Use cmp::Reverse instead of subtraction

src/librustc_mir/monomorphize/partitioning.rs

@@ -112,11 +112,11 @@
 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;
 
@@ -509,7 +509,7 @@ 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_cached_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_trans/base.rs

@@ -82,7 +82,8 @@
 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_cached_key(|cgu| usize::MAX - cgu.size_estimate());
+        codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
         codegen_units
     };