Auto merge of #88627 - cjgillot:noallocuse, r=petrochenkov

Do not preallocate HirIds

Part of https://github.com/rust-lang/rust/pull/87234

r? `@petrochenkov`

4 files changed, 32 insertions, 100 deletions

diff --git a/compiler/rustc_ast_lowering/src/block.rs b/compiler/rustc_ast_lowering/src/block.rs
index ca804ec6758..14a894d61f4 100644
--- a/compiler/rustc_ast_lowering/src/block.rs
+++ b/compiler/rustc_ast_lowering/src/block.rs
@@ -55,7 +55,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }
                 }
                 StmtKind::Item(ref it) => {
-                    stmts.extend(self.lower_item_id(it).into_iter().enumerate().map(
+                    stmts.extend(self.lower_item_ref(it).into_iter().enumerate().map(
                         |(i, item_id)| {
                             let hir_id = match i {
                                 0 => self.lower_node_id(s.id),
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index a77e3e1997f..520faa6dcd6 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -40,6 +40,7 @@ impl ItemLowerer<'_, '_, '_> {
 
 impl<'a> Visitor<'a> for ItemLowerer<'a, '_, '_> {
     fn visit_item(&mut self, item: &'a Item) {
+        self.lctx.allocate_hir_id_counter(item.id);
         let hir_id = self.lctx.with_hir_id_owner(item.id, |lctx| {
             lctx.without_in_scope_lifetime_defs(|lctx| {
                 let hir_item = lctx.lower_item(item);
@@ -77,6 +78,7 @@ impl<'a> Visitor<'a> for ItemLowerer<'a, '_, '_> {
     }
 
     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
+        self.lctx.allocate_hir_id_counter(item.id);
         self.lctx.with_hir_id_owner(item.id, |lctx| match ctxt {
             AssocCtxt::Trait => {
                 let hir_item = lctx.lower_trait_item(item);
@@ -154,41 +156,28 @@ impl<'hir> LoweringContext<'_, 'hir> {
     pub(super) fn lower_mod(&mut self, items: &[P<Item>], inner: Span) -> hir::Mod<'hir> {
         hir::Mod {
             inner: self.lower_span(inner),
-            item_ids: self.arena.alloc_from_iter(items.iter().flat_map(|x| self.lower_item_id(x))),
+            item_ids: self.arena.alloc_from_iter(items.iter().flat_map(|x| self.lower_item_ref(x))),
         }
     }
 
-    pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
-        let node_ids = match i.kind {
-            ItemKind::Use(ref use_tree) => {
-                let mut vec = smallvec![i.id];
-                self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
-                vec
-            }
-            ItemKind::Fn(..) | ItemKind::Impl(box ImplKind { of_trait: None, .. }) => {
-                smallvec![i.id]
-            }
-            _ => smallvec![i.id],
-        };
-
+    pub(super) fn lower_item_ref(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
+        let mut node_ids = smallvec![hir::ItemId { def_id: self.resolver.local_def_id(i.id) }];
+        if let ItemKind::Use(ref use_tree) = &i.kind {
+            self.lower_item_id_use_tree(use_tree, i.id, &mut node_ids);
+        }
         node_ids
-            .into_iter()
-            .map(|node_id| hir::ItemId {
-                def_id: self.allocate_hir_id_counter(node_id).expect_owner(),
-            })
-            .collect()
     }
 
     fn lower_item_id_use_tree(
         &mut self,
         tree: &UseTree,
         base_id: NodeId,
-        vec: &mut SmallVec<[NodeId; 1]>,
+        vec: &mut SmallVec<[hir::ItemId; 1]>,
     ) {
         match tree.kind {
             UseTreeKind::Nested(ref nested_vec) => {
                 for &(ref nested, id) in nested_vec {
-                    vec.push(id);
+                    vec.push(hir::ItemId { def_id: self.resolver.local_def_id(id) });
                     self.lower_item_id_use_tree(nested, id, vec);
                 }
             }
@@ -197,7 +186,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 for (_, &id) in
                     iter::zip(self.expect_full_res_from_use(base_id).skip(1), &[id1, id2])
                 {
-                    vec.push(id);
+                    vec.push(hir::ItemId { def_id: self.resolver.local_def_id(id) });
                 }
             }
         }
@@ -486,7 +475,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     }
                 }
 
-                let mut resolutions = self.expect_full_res_from_use(id);
+                let mut resolutions = self.expect_full_res_from_use(id).fuse();
                 // We want to return *something* from this function, so hold onto the first item
                 // for later.
                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
@@ -496,7 +485,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // won't be dealing with macros in the rest of the compiler.
                 // Essentially a single `use` which imports two names is desugared into
                 // two imports.
-                for (res, &new_node_id) in iter::zip(resolutions, &[id1, id2]) {
+                for new_node_id in [id1, id2] {
+                    // Associate an HirId to both ids even if there is no resolution.
+                    let new_id = self.allocate_hir_id_counter(new_node_id);
+
+                    let res = if let Some(res) = resolutions.next() { res } else { continue };
                     let ident = *ident;
                     let mut path = path.clone();
                     for seg in &mut path.segments {
@@ -505,17 +498,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     let span = path.span;
 
                     self.with_hir_id_owner(new_node_id, |this| {
-                        let new_id = this.lower_node_id(new_node_id);
                         let res = this.lower_res(res);
                         let path = this.lower_path_extra(res, &path, ParamMode::Explicit, None);
                         let kind = hir::ItemKind::Use(path, hir::UseKind::Single);
                         let vis = this.rebuild_vis(&vis);
                         if let Some(attrs) = attrs {
-                            this.attrs.insert(new_id, attrs);
+                            this.attrs.insert(hir::HirId::make_owner(new_id), attrs);
                         }
 
                         this.insert_item(hir::Item {
-                            def_id: new_id.expect_owner(),
+                            def_id: new_id,
                             ident: this.lower_ident(ident),
                             kind,
                             vis,
@@ -564,7 +556,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
                 // Add all the nested `PathListItem`s to the HIR.
                 for &(ref use_tree, id) in trees {
-                    let new_hir_id = self.lower_node_id(id);
+                    let new_hir_id = self.allocate_hir_id_counter(id);
 
                     let mut prefix = prefix.clone();
 
@@ -585,11 +577,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         let kind =
                             this.lower_use_tree(use_tree, &prefix, id, &mut vis, &mut ident, attrs);
                         if let Some(attrs) = attrs {
-                            this.attrs.insert(new_hir_id, attrs);
+                            this.attrs.insert(hir::HirId::make_owner(new_hir_id), attrs);
                         }
 
                         this.insert_item(hir::Item {
-                            def_id: new_hir_id.expect_owner(),
+                            def_id: new_hir_id,
                             ident: this.lower_ident(ident),
                             kind,
                             vis,
@@ -700,7 +692,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_foreign_item_ref(&mut self, i: &ForeignItem) -> hir::ForeignItemRef<'hir> {
         hir::ForeignItemRef {
-            id: hir::ForeignItemId { def_id: self.lower_node_id(i.id).expect_owner() },
+            id: hir::ForeignItemId { def_id: self.allocate_hir_id_counter(i.id) },
             ident: self.lower_ident(i.ident),
             span: self.lower_span(i.span),
             vis: self.lower_visibility(&i.vis, Some(i.id)),
@@ -839,7 +831,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
             AssocItemKind::MacCall(..) => unimplemented!(),
         };
-        let id = hir::TraitItemId { def_id: self.lower_node_id(i.id).expect_owner() };
+        let id = hir::TraitItemId { def_id: self.resolver.local_def_id(i.id) };
         let defaultness = hir::Defaultness::Default { has_value: has_default };
         hir::TraitItemRef {
             id,
@@ -925,7 +917,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let has_value = true;
         let (defaultness, _) = self.lower_defaultness(i.kind.defaultness(), has_value);
         hir::ImplItemRef {
-            id: hir::ImplItemId { def_id: self.lower_node_id(i.id).expect_owner() },
+            id: hir::ImplItemId { def_id: self.allocate_hir_id_counter(i.id) },
             ident: self.lower_ident(i.ident),
             span: self.lower_span(i.span),
             vis: self.lower_visibility(&i.vis, Some(i.id)),
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 4cf54b07dbe..fb8d5db034a 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -38,7 +38,7 @@
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::token::{self, Token};
 use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream, TokenTree};
-use rustc_ast::visit::{self, AssocCtxt, Visitor};
+use rustc_ast::visit;
 use rustc_ast::{self as ast, *};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::captures::Captures;
@@ -418,60 +418,9 @@ enum AnonymousLifetimeMode {
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_crate(mut self, c: &Crate) -> &'hir hir::Crate<'hir> {
-        /// Full-crate AST visitor that inserts into a fresh
-        /// `LoweringContext` any information that may be
-        /// needed from arbitrary locations in the crate,
-        /// e.g., the number of lifetime generic parameters
-        /// declared for every type and trait definition.
-        struct MiscCollector<'tcx, 'lowering, 'hir> {
-            lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
-        }
-
-        impl MiscCollector<'_, '_, '_> {
-            fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree) {
-                match tree.kind {
-                    UseTreeKind::Simple(_, id1, id2) => {
-                        for id in [id1, id2] {
-                            self.lctx.allocate_hir_id_counter(id);
-                        }
-                    }
-                    UseTreeKind::Glob => (),
-                    UseTreeKind::Nested(ref trees) => {
-                        for &(ref use_tree, id) in trees {
-                            self.lctx.allocate_hir_id_counter(id);
-                            self.allocate_use_tree_hir_id_counters(use_tree);
-                        }
-                    }
-                }
-            }
-        }
-
-        impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
-            fn visit_item(&mut self, item: &'tcx Item) {
-                self.lctx.allocate_hir_id_counter(item.id);
-
-                if let ItemKind::Use(ref use_tree) = item.kind {
-                    self.allocate_use_tree_hir_id_counters(use_tree);
-                }
-
-                visit::walk_item(self, item);
-            }
-
-            fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
-                self.lctx.allocate_hir_id_counter(item.id);
-                visit::walk_assoc_item(self, item, ctxt);
-            }
-
-            fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) {
-                self.lctx.allocate_hir_id_counter(item.id);
-                visit::walk_foreign_item(self, item);
-            }
-        }
-
         self.lower_node_id(CRATE_NODE_ID);
         debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
 
-        visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
         visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
 
         let module = self.arena.alloc(self.lower_mod(&c.items, c.span));
@@ -554,13 +503,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         id
     }
 
-    fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
+    fn allocate_hir_id_counter(&mut self, owner: NodeId) -> LocalDefId {
         // Set up the counter if needed.
         self.item_local_id_counters.entry(owner).or_insert(0);
         // Always allocate the first `HirId` for the owner itself.
         let lowered = self.lower_node_id_with_owner(owner, owner);
         debug_assert_eq!(lowered.local_id.as_u32(), 0);
-        lowered
+        lowered.owner
     }
 
     fn create_stable_hashing_context(&self) -> LoweringHasher<'_> {
@@ -1494,9 +1443,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // frequently opened issues show.
         let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
 
-        let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
-
-        self.allocate_hir_id_counter(opaque_ty_node_id);
+        let opaque_ty_def_id = self.allocate_hir_id_counter(opaque_ty_node_id);
 
         let collected_lifetimes = self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
             let hir_bounds = lower_bounds(lctx);
@@ -1753,9 +1700,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
 
-        let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
-
-        self.allocate_hir_id_counter(opaque_ty_node_id);
+        let opaque_ty_def_id = self.allocate_hir_id_counter(opaque_ty_node_id);
 
         // When we create the opaque type for this async fn, it is going to have
         // to capture all the lifetimes involved in the signature (including in the
diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
index 10714a4b706..495c5e17197 100644
--- a/compiler/rustc_middle/src/hir/map/mod.rs
+++ b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -7,7 +7,7 @@ use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::svh::Svh;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
@@ -206,11 +206,6 @@ impl<'hir> Map<'hir> {
     }
 
     pub fn opt_def_kind(&self, local_def_id: LocalDefId) -> Option<DefKind> {
-        // FIXME(eddyb) support `find` on the crate root.
-        if local_def_id.to_def_id().index == CRATE_DEF_INDEX {
-            return Some(DefKind::Mod);
-        }
-
         let hir_id = self.local_def_id_to_hir_id(local_def_id);
         let def_kind = match self.find(hir_id)? {
             Node::Item(item) => match item.kind {