1 use std::cell::RefCell;
2 use std::collections::HashSet;
5 use std::num::NonZeroU64;
7 use rustc::ty::{self, layout::Size};
8 use rustc::hir::{MutMutable, MutImmutable};
9 use rustc::mir::RetagKind;
12 EvalResult, InterpError, MiriEvalContext, HelpersEvalContextExt, Evaluator, MutValueVisitor,
13 MemoryKind, MiriMemoryKind, RangeMap, Allocation, AllocationExtra,
14 Pointer, Immediate, ImmTy, PlaceTy, MPlaceTy,
17 pub type PtrId = NonZeroU64;
18 pub type CallId = NonZeroU64;
20 /// Tracking pointer provenance
21 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
27 impl fmt::Display for Tag {
28 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
30 Tag::Tagged(id) => write!(f, "{}", id),
31 Tag::Untagged => write!(f, "<untagged>"),
36 /// Indicates which permission is granted (by this item to some pointers)
37 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
39 /// Grants unique mutable access.
41 /// Grants shared mutable access.
43 /// Greants shared read-only access.
47 /// An item in the per-location borrow stack.
48 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
50 /// The permission this item grants.
52 /// The pointers the permission is granted to.
54 /// An optional protector, ensuring the item cannot get popped until `CallId` is over.
55 protector: Option<CallId>,
58 impl fmt::Display for Item {
59 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
60 write!(f, "[{:?} for {}", self.perm, self.tag)?;
61 if let Some(call) = self.protector {
62 write!(f, " (call {})", call)?;
69 /// Extra per-location state.
70 #[derive(Clone, Debug, PartialEq, Eq)]
72 /// Used *mostly* as a stack; never empty.
73 /// We sometimes push into the middle but never remove from the middle.
74 /// The same tag may occur multiple times, e.g. from a two-phase borrow.
76 /// * Above a `SharedReadOnly` there can only be more `SharedReadOnly`.
81 /// Extra per-allocation state.
82 #[derive(Clone, Debug)]
84 // Even reading memory can have effects on the stack, so we need a `RefCell` here.
85 stacks: RefCell<RangeMap<Stack>>,
86 // Pointer to global state
90 /// Extra global state, available to the memory access hooks.
92 pub struct GlobalState {
95 active_calls: HashSet<CallId>,
97 pub type MemoryState = Rc<RefCell<GlobalState>>;
99 /// Indicates which kind of access is being performed.
100 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
101 pub enum AccessKind {
106 impl fmt::Display for AccessKind {
107 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
109 AccessKind::Read => write!(f, "read"),
110 AccessKind::Write => write!(f, "write"),
115 /// Indicates which kind of reference is being created.
116 /// Used by high-level `reborrow` to compute which permissions to grant to the
118 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
120 /// `&mut` and `Box`.
122 /// `&` with or without interior mutability.
124 /// `*mut`/`*const` (raw pointers).
125 Raw { mutable: bool },
128 impl fmt::Display for RefKind {
129 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
131 RefKind::Unique => write!(f, "unique"),
132 RefKind::Shared => write!(f, "shared"),
133 RefKind::Raw { mutable: true } => write!(f, "raw (mutable)"),
134 RefKind::Raw { mutable: false } => write!(f, "raw (constant)"),
139 /// Utilities for initialization and ID generation
140 impl Default for GlobalState {
141 fn default() -> Self {
143 next_ptr_id: NonZeroU64::new(1).unwrap(),
144 next_call_id: NonZeroU64::new(1).unwrap(),
145 active_calls: HashSet::default(),
151 pub fn new_ptr(&mut self) -> PtrId {
152 let id = self.next_ptr_id;
153 self.next_ptr_id = NonZeroU64::new(id.get() + 1).unwrap();
157 pub fn new_call(&mut self) -> CallId {
158 let id = self.next_call_id;
159 trace!("new_call: Assigning ID {}", id);
160 self.active_calls.insert(id);
161 self.next_call_id = NonZeroU64::new(id.get() + 1).unwrap();
165 pub fn end_call(&mut self, id: CallId) {
166 assert!(self.active_calls.remove(&id));
169 fn is_active(&self, id: CallId) -> bool {
170 self.active_calls.contains(&id)
174 // # Stacked Borrows Core Begin
176 /// We need to make at least the following things true:
178 /// U1: After creating a `Uniq`, it is at the top.
179 /// U2: If the top is `Uniq`, accesses must be through that `Uniq` or remove it it.
180 /// U3: If an access happens with a `Uniq`, it requires the `Uniq` to be in the stack.
182 /// F1: After creating a `&`, the parts outside `UnsafeCell` have our `SharedReadOnly` on top.
183 /// F2: If a write access happens, it pops the `SharedReadOnly`. This has three pieces:
184 /// F2a: If a write happens granted by an item below our `SharedReadOnly`, the `SharedReadOnly`
186 /// F2b: No `SharedReadWrite` or `Unique` will ever be added on top of our `SharedReadOnly`.
187 /// F3: If an access happens with an `&` outside `UnsafeCell`,
188 /// it requires the `SharedReadOnly` to still be in the stack.
190 impl Default for Tag {
192 fn default() -> Tag {
197 /// Core relations on `Permission` define which accesses are allowed:
198 /// On every access, we try to find a *granting* item, and then we remove all
199 /// *incompatible* items above it.
201 /// This defines for a given permission, whether it permits the given kind of access.
202 fn grants(self, access: AccessKind) -> bool {
203 match (self, access) {
204 // Unique and SharedReadWrite allow any kind of access.
205 (Permission::Unique, _) |
206 (Permission::SharedReadWrite, _) =>
208 // SharedReadOnly only permits read access.
209 (Permission::SharedReadOnly, AccessKind::Read) =>
211 (Permission::SharedReadOnly, AccessKind::Write) =>
216 /// This defines for a given permission, which other permissions it can tolerate "above" itself
217 /// for which kinds of accesses.
218 /// If true, then `other` is allowed to remain on top of `self` when `access` happens.
219 fn compatible_with(self, access: AccessKind, other: Permission) -> bool {
220 use self::Permission::*;
222 match (self, access, other) {
223 // Some cases are impossible.
224 (SharedReadOnly, _, SharedReadWrite) |
225 (SharedReadOnly, _, Unique) =>
226 bug!("There can never be a SharedReadWrite or a Unique on top of a SharedReadOnly"),
227 // When `other` is `SharedReadOnly`, that is NEVER compatible with
229 // This makes sure read-only pointers become invalid on write accesses (ensures F2a).
230 (_, AccessKind::Write, SharedReadOnly) =>
232 // When `other` is `Unique`, that is compatible with nothing.
233 // This makes sure unique pointers become invalid on incompatible accesses (ensures U2).
236 // When we are unique and this is a write/dealloc, we tolerate nothing.
237 // This makes sure we re-assert uniqueness ("being on top") on write accesses.
238 // (This is particularily important such that when a new mutable ref gets created, it gets
239 // pushed onto the right item -- this behaves like a write and we assert uniqueness of the
240 // pointer from which this comes, *if* it was a unique pointer.)
241 (Unique, AccessKind::Write, _) =>
243 // `SharedReadWrite` items can tolerate any other akin items for any kind of access.
244 (SharedReadWrite, _, SharedReadWrite) =>
246 // Any item can tolerate read accesses for shared items.
247 // This includes unique items! Reads from unique pointers do not invalidate
249 (_, AccessKind::Read, SharedReadWrite) |
250 (_, AccessKind::Read, SharedReadOnly) =>
257 /// Core per-location operations: access, dealloc, reborrow.
259 /// Find the item granting the given kind of access to the given tag, and where
260 /// *the first incompatible item above it* is on the stack.
261 fn find_granting(&self, access: AccessKind, tag: Tag) -> Option<(Permission, usize)> {
262 let (perm, idx) = self.borrows.iter()
263 .enumerate() // we also need to know *where* in the stack
264 .rev() // search top-to-bottom
265 // Return permission of first item that grants access.
266 // We require a permission with the right tag, ensuring U3 and F3.
267 .find_map(|(idx, item)|
268 if item.perm.grants(access) && tag == item.tag {
269 Some((item.perm, idx))
275 let mut first_incompatible_idx = idx+1;
276 while let Some(item) = self.borrows.get(first_incompatible_idx) {
277 if perm.compatible_with(access, item.perm) {
278 // Keep this, check next.
279 first_incompatible_idx += 1;
285 return Some((perm, first_incompatible_idx));
288 /// Test if a memory `access` using pointer tagged `tag` is granted.
289 /// If yes, return the index of the item that granted it.
294 global: &GlobalState,
295 ) -> EvalResult<'tcx> {
296 // Two main steps: Find granting item, remove all incompatible items above.
298 // Step 1: Find granting item.
299 let (granting_perm, first_incompatible_idx) = self.find_granting(access, tag)
300 .ok_or_else(|| InterpError::MachineError(format!(
301 "no item granting {} access to tag {} found in borrow stack",
305 // Step 2: Remove everything incompatible above them. Make sure we do not remove protected
307 // For writes, this is a simple stack. For reads, however, it is not:
308 // in `let raw = &mut *x as *mut _; let _val = *x;`, the second statement would pop the `Unique`
309 // from the reborrow of the first statement, and subsequently also pop the `SharedReadWrite` for `raw`.
310 // This pattern occurs a lot in the standard library: create a raw pointer, then also create a shared
311 // reference and use that.
313 // Implemented with indices because there does not seem to be a nice iterator and range-based
315 let mut cur = first_incompatible_idx;
316 while let Some(item) = self.borrows.get(cur) {
317 // If this is a read, we double-check if we really want to kill this.
318 if access == AccessKind::Read && granting_perm.compatible_with(access, item.perm) {
319 // Keep this, check next.
322 // Aha! This is a bad one, remove it, and make sure it is not protected.
323 let item = self.borrows.remove(cur);
324 if let Some(call) = item.protector {
325 if global.is_active(call) {
326 return err!(MachineError(format!(
327 "not granting {} access to tag {} because incompatible item {} is protected",
332 trace!("access: removing item {}", item);
341 /// Deallocate a location: Like a write access, but also there must be no
342 /// active protectors at all.
346 global: &GlobalState,
347 ) -> EvalResult<'tcx> {
348 // Step 1: Find granting item.
349 self.find_granting(AccessKind::Write, tag)
350 .ok_or_else(|| InterpError::MachineError(format!(
351 "no item granting write access for deallocation to tag {} found in borrow stack",
355 // We must make sure there are no protected items remaining on the stack.
356 // Also clear the stack, no more accesses are possible.
357 for item in self.borrows.drain(..) {
358 if let Some(call) = item.protector {
359 if global.is_active(call) {
360 return err!(MachineError(format!(
361 "deallocating with active protector ({})", call
370 /// `reborrow` helper function: test that the stack invariants are still maintained.
371 fn test_invariants(&self) {
372 let mut saw_shared_read_only = false;
373 for item in self.borrows.iter() {
375 Permission::SharedReadOnly => {
376 saw_shared_read_only = true;
378 // Otherwise, if we saw one before, that's a bug.
379 perm if saw_shared_read_only => {
380 bug!("Found {:?} on top of a SharedReadOnly!", perm);
387 /// Derived a new pointer from one with the given tag.
388 /// `weak` controls whether this operation is weak or strong: weak granting does not act as
389 /// an access, and they add the new item directly on top of the one it is derived
390 /// from instead of all the way at the top of the stack.
396 global: &GlobalState,
397 ) -> EvalResult<'tcx> {
398 // Figure out which access `perm` corresponds to.
399 let access = if new.perm.grants(AccessKind::Write) {
404 // Now we figure out which item grants our parent (`derived_from`) this kind of access.
405 // We use that to determine where to put the new item.
406 let (_, first_incompatible_idx) = self.find_granting(access, derived_from)
407 .ok_or_else(|| InterpError::MachineError(format!(
408 "no item to reborrow for {:?} from tag {} found in borrow stack", new.perm, derived_from,
411 // Compute where to put the new item.
412 // Either way, we ensure that we insert the new item in a way that between
413 // `derived_from` and the new one, there are only items *compatible with* `derived_from`.
414 let new_idx = if weak {
415 // A weak SharedReadOnly reborrow might be added below other items, violating the
416 // invariant that only SharedReadOnly can sit on top of SharedReadOnly.
417 assert!(new.perm != Permission::SharedReadOnly, "Weak SharedReadOnly reborrows don't work");
418 // A very liberal reborrow because the new pointer does not expect any kind of aliasing guarantee.
419 // Just insert new permission as child of old permission, and maintain everything else.
420 // This inserts "as far down as possible", which is good because it makes this pointer as
421 // long-lived as possible *and* we want all the items that are incompatible with this
422 // to actually get removed from the stack. If we pushed a `SharedReadWrite` on top of
423 // a `SharedReadOnly`, we'd violate the invariant that `SaredReadOnly` are at the top
424 // and we'd allow write access without invalidating frozen shared references!
425 // This ensures F2b for `SharedReadWrite` by adding the new item below any
426 // potentially existing `SharedReadOnly`.
427 first_incompatible_idx
429 // A "safe" reborrow for a pointer that actually expects some aliasing guarantees.
430 // Here, creating a reference actually counts as an access, and pops incompatible
431 // stuff off the stack.
432 // This ensures F2b for `Unique`, by removing offending `SharedReadOnly`.
433 self.access(access, derived_from, global)?;
434 if access == AccessKind::Write {
435 // For write accesses, the position is the same as what it would have been weakly!
436 assert_eq!(first_incompatible_idx, self.borrows.len());
439 // We insert "as far up as possible": We know only compatible items are remaining
440 // on top of `derived_from`, and we want the new item at the top so that we
441 // get the strongest possible guarantees.
442 // This ensures U1 and F1.
446 // Put the new item there. As an optimization, deduplicate if it is equal to one of its new neighbors.
447 if self.borrows[new_idx-1] == new || self.borrows.get(new_idx) == Some(&new) {
448 // Optimization applies, done.
449 trace!("reborrow: avoiding adding redundant item {}", new);
451 trace!("reborrow: adding item {}", new);
452 self.borrows.insert(new_idx, new);
455 // Make sure that after all this, the stack's invariant is still maintained.
456 if cfg!(debug_assertions) {
457 self.test_invariants();
463 // # Stacked Borrows Core End
465 /// Map per-stack operations to higher-level per-location-range operations.
467 /// Creates new stack with initial tag.
473 let item = Item { perm: Permission::Unique, tag, protector: None };
478 stacks: RefCell::new(RangeMap::new(size, stack)),
483 /// Call `f` on every stack in the range.
488 f: impl Fn(&mut Stack, &GlobalState) -> EvalResult<'tcx>,
489 ) -> EvalResult<'tcx> {
490 let global = self.global.borrow();
491 let mut stacks = self.stacks.borrow_mut();
492 for stack in stacks.iter_mut(ptr.offset, size) {
499 /// Glue code to connect with Miri Machine Hooks
501 pub fn new_allocation(
504 kind: MemoryKind<MiriMemoryKind>,
506 let tag = match kind {
507 MemoryKind::Stack => {
508 // New unique borrow. This `Uniq` is not accessible by the program,
509 // so it will only ever be used when using the local directly (i.e.,
510 // not through a pointer). That is, whenever we directly use a local, this will pop
511 // everything else off the stack, invalidating all previous pointers,
512 // and in particular, *all* raw pointers. This subsumes the explicit
513 // `reset` which the blog post [1] says to perform when accessing a local.
515 // [1]: <https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html>
516 Tag::Tagged(extra.borrow_mut().new_ptr())
522 let stack = Stacks::new(size, tag, Rc::clone(extra));
527 impl AllocationExtra<Tag> for Stacks {
529 fn memory_read<'tcx>(
530 alloc: &Allocation<Tag, Stacks>,
533 ) -> EvalResult<'tcx> {
534 trace!("read access with tag {}: {:?}, size {}", ptr.tag, ptr, size.bytes());
535 alloc.extra.for_each(ptr, size, |stack, global| {
536 stack.access(AccessKind::Read, ptr.tag, global)?;
542 fn memory_written<'tcx>(
543 alloc: &mut Allocation<Tag, Stacks>,
546 ) -> EvalResult<'tcx> {
547 trace!("write access with tag {}: {:?}, size {}", ptr.tag, ptr, size.bytes());
548 alloc.extra.for_each(ptr, size, |stack, global| {
549 stack.access(AccessKind::Write, ptr.tag, global)?;
555 fn memory_deallocated<'tcx>(
556 alloc: &mut Allocation<Tag, Stacks>,
559 ) -> EvalResult<'tcx> {
560 trace!("deallocation with tag {}: {:?}, size {}", ptr.tag, ptr, size.bytes());
561 alloc.extra.for_each(ptr, size, |stack, global| {
562 stack.dealloc(ptr.tag, global)
567 /// Retagging/reborrowing. There is some policy in here, such as which permissions
568 /// to grant for which references, when to add protectors, and how to realize two-phase
569 /// borrows in terms of the primitives above.
570 impl<'a, 'mir, 'tcx> EvalContextPrivExt<'a, 'mir, 'tcx> for crate::MiriEvalContext<'a, 'mir, 'tcx> {}
571 trait EvalContextPrivExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a, 'mir, 'tcx> {
574 place: MPlaceTy<'tcx, Tag>,
580 ) -> EvalResult<'tcx> {
581 let this = self.eval_context_mut();
582 let protector = if protect { Some(this.frame().extra) } else { None };
583 let ptr = place.ptr.to_ptr()?;
584 trace!("reborrow: {:?} reference {} derived from {} (pointee {}): {:?}, size {}",
585 kind, new_tag, ptr.tag, place.layout.ty, ptr, size.bytes());
587 // Get the allocation. It might not be mutable, so we cannot use `get_mut`.
588 let alloc = this.memory().get(ptr.alloc_id)?;
589 alloc.check_bounds(this, ptr, size)?;
590 // Update the stacks.
591 // Make sure that raw pointers and mutable shared references are reborrowed "weak":
592 // There could be existing unique pointers reborrowed from them that should remain valid!
593 let perm = match kind {
594 RefKind::Unique => Permission::Unique,
595 RefKind::Raw { mutable: true } => Permission::SharedReadWrite,
596 RefKind::Shared | RefKind::Raw { mutable: false } => {
597 // Shared references and *const are a whole different kind of game, the
598 // permission is not uniform across the entire range!
599 // We need a frozen-sensitive reborrow.
600 return this.visit_freeze_sensitive(place, size, |cur_ptr, size, frozen| {
601 // We are only ever `SharedReadOnly` inside the frozen bits.
602 let perm = if frozen { Permission::SharedReadOnly } else { Permission::SharedReadWrite };
603 let weak = perm == Permission::SharedReadWrite;
604 let item = Item { perm, tag: new_tag, protector };
605 alloc.extra.for_each(cur_ptr, size, |stack, global| {
606 stack.grant(cur_ptr.tag, force_weak || weak, item, global)
611 debug_assert_ne!(perm, Permission::SharedReadOnly, "SharedReadOnly must be used frozen-sensitive");
612 let weak = perm == Permission::SharedReadWrite;
613 let item = Item { perm, tag: new_tag, protector };
614 alloc.extra.for_each(ptr, size, |stack, global| {
615 stack.grant(ptr.tag, force_weak || weak, item, global)
619 /// Retags an indidual pointer, returning the retagged version.
620 /// `mutbl` can be `None` to make this a raw pointer.
623 val: ImmTy<'tcx, Tag>,
627 ) -> EvalResult<'tcx, Immediate<Tag>> {
628 let this = self.eval_context_mut();
629 // We want a place for where the ptr *points to*, so we get one.
630 let place = this.ref_to_mplace(val)?;
631 let size = this.size_and_align_of_mplace(place)?
632 .map(|(size, _)| size)
633 .unwrap_or_else(|| place.layout.size);
634 if size == Size::ZERO {
635 // Nothing to do for ZSTs.
639 // Compute new borrow.
640 let new_tag = match kind {
641 RefKind::Raw { .. } => Tag::Untagged,
642 _ => Tag::Tagged(this.memory().extra.borrow_mut().new_ptr()),
646 // TODO: With `two_phase == true`, this performs a weak reborrow for a `Unique`. That
647 // can lead to some possibly surprising effects, if the parent permission is
648 // `SharedReadWrite` then we now have a `Unique` in the middle of them, which "splits"
649 // them in terms of what remains valid when the `Unique` gets used. Is that really
651 this.reborrow(place, size, kind, new_tag, /*force_weak:*/ two_phase, protect)?;
652 let new_place = place.replace_tag(new_tag);
653 // Handle two-phase borrows.
655 assert!(kind == RefKind::Unique, "two-phase shared borrows make no sense");
656 // Grant read access *to the parent pointer* with the old tag *derived from the new tag* (`new_place`).
657 // This means the old pointer has multiple items in the stack now, which otherwise cannot happen
658 // for unique references -- but in this case it precisely expresses the semantics we want.
659 let old_tag = place.ptr.to_ptr().unwrap().tag;
660 this.reborrow(new_place, size, RefKind::Shared, old_tag, /*force_weak:*/ false, /*protect:*/ false)?;
663 // Return new pointer.
664 Ok(new_place.to_ref())
668 impl<'a, 'mir, 'tcx> EvalContextExt<'a, 'mir, 'tcx> for crate::MiriEvalContext<'a, 'mir, 'tcx> {}
669 pub trait EvalContextExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a, 'mir, 'tcx> {
673 place: PlaceTy<'tcx, Tag>
674 ) -> EvalResult<'tcx> {
675 let this = self.eval_context_mut();
676 // Determine mutability and whether to add a protector.
677 // Cannot use `builtin_deref` because that reports *immutable* for `Box`,
678 // making it useless.
679 fn qualify(ty: ty::Ty<'_>, kind: RetagKind) -> Option<(RefKind, bool)> {
681 // References are simple.
682 ty::Ref(_, _, MutMutable) =>
683 Some((RefKind::Unique, kind == RetagKind::FnEntry)),
684 ty::Ref(_, _, MutImmutable) =>
685 Some((RefKind::Shared, kind == RetagKind::FnEntry)),
686 // Raw pointers need to be enabled.
687 ty::RawPtr(tym) if kind == RetagKind::Raw =>
688 Some((RefKind::Raw { mutable: tym.mutbl == MutMutable }, false)),
689 // Boxes do not get a protector: protectors reflect that references outlive the call
690 // they were passed in to; that's just not the case for boxes.
691 ty::Adt(..) if ty.is_box() => Some((RefKind::Unique, false)),
696 // We need a visitor to visit all references. However, that requires
697 // a `MemPlace`, so we have a fast path for reference types that
698 // avoids allocating.
699 if let Some((mutbl, protector)) = qualify(place.layout.ty, kind) {
701 let val = this.read_immediate(this.place_to_op(place)?)?;
702 let val = this.retag_reference(val, mutbl, protector, kind == RetagKind::TwoPhase)?;
703 this.write_immediate(val, place)?;
706 let place = this.force_allocation(place)?;
708 let mut visitor = RetagVisitor { ecx: this, kind };
709 visitor.visit_value(place)?;
711 // The actual visitor.
712 struct RetagVisitor<'ecx, 'a, 'mir, 'tcx> {
713 ecx: &'ecx mut MiriEvalContext<'a, 'mir, 'tcx>,
716 impl<'ecx, 'a, 'mir, 'tcx>
717 MutValueVisitor<'a, 'mir, 'tcx, Evaluator<'tcx>>
719 RetagVisitor<'ecx, 'a, 'mir, 'tcx>
721 type V = MPlaceTy<'tcx, Tag>;
724 fn ecx(&mut self) -> &mut MiriEvalContext<'a, 'mir, 'tcx> {
728 // Primitives of reference type, that is the one thing we are interested in.
729 fn visit_primitive(&mut self, place: MPlaceTy<'tcx, Tag>) -> EvalResult<'tcx>
731 // Cannot use `builtin_deref` because that reports *immutable* for `Box`,
732 // making it useless.
733 if let Some((mutbl, protector)) = qualify(place.layout.ty, self.kind) {
734 let val = self.ecx.read_immediate(place.into())?;
735 let val = self.ecx.retag_reference(
739 self.kind == RetagKind::TwoPhase
741 self.ecx.write_immediate(val, place.into())?;