Rollup merge of rust-lang#49525 - varkor:sort_by_cached_key-conversion, r=scottmcm

Use sort_by_cached_key where appropriate

A follow-up to rust-lang#48639, converting various slice sorting calls to `sort_by_cached_key` when the key functions are more expensive.

Author: kennytm

src/liballoc/slice.rs

@@ -1400,6 +1400,7 @@ impl<T> [T] {
         let sz_usize = mem::size_of::<(K, usize)>();
 
         let len = self.len();
+        if len < 2 { return }
         if sz_u8  < sz_u16   && len <= ( u8::MAX as usize) { return sort_by_key!( u8, self, f) }
         if sz_u16 < sz_u32   && len <= (u16::MAX as usize) { return sort_by_key!(u16, self, f) }
         if sz_u32 < sz_usize && len <= (u32::MAX as usize) { return sort_by_key!(u32, self, f) }

src/librustc/lib.rs

@@ -60,6 +60,7 @@
 #![feature(refcell_replace_swap)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(specialization)]
 #![feature(unboxed_closures)]
 #![feature(trace_macros)]

src/librustc/middle/cstore.rs

@@ -401,7 +401,7 @@ pub fn used_crates(tcx: TyCtxt, prefer: LinkagePreference)
         .collect::<Vec<_>>();
     let mut ordering = tcx.postorder_cnums(LOCAL_CRATE);
     Lrc::make_mut(&mut ordering).reverse();
-    libs.sort_by_key(|&(a, _)| {
+    libs.sort_by_cached_key(|&(a, _)| {
         ordering.iter().position(|x| *x == a)
     });
     libs

src/librustc_driver/lib.rs

@@ -22,6 +22,7 @@
 #![cfg_attr(unix, feature(libc))]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(set_stdio)]
 #![feature(rustc_stack_internals)]
 
@@ -82,7 +83,6 @@ use rustc_trans_utils::trans_crate::TransCrate;
 use serialize::json::ToJson;
 
 use std::any::Any;
-use std::cmp::Ordering::Equal;
 use std::cmp::max;
 use std::default::Default;
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
@@ -1176,13 +1176,8 @@ Available lint options:
 
     fn sort_lints(sess: &Session, lints: Vec<(&'static Lint, bool)>) -> Vec<&'static Lint> {
         let mut lints: Vec<_> = lints.into_iter().map(|(x, _)| x).collect();
-        lints.sort_by(|x: &&Lint, y: &&Lint| {
-            match x.default_level(sess).cmp(&y.default_level(sess)) {
-                // The sort doesn't case-fold but it's doubtful we care.
-                Equal => x.name.cmp(y.name),
-                r => r,
-            }
-        });
+        // The sort doesn't case-fold but it's doubtful we care.
+        lints.sort_by_cached_key(|x: &&Lint| (x.default_level(sess), x.name));
         lints
     }
 

src/librustc_metadata/encoder.rs

@@ -1414,15 +1414,15 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
         let mut all_impls: Vec<_> = visitor.impls.into_iter().collect();
 
         // Bring everything into deterministic order for hashing
-        all_impls.sort_unstable_by_key(|&(trait_def_id, _)| {
+        all_impls.sort_by_cached_key(|&(trait_def_id, _)| {
             tcx.def_path_hash(trait_def_id)
         });
 
         let all_impls: Vec<_> = all_impls
             .into_iter()
             .map(|(trait_def_id, mut impls)| {
                 // Bring everything into deterministic order for hashing
-                impls.sort_unstable_by_key(|&def_index| {
+                impls.sort_by_cached_key(|&def_index| {
                     tcx.hir.definitions().def_path_hash(def_index)
                 });
 

src/librustc_metadata/lib.rs

@@ -20,6 +20,7 @@
 #![feature(macro_lifetime_matcher)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(specialization)]
 #![feature(rustc_private)]
 

src/librustc_mir/lib.rs

@@ -15,6 +15,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 */
 
 #![feature(slice_patterns)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(from_ref)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]

src/librustc_mir/monomorphize/partitioning.rs

@@ -112,11 +112,11 @@ use rustc::ty::{self, TyCtxt, InstanceDef};
 use rustc::ty::item_path::characteristic_def_id_of_type;
 use rustc::util::nodemap::{FxHashMap, FxHashSet};
 use std::collections::hash_map::Entry;
+use std::cmp;
 use syntax::ast::NodeId;
 use syntax::symbol::{Symbol, InternedString};
 use rustc::mir::mono::MonoItem;
 use monomorphize::item::{MonoItemExt, InstantiationMode};
-use core::usize;
 
 pub use rustc::mir::mono::CodegenUnit;
 
@@ -189,11 +189,9 @@ pub trait CodegenUnitExt<'tcx> {
             }, item.symbol_name(tcx))
         }
 
-        let items: Vec<_> = self.items().iter().map(|(&i, &l)| (i, l)).collect();
-        let mut items : Vec<_> = items.iter()
-            .map(|il| (il, item_sort_key(tcx, il.0))).collect();
-        items.sort_by(|&(_, ref key1), &(_, ref key2)| key1.cmp(key2));
-        items.into_iter().map(|(&item_linkage, _)| item_linkage).collect()
+        let mut items: Vec<_> = self.items().iter().map(|(&i, &l)| (i, l)).collect();
+        items.sort_by_cached_key(|&(i, _)| item_sort_key(tcx, i));
+        items
     }
 }
 
@@ -509,7 +507,7 @@ fn merge_codegen_units<'tcx>(initial_partitioning: &mut PreInliningPartitioning<
     // Merge the two smallest codegen units until the target size is reached.
     while codegen_units.len() > target_cgu_count {
         // Sort small cgus to the back
-        codegen_units.sort_by_key(|cgu| usize::MAX - cgu.size_estimate());
+        codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
         let mut smallest = codegen_units.pop().unwrap();
         let second_smallest = codegen_units.last_mut().unwrap();
 

src/librustc_resolve/lib.rs

@@ -13,6 +13,7 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 
 #[macro_use]
 extern crate log;
@@ -1149,13 +1150,9 @@ impl<'a> ModuleData<'a> {
 
     fn for_each_child_stable<F: FnMut(Ident, Namespace, &'a NameBinding<'a>)>(&self, mut f: F) {
         let resolutions = self.resolutions.borrow();
-        let mut resolutions = resolutions.iter().map(|(&(ident, ns), &resolution)| {
-                                                    // Pre-compute keys for sorting
-                                                    (ident.name.as_str(), ns, ident, resolution)
-                                                })
-                                                .collect::<Vec<_>>();
-        resolutions.sort_unstable_by_key(|&(str, ns, ..)| (str, ns));
-        for &(_, ns, ident, resolution) in resolutions.iter() {
+        let mut resolutions = resolutions.iter().collect::<Vec<_>>();
+        resolutions.sort_by_cached_key(|&(&(ident, ns), _)| (ident.name.as_str(), ns));
+        for &(&(ident, ns), &resolution) in resolutions.iter() {
             resolution.borrow().binding.map(|binding| f(ident, ns, binding));
         }
     }
@@ -3340,7 +3337,9 @@ impl<'a> Resolver<'a> {
                         let is_mod = |def| match def { Def::Mod(..) => true, _ => false };
                         let mut candidates =
                             self.lookup_import_candidates(name, TypeNS, is_mod);
-                        candidates.sort_by_key(|c| (c.path.segments.len(), c.path.to_string()));
+                        candidates.sort_by_cached_key(|c| {
+                            (c.path.segments.len(), c.path.to_string())
+                        });
                         if let Some(candidate) = candidates.get(0) {
                             format!("Did you mean `{}`?", candidate.path)
                         } else {
@@ -3578,7 +3577,7 @@ impl<'a> Resolver<'a> {
 
         let name = path[path.len() - 1].name;
         // Make sure error reporting is deterministic.
-        names.sort_by_key(|name| name.as_str());
+        names.sort_by_cached_key(|name| name.as_str());
         match find_best_match_for_name(names.iter(), &name.as_str(), None) {
             Some(found) if found != name => Some(found),
             _ => None,

src/librustc_trans/base.rs

@@ -82,7 +82,8 @@ use std::ffi::CString;
 use std::str;
 use std::sync::Arc;
 use std::time::{Instant, Duration};
-use std::{i32, usize};
+use std::i32;
+use std::cmp;
 use std::sync::mpsc;
 use syntax_pos::Span;
 use syntax_pos::symbol::InternedString;
@@ -830,7 +831,7 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     // a bit more efficiently.
     let codegen_units = {
         let mut codegen_units = codegen_units;
-        codegen_units.sort_by_key(|cgu| usize::MAX - cgu.size_estimate());
+        codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
         codegen_units
     };