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Auto merge of #142471 - lqd:sparse-borrows, r=nnethercote

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use `MixedBitSet` for borrows-in-scope dataflow analysis

The `Borrows` dataflow analysis uses a dense bitset, but a bitset supporting _some_ amount of sparseness is better suited for big functions with a big number of loans.

The cutoff between dense and chunked bitset is around 2K loans IIRC, and we could finesse that value if we wanted to, but as-is it happens to a couple of rustc-perf benchmarks (which IIRC are at least partially generated from macros and the likes.). It's a small win on these two, and shouldn't have any impact on the others.

r? `@matthewjasper`
This commit is contained in:
bors 2025-06-15 21:38:13 +00:00
commit f768dc01da
2 changed files with 6 additions and 6 deletions
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6
compiler/rustc_borrowck/src/dataflow.rs
View file

@ -2,7 +2,7 @@ use std::fmt;
use rustc_data_structures::fx::FxIndexMap;
use rustc_data_structures::graph;
use rustc_index::bit_set::DenseBitSet;
use rustc_index::bit_set::{DenseBitSet, MixedBitSet};
use rustc_middle::mir::{
self, BasicBlock, Body, CallReturnPlaces, Location, Place, TerminatorEdges,
};
@ -548,7 +548,7 @@ impl<'a, 'tcx> Borrows<'a, 'tcx> {
}
}
type BorrowsDomain = DenseBitSet<BorrowIndex>;
type BorrowsDomain = MixedBitSet<BorrowIndex>;
/// Forward dataflow computation of the set of borrows that are in scope at a particular location.
/// - we gen the introduced loans
@ -564,7 +564,7 @@ impl<'tcx> rustc_mir_dataflow::Analysis<'tcx> for Borrows<'_, 'tcx> {
fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
// bottom = nothing is reserved or activated yet;
DenseBitSet::new_empty(self.borrow_set.len())
MixedBitSet::new_empty(self.borrow_set.len())
}
fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {

6
compiler/rustc_borrowck/src/lib.rs
View file

@ -29,7 +29,7 @@ use rustc_errors::LintDiagnostic;
use rustc_hir as hir;
use rustc_hir::CRATE_HIR_ID;
use rustc_hir::def_id::LocalDefId;
use rustc_index::bit_set::{DenseBitSet, MixedBitSet};
use rustc_index::bit_set::MixedBitSet;
use rustc_index::{IndexSlice, IndexVec};
use rustc_infer::infer::{
InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin, TyCtxtInferExt,
@ -1151,11 +1151,11 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
&self,
location: Location,
state: &'s BorrowckDomain,
) -> Cow<'s, DenseBitSet<BorrowIndex>> {
) -> Cow<'s, MixedBitSet<BorrowIndex>> {
if let Some(polonius) = &self.polonius_output {
// Use polonius output if it has been enabled.
let location = self.location_table.start_index(location);
let mut polonius_output = DenseBitSet::new_empty(self.borrow_set.len());
let mut polonius_output = MixedBitSet::new_empty(self.borrow_set.len());
for &idx in polonius.errors_at(location) {
polonius_output.insert(idx);
}