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Rollup merge of #112236 - cjgillot:interval-kill, r=davidtwco 

Simplify computation of killed borrows

Follow-up to https://github.com/rust-lang/rust/pull/111759

Processing the first block manually once makes the pre-order walk simpler.
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Dylan DPC 2023-06-28 18:28:46 +05:30 committed by GitHub
parent fa56e01b35 f10aa7dddc
commit dabcbae535
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1 changed files with 43 additions and 51 deletions
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94
compiler/rustc_borrowck/src/dataflow.rs
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@ -125,15 +125,9 @@ pub struct Borrows<'a, 'tcx> {
borrows_out_of_scope_at_location: FxIndexMap<Location, Vec<BorrowIndex>>,
}
struct StackEntry {
bb: mir::BasicBlock,
lo: usize,
hi: usize,
}
struct OutOfScopePrecomputer<'a, 'tcx> {
visited: BitSet<mir::BasicBlock>,
visit_stack: Vec<StackEntry>,
visit_stack: Vec<mir::BasicBlock>,
body: &'a Body<'tcx>,
regioncx: &'a RegionInferenceContext<'tcx>,
borrows_out_of_scope_at_location: FxIndexMap<Location, Vec<BorrowIndex>>,
@ -158,29 +152,50 @@ impl<'tcx> OutOfScopePrecomputer<'_, 'tcx> {
borrow_region: RegionVid,
first_location: Location,
) {
// We visit one BB at a time. The complication is that we may start in the
// middle of the first BB visited (the one containing `first_location`), in which
// case we may have to later on process the first part of that BB if there
// is a path back to its start.
// For visited BBs, we record the index of the first statement processed.
// (In fully processed BBs this index is 0.) Note also that we add BBs to
// `visited` once they are added to `stack`, before they are actually
// processed, because this avoids the need to look them up again on
// completion.
self.visited.insert(first_location.block);
let first_block = first_location.block;
let mut first_lo = first_location.statement_index;
let first_hi = self.body[first_block].statements.len();
let first_bb_data = &self.body.basic_blocks[first_block];
self.visit_stack.push(StackEntry { bb: first_block, lo: first_lo, hi: first_hi });
// This is the first block, we only want to visit it from the creation of the borrow at
// `first_location`.
let first_lo = first_location.statement_index;
let first_hi = first_bb_data.statements.len();
'preorder: while let Some(StackEntry { bb, lo, hi }) = self.visit_stack.pop() {
if let Some(kill_stmt) = self.regioncx.first_non_contained_inclusive(
borrow_region,
first_block,
first_lo,
first_hi,
) {
let kill_location = Location { block: first_block, statement_index: kill_stmt };
// If region does not contain a point at the location, then add to list and skip
// successor locations.
debug!("borrow {:?} gets killed at {:?}", borrow_index, kill_location);
self.borrows_out_of_scope_at_location
.entry(kill_location)
.or_default()
.push(borrow_index);
// The borrow is already dead, there is no need to visit other blocks.
return;
}
// The borrow is not dead. Add successor BBs to the work list, if necessary.
for succ_bb in first_bb_data.terminator().successors() {
if self.visited.insert(succ_bb) {
self.visit_stack.push(succ_bb);
}
}
// We may end up visiting `first_block` again. This is not an issue: we know at this point
// that it does not kill the borrow in the `first_lo..=first_hi` range, so checking the
// `0..first_lo` range and the `0..first_hi` range give the same result.
while let Some(block) = self.visit_stack.pop() {
let bb_data = &self.body[block];
let num_stmts = bb_data.statements.len();
if let Some(kill_stmt) =
self.regioncx.first_non_contained_inclusive(borrow_region, bb, lo, hi)
self.regioncx.first_non_contained_inclusive(borrow_region, block, 0, num_stmts)
{
let kill_location = Location { block: bb, statement_index: kill_stmt };
let kill_location = Location { block, statement_index: kill_stmt };
// If region does not contain a point at the location, then add to list and skip
// successor locations.
debug!("borrow {:?} gets killed at {:?}", borrow_index, kill_location);
@ -188,38 +203,15 @@ impl<'tcx> OutOfScopePrecomputer<'_, 'tcx> {
.entry(kill_location)
.or_default()
.push(borrow_index);
continue 'preorder;
}
// If we process the first part of the first basic block (i.e. we encounter that block
// for the second time), we no longer have to visit its successors again.
if bb == first_block && hi != first_hi {
// We killed the borrow, so we do not visit this block's successors.
continue;
}
// Add successor BBs to the work list, if necessary.
let bb_data = &self.body[bb];
debug_assert!(hi == bb_data.statements.len());
for succ_bb in bb_data.terminator().successors() {
if !self.visited.insert(succ_bb) {
if succ_bb == first_block && first_lo > 0 {
// `succ_bb` has been seen before. If it wasn't
// fully processed, add its first part to `stack`
// for processing.
self.visit_stack.push(StackEntry { bb: succ_bb, lo: 0, hi: first_lo - 1 });
// And update this entry with 0, to represent the
// whole BB being processed.
first_lo = 0;
}
} else {
// succ_bb hasn't been seen before. Add it to
// `stack` for processing.
self.visit_stack.push(StackEntry {
bb: succ_bb,
lo: 0,
hi: self.body[succ_bb].statements.len(),
});
if self.visited.insert(succ_bb) {
self.visit_stack.push(succ_bb);
}
}
}