Skip to content

[ConstProp] Use a BitSet<Local> instead of IndexVec<Local, bool> #71312

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Apr 23, 2020
Merged

[ConstProp] Use a BitSet<Local> instead of IndexVec<Local, bool> #71312

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 4 additions & 5 deletions src/librustc_mir/transform/const_prop.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ use rustc_ast::ast::Mutability;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def::DefKind;
use rustc_hir::HirId;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::IndexVec;
use rustc_middle::mir::interpret::{InterpResult, Scalar};
use rustc_middle::mir::visit::{
Expand Down Expand Up @@ -754,15 +755,15 @@ enum ConstPropMode {
struct CanConstProp {
can_const_prop: IndexVec<Local, ConstPropMode>,
// false at the beginning, once set, there are not allowed to be any more assignments
found_assignment: IndexVec<Local, bool>,
found_assignment: BitSet<Local>,
}

impl CanConstProp {
/// returns true if `local` can be propagated
fn check(body: ReadOnlyBodyAndCache<'_, '_>) -> IndexVec<Local, ConstPropMode> {
let mut cpv = CanConstProp {
can_const_prop: IndexVec::from_elem(ConstPropMode::FullConstProp, &body.local_decls),
found_assignment: IndexVec::from_elem(false, &body.local_decls),
found_assignment: BitSet::new_empty(body.local_decls.len()),
};
for (local, val) in cpv.can_const_prop.iter_enumerated_mut() {
// cannot use args at all
Expand Down Expand Up @@ -790,11 +791,9 @@ impl<'tcx> Visitor<'tcx> for CanConstProp {
// FIXME(oli-obk): we could be more powerful here, if the multiple writes
// only occur in independent execution paths
MutatingUse(MutatingUseContext::Store) => {
if self.found_assignment[local] {
if !self.found_assignment.insert(local) {
trace!("local {:?} can't be propagated because of multiple assignments", local);
self.can_const_prop[local] = ConstPropMode::NoPropagation;
} else {
self.found_assignment[local] = true
}
}
// Reading constants is allowed an arbitrary number of times
Expand Down