1 use rustc_middle::mir::*;
2 use rustc_middle::ty::TyCtxt;
6 use rustc_middle::mir::patch::MirPatch;
8 /// This pass moves values being dropped that are within a packed
9 /// struct to a separate local before dropping them, to ensure that
10 /// they are dropped from an aligned address.
12 /// For example, if we have something like
13 /// ```ignore (ilustrative)
23 /// We want to call `drop_in_place::<Vec<u8>>` on `data` from an aligned
24 /// address. This means we can't simply drop `foo.data` directly, because
25 /// its address is not aligned.
27 /// Instead, we move `foo.data` to a local and drop that:
28 /// ```ignore (ilustrative)
29 /// storage.live(drop_temp)
30 /// drop_temp = foo.data;
31 /// drop(drop_temp) -> next
33 /// storage.dead(drop_temp)
36 /// The storage instructions are required to avoid stack space
38 pub struct AddMovesForPackedDrops;
40 impl<'tcx> MirPass<'tcx> for AddMovesForPackedDrops {
41 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
42 debug!("add_moves_for_packed_drops({:?} @ {:?})", body.source, body.span);
43 add_moves_for_packed_drops(tcx, body);
47 pub fn add_moves_for_packed_drops<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
48 let patch = add_moves_for_packed_drops_patch(tcx, body);
52 fn add_moves_for_packed_drops_patch<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) -> MirPatch<'tcx> {
53 let def_id = body.source.def_id();
54 let mut patch = MirPatch::new(body);
55 let param_env = tcx.param_env(def_id);
57 for (bb, data) in body.basic_blocks.iter_enumerated() {
58 let loc = Location { block: bb, statement_index: data.statements.len() };
59 let terminator = data.terminator();
61 match terminator.kind {
62 TerminatorKind::Drop { place, .. }
63 if util::is_disaligned(tcx, body, param_env, place) =>
65 add_move_for_packed_drop(tcx, body, &mut patch, terminator, loc, data.is_cleanup);
67 TerminatorKind::DropAndReplace { .. } => {
68 span_bug!(terminator.source_info.span, "replace in AddMovesForPackedDrops");
77 fn add_move_for_packed_drop<'tcx>(
80 patch: &mut MirPatch<'tcx>,
81 terminator: &Terminator<'tcx>,
85 debug!("add_move_for_packed_drop({:?} @ {:?})", terminator, loc);
86 let TerminatorKind::Drop { ref place, target, unwind } = terminator.kind else {
90 let source_info = terminator.source_info;
91 let ty = place.ty(body, tcx).ty;
92 let temp = patch.new_temp(ty, terminator.source_info.span);
94 let storage_dead_block = patch.new_block(BasicBlockData {
95 statements: vec![Statement { source_info, kind: StatementKind::StorageDead(temp) }],
96 terminator: Some(Terminator { source_info, kind: TerminatorKind::Goto { target } }),
100 patch.add_statement(loc, StatementKind::StorageLive(temp));
101 patch.add_assign(loc, Place::from(temp), Rvalue::Use(Operand::Move(*place)));
102 patch.patch_terminator(
104 TerminatorKind::Drop { place: Place::from(temp), target: storage_dead_block, unwind },