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Auto merge of #127288 - lqd:typelen-cache, r=compiler-errors 

cache type sizes in type-size limit visitor

This is basically https://github.com/rust-lang/rust/pull/125507#issuecomment-2206813779 as lcnr can't open the PR now.

Locally it reduces the `itertools` regression by quite a bit, to "only +50%" compared to nightly (that includes overhead from the local lack of artifact post-processing, and is just a data point to compare to the 10-20x timings without the cache).

```console
Benchmark 1: cargo +stage1 build --release
  Time (mean ± σ):      2.721 s ±  0.009 s    [User: 2.446 s, System: 0.325 s]
  Range (min … max):    2.710 s …  2.738 s    10 runs

Benchmark 2: cargo +nightly build --release
  Time (mean ± σ):      1.784 s ±  0.005 s    [User: 1.540 s, System: 0.279 s]
  Range (min … max):    1.778 s …  1.792 s    10 runs

Summary
  cargo +nightly build --release ran
    1.52 ± 0.01 times faster than cargo +stage1 build --release
```

On master, it's from 34s to the 2.7s above.

r? compiler-errors
This commit is contained in:
bors 2024-07-04 21:17:19 +00:00
parent c422581297 529a3f4ce6
commit cc8da78a03
1 changed files with 16 additions and 3 deletions
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19
compiler/rustc_middle/src/ty/instance.rs
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@ -5,6 +5,7 @@ use crate::ty::{
self, EarlyBinder, GenericArgs, GenericArgsRef, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, self, EarlyBinder, GenericArgs, GenericArgsRef, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
}; };
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::ErrorGuaranteed; use rustc_errors::ErrorGuaranteed;
use rustc_hir as hir; use rustc_hir as hir;
use rustc_hir::def::Namespace; use rustc_hir::def::Namespace;
@ -388,13 +389,25 @@ impl<'tcx> InstanceKind<'tcx> {
} }
fn type_length<'tcx>(item: impl TypeVisitable<TyCtxt<'tcx>>) -> usize { fn type_length<'tcx>(item: impl TypeVisitable<TyCtxt<'tcx>>) -> usize {
struct Visitor { struct Visitor<'tcx> {
type_length: usize, type_length: usize,
cache: FxHashMap<Ty<'tcx>, usize>,
} }
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Visitor { impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Visitor<'tcx> {
fn visit_ty(&mut self, t: Ty<'tcx>) { fn visit_ty(&mut self, t: Ty<'tcx>) {
if let Some(&value) = self.cache.get(&t) {
self.type_length += value;
return;
}
let prev = self.type_length;
self.type_length += 1; self.type_length += 1;
t.super_visit_with(self); t.super_visit_with(self);
// We don't try to use the cache if the type is fairly small.
if self.type_length > 16 {
self.cache.insert(t, self.type_length - prev);
}
} }
fn visit_const(&mut self, ct: ty::Const<'tcx>) { fn visit_const(&mut self, ct: ty::Const<'tcx>) {
@ -402,7 +415,7 @@ fn type_length<'tcx>(item: impl TypeVisitable<TyCtxt<'tcx>>) -> usize {
ct.super_visit_with(self); ct.super_visit_with(self);
} }
} }
let mut visitor = Visitor { type_length: 0 }; let mut visitor = Visitor { type_length: 0, cache: Default::default() };
item.visit_with(&mut visitor); item.visit_with(&mut visitor);
visitor.type_length visitor.type_length