]
 pub enum OutlivesBound<'tcx> {
     RegionSubRegion(ty::Region<'tcx>, ty::Region<'tcx>),
-    RegionSubParam(ty::Region<'tcx>, ty::ParamTy),
-    RegionSubProjection(ty::Region<'tcx>, ty::ProjectionTy<'tcx>),
+    RegionSubParam(ty::Region<'tcx>, ty::View<'tcx, ty::ParamTy>),
+    RegionSubProjection(ty::Region<'tcx>, ty::View<'tcx, ty::ProjectionTy<'tcx>>),
 }
 
 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for OutlivesBound<'tcx> {

src/librustc/ty/mod.rs

@@ -91,6 +91,8 @@ pub use self::trait_def::TraitDef;
 
 pub use self::query::queries;
 
+pub use self::view::View;
+
 pub mod adjustment;
 pub mod binding;
 pub mod cast;
@@ -114,6 +116,7 @@ pub mod steal;
 pub mod subst;
 pub mod trait_def;
 pub mod util;
+pub mod view;
 pub mod walk;
 
 mod context;