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Fix variable deallocation order in panic unwinding paths #149434

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Fix variable deallocation order in panic unwinding paths #149434

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32 changes: 8 additions & 24 deletions compiler/rustc_mir_build/src/build/scope.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -214,21 +214,10 @@ struct DropTree {

impl Scope {
/// Whether there's anything to do for the cleanup path, that is,
/// when unwinding through this scope. This includes destructors,
/// but not StorageDead statements, which don't get emitted at all
/// for unwinding, for several reasons:
/// * clang doesn't emit llvm.lifetime.end for C++ unwinding
/// * LLVM's memory dependency analysis can't handle it atm
/// * polluting the cleanup MIR with StorageDead creates
/// landing pads even though there's no actual destructors
/// * freeing up stack space has no effect during unwinding
/// Note that for generators we do emit StorageDeads, for the
/// use of optimizations in the MIR generator transform.
/// when unwinding through this scope. This includes destructors
/// and StorageDead statements to maintain proper drop ordering.
fn needs_cleanup(&self) -> bool {
self.drops.iter().any(|drop| match drop.kind {
DropKind::Value => true,
DropKind::Storage => false,
})
!self.drops.is_empty()
}

fn invalidate_cache(&mut self) {
Expand Down Expand Up @@ -1346,7 +1335,6 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
blocks[ROOT_NODE] = continue_block;

drops.build_mir::<ExitScopes>(&mut self.cfg, &mut blocks);
let is_generator = self.generator_kind.is_some();

// Link the exit drop tree to unwind drop tree.
if drops.drops.iter().any(|(drop, _)| drop.kind == DropKind::Value) {
Expand All @@ -1355,15 +1343,11 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
for (drop_idx, drop_data) in drops.drops.iter_enumerated().skip(1) {
match drop_data.0.kind {
DropKind::Storage => {
if is_generator {
let unwind_drop = self
.scopes
.unwind_drops
.add_drop(drop_data.0, unwind_indices[drop_data.1]);
unwind_indices.push(unwind_drop);
} else {
unwind_indices.push(unwind_indices[drop_data.1]);
}
let unwind_drop = self
.scopes
.unwind_drops
.add_drop(drop_data.0, unwind_indices[drop_data.1]);
unwind_indices.push(unwind_drop);
}
DropKind::Value => {
let unwind_drop = self
Expand Down