From 8c31219d5c6fe11654060ab968285705f00b1ec8 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Thu, 20 Jul 2023 09:52:26 +1000 Subject: [PATCH] Tweak CGU sorting in a couple of places. In `base.rs`, tweak how the CGU size interleaving works. Since #113777, it's much more common to have multiple CGUs with identical sizes. With the existing code these same-sized items ended up in the opposite-to-desired order due to the stable sorting. The code now starts with a reverse sort (like is done in `partitioning.rs`) which gives the behaviour we want. This doesn't matter much for perf, but makes profiles in `samply` look more like what we expect. In `partitioning.rs`, we can use `sort_by_key` instead of `sort_by_cached_key` because `CGU::size_estimate()` is cheap. (There is an identical CGU sort earlier in that function that already uses `sort_by_key`.) --- compiler/rustc_codegen_ssa/src/base.rs | 5 +++-- compiler/rustc_monomorphize/src/partitioning.rs | 2 +- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs index dc862803274..79c284ecfbf 100644 --- a/compiler/rustc_codegen_ssa/src/base.rs +++ b/compiler/rustc_codegen_ssa/src/base.rs @@ -38,6 +38,7 @@ use rustc_span::symbol::sym; use rustc_span::Symbol; use rustc_target::abi::{Align, FIRST_VARIANT}; +use std::cmp; use std::collections::BTreeSet; use std::time::{Duration, Instant}; @@ -682,10 +683,10 @@ pub fn codegen_crate( // are large size variations, this can reduce memory usage significantly. let codegen_units: Vec<_> = { let mut sorted_cgus = codegen_units.iter().collect::>(); - sorted_cgus.sort_by_cached_key(|cgu| cgu.size_estimate()); + sorted_cgus.sort_by_key(|cgu| cmp::Reverse(cgu.size_estimate())); let (first_half, second_half) = sorted_cgus.split_at(sorted_cgus.len() / 2); - second_half.iter().rev().interleave(first_half).copied().collect() + first_half.iter().interleave(second_half.iter().rev()).copied().collect() }; // Calculate the CGU reuse diff --git a/compiler/rustc_monomorphize/src/partitioning.rs b/compiler/rustc_monomorphize/src/partitioning.rs index 71aef53192f..4a9d6c9e6c8 100644 --- a/compiler/rustc_monomorphize/src/partitioning.rs +++ b/compiler/rustc_monomorphize/src/partitioning.rs @@ -394,7 +394,7 @@ fn merge_codegen_units<'tcx>( && codegen_units.iter().any(|cgu| cgu.size_estimate() < NON_INCR_MIN_CGU_SIZE) { // Sort small cgus to the back. - codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate())); + codegen_units.sort_by_key(|cgu| cmp::Reverse(cgu.size_estimate())); let mut smallest = codegen_units.pop().unwrap(); let second_smallest = codegen_units.last_mut().unwrap();