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try to downgrade Arc -> Lrc -> Rc -> no-Rc in few places #111014

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merged 3 commits into from
May 4, 2023
Merged

try to downgrade Arc -> Lrc -> Rc -> no-Rc in few places #111014

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a621ec3
RegionInferenceContext: remove Rc from rev_scc_graph field
klensy Apr 24, 2023
597c651
Arc -> Lrc
klensy Apr 28, 2023
0726636
Lrc -> Rc
klensy Apr 29, 2023
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6 changes: 3 additions & 3 deletions compiler/rustc_borrowck/src/region_infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,7 @@ pub struct RegionInferenceContext<'tcx> {
/// Reverse of the SCC constraint graph -- i.e., an edge `A -> B` exists if
/// `B: A`. This is used to compute the universal regions that are required
/// to outlive a given SCC. Computed lazily.
rev_scc_graph: Option<Rc<ReverseSccGraph>>,
rev_scc_graph: Option<ReverseSccGraph>,

/// The "R0 member of [R1..Rn]" constraints, indexed by SCC.
member_constraints: Rc<MemberConstraintSet<'tcx, ConstraintSccIndex>>,
Expand Down Expand Up @@ -813,9 +813,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
// free region that must outlive the member region `R0` (`UB:
// R0`). Therefore, we need only keep an option `O` if `UB: O`
// for all UB.
let rev_scc_graph = self.reverse_scc_graph();
self.compute_reverse_scc_graph();
let universal_region_relations = &self.universal_region_relations;
for ub in rev_scc_graph.upper_bounds(scc) {
for ub in self.rev_scc_graph.as_ref().unwrap().upper_bounds(scc) {
debug!(?ub);
choice_regions.retain(|&o_r| universal_region_relations.outlives(ub, o_r));
}
Expand Down
13 changes: 5 additions & 8 deletions compiler/rustc_borrowck/src/region_infer/reverse_sccs.rs
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Expand Up @@ -8,7 +8,6 @@ use rustc_data_structures::graph::vec_graph::VecGraph;
use rustc_data_structures::graph::WithSuccessors;
use rustc_middle::ty::RegionVid;
use std::ops::Range;
use std::rc::Rc;

pub(crate) struct ReverseSccGraph {
graph: VecGraph<ConstraintSccIndex>,
Expand Down Expand Up @@ -40,10 +39,10 @@ impl ReverseSccGraph {
}

impl RegionInferenceContext<'_> {
/// Compute and return the reverse SCC-based constraint graph (lazily).
pub(super) fn reverse_scc_graph(&mut self) -> Rc<ReverseSccGraph> {
if let Some(g) = &self.rev_scc_graph {
return g.clone();
/// Compute the reverse SCC-based constraint graph (lazily).
pub(super) fn compute_reverse_scc_graph(&mut self) {
if self.rev_scc_graph.is_some() {
return;
}

let graph = self.constraint_sccs.reverse();
Expand All @@ -63,8 +62,6 @@ impl RegionInferenceContext<'_> {
start += group_size;
}

let rev_graph = Rc::new(ReverseSccGraph { graph, scc_regions, universal_regions });
self.rev_scc_graph = Some(rev_graph.clone());
rev_graph
self.rev_scc_graph = Some(ReverseSccGraph { graph, scc_regions, universal_regions });
}
}
23 changes: 12 additions & 11 deletions compiler/rustc_expand/src/mbe/macro_parser.rs
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Expand Up @@ -88,6 +88,7 @@ use rustc_span::Span;
use std::borrow::Cow;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use std::fmt::Display;
use std::rc::Rc;

/// A unit within a matcher that a `MatcherPos` can refer to. Similar to (and derived from)
/// `mbe::TokenTree`, but designed specifically for fast and easy traversal during matching.
Expand Down Expand Up @@ -257,10 +258,10 @@ struct MatcherPos {
/// against the relevant metavar by the black box parser. An element will be a `MatchedSeq` if
/// the corresponding metavar decl is within a sequence.
///
/// It is critical to performance that this is an `Lrc`, because it gets cloned frequently when
/// It is critical to performance that this is an `Rc`, because it gets cloned frequently when
/// processing sequences. Mostly for sequence-ending possibilities that must be tried but end
/// up failing.
matches: Lrc<Vec<NamedMatch>>,
matches: Rc<Vec<NamedMatch>>,
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could this be Rc<[NamedMatch]>? would it be better?

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@klensy klensy May 4, 2023 •
edited
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Maybe. I've tried to only change rc stuff. This thing noted as hot, so changing vec<->slice can potentially shadow other changes. @nnethercote changed this last time, maybe he already tried that and found, that there no gains?

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Okay, we can leave those nits for the future.

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I just tried it, there are tons of problems.

error[E0277]: the trait bound `[NamedMatch]: Clone` is not satisfied
    --> compiler/rustc_expand/src/mbe/macro_parser.rs:275:37
     |
275  |         let matches = Lrc::make_mut(&mut self.matches);
     |                       ------------- ^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `[NamedMatch]`
     |                       |
     |                       required by a bound introduced by this call
     |
     = help: the trait `Clone` is implemented for `[T; N]`
note: required by a bound in `Lrc::<T>::make_mut`
    --> /home/njn/dev/rust1/library/alloc/src/rc.rs:1191:9
     |
1191 | impl<T: Clone> Rc<T> {
     |         ^^^^^ required by this bound in `Rc::<T>::make_mut`

error[E0599]: no method named `push` found for mutable reference `&mut [NamedMatch]` in the current scope
   --> compiler/rustc_expand/src/mbe/macro_parser.rs:280:25
    |
280 |                 matches.push(m);
    |                         ^^^^ method not found in `&mut [NamedMatch]`

error[E0277]: the trait bound `[NamedMatch]: Clone` is not satisfied
    --> compiler/rustc_expand/src/mbe/macro_parser.rs:591:35
     |
591  |                     Lrc::make_mut(&mut eof_mp.matches);
     |                     ------------- ^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `[NamedMatch]`
     |                     |
     |                     required by a bound introduced by this call
     |
     = help: the trait `Clone` is implemented for `[T; N]`
note: required by a bound in `Lrc::<T>::make_mut`
    --> /home/njn/dev/rust1/library/alloc/src/rc.rs:1191:9
     |
1191 | impl<T: Clone> Rc<T> {
     |         ^^^^^ required by this bound in `Rc::<T>::make_mut`

error[E0277]: the size for values of type `[NamedMatch]` cannot be known at compilation time
   --> compiler/rustc_expand/src/mbe/macro_parser.rs:592:51
    |
592 |                     let matches = Lrc::try_unwrap(eof_mp.matches).unwrap().into_iter();
    |                                   --------------- ^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |                                   |
    |                                   required by a bound introduced by this call
    |
    = help: the trait `Sized` is not implemented for `[NamedMatch]`
note: required by a bound in `Lrc::<T>::try_unwrap`
   --> /home/njn/dev/rust1/library/alloc/src/rc.rs:360:6
    |
360 | impl<T> Rc<T> {
    |      ^ required by this bound in `Rc::<T>::try_unwrap`

error[E0599]: the method `unwrap` exists for enum `Result<[NamedMatch], Rc<[NamedMatch]>>`, but its trait bounds were not satisfied
   --> compiler/rustc_expand/src/mbe/macro_parser.rs:592:67
    |
592 |                     let matches = Lrc::try_unwrap(eof_mp.matches).unwrap().into_iter();
    |                                                                   ^^^^^^ method cannot be called on `Result<[NamedMatch], Rc<[NamedMatch]>>` due to unsatisfied trait bounds
    |
    = note: the following trait bounds were not satisfied:
            `[NamedMatch]: Sized`

error[E0277]: the size for values of type `[NamedMatch]` cannot be known at compilation time
   --> compiler/rustc_expand/src/mbe/macro_parser.rs:592:35
    |
592 |                     let matches = Lrc::try_unwrap(eof_mp.matches).unwrap().into_iter();
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[NamedMatch]`
note: required by a bound in `Result`
   --> /home/njn/dev/rust1/library/core/src/result.rs:502:17
    |
502 | pub enum Result<T, E> {
    |                 ^ required by this bound in `Result`

error[E0308]: mismatched types
   --> compiler/rustc_expand/src/mbe/macro_parser.rs:625:57
    |
625 |         self.cur_mps.push(MatcherPos { idx: 0, matches: self.empty_matches.clone() });
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Rc<[NamedMatch]>`, found `Rc<Vec<NamedMatch>>`
    |
    = note: expected struct `Lrc<[NamedMatch]>`
               found struct `Lrc<Vec<NamedMatch>>`

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Ugh. Clone requiring Sized was a mistake :(

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Perhaps, but that's not the only problem here.

}

// This type is used a lot. Make sure it doesn't unintentionally get bigger.
Expand All @@ -272,7 +273,7 @@ impl MatcherPos {
/// and both are hot enough to be always worth inlining.
#[inline(always)]
fn push_match(&mut self, metavar_idx: usize, seq_depth: usize, m: NamedMatch) {
let matches = Lrc::make_mut(&mut self.matches);
let matches = Rc::make_mut(&mut self.matches);
match seq_depth {
0 => {
// We are not within a sequence. Just append `m`.
Expand Down Expand Up @@ -427,7 +428,7 @@ pub struct TtParser {

/// Pre-allocate an empty match array, so it can be cloned cheaply for macros with many rules
/// that have no metavars.
empty_matches: Lrc<Vec<NamedMatch>>,
empty_matches: Rc<Vec<NamedMatch>>,
}

impl TtParser {
Expand All @@ -437,7 +438,7 @@ impl TtParser {
cur_mps: vec![],
next_mps: vec![],
bb_mps: vec![],
empty_matches: Lrc::new(vec![]),
empty_matches: Rc::new(vec![]),
}
}

Expand Down Expand Up @@ -507,7 +508,7 @@ impl TtParser {
// Try zero matches of this sequence, by skipping over it.
self.cur_mps.push(MatcherPos {
idx: idx_first_after,
matches: Lrc::clone(&mp.matches),
matches: Rc::clone(&mp.matches),
});
}

Expand All @@ -521,7 +522,7 @@ impl TtParser {
// processed next time around the loop.
let ending_mp = MatcherPos {
idx: mp.idx + 1, // +1 skips the Kleene op
matches: Lrc::clone(&mp.matches),
matches: Rc::clone(&mp.matches),
};
self.cur_mps.push(ending_mp);

Expand All @@ -537,7 +538,7 @@ impl TtParser {
// will fail quietly when it is processed next time around the loop.
let ending_mp = MatcherPos {
idx: mp.idx + 2, // +2 skips the separator and the Kleene op
matches: Lrc::clone(&mp.matches),
matches: Rc::clone(&mp.matches),
};
self.cur_mps.push(ending_mp);

Expand Down Expand Up @@ -587,9 +588,9 @@ impl TtParser {
if *token == token::Eof {
Some(match eof_mps {
EofMatcherPositions::One(mut eof_mp) => {
// Need to take ownership of the matches from within the `Lrc`.
Lrc::make_mut(&mut eof_mp.matches);
let matches = Lrc::try_unwrap(eof_mp.matches).unwrap().into_iter();
// Need to take ownership of the matches from within the `Rc`.
Rc::make_mut(&mut eof_mp.matches);
let matches = Rc::try_unwrap(eof_mp.matches).unwrap().into_iter();
Comment on lines +592 to +593
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Would it make sense to just

Suggested change
Rc::make_mut(&mut eof_mp.matches);
let matches = Rc::try_unwrap(eof_mp.matches).unwrap().into_iter();
let matches = Rc::make_mut(&mut eof_mp.matches).take().into_iter();

or even

Suggested change
Rc::make_mut(&mut eof_mp.matches);
let matches = Rc::try_unwrap(eof_mp.matches).unwrap().into_iter();
eof_mp.matches.iter().cloned()

self.nameize(matcher, matches)
}
EofMatcherPositions::Multiple => {
Expand Down
5 changes: 2 additions & 3 deletions compiler/rustc_passes/src/debugger_visualizer.rs
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Expand Up @@ -2,15 +2,14 @@

use hir::CRATE_HIR_ID;
use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::sync::Lrc;
use rustc_expand::base::resolve_path;
use rustc_hir as hir;
use rustc_hir::HirId;
use rustc_middle::ty::TyCtxt;
use rustc_middle::{query::LocalCrate, ty::query::Providers};
use rustc_span::{sym, DebuggerVisualizerFile, DebuggerVisualizerType};

use std::sync::Arc;

use crate::errors::DebugVisualizerUnreadable;

fn check_for_debugger_visualizer(
Expand Down Expand Up @@ -52,7 +51,7 @@ fn check_for_debugger_visualizer(
match std::fs::read(&file) {
Ok(contents) => {
debugger_visualizers
.insert(DebuggerVisualizerFile::new(Arc::from(contents), visualizer_type));
.insert(DebuggerVisualizerFile::new(Lrc::from(contents), visualizer_type));
}
Err(error) => {
tcx.sess.emit_err(DebugVisualizerUnreadable {
Expand Down
5 changes: 2 additions & 3 deletions compiler/rustc_span/src/lib.rs
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Expand Up @@ -69,7 +69,6 @@ use std::hash::Hash;
use std::ops::{Add, Range, Sub};
use std::path::{Path, PathBuf};
use std::str::FromStr;
use std::sync::Arc;

use md5::Digest;
use md5::Md5;
Expand Down Expand Up @@ -1269,13 +1268,13 @@ pub enum DebuggerVisualizerType {
#[derive(Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord, Encodable, Decodable)]
pub struct DebuggerVisualizerFile {
/// The complete debugger visualizer source.
pub src: Arc<[u8]>,
pub src: Lrc<[u8]>,
/// Indicates which visualizer type this targets.
pub visualizer_type: DebuggerVisualizerType,
}

impl DebuggerVisualizerFile {
pub fn new(src: Arc<[u8]>, visualizer_type: DebuggerVisualizerType) -> Self {
pub fn new(src: Lrc<[u8]>, visualizer_type: DebuggerVisualizerType) -> Self {
DebuggerVisualizerFile { src, visualizer_type }
}
}
Expand Down