Auto merge of #53824 - ljedrz:begone_onevector, r=michaelwoerister

Remove OneVector, increase related SmallVec capacities

Removes the `OneVector` type alias (equivalent to `SmallVec<[T; 1]>`); it is used in scenarios where the capacity of 1 is often exceeded, which might be nullifying the performance wins (due to spilling to the heap) expected when using `SmallVec` instead of `Vec`.

The numbers I used in this PR are very rough estimates - it would probably be a good idea to adjust some/all of them, which is what this proposal is all about.

It might be a good idea to additionally create some local type aliases for the `SmallVec`s in the `Folder` trait, as they are repeated in quite a few spots; I'd be happy to apply this sort of adjustments.

src/Cargo.lock

@@ -2177,6 +2177,7 @@ dependencies = [
  "rustc_typeck 0.0.0",
  "scoped-tls 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "serialize 0.0.0",
+ "smallvec 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntax 0.0.0",
  "syntax_ext 0.0.0",
  "syntax_pos 0.0.0",

src/librustc/hir/lowering.rs

@@ -52,7 +52,6 @@ use lint::builtin::{self, PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
 use middle::cstore::CrateStore;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::indexed_vec::IndexVec;
-use rustc_data_structures::small_vec::OneVector;
 use rustc_data_structures::thin_vec::ThinVec;
 use session::Session;
 use util::common::FN_OUTPUT_NAME;
@@ -62,6 +61,7 @@ use std::collections::BTreeMap;
 use std::fmt::Debug;
 use std::iter;
 use std::mem;
+use smallvec::SmallVec;
 use syntax::attr;
 use syntax::ast;
 use syntax::ast::*;
@@ -307,7 +307,7 @@ enum AnonymousLifetimeMode {
     PassThrough,
 }
 
-struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut OneVector<hir::ItemId> }
+struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut SmallVec<[hir::ItemId; 1]> }
 
 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
     fn visit_ty(&mut self, ty: &'a Ty) {
@@ -1901,9 +1901,9 @@ impl<'a> LoweringContext<'a> {
         )
     }
 
-    fn lower_local(&mut self, l: &Local) -> (P<hir::Local>, OneVector<hir::ItemId>) {
+    fn lower_local(&mut self, l: &Local) -> (P<hir::Local>, SmallVec<[hir::ItemId; 1]>) {
         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(l.id);
-        let mut ids = OneVector::<hir::ItemId>::new();
+        let mut ids = SmallVec::<[hir::ItemId; 1]>::new();
         if self.sess.features_untracked().impl_trait_in_bindings {
             if let Some(ref ty) = l.ty {
                 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
@@ -3211,7 +3211,7 @@ impl<'a> LoweringContext<'a> {
         &mut self,
         decl: &FnDecl,
         header: &FnHeader,
-        ids: &mut OneVector<hir::ItemId>,
+        ids: &mut SmallVec<[hir::ItemId; 1]>,
     ) {
         if let Some(id) = header.asyncness.opt_return_id() {
             ids.push(hir::ItemId { id });
@@ -3223,14 +3223,14 @@ impl<'a> LoweringContext<'a> {
         }
     }
 
-    fn lower_item_id(&mut self, i: &Item) -> OneVector<hir::ItemId> {
+    fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
         match i.node {
             ItemKind::Use(ref use_tree) => {
                 let mut vec = smallvec![hir::ItemId { id: i.id }];
                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
                 vec
             }
-            ItemKind::MacroDef(..) => OneVector::new(),
+            ItemKind::MacroDef(..) => SmallVec::new(),
             ItemKind::Fn(ref decl, ref header, ..) => {
                 let mut ids = smallvec![hir::ItemId { id: i.id }];
                 self.lower_fn_impl_trait_ids(decl, header, &mut ids);
@@ -3268,7 +3268,7 @@ impl<'a> LoweringContext<'a> {
     fn lower_item_id_use_tree(&mut self,
                               tree: &UseTree,
                               base_id: NodeId,
-                              vec: &mut OneVector<hir::ItemId>)
+                              vec: &mut SmallVec<[hir::ItemId; 1]>)
     {
         match tree.kind {
             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
@@ -4369,11 +4369,11 @@ impl<'a> LoweringContext<'a> {
         }
     }
 
-    fn lower_stmt(&mut self, s: &Stmt) -> OneVector<hir::Stmt> {
+    fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt; 1]> {
         smallvec![match s.node {
             StmtKind::Local(ref l) => {
                 let (l, item_ids) = self.lower_local(l);
-                let mut ids: OneVector<hir::Stmt> = item_ids
+                let mut ids: SmallVec<[hir::Stmt; 1]> = item_ids
                     .into_iter()
                     .map(|item_id| Spanned {
                         node: hir::StmtKind::Decl(

src/librustc_allocator/expand.rs

@@ -9,8 +9,8 @@
 // except according to those terms.
 
 use rustc::middle::allocator::AllocatorKind;
-use rustc_data_structures::small_vec::OneVector;
 use rustc_errors;
+use smallvec::SmallVec;
 use syntax::{
     ast::{
         self, Arg, Attribute, Crate, Expr, FnHeader, Generics, Ident, Item, ItemKind,
@@ -65,7 +65,7 @@ struct ExpandAllocatorDirectives<'a> {
 }
 
 impl<'a> Folder for ExpandAllocatorDirectives<'a> {
-    fn fold_item(&mut self, item: P<Item>) -> OneVector<P<Item>> {
+    fn fold_item(&mut self, item: P<Item>) -> SmallVec<[P<Item>; 1]> {
         debug!("in submodule {}", self.in_submod);
 
         let name = if attr::contains_name(&item.attrs, "global_allocator") {
@@ -152,11 +152,7 @@ impl<'a> Folder for ExpandAllocatorDirectives<'a> {
         let module = f.cx.monotonic_expander().fold_item(module).pop().unwrap();
 
         // Return the item and new submodule
-        let mut ret = OneVector::with_capacity(2);
-        ret.push(item);
-        ret.push(module);
-
-        return ret;
+        smallvec![item, module]
     }
 
     // If we enter a submodule, take note.

src/librustc_data_structures/lib.rs

@@ -50,7 +50,6 @@ extern crate rustc_rayon as rayon;
 extern crate rustc_rayon_core as rayon_core;
 extern crate rustc_hash;
 extern crate serialize;
-#[cfg_attr(test, macro_use)]
 extern crate smallvec;
 
 // See librustc_cratesio_shim/Cargo.toml for a comment explaining this.
@@ -72,7 +71,6 @@ pub mod owning_ref;
 pub mod ptr_key;
 pub mod sip128;
 pub mod small_c_str;
-pub mod small_vec;
 pub mod snapshot_map;
 pub use ena::snapshot_vec;
 pub mod sorted_map;

src/librustc_driver/Cargo.toml

@@ -35,5 +35,6 @@ rustc_codegen_utils = { path = "../librustc_codegen_utils" }
 rustc_typeck = { path = "../librustc_typeck" }
 serialize = { path = "../libserialize" }
 syntax = { path = "../libsyntax" }
+smallvec = { version = "0.6.5", features = ["union"] }
 syntax_ext = { path = "../libsyntax_ext" }
 syntax_pos = { path = "../libsyntax_pos" }

src/librustc_driver/lib.rs

@@ -58,6 +58,7 @@ extern crate rustc_codegen_utils;
 extern crate rustc_typeck;
 extern crate scoped_tls;
 extern crate serialize;
+extern crate smallvec;
 #[macro_use]
 extern crate log;
 extern crate syntax;

src/librustc_driver/pretty.rs

@@ -24,7 +24,6 @@ use rustc::session::Session;
 use rustc::session::config::{Input, OutputFilenames};
 use rustc_borrowck as borrowck;
 use rustc_borrowck::graphviz as borrowck_dot;
-use rustc_data_structures::small_vec::OneVector;
 use rustc_data_structures::thin_vec::ThinVec;
 use rustc_metadata::cstore::CStore;
 
@@ -38,6 +37,7 @@ use syntax::ptr::P;
 use syntax_pos::{self, FileName};
 
 use graphviz as dot;
+use smallvec::SmallVec;
 
 use std::cell::Cell;
 use std::fs::File;
@@ -727,7 +727,7 @@ impl<'a> fold::Folder for ReplaceBodyWithLoop<'a> {
         self.run(is_const, |s| fold::noop_fold_item_kind(i, s))
     }
 
-    fn fold_trait_item(&mut self, i: ast::TraitItem) -> OneVector<ast::TraitItem> {
+    fn fold_trait_item(&mut self, i: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
         let is_const = match i.node {
             ast::TraitItemKind::Const(..) => true,
             ast::TraitItemKind::Method(ast::MethodSig { ref decl, ref header, .. }, _) =>
@@ -737,7 +737,7 @@ impl<'a> fold::Folder for ReplaceBodyWithLoop<'a> {
         self.run(is_const, |s| fold::noop_fold_trait_item(i, s))
     }
 
-    fn fold_impl_item(&mut self, i: ast::ImplItem) -> OneVector<ast::ImplItem> {
+    fn fold_impl_item(&mut self, i: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]> {
         let is_const = match i.node {
             ast::ImplItemKind::Const(..) => true,
             ast::ImplItemKind::Method(ast::MethodSig { ref decl, ref header, .. }, _) =>

src/librustc_resolve/macros.rs

@@ -42,7 +42,6 @@ use errors::Applicability;
 use std::cell::Cell;
 use std::mem;
 use rustc_data_structures::sync::Lrc;
-use rustc_data_structures::small_vec::ExpectOne;
 
 #[derive(Clone, Copy)]
 crate struct FromPrelude(bool);
@@ -190,7 +189,9 @@ impl<'a, 'crateloader: 'a> base::Resolver for Resolver<'a, 'crateloader> {
             }
         }
 
-        EliminateCrateVar(self, item.span).fold_item(item).expect_one("")
+        let ret = EliminateCrateVar(self, item.span).fold_item(item);
+        assert!(ret.len() == 1);
+        ret.into_iter().next().unwrap()
     }
 
     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool {

src/libsyntax/config.rs

@@ -15,7 +15,7 @@ use ast;
 use source_map::Spanned;
 use edition::Edition;
 use parse::{token, ParseSess};
-use OneVector;
+use smallvec::SmallVec;
 use errors::Applicability;
 
 use ptr::P;
@@ -338,22 +338,23 @@ impl<'a> fold::Folder for StripUnconfigured<'a> {
         Some(P(fold::noop_fold_expr(expr, self)))
     }
 
-    fn fold_stmt(&mut self, stmt: ast::Stmt) -> OneVector<ast::Stmt> {
+    fn fold_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
         match self.configure_stmt(stmt) {
             Some(stmt) => fold::noop_fold_stmt(stmt, self),
-            None => return OneVector::new(),
+            None => return SmallVec::new(),
         }
     }
 
-    fn fold_item(&mut self, item: P<ast::Item>) -> OneVector<P<ast::Item>> {
+    fn fold_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
         fold::noop_fold_item(configure!(self, item), self)
     }
 
-    fn fold_impl_item(&mut self, item: ast::ImplItem) -> OneVector<ast::ImplItem> {
+    fn fold_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]>
+    {
         fold::noop_fold_impl_item(configure!(self, item), self)
     }
 
-    fn fold_trait_item(&mut self, item: ast::TraitItem) -> OneVector<ast::TraitItem> {
+    fn fold_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
         fold::noop_fold_trait_item(configure!(self, item), self)
     }
 

src/libsyntax/diagnostics/plugin.rs

@@ -19,7 +19,6 @@ use ext::base::{ExtCtxt, MacEager, MacResult};
 use ext::build::AstBuilder;
 use parse::token;
 use ptr::P;
-use OneVector;
 use symbol::{keywords, Symbol};
 use tokenstream::{TokenTree};
 
@@ -131,15 +130,15 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
     let sym = Ident::with_empty_ctxt(Symbol::gensym(&format!(
         "__register_diagnostic_{}", code
     )));
-    MacEager::items(OneVector::from_vec(vec![
+    MacEager::items(smallvec![
         ecx.item_mod(
             span,
             span,
             sym,
             Vec::new(),
             Vec::new()
         )
-    ]))
+    ])
 }
 
 pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
@@ -214,7 +213,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
         ),
     );
 
-    MacEager::items(OneVector::from_vec(vec![
+    MacEager::items(smallvec![
         P(ast::Item {
             ident: *name,
             attrs: Vec::new(),
@@ -227,5 +226,5 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
             span,
             tokens: None,
         })
-    ]))
+    ])
 }