Auto merge of #81398 - bugadani:rustdoc-perf, r=GuillaumeGomez

rustdoc tweaking

* Reuse memory
* simplify `next_def_id`, avoid multiple hashing and unnecessary lookups
* remove `all_fake_def_ids`, use the global map instead (probably not a good step toward parallelization, though...)
* convert `add_deref_target` to iterative implementation
* use `ArrayVec` where we know the max number of elements
* minor touchups here and there
* avoid building temporary vectors that get appended to other vectors

At most places I may or may not be doing the compiler's job is this PR.

Cargo.lock

@@ -4386,6 +4386,7 @@ dependencies = [
 name = "rustdoc"
 version = "0.0.0"
 dependencies = [
+ "arrayvec",
  "expect-test",
  "itertools 0.9.0",
  "minifier",

src/librustdoc/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2018"
 path = "lib.rs"
 
 [dependencies]
+arrayvec = { version = "0.5.1", default-features = false }
 pulldown-cmark = { version = "0.8", default-features = false }
 minifier = "0.0.33"
 rayon = { version = "0.3.0", package = "rustc-rayon" }

src/librustdoc/clean/inline.rs

@@ -56,7 +56,7 @@ crate fn try_inline(
     let kind = match res {
         Res::Def(DefKind::Trait, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Trait);
-            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
+            build_impls(cx, Some(parent_module), did, attrs, &mut ret);
             clean::TraitItem(build_external_trait(cx, did))
         }
         Res::Def(DefKind::Fn, did) => {
@@ -65,27 +65,27 @@ crate fn try_inline(
         }
         Res::Def(DefKind::Struct, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Struct);
-            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
+            build_impls(cx, Some(parent_module), did, attrs, &mut ret);
             clean::StructItem(build_struct(cx, did))
         }
         Res::Def(DefKind::Union, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Union);
-            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
+            build_impls(cx, Some(parent_module), did, attrs, &mut ret);
             clean::UnionItem(build_union(cx, did))
         }
         Res::Def(DefKind::TyAlias, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Typedef);
-            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
+            build_impls(cx, Some(parent_module), did, attrs, &mut ret);
             clean::TypedefItem(build_type_alias(cx, did), false)
         }
         Res::Def(DefKind::Enum, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Enum);
-            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
+            build_impls(cx, Some(parent_module), did, attrs, &mut ret);
             clean::EnumItem(build_enum(cx, did))
         }
         Res::Def(DefKind::ForeignTy, did) => {
             record_extern_fqn(cx, did, clean::TypeKind::Foreign);
-            ret.extend(build_impls(cx, Some(parent_module), did, attrs));
+            build_impls(cx, Some(parent_module), did, attrs, &mut ret);
             clean::ForeignTypeItem
         }
         // Never inline enum variants but leave them shown as re-exports.
@@ -133,10 +133,7 @@ crate fn try_inline_glob(
     res: Res,
     visited: &mut FxHashSet<DefId>,
 ) -> Option<Vec<clean::Item>> {
-    if res == Res::Err {
-        return None;
-    }
-    let did = res.def_id();
+    let did = res.opt_def_id()?;
     if did.is_local() {
         return None;
     }
@@ -280,16 +277,14 @@ crate fn build_impls(
     parent_module: Option<DefId>,
     did: DefId,
     attrs: Option<Attrs<'_>>,
-) -> Vec<clean::Item> {
+    ret: &mut Vec<clean::Item>,
+) {
     let tcx = cx.tcx;
-    let mut impls = Vec::new();
 
     // for each implementation of an item represented by `did`, build the clean::Item for that impl
     for &did in tcx.inherent_impls(did).iter() {
-        build_impl(cx, parent_module, did, attrs, &mut impls);
+        build_impl(cx, parent_module, did, attrs, ret);
     }
-
-    impls
 }
 
 /// `parent_module` refers to the parent of the re-export, not the original item

src/librustdoc/clean/types.rs

@@ -8,6 +8,7 @@ use std::rc::Rc;
 use std::sync::Arc;
 use std::{slice, vec};
 
+use arrayvec::ArrayVec;
 use rustc_ast::attr;
 use rustc_ast::util::comments::beautify_doc_string;
 use rustc_ast::{self as ast, AttrStyle};
@@ -16,7 +17,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_feature::UnstableFeatures;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId};
+use rustc_hir::def_id::{CrateNum, DefId, DefIndex};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::Mutability;
 use rustc_index::vec::IndexVec;
@@ -28,7 +29,6 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol, SymbolStr};
 use rustc_span::{self, FileName, Loc};
 use rustc_target::abi::VariantIdx;
 use rustc_target::spec::abi::Abi;
-use smallvec::{smallvec, SmallVec};
 
 use crate::clean::cfg::Cfg;
 use crate::clean::external_path;
@@ -45,7 +45,7 @@ use self::ItemKind::*;
 use self::SelfTy::*;
 use self::Type::*;
 
-thread_local!(crate static MAX_DEF_ID: RefCell<FxHashMap<CrateNum, DefId>> = Default::default());
+thread_local!(crate static MAX_DEF_IDX: RefCell<FxHashMap<CrateNum, DefIndex>> = Default::default());
 
 #[derive(Clone, Debug)]
 crate struct Crate {
@@ -293,8 +293,8 @@ impl Item {
     ///
     /// [`next_def_id()`]: DocContext::next_def_id()
     crate fn is_fake(&self) -> bool {
-        MAX_DEF_ID.with(|m| {
-            m.borrow().get(&self.def_id.krate).map(|id| self.def_id >= *id).unwrap_or(false)
+        MAX_DEF_IDX.with(|m| {
+            m.borrow().get(&self.def_id.krate).map(|&idx| idx <= self.def_id.index).unwrap_or(false)
         })
     }
 }
@@ -1539,12 +1539,12 @@ impl PrimitiveType {
         }
     }
 
-    crate fn impls(&self, tcx: TyCtxt<'_>) -> &'static SmallVec<[DefId; 4]> {
+    crate fn impls(&self, tcx: TyCtxt<'_>) -> &'static ArrayVec<[DefId; 4]> {
         Self::all_impls(tcx).get(self).expect("missing impl for primitive type")
     }
 
-    crate fn all_impls(tcx: TyCtxt<'_>) -> &'static FxHashMap<PrimitiveType, SmallVec<[DefId; 4]>> {
-        static CELL: OnceCell<FxHashMap<PrimitiveType, SmallVec<[DefId; 4]>>> = OnceCell::new();
+    crate fn all_impls(tcx: TyCtxt<'_>) -> &'static FxHashMap<PrimitiveType, ArrayVec<[DefId; 4]>> {
+        static CELL: OnceCell<FxHashMap<PrimitiveType, ArrayVec<[DefId; 4]>>> = OnceCell::new();
 
         CELL.get_or_init(move || {
             use self::PrimitiveType::*;
@@ -1568,7 +1568,7 @@ impl PrimitiveType {
             }
 
             let single = |a: Option<DefId>| a.into_iter().collect();
-            let both = |a: Option<DefId>, b: Option<DefId>| -> SmallVec<_> {
+            let both = |a: Option<DefId>, b: Option<DefId>| -> ArrayVec<_> {
                 a.into_iter().chain(b).collect()
             };
 
@@ -1601,8 +1601,8 @@ impl PrimitiveType {
                         .collect()
                 },
                 Array => single(lang_items.array_impl()),
-                Tuple => smallvec![],
-                Unit => smallvec![],
+                Tuple => ArrayVec::new(),
+                Unit => ArrayVec::new(),
                 RawPointer => {
                     lang_items
                         .const_ptr_impl()
@@ -1612,9 +1612,9 @@ impl PrimitiveType {
                         .chain(lang_items.mut_slice_ptr_impl())
                         .collect()
                 },
-                Reference => smallvec![],
-                Fn => smallvec![],
-                Never => smallvec![],
+                Reference => ArrayVec::new(),
+                Fn => ArrayVec::new(),
+                Never => ArrayVec::new(),
             }
         })
     }

src/librustdoc/clean/utils.rs

@@ -322,20 +322,14 @@ crate fn build_deref_target_impls(cx: &DocContext<'_>, items: &[Item], ret: &mut
             ItemKind::TypedefItem(ref t, true) => &t.type_,
             _ => continue,
         };
-        let primitive = match *target {
-            ResolvedPath { did, .. } if did.is_local() => continue,
-            ResolvedPath { did, .. } => {
-                ret.extend(inline::build_impls(cx, None, did, None));
-                continue;
+
+        if let Some(prim) = target.primitive_type() {
+            for &did in prim.impls(tcx).iter().filter(|did| !did.is_local()) {
+                inline::build_impl(cx, None, did, None, ret);
             }
-            _ => match target.primitive_type() {
-                Some(prim) => prim,
-                None => continue,
-            },
-        };
-        for &did in primitive.impls(tcx) {
+        } else if let ResolvedPath { did, .. } = *target {
             if !did.is_local() {
-                inline::build_impl(cx, None, did, None, ret);
+                inline::build_impls(cx, None, did, None, ret);
             }
         }
     }

src/librustdoc/config.rs

@@ -474,7 +474,7 @@ impl Options {
         };
 
         let mut id_map = html::markdown::IdMap::new();
-        id_map.populate(html::render::initial_ids());
+        id_map.populate(&html::render::INITIAL_IDS);
         let external_html = match ExternalHtml::load(
             &matches.opt_strs("html-in-header"),
             &matches.opt_strs("html-before-content"),

src/librustdoc/core.rs

@@ -24,12 +24,15 @@ use rustc_span::source_map;
 use rustc_span::symbol::sym;
 use rustc_span::DUMMY_SP;
 
-use std::cell::{Cell, RefCell};
 use std::mem;
 use std::rc::Rc;
+use std::{
+    cell::{Cell, RefCell},
+    collections::hash_map::Entry,
+};
 
 use crate::clean;
-use crate::clean::{AttributesExt, MAX_DEF_ID};
+use crate::clean::{AttributesExt, MAX_DEF_IDX};
 use crate::config::{Options as RustdocOptions, RenderOptions};
 use crate::config::{OutputFormat, RenderInfo};
 use crate::formats::cache::Cache;
@@ -63,8 +66,7 @@ crate struct DocContext<'tcx> {
     crate ct_substs: RefCell<FxHashMap<DefId, clean::Constant>>,
     /// Table synthetic type parameter for `impl Trait` in argument position -> bounds
     crate impl_trait_bounds: RefCell<FxHashMap<ImplTraitParam, Vec<clean::GenericBound>>>,
-    crate fake_def_ids: RefCell<FxHashMap<CrateNum, DefId>>,
-    crate all_fake_def_ids: RefCell<FxHashSet<DefId>>,
+    crate fake_def_ids: RefCell<FxHashMap<CrateNum, DefIndex>>,
     /// Auto-trait or blanket impls processed so far, as `(self_ty, trait_def_id)`.
     // FIXME(eddyb) make this a `ty::TraitRef<'tcx>` set.
     crate generated_synthetics: RefCell<FxHashSet<(Ty<'tcx>, DefId)>>,
@@ -138,37 +140,38 @@ impl<'tcx> DocContext<'tcx> {
     /// [`Debug`]: std::fmt::Debug
     /// [`clean::Item`]: crate::clean::types::Item
     crate fn next_def_id(&self, crate_num: CrateNum) -> DefId {
-        let start_def_id = {
-            let num_def_ids = if crate_num == LOCAL_CRATE {
-                self.tcx.hir().definitions().def_path_table().num_def_ids()
-            } else {
-                self.enter_resolver(|r| r.cstore().num_def_ids(crate_num))
-            };
-
-            DefId { krate: crate_num, index: DefIndex::from_usize(num_def_ids) }
-        };
-
         let mut fake_ids = self.fake_def_ids.borrow_mut();
 
-        let def_id = *fake_ids.entry(crate_num).or_insert(start_def_id);
-        fake_ids.insert(
-            crate_num,
-            DefId { krate: crate_num, index: DefIndex::from(def_id.index.index() + 1) },
-        );
-
-        MAX_DEF_ID.with(|m| {
-            m.borrow_mut().entry(def_id.krate).or_insert(start_def_id);
-        });
-
-        self.all_fake_def_ids.borrow_mut().insert(def_id);
+        let def_index = match fake_ids.entry(crate_num) {
+            Entry::Vacant(e) => {
+                let num_def_idx = {
+                    let num_def_idx = if crate_num == LOCAL_CRATE {
+                        self.tcx.hir().definitions().def_path_table().num_def_ids()
+                    } else {
+                        self.enter_resolver(|r| r.cstore().num_def_ids(crate_num))
+                    };
+
+                    DefIndex::from_usize(num_def_idx)
+                };
+
+                MAX_DEF_IDX.with(|m| {
+                    m.borrow_mut().insert(crate_num, num_def_idx);
+                });
+                e.insert(num_def_idx)
+            }
+            Entry::Occupied(e) => e.into_mut(),
+        };
+        *def_index = DefIndex::from(*def_index + 1);
 
-        def_id
+        DefId { krate: crate_num, index: *def_index }
     }
 
     /// Like `hir().local_def_id_to_hir_id()`, but skips calling it on fake DefIds.
     /// (This avoids a slice-index-out-of-bounds panic.)
     crate fn as_local_hir_id(&self, def_id: DefId) -> Option<HirId> {
-        if self.all_fake_def_ids.borrow().contains(&def_id) {
+        if MAX_DEF_IDX.with(|m| {
+            m.borrow().get(&def_id.krate).map(|&idx| idx <= def_id.index).unwrap_or(false)
+        }) {
             None
         } else {
             def_id.as_local().map(|def_id| self.tcx.hir().local_def_id_to_hir_id(def_id))
@@ -517,7 +520,6 @@ crate fn run_global_ctxt(
         ct_substs: Default::default(),
         impl_trait_bounds: Default::default(),
         fake_def_ids: Default::default(),
-        all_fake_def_ids: Default::default(),
         generated_synthetics: Default::default(),
         auto_traits: tcx
             .all_traits(LOCAL_CRATE)

src/librustdoc/formats/item_type.rs

@@ -158,6 +158,6 @@ impl ItemType {
 
 impl fmt::Display for ItemType {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.as_str())
+        f.write_str(self.as_str())
     }
 }

src/librustdoc/html/escape.rs

@@ -16,23 +16,20 @@ impl<'a> fmt::Display for Escape<'a> {
         let Escape(s) = *self;
         let pile_o_bits = s;
         let mut last = 0;
-        for (i, ch) in s.bytes().enumerate() {
-            match ch as char {
-                '<' | '>' | '&' | '\'' | '"' => {
-                    fmt.write_str(&pile_o_bits[last..i])?;
-                    let s = match ch as char {
-                        '>' => "&gt;",
-                        '<' => "&lt;",
-                        '&' => "&amp;",
-                        '\'' => "&#39;",
-                        '"' => "&quot;",
-                        _ => unreachable!(),
-                    };
-                    fmt.write_str(s)?;
-                    last = i + 1;
-                }
-                _ => {}
-            }
+        for (i, ch) in s.char_indices() {
+            let s = match ch {
+                '>' => "&gt;",
+                '<' => "&lt;",
+                '&' => "&amp;",
+                '\'' => "&#39;",
+                '"' => "&quot;",
+                _ => continue,
+            };
+            fmt.write_str(&pile_o_bits[last..i])?;
+            fmt.write_str(s)?;
+            // NOTE: we only expect single byte characters here - which is fine as long as we
+            // only match single byte characters
+            last = i + 1;
         }
 
         if last < s.len() {