Arena-allocate `hir::Lifetime`.

This shrinks `hir::Ty` from 72 to 48 bytes.

`visit_lifetime` is added to the HIR stats collector because these types
are now stored in memory on their own, instead of being within other
types.

6 files changed, 65 insertions, 56 deletions

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index e7bbf7dbdec..e484f77cad4 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -1196,7 +1196,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let lifetime_bound = this.elided_dyn_bound(t.span);
                 (bounds, lifetime_bound)
             });
-            let kind = hir::TyKind::TraitObject(bounds, lifetime_bound, TraitObjectSyntax::None);
+            let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
             return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
         }
 
@@ -1934,8 +1934,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let res = res.unwrap_or(
                     self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
                 );
-                let l = self.new_named_lifetime_with_res(id, span, ident, res);
-                hir::GenericArg::Lifetime(l)
+                hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, span, ident, res))
             },
         ));
 
@@ -2004,7 +2003,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         }
     }
 
-    fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
+    fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
         let span = self.lower_span(l.ident.span);
         let ident = self.lower_ident(l.ident);
         self.new_named_lifetime(l.id, l.id, span, ident)
@@ -2017,7 +2016,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         span: Span,
         ident: Ident,
         res: LifetimeRes,
-    ) -> hir::Lifetime {
+    ) -> &'hir hir::Lifetime {
         let name = match res {
             LifetimeRes::Param { param, .. } => {
                 let p_name = ParamName::Plain(ident);
@@ -2038,7 +2037,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         };
 
         debug!(?name);
-        hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
+        self.arena.alloc(hir::Lifetime {
+            hir_id: self.lower_node_id(id),
+            span: self.lower_span(span),
+            name,
+        })
     }
 
     #[instrument(level = "debug", skip(self))]
@@ -2048,7 +2051,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         new_id: NodeId,
         span: Span,
         ident: Ident,
-    ) -> hir::Lifetime {
+    ) -> &'hir hir::Lifetime {
         let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
         self.new_named_lifetime_with_res(new_id, span, ident, res)
     }
@@ -2462,14 +2465,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
     /// when the bound is written, even if it is written with `'_` like in
     /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
-    fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
+    fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
         let r = hir::Lifetime {
             hir_id: self.next_id(),
             span: self.lower_span(span),
             name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
         };
         debug!("elided_dyn_bound: r={:?}", r);
-        r
+        self.arena.alloc(r)
     }
 }
 
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index a668c0e95ce..8eb0f6dd812 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -259,7 +259,7 @@ impl InferArg {
 
 #[derive(Debug, HashStable_Generic)]
 pub enum GenericArg<'hir> {
-    Lifetime(Lifetime),
+    Lifetime(&'hir Lifetime),
     Type(&'hir Ty<'hir>),
     Const(ConstArg),
     Infer(InferArg),
@@ -430,7 +430,7 @@ pub enum GenericBound<'hir> {
     Trait(PolyTraitRef<'hir>, TraitBoundModifier),
     // FIXME(davidtwco): Introduce `PolyTraitRef::LangItem`
     LangItemTrait(LangItem, Span, HirId, &'hir GenericArgs<'hir>),
-    Outlives(Lifetime),
+    Outlives(&'hir Lifetime),
 }
 
 impl GenericBound<'_> {
@@ -756,7 +756,7 @@ impl<'hir> WhereBoundPredicate<'hir> {
 pub struct WhereRegionPredicate<'hir> {
     pub span: Span,
     pub in_where_clause: bool,
-    pub lifetime: Lifetime,
+    pub lifetime: &'hir Lifetime,
     pub bounds: GenericBounds<'hir>,
 }
 
@@ -2499,7 +2499,7 @@ pub enum TyKind<'hir> {
     /// A raw pointer (i.e., `*const T` or `*mut T`).
     Ptr(MutTy<'hir>),
     /// A reference (i.e., `&'a T` or `&'a mut T`).
-    Rptr(Lifetime, MutTy<'hir>),
+    Rptr(&'hir Lifetime, MutTy<'hir>),
     /// A bare function (e.g., `fn(usize) -> bool`).
     BareFn(&'hir BareFnTy<'hir>),
     /// The never type (`!`).
@@ -2518,7 +2518,7 @@ pub enum TyKind<'hir> {
     OpaqueDef(ItemId, &'hir [GenericArg<'hir>]),
     /// A trait object type `Bound1 + Bound2 + Bound3`
     /// where `Bound` is a trait or a lifetime.
-    TraitObject(&'hir [PolyTraitRef<'hir>], Lifetime, TraitObjectSyntax),
+    TraitObject(&'hir [PolyTraitRef<'hir>], &'hir Lifetime, TraitObjectSyntax),
     /// Unused for now.
     Typeof(AnonConst),
     /// `TyKind::Infer` means the type should be inferred instead of it having been
@@ -3474,7 +3474,7 @@ mod size_asserts {
     static_assert_size!(ForeignItem<'_>, 72);
     static_assert_size!(ForeignItemKind<'_>, 40);
     #[cfg(not(bootstrap))]
-    static_assert_size!(GenericArg<'_>, 32);
+    static_assert_size!(GenericArg<'_>, 24);
     static_assert_size!(GenericBound<'_>, 48);
     static_assert_size!(Generics<'_>, 56);
     static_assert_size!(Impl<'_>, 80);
@@ -3494,9 +3494,9 @@ mod size_asserts {
     static_assert_size!(Stmt<'_>, 32);
     static_assert_size!(StmtKind<'_>, 16);
     #[cfg(not(bootstrap))]
-    static_assert_size!(TraitItem<'static>, 88);
+    static_assert_size!(TraitItem<'_>, 88);
     #[cfg(not(bootstrap))]
     static_assert_size!(TraitItemKind<'_>, 48);
-    static_assert_size!(Ty<'_>, 72);
-    static_assert_size!(TyKind<'_>, 56);
+    static_assert_size!(Ty<'_>, 48);
+    static_assert_size!(TyKind<'_>, 32);
 }
diff --git a/compiler/rustc_passes/src/hir_stats.rs b/compiler/rustc_passes/src/hir_stats.rs
index 81ac0e1b6d4..075069feb52 100644
--- a/compiler/rustc_passes/src/hir_stats.rs
+++ b/compiler/rustc_passes/src/hir_stats.rs
@@ -437,6 +437,11 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
         }
     }
 
+    fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
+        self.record("Lifetime", Id::Node(lifetime.hir_id), lifetime);
+        hir_visit::walk_lifetime(self, lifetime)
+    }
+
     fn visit_path(&mut self, path: &'v hir::Path<'v>, _id: hir::HirId) {
         self.record("Path", Id::None, path);
         hir_visit::walk_path(self, path)
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 980a1485b59..2829ab45d47 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -190,7 +190,7 @@ fn clean_poly_trait_ref_with_bindings<'tcx>(
     )
 }
 
-fn clean_lifetime<'tcx>(lifetime: hir::Lifetime, cx: &mut DocContext<'tcx>) -> Lifetime {
+fn clean_lifetime<'tcx>(lifetime: &hir::Lifetime, cx: &mut DocContext<'tcx>) -> Lifetime {
     let def = cx.tcx.named_region(lifetime.hir_id);
     if let Some(
         rl::Region::EarlyBound(node_id)
@@ -495,7 +495,7 @@ fn clean_generic_param<'tcx>(
                     .filter(|bp| !bp.in_where_clause)
                     .flat_map(|bp| bp.bounds)
                     .map(|bound| match bound {
-                        hir::GenericBound::Outlives(lt) => clean_lifetime(*lt, cx),
+                        hir::GenericBound::Outlives(lt) => clean_lifetime(lt, cx),
                         _ => panic!(),
                     })
                     .collect()
@@ -1392,7 +1392,7 @@ fn maybe_expand_private_type_alias<'tcx>(
                     }
                     _ => None,
                 });
-                if let Some(lt) = lifetime.cloned() {
+                if let Some(lt) = lifetime {
                     let lt_def_id = cx.tcx.hir().local_def_id(param.hir_id);
                     let cleaned =
                         if !lt.is_elided() { clean_lifetime(lt, cx) } else { Lifetime::elided() };
diff --git a/src/test/ui/stats/hir-stats.stderr b/src/test/ui/stats/hir-stats.stderr
index c8ceb6ff22d..24c281a0c99 100644
--- a/src/test/ui/stats/hir-stats.stderr
+++ b/src/test/ui/stats/hir-stats.stderr
@@ -119,59 +119,60 @@ hir-stats HIR STATS
 hir-stats Name                Accumulated Size         Count     Item Size
 hir-stats ----------------------------------------------------------------
 hir-stats ForeignItemRef            24 ( 0.2%)             1            24
+hir-stats Lifetime                  32 ( 0.3%)             1            32
 hir-stats Mod                       32 ( 0.3%)             1            32
 hir-stats ExprField                 40 ( 0.4%)             1            40
 hir-stats TraitItemRef              56 ( 0.6%)             2            28
-hir-stats Param                     64 ( 0.6%)             2            32
-hir-stats Local                     64 ( 0.6%)             1            64
+hir-stats Local                     64 ( 0.7%)             1            64
+hir-stats Param                     64 ( 0.7%)             2            32
 hir-stats InlineAsm                 72 ( 0.7%)             1            72
 hir-stats ImplItemRef               72 ( 0.7%)             2            36
-hir-stats FieldDef                  96 ( 0.9%)             2            48
-hir-stats Arm                       96 ( 0.9%)             2            48
-hir-stats Body                      96 ( 0.9%)             3            32
-hir-stats Stmt                      96 ( 0.9%)             3            32
+hir-stats Body                      96 ( 1.0%)             3            32
+hir-stats GenericArg                96 ( 1.0%)             4            24
+hir-stats - Type                      24 ( 0.2%)             1
+hir-stats - Lifetime                  72 ( 0.7%)             3
+hir-stats FieldDef                  96 ( 1.0%)             2            48
+hir-stats Arm                       96 ( 1.0%)             2            48
+hir-stats Stmt                      96 ( 1.0%)             3            32
 hir-stats - Local                     32 ( 0.3%)             1
 hir-stats - Semi                      32 ( 0.3%)             1
 hir-stats - Expr                      32 ( 0.3%)             1
 hir-stats FnDecl                   120 ( 1.2%)             3            40
 hir-stats Attribute                128 ( 1.3%)             4            32
-hir-stats GenericArg               128 ( 1.3%)             4            32
-hir-stats - Type                      32 ( 0.3%)             1
-hir-stats - Lifetime                  96 ( 0.9%)             3
-hir-stats GenericArgs              144 ( 1.4%)             3            48
+hir-stats GenericArgs              144 ( 1.5%)             3            48
 hir-stats Variant                  160 ( 1.6%)             2            80
-hir-stats GenericBound             192 ( 1.9%)             4            48
-hir-stats - Trait                    192 ( 1.9%)             4
-hir-stats WherePredicate           216 ( 2.1%)             3            72
-hir-stats - BoundPredicate           216 ( 2.1%)             3
-hir-stats Block                    288 ( 2.8%)             6            48
-hir-stats GenericParam             400 ( 3.9%)             5            80
-hir-stats Pat                      440 ( 4.3%)             5            88
+hir-stats WherePredicate           168 ( 1.7%)             3            56
+hir-stats - BoundPredicate           168 ( 1.7%)             3
+hir-stats GenericBound             192 ( 2.0%)             4            48
+hir-stats - Trait                    192 ( 2.0%)             4
+hir-stats Block                    288 ( 3.0%)             6            48
+hir-stats GenericParam             400 ( 4.1%)             5            80
+hir-stats Pat                      440 ( 4.5%)             5            88
 hir-stats - Wild                      88 ( 0.9%)             1
 hir-stats - Struct                    88 ( 0.9%)             1
-hir-stats - Binding                  264 ( 2.6%)             3
-hir-stats Generics                 560 ( 5.5%)            10            56
-hir-stats Expr                     768 ( 7.6%)            12            64
-hir-stats - Path                      64 ( 0.6%)             1
-hir-stats - Struct                    64 ( 0.6%)             1
-hir-stats - Match                     64 ( 0.6%)             1
-hir-stats - InlineAsm                 64 ( 0.6%)             1
+hir-stats - Binding                  264 ( 2.7%)             3
+hir-stats Generics                 560 ( 5.7%)            10            56
+hir-stats Ty                       720 ( 7.4%)            15            48
+hir-stats - Ptr                       48 ( 0.5%)             1
+hir-stats - Rptr                      48 ( 0.5%)             1
+hir-stats - Path                     624 ( 6.4%)            13
+hir-stats Expr                     768 ( 7.9%)            12            64
+hir-stats - Path                      64 ( 0.7%)             1
+hir-stats - Struct                    64 ( 0.7%)             1
+hir-stats - Match                     64 ( 0.7%)             1
+hir-stats - InlineAsm                 64 ( 0.7%)             1
 hir-stats - Lit                      128 ( 1.3%)             2
-hir-stats - Block                    384 ( 3.8%)             6
-hir-stats Item                     960 ( 9.4%)            12            80
+hir-stats - Block                    384 ( 3.9%)             6
+hir-stats Item                     960 ( 9.8%)            12            80
 hir-stats - Trait                     80 ( 0.8%)             1
 hir-stats - Enum                      80 ( 0.8%)             1
 hir-stats - ExternCrate               80 ( 0.8%)             1
 hir-stats - ForeignMod                80 ( 0.8%)             1
 hir-stats - Impl                      80 ( 0.8%)             1
 hir-stats - Fn                       160 ( 1.6%)             2
-hir-stats - Use                      400 ( 3.9%)             5
-hir-stats Ty                     1_080 (10.6%)            15            72
-hir-stats - Ptr                       72 ( 0.7%)             1
-hir-stats - Rptr                      72 ( 0.7%)             1
-hir-stats - Path                     936 ( 9.2%)            13
-hir-stats Path                   1_536 (15.1%)            32            48
-hir-stats PathSegment            2_240 (22.0%)            40            56
+hir-stats - Use                      400 ( 4.1%)             5
+hir-stats Path                   1_536 (15.7%)            32            48
+hir-stats PathSegment            2_240 (23.0%)            40            56
 hir-stats ----------------------------------------------------------------
-hir-stats Total                 10_168
+hir-stats Total                  9_760
 hir-stats
diff --git a/src/tools/clippy/clippy_utils/src/hir_utils.rs b/src/tools/clippy/clippy_utils/src/hir_utils.rs
index 57448f716d4..ff23ed5fffa 100644
--- a/src/tools/clippy/clippy_utils/src/hir_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/hir_utils.rs
@@ -929,7 +929,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
         }
     }
 
-    pub fn hash_lifetime(&mut self, lifetime: Lifetime) {
+    pub fn hash_lifetime(&mut self, lifetime: &Lifetime) {
         std::mem::discriminant(&lifetime.name).hash(&mut self.s);
         if let LifetimeName::Param(param_id, ref name) = lifetime.name {
             std::mem::discriminant(name).hash(&mut self.s);