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
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:
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
39 pub struct AddMovesForPackedDrops;
41 impl<'tcx> MirPass<'tcx> for AddMovesForPackedDrops {
42 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
43 debug!("add_moves_for_packed_drops({:?} @ {:?})", body.source, body.span);
44 add_moves_for_packed_drops(tcx, body);
48 pub fn add_moves_for_packed_drops<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
49 let patch = add_moves_for_packed_drops_patch(tcx, body);
53 fn add_moves_for_packed_drops_patch<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) -> MirPatch<'tcx> {
54 let def_id = body.source.def_id();
55 let mut patch = MirPatch::new(body);
56 let param_env = tcx.param_env(def_id);
58 for (bb, data) in body.basic_blocks().iter_enumerated() {
59 let loc = Location { block: bb, statement_index: data.statements.len() };
60 let terminator = data.terminator();
62 match terminator.kind {
63 TerminatorKind::Drop { place, .. }
64 if util::is_disaligned(tcx, body, param_env, place) =>
66 add_move_for_packed_drop(tcx, body, &mut patch, terminator, loc, data.is_cleanup);
68 TerminatorKind::DropAndReplace { .. } => {
69 span_bug!(terminator.source_info.span, "replace in AddMovesForPackedDrops");
78 fn add_move_for_packed_drop<'tcx>(
81 patch: &mut MirPatch<'tcx>,
82 terminator: &Terminator<'tcx>,
86 debug!("add_move_for_packed_drop({:?} @ {:?})", terminator, loc);
87 let (place, target, unwind) = match terminator.kind {
88 TerminatorKind::Drop { ref place, target, unwind } => (place, target, unwind),
92 let source_info = terminator.source_info;
93 let ty = place.ty(body, tcx).ty;
94 let temp = patch.new_temp(ty, terminator.source_info.span);
96 let storage_dead_block = patch.new_block(BasicBlockData {
97 statements: vec![Statement { source_info, kind: StatementKind::StorageDead(temp) }],
98 terminator: Some(Terminator { source_info, kind: TerminatorKind::Goto { target } }),
102 patch.add_statement(loc, StatementKind::StorageLive(temp));
103 patch.add_assign(loc, Place::from(temp), Rvalue::Use(Operand::Move(*place)));
104 patch.patch_terminator(
106 TerminatorKind::Drop { place: Place::from(temp), target: storage_dead_block, unwind },