1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 // Code relating to drop glue.
19 use llvm::{ValueRef, get_param};
20 use middle::lang_items::ExchangeFreeFnLangItem;
21 use middle::subst::{Substs};
23 use middle::ty::{self, Ty, TyCtxt};
24 use trans::abi::{Abi, FnType};
26 use trans::adt::GetDtorType; // for tcx.dtor_type()
29 use trans::callee::{Callee, ArgVals};
31 use trans::cleanup::CleanupMethods;
32 use trans::collector::{self, TransItem};
34 use trans::debuginfo::DebugLoc;
37 use trans::machine::*;
38 use trans::monomorphize;
39 use trans::type_of::{type_of, sizing_type_of, align_of};
40 use trans::type_::Type;
41 use trans::value::Value;
43 use arena::TypedArena;
44 use syntax::codemap::DUMMY_SP;
46 pub fn trans_exchange_free_dyn<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
51 -> Block<'blk, 'tcx> {
52 let _icx = push_ctxt("trans_exchange_free");
54 let def_id = langcall(bcx, None, "", ExchangeFreeFnLangItem);
55 let args = [PointerCast(bcx, v, Type::i8p(bcx.ccx())), size, align];
56 Callee::def(bcx.ccx(), def_id, bcx.tcx().mk_substs(Substs::empty()))
57 .call(bcx, debug_loc, ArgVals(&args), None).bcx
60 pub fn trans_exchange_free<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
65 -> Block<'blk, 'tcx> {
66 trans_exchange_free_dyn(cx,
68 C_uint(cx.ccx(), size),
69 C_uint(cx.ccx(), align),
73 pub fn trans_exchange_free_ty<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
77 -> Block<'blk, 'tcx> {
78 assert!(type_is_sized(bcx.ccx().tcx(), content_ty));
79 let sizing_type = sizing_type_of(bcx.ccx(), content_ty);
80 let content_size = llsize_of_alloc(bcx.ccx(), sizing_type);
82 // `Box<ZeroSizeType>` does not allocate.
83 if content_size != 0 {
84 let content_align = align_of(bcx.ccx(), content_ty);
85 trans_exchange_free(bcx, ptr, content_size, content_align, debug_loc)
91 pub fn type_needs_drop<'tcx>(tcx: &TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
92 tcx.type_needs_drop_given_env(ty, &tcx.empty_parameter_environment())
95 pub fn get_drop_glue_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
96 t: Ty<'tcx>) -> Ty<'tcx> {
98 // Even if there is no dtor for t, there might be one deeper down and we
99 // might need to pass in the vtable ptr.
100 if !type_is_sized(tcx, t) {
104 // FIXME (#22815): note that type_needs_drop conservatively
105 // approximates in some cases and may say a type expression
106 // requires drop glue when it actually does not.
108 // (In this case it is not clear whether any harm is done, i.e.
109 // erroneously returning `t` in some cases where we could have
110 // returned `tcx.types.i8` does not appear unsound. The impact on
111 // code quality is unknown at this time.)
113 if !type_needs_drop(&tcx, t) {
117 ty::TyBox(typ) if !type_needs_drop(&tcx, typ)
118 && type_is_sized(tcx, typ) => {
119 let llty = sizing_type_of(ccx, typ);
120 // `Box<ZeroSizeType>` does not allocate.
121 if llsize_of_alloc(ccx, llty) == 0 {
131 pub fn drop_ty<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
134 debug_loc: DebugLoc) -> Block<'blk, 'tcx> {
135 drop_ty_core(bcx, v, t, debug_loc, false, None)
138 pub fn drop_ty_core<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
143 drop_hint: Option<cleanup::DropHintValue>)
144 -> Block<'blk, 'tcx> {
145 // NB: v is an *alias* of type t here, not a direct value.
146 debug!("drop_ty_core(t={:?}, skip_dtor={} drop_hint={:?})", t, skip_dtor, drop_hint);
147 let _icx = push_ctxt("drop_ty");
149 if bcx.fcx.type_needs_drop(t) {
151 let g = if skip_dtor {
152 DropGlueKind::TyContents(t)
156 let glue = get_drop_glue_core(ccx, g);
157 let glue_type = get_drop_glue_type(ccx, t);
158 let ptr = if glue_type != t {
159 PointerCast(bcx, v, type_of(ccx, glue_type).ptr_to())
166 let hint_val = load_ty(bcx, drop_hint.value(), bcx.tcx().types.u8);
168 C_integral(Type::i8(bcx.ccx()), adt::DTOR_MOVED_HINT as u64, false);
170 ICmp(bcx, llvm::IntNE, hint_val, moved_val, DebugLoc::None);
171 bcx = with_cond(bcx, may_need_drop, |cx| {
172 Call(cx, glue, &[ptr], debug_loc);
177 // No drop-hint ==> call standard drop glue
178 Call(bcx, glue, &[ptr], debug_loc);
185 pub fn drop_ty_immediate<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
190 -> Block<'blk, 'tcx> {
191 let _icx = push_ctxt("drop_ty_immediate");
192 let vp = alloc_ty(bcx, t, "");
193 call_lifetime_start(bcx, vp);
194 store_ty(bcx, v, vp, t);
195 let bcx = drop_ty_core(bcx, vp, t, debug_loc, skip_dtor, None);
196 call_lifetime_end(bcx, vp);
200 pub fn get_drop_glue<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> ValueRef {
201 get_drop_glue_core(ccx, DropGlueKind::Ty(t))
204 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
205 pub enum DropGlueKind<'tcx> {
206 /// The normal path; runs the dtor, and then recurs on the contents
208 /// Skips the dtor, if any, for ty; drops the contents directly.
209 /// Note that the dtor is only skipped at the most *shallow*
210 /// level, namely, an `impl Drop for Ty` itself. So, for example,
211 /// if Ty is Newtype(S) then only the Drop impl for Newtype itself
212 /// will be skipped, while the Drop impl for S, if any, will be
214 TyContents(Ty<'tcx>),
217 impl<'tcx> DropGlueKind<'tcx> {
218 fn ty(&self) -> Ty<'tcx> {
219 match *self { DropGlueKind::Ty(t) | DropGlueKind::TyContents(t) => t }
222 fn map_ty<F>(&self, mut f: F) -> DropGlueKind<'tcx> where F: FnMut(Ty<'tcx>) -> Ty<'tcx>
225 DropGlueKind::Ty(t) => DropGlueKind::Ty(f(t)),
226 DropGlueKind::TyContents(t) => DropGlueKind::TyContents(f(t)),
231 fn get_drop_glue_core<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
232 g: DropGlueKind<'tcx>) -> ValueRef {
233 debug!("make drop glue for {:?}", g);
234 let g = g.map_ty(|t| get_drop_glue_type(ccx, t));
235 debug!("drop glue type {:?}", g);
236 match ccx.drop_glues().borrow().get(&g) {
237 Some(&glue) => return glue,
243 let sig = ty::FnSig {
244 inputs: vec![tcx.mk_mut_ptr(tcx.types.i8)],
245 output: ty::FnOutput::FnConverging(tcx.mk_nil()),
248 // Create a FnType for fn(*mut i8) and substitute the real type in
249 // later - that prevents FnType from splitting fat pointers up.
250 let mut fn_ty = FnType::new(ccx, Abi::Rust, &sig, &[]);
251 fn_ty.args[0].original_ty = type_of(ccx, t).ptr_to();
252 let llfnty = fn_ty.llvm_type(ccx);
254 // To avoid infinite recursion, don't `make_drop_glue` until after we've
255 // added the entry to the `drop_glues` cache.
256 if let Some(old_sym) = ccx.available_drop_glues().borrow().get(&g) {
257 let llfn = declare::declare_cfn(ccx, &old_sym, llfnty);
258 ccx.drop_glues().borrow_mut().insert(g, llfn);
262 let fn_nm = link::mangle_internal_name_by_type_and_seq(ccx, t, "drop");
263 assert!(declare::get_defined_value(ccx, &fn_nm).is_none());
264 let llfn = declare::declare_cfn(ccx, &fn_nm, llfnty);
265 ccx.available_drop_glues().borrow_mut().insert(g, fn_nm);
266 ccx.drop_glues().borrow_mut().insert(g, llfn);
268 let _s = StatRecorder::new(ccx, format!("drop {:?}", t));
270 let empty_substs = tcx.mk_substs(Substs::trans_empty());
271 let (arena, fcx): (TypedArena<_>, FunctionContext);
272 arena = TypedArena::new();
273 fcx = FunctionContext::new(ccx, llfn, fn_ty, None, empty_substs, &arena);
275 let bcx = fcx.init(false, None);
277 update_linkage(ccx, llfn, None, OriginalTranslation);
279 ccx.stats().n_glues_created.set(ccx.stats().n_glues_created.get() + 1);
280 // All glue functions take values passed *by alias*; this is a
281 // requirement since in many contexts glue is invoked indirectly and
282 // the caller has no idea if it's dealing with something that can be
285 // llfn is expected be declared to take a parameter of the appropriate
286 // type, so we don't need to explicitly cast the function parameter.
288 let bcx = make_drop_glue(bcx, get_param(llfn, 0), g);
289 fcx.finish(bcx, DebugLoc::None);
294 fn trans_struct_drop_flag<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
296 struct_data: ValueRef)
297 -> Block<'blk, 'tcx> {
298 assert!(type_is_sized(bcx.tcx(), t), "Precondition: caller must ensure t is sized");
300 let repr = adt::represent_type(bcx.ccx(), t);
301 let drop_flag = unpack_datum!(bcx, adt::trans_drop_flag_ptr(bcx, &repr, struct_data));
302 let loaded = load_ty(bcx, drop_flag.val, bcx.tcx().dtor_type());
303 let drop_flag_llty = type_of(bcx.fcx.ccx, bcx.tcx().dtor_type());
304 let init_val = C_integral(drop_flag_llty, adt::DTOR_NEEDED as u64, false);
306 let bcx = if !bcx.ccx().check_drop_flag_for_sanity() {
309 let drop_flag_llty = type_of(bcx.fcx.ccx, bcx.tcx().dtor_type());
310 let done_val = C_integral(drop_flag_llty, adt::DTOR_DONE as u64, false);
311 let not_init = ICmp(bcx, llvm::IntNE, loaded, init_val, DebugLoc::None);
312 let not_done = ICmp(bcx, llvm::IntNE, loaded, done_val, DebugLoc::None);
313 let drop_flag_neither_initialized_nor_cleared =
314 And(bcx, not_init, not_done, DebugLoc::None);
315 with_cond(bcx, drop_flag_neither_initialized_nor_cleared, |cx| {
316 let llfn = cx.ccx().get_intrinsic(&("llvm.debugtrap"));
317 Call(cx, llfn, &[], DebugLoc::None);
322 let drop_flag_dtor_needed = ICmp(bcx, llvm::IntEQ, loaded, init_val, DebugLoc::None);
323 with_cond(bcx, drop_flag_dtor_needed, |cx| {
324 trans_struct_drop(cx, t, struct_data)
327 fn trans_struct_drop<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
332 debug!("trans_struct_drop t: {}", t);
336 let def = t.ty_adt_def().unwrap();
338 // Be sure to put the contents into a scope so we can use an invoke
339 // instruction to call the user destructor but still call the field
340 // destructors if the user destructor panics.
342 // FIXME (#14875) panic-in-drop semantics might be unsupported; we
343 // might well consider changing below to more direct code.
344 let contents_scope = bcx.fcx.push_custom_cleanup_scope();
346 // Issue #23611: schedule cleanup of contents, re-inspecting the
347 // discriminant (if any) in case of variant swap in drop code.
348 bcx.fcx.schedule_drop_adt_contents(cleanup::CustomScope(contents_scope), v0, t);
350 let (sized_args, unsized_args);
351 let args: &[ValueRef] = if type_is_sized(tcx, t) {
355 unsized_args = [Load(bcx, expr::get_dataptr(bcx, v0)), Load(bcx, expr::get_meta(bcx, v0))];
359 let trait_ref = ty::Binder(ty::TraitRef {
360 def_id: tcx.lang_items.drop_trait().unwrap(),
361 substs: tcx.mk_substs(Substs::trans_empty().with_self_ty(t))
363 let vtbl = match fulfill_obligation(bcx.ccx(), DUMMY_SP, trait_ref) {
364 traits::VtableImpl(data) => data,
365 _ => tcx.sess.bug(&format!("dtor for {:?} is not an impl???", t))
367 let dtor_did = def.destructor().unwrap();
368 bcx = Callee::def(bcx.ccx(), dtor_did, vtbl.substs)
369 .call(bcx, DebugLoc::None, ArgVals(args), None).bcx;
371 bcx.fcx.pop_and_trans_custom_cleanup_scope(bcx, contents_scope)
374 pub fn size_and_align_of_dst<'blk, 'tcx>(bcx: &BlockAndBuilder<'blk, 'tcx>,
375 t: Ty<'tcx>, info: ValueRef)
376 -> (ValueRef, ValueRef) {
377 debug!("calculate size of DST: {}; with lost info: {:?}",
379 if type_is_sized(bcx.tcx(), t) {
380 let sizing_type = sizing_type_of(bcx.ccx(), t);
381 let size = llsize_of_alloc(bcx.ccx(), sizing_type);
382 let align = align_of(bcx.ccx(), t);
383 debug!("size_and_align_of_dst t={} info={:?} size: {} align: {}",
384 t, Value(info), size, align);
385 let size = C_uint(bcx.ccx(), size);
386 let align = C_uint(bcx.ccx(), align);
387 return (size, align);
389 if bcx.is_unreachable() {
390 let llty = Type::int(bcx.ccx());
391 return (C_undef(llty), C_undef(llty));
394 ty::TyStruct(def, substs) => {
396 // First get the size of all statically known fields.
397 // Don't use type_of::sizing_type_of because that expects t to be sized.
398 assert!(!t.is_simd());
399 let repr = adt::represent_type(ccx, t);
400 let sizing_type = adt::sizing_type_context_of(ccx, &repr, true);
401 debug!("DST {} sizing_type: {:?}", t, sizing_type);
402 let sized_size = llsize_of_alloc(ccx, sizing_type.prefix());
403 let sized_align = llalign_of_min(ccx, sizing_type.prefix());
404 debug!("DST {} statically sized prefix size: {} align: {}",
405 t, sized_size, sized_align);
406 let sized_size = C_uint(ccx, sized_size);
407 let sized_align = C_uint(ccx, sized_align);
409 // Recurse to get the size of the dynamically sized field (must be
411 let last_field = def.struct_variant().fields.last().unwrap();
412 let field_ty = monomorphize::field_ty(bcx.tcx(), substs, last_field);
413 let (unsized_size, unsized_align) = size_and_align_of_dst(bcx, field_ty, info);
415 // FIXME (#26403, #27023): We should be adding padding
416 // to `sized_size` (to accommodate the `unsized_align`
417 // required of the unsized field that follows) before
418 // summing it with `sized_size`. (Note that since #26403
419 // is unfixed, we do not yet add the necessary padding
420 // here. But this is where the add would go.)
422 // Return the sum of sizes and max of aligns.
423 let mut size = bcx.add(sized_size, unsized_size);
425 // Issue #27023: If there is a drop flag, *now* we add 1
426 // to the size. (We can do this without adding any
427 // padding because drop flags do not have any alignment
429 if sizing_type.needs_drop_flag() {
430 size = bcx.add(size, C_uint(bcx.ccx(), 1_u64));
433 // Choose max of two known alignments (combined value must
434 // be aligned according to more restrictive of the two).
435 let align = match (const_to_opt_uint(sized_align), const_to_opt_uint(unsized_align)) {
436 (Some(sized_align), Some(unsized_align)) => {
437 // If both alignments are constant, (the sized_align should always be), then
438 // pick the correct alignment statically.
439 C_uint(ccx, std::cmp::max(sized_align, unsized_align))
441 _ => bcx.select(bcx.icmp(llvm::IntUGT, sized_align, unsized_align),
446 // Issue #27023: must add any necessary padding to `size`
447 // (to make it a multiple of `align`) before returning it.
449 // Namely, the returned size should be, in C notation:
451 // `size + ((size & (align-1)) ? align : 0)`
453 // emulated via the semi-standard fast bit trick:
455 // `(size + (align-1)) & -align`
457 let addend = bcx.sub(align, C_uint(bcx.ccx(), 1_u64));
458 let size = bcx.and(bcx.add(size, addend), bcx.neg(align));
463 // info points to the vtable and the second entry in the vtable is the
464 // dynamic size of the object.
465 let info = bcx.pointercast(info, Type::int(bcx.ccx()).ptr_to());
466 let size_ptr = bcx.gepi(info, &[1]);
467 let align_ptr = bcx.gepi(info, &[2]);
468 (bcx.load(size_ptr), bcx.load(align_ptr))
470 ty::TySlice(_) | ty::TyStr => {
471 let unit_ty = t.sequence_element_type(bcx.tcx());
472 // The info in this case is the length of the str, so the size is that
473 // times the unit size.
474 let llunit_ty = sizing_type_of(bcx.ccx(), unit_ty);
475 let unit_align = llalign_of_min(bcx.ccx(), llunit_ty);
476 let unit_size = llsize_of_alloc(bcx.ccx(), llunit_ty);
477 (bcx.mul(info, C_uint(bcx.ccx(), unit_size)),
478 C_uint(bcx.ccx(), unit_align))
480 _ => bcx.sess().bug(&format!("Unexpected unsized type, found {}", t))
484 fn make_drop_glue<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, v0: ValueRef, g: DropGlueKind<'tcx>)
485 -> Block<'blk, 'tcx> {
488 if collector::collecting_debug_information(bcx.ccx()) {
490 .record_translation_item_as_generated(TransItem::DropGlue(bcx.tcx()
491 .erase_regions(&t)));
494 let skip_dtor = match g { DropGlueKind::Ty(_) => false, DropGlueKind::TyContents(_) => true };
495 // NB: v0 is an *alias* of type t here, not a direct value.
496 let _icx = push_ctxt("make_drop_glue");
498 // Only drop the value when it ... well, we used to check for
499 // non-null, (and maybe we need to continue doing so), but we now
500 // must definitely check for special bit-patterns corresponding to
501 // the special dtor markings.
503 let inttype = Type::int(bcx.ccx());
504 let dropped_pattern = C_integral(inttype, adt::DTOR_DONE_U64, false);
507 ty::TyBox(content_ty) => {
508 // Support for TyBox is built-in and its drop glue is
509 // special. It may move to library and have Drop impl. As
510 // a safe-guard, assert TyBox not used with TyContents.
512 if !type_is_sized(bcx.tcx(), content_ty) {
513 let llval = expr::get_dataptr(bcx, v0);
514 let llbox = Load(bcx, llval);
515 let llbox_as_usize = PtrToInt(bcx, llbox, Type::int(bcx.ccx()));
516 let drop_flag_not_dropped_already =
517 ICmp(bcx, llvm::IntNE, llbox_as_usize, dropped_pattern, DebugLoc::None);
518 with_cond(bcx, drop_flag_not_dropped_already, |bcx| {
519 let bcx = drop_ty(bcx, v0, content_ty, DebugLoc::None);
520 let info = expr::get_meta(bcx, v0);
521 let info = Load(bcx, info);
522 let (llsize, llalign) =
523 size_and_align_of_dst(&bcx.build(), content_ty, info);
525 // `Box<ZeroSizeType>` does not allocate.
526 let needs_free = ICmp(bcx,
529 C_uint(bcx.ccx(), 0u64),
531 with_cond(bcx, needs_free, |bcx| {
532 trans_exchange_free_dyn(bcx, llbox, llsize, llalign, DebugLoc::None)
537 let llbox = Load(bcx, llval);
538 let llbox_as_usize = PtrToInt(bcx, llbox, inttype);
539 let drop_flag_not_dropped_already =
540 ICmp(bcx, llvm::IntNE, llbox_as_usize, dropped_pattern, DebugLoc::None);
541 with_cond(bcx, drop_flag_not_dropped_already, |bcx| {
542 let bcx = drop_ty(bcx, llbox, content_ty, DebugLoc::None);
543 trans_exchange_free_ty(bcx, llbox, content_ty, DebugLoc::None)
547 ty::TyStruct(def, _) | ty::TyEnum(def, _) => {
548 match (def.dtor_kind(), skip_dtor) {
549 (ty::TraitDtor(true), false) => {
550 // FIXME(16758) Since the struct is unsized, it is hard to
551 // find the drop flag (which is at the end of the struct).
552 // Lets just ignore the flag and pretend everything will be
554 if type_is_sized(bcx.tcx(), t) {
555 trans_struct_drop_flag(bcx, t, v0)
557 // Give the user a heads up that we are doing something
558 // stupid and dangerous.
559 bcx.sess().warn(&format!("Ignoring drop flag in destructor for {}\
560 because the struct is unsized. See issue\
562 trans_struct_drop(bcx, t, v0)
565 (ty::TraitDtor(false), false) => {
566 trans_struct_drop(bcx, t, v0)
568 (ty::NoDtor, _) | (_, true) => {
569 // No dtor? Just the default case
570 iter_structural_ty(bcx, v0, t, |bb, vv, tt| drop_ty(bb, vv, tt, DebugLoc::None))
575 // No support in vtable for distinguishing destroying with
576 // versus without calling Drop::drop. Assert caller is
577 // okay with always calling the Drop impl, if any.
579 let data_ptr = expr::get_dataptr(bcx, v0);
580 let vtable_ptr = Load(bcx, expr::get_meta(bcx, v0));
581 let dtor = Load(bcx, vtable_ptr);
584 &[PointerCast(bcx, Load(bcx, data_ptr), Type::i8p(bcx.ccx()))],
589 if bcx.fcx.type_needs_drop(t) {
590 iter_structural_ty(bcx,
593 |bb, vv, tt| drop_ty(bb, vv, tt, DebugLoc::None))