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Auto merge of #71312 - wesleywiser:const_prop_bitset, r=Mark-Simulacrum

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[ConstProp] Use a `BitSet<Local>` instead of `IndexVec<Local, bool>`
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bors 2020-04-23 03:44:28 +00:00
commit 8af87b1126
1 changed files with 4 additions and 5 deletions
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9
src/librustc_mir/transform/const_prop.rs
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@ -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::{
@ -775,7 +776,7 @@ 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 {
@ -783,7 +784,7 @@ impl CanConstProp {
fn check(body: &Body<'_>) -> 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
@ -811,11 +812,9 @@ 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