Implement `MaybeDangling` compiler support by WaffleLapkin · Pull Request #150447 · rust-lang/rust

WaffleLapkin · 2025-12-27T21:16:15Z

View all comments

Tracking issue: #118166

cc @RalfJung

tests/codegen-llvm/manually_drop_refs.rs

compiler/rustc_middle/src/ty/layout.rs

WaffleLapkin · 2026-02-26T15:59:48Z

@RalfJung this is finally ready for review :)

Let me know if you'd prefer the PointeeInfo changes in a separate PR.

RalfJung

This looks generally great, thanks! Nice cleanup for getting rid of those align 1 everywhere.

I left some comments. I don't understand why the may_dangle field exists. Please resolve the conflicts so we can do a perf run.

View changes since this review

compiler/rustc_abi/src/lib.rs

compiler/rustc_middle/src/ty/layout.rs

compiler/rustc_ty_utils/src/abi.rs

compiler/rustc_abi/src/lib.rs

rustbot · 2026-03-02T13:43:06Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

theemathas · 2026-03-02T14:25:59Z

This PR can result in stable code using ManuallyDrop getting less optimization, right?

WaffleLapkin · 2026-03-02T14:27:42Z

@theemathas yes. Importantly also less UB ^^'

RalfJung · 2026-03-02T15:14:58Z

Indeed, that is the intent of this PR. ;)

Note that this PR does not guarantee the absence of those optimizations on stable. It only guarantees it for code that uses MaybeDangling directly, which remains unstable.

RalfJung · 2026-03-02T17:04:24Z

compiler/rustc_ty_utils/src/abi.rs

-// Handle safe Rust thin and wide pointers.
+/// Returns argument attributes for a scalar argument.
+///
+/// `drop_target_pointee` is used to special-case the argument of `ptr::drop_in_place`,


Suggested change

/// `drop_target_pointee` is used to special-case the argument of `ptr::drop_in_place`,

/// `drop_target_pointee`, if set, causes the scalar, if it is a pointer, to be treated as a mutable

/// reference to the given type. This is used to special-case the argument of `ptr::drop_in_place`,

This is unlike before where that treatment only happened if the scalar was by itself not already a safe pointer -- right?

if it is a pointer

that is not quite correct, we have an assertion that it's a pointer, not a check.

This is unlike before where that treatment only happened if the scalar was by itself not already a safe pointer -- right?

Yes, before it happened if the scalar was a pointer, and specifically a raw one.

Okay, please make the docs whatever the correct thing is then. :)

I've tried to clarify the docs, is this better?

tests/codegen-llvm/manually_drop_refs.rs

compiler/rustc_middle/src/ty/layout.rs

tests/codegen-llvm/manually_drop_refs.rs

RalfJung · 2026-03-02T17:09:10Z

compiler/rustc_middle/src/ty/adt.rs

        /// Indicates whether the type is `FieldRepresentingType`.
        const IS_FIELD_REPRESENTING_TYPE    = 1 << 13;
+        /// Indicates whether the type is `MaybeDangling<_>`.
+        const IS_MAYBE_DANGLING             = 1 << 14;


Most of these are mutually exclusive so it is a huge waste of bits to have a separate bit for each of them... 🤷 that's pre-existing though, not for this PR to fix.

Make `size`/`align` always correct rather than conditionally on the `safe` field. This makes it less error prone and easier to work with for `MaybeDangling` / potential future pointer kinds like `Aligned<_>`.

Instead of defaulting to `None` it now defaults to `Align::ONE` i.e. no alignment restriction. Codegen test changes are due to us now skipping `align 1` annotations (they are useless; not skipping them makes all the raw pointers gain an `align 1` annotation which doesn't seem any good)

WaffleLapkin · 2026-03-03T10:57:45Z

@bors try @rust-timer queue

rust-timer · 2026-03-03T10:57:48Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

rust-bors · 2026-03-03T10:57:50Z

⌛ Trying commit f308311 with merge e147e93…

To cancel the try build, run the command @bors try cancel.

Workflow: https://github.com/rust-lang/rust/actions/runs/22619884618

Implement `MaybeDangling` compiler support

rust-log-analyzer · 2026-03-03T11:41:34Z

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

/dev/sda15      105M  6.2M   99M   6% /boot/efi
tmpfs           1.6G   12K  1.6G   1% /run/user/1001
================================================================================

Sufficient disk space available (94917444KB >= 52428800KB). Skipping cleanup.
##[group]Run echo "[CI_PR_NUMBER=$num]"
echo "[CI_PR_NUMBER=$num]"
shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
---
test num::bignum::test_ord ... ok
test num::bignum::test_sub ... ok
test num::bignum::test_sub_underflow_1 ... ok
test num::bignum::test_sub_underflow_2 ... ok
test num::carryless_mul::carrying_carryless_mul ... ok
test num::carryless_mul::carryless_mul_u128 ... ok
test num::carryless_mul::carryless_mul_u16 ... ok
test num::carryless_mul::carryless_mul_u32 ... ok
test num::carryless_mul::carryless_mul_u64 ... ok
test num::carryless_mul::carryless_mul_u8 ... ok
test num::carryless_mul::widening_carryless_mul ... ok
test num::const_from::from ... ok
test num::dec2flt::decimal::check_fast_path_f16 ... ok
test num::dec2flt::decimal::check_fast_path_f32 ... ok
test num::dec2flt::decimal::check_fast_path_f64 ... ok
test num::dec2flt::decimal_seq::test_parse ... ok
---
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap (line 72) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,RandomState>::new (line 264) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,RandomState>::from (line 1504) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,RandomState>::with_capacity (line 283) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::capacity (line 445) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::clear (line 819) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::contains_key (line 1220) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::drain (line 721) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::entry (line 959) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::get (line 987) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::extract_if (line 761) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::get_disjoint_mut (line 1077) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::get_disjoint_mut (line 1119) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::hasher (line 837) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::get_disjoint_unchecked_mut (line 1162) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::get_key_value (line 1017) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::get_mut (line 1247) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::insert (line 1280) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::into_iter (line 2053) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::into_keys (line 491) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::into_values (line 586) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::is_empty (line 698) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::iter (line 618) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::iter_mut (line 648) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::keys (line 461) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::len (line 681) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::remove (line 1339) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::remove_entry (line 1367) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::reserve (line 870) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::retain (line 792) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::shrink_to (line 937) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::shrink_to_fit (line 913) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::try_insert (line 1309) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::try_reserve (line 895) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::values (line 523) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S>::with_capacity_and_hasher (line 383) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S,A>::values_mut (line 552) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::HashMap<K,V,S>::with_hasher (line 351) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::IntoIter (line 1611) ... ok
test library/std/src/collections/hash/map.rs - collections::hash::map::IntoKeys (line 1843) ... ok
---
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,RandomState>::new (line 142) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,RandomState>::with_capacity (line 161) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::capacity (line 313) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,RandomState>::from (line 1180) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::clear (line 490) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::contains (line 758) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::drain (line 398) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::difference (line 630) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::entry (line 861) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::extract_if (line 434) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::get (line 783) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::get_or_insert (line 805) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::hasher (line 508) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::get_or_insert_with (line 829) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::insert (line 983) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::intersection (line 697) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::into_iter (line 1643) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::is_disjoint (line 903) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::is_empty (line 375) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::iter (line 329) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::is_superset (line 951) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::is_subset (line 929) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::len (line 357) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::reserve (line 541) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::remove (line 1030) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::replace (line 1004) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::retain (line 465) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::shrink_to (line 607) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::shrink_to_fit (line 584) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::symmetric_difference (line 660) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::take (line 1058) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::try_reserve (line 567) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S>::with_capacity_and_hasher (line 255) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S,A>::union (line 726) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::HashSet<T,S>::with_hasher (line 223) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::Intersection (line 1507) ... ok
test library/std/src/collections/hash/set.rs - collections::hash::set::Iter (line 1392) ... ok
---

---- [codegen] tests/codegen-llvm/maybe_dangling_refs.rs stdout ----
------FileCheck stdout------------------------------

------FileCheck stderr------------------------------
/checkout/tests/codegen-llvm/maybe_dangling_refs.rs:12:11: error: CHECK: expected string not found in input
// CHECK: define noundef nonnull ptr @f(ptr noundef nonnull %x) unnamed_addr
          ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll:1:1: note: scanning from here
; ModuleID = 'maybe_dangling_refs.9ac11b7eb2eadbaf-cgu.0'
^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll:7:11: note: possible intended match here
define dso_local noundef nonnull ptr @f(ptr noundef nonnull %x) unnamed_addr #0 {
          ^

Input file: /checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll
Check file: /checkout/tests/codegen-llvm/maybe_dangling_refs.rs

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            1: ; ModuleID = 'maybe_dangling_refs.9ac11b7eb2eadbaf-cgu.0' 
check:12'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
            2: source_filename = "maybe_dangling_refs.9ac11b7eb2eadbaf-cgu.0" 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            3: target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-i128:128-n32:64-S128-ni:1:10:20" 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            4: target triple = "wasm32-unknown-wasip1" 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            5:  
check:12'0     ~
            6: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
            7: define dso_local noundef nonnull ptr @f(ptr noundef nonnull %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:12'1               ?                                                                        possible intended match
            8: start: 
check:12'0     ~~~~~~~
            9:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           10: } 
check:12'0     ~~
           11:  
check:12'0     ~
           12: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           13: define dso_local noundef nonnull ptr @g(ptr noundef nonnull %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           14: start: 
check:12'0     ~~~~~~~
           15:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           16: } 
check:12'0     ~~
           17:  
check:12'0     ~
           18: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           19: define dso_local noundef nonnull ptr @h(ptr noundef nonnull %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           20: start: 
check:12'0     ~~~~~~~
           21:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           22: } 
check:12'0     ~~
           23:  
check:12'0     ~
           24: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           25: define dso_local noundef nonnull align 4 ptr @i(ptr noundef nonnull align 4 %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           26: start: 
check:12'0     ~~~~~~~
           27:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           28: } 
check:12'0     ~~
           29:  
check:12'0     ~
           30: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           31: define dso_local noundef nonnull align 4 ptr @j(ptr noundef nonnull align 4 %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           32: start: 
check:12'0     ~~~~~~~
           33:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           34: } 
check:12'0     ~~
           35:  
check:12'0     ~
           36: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           37: define dso_local noundef nonnull align 4 ptr @k(ptr noundef nonnull align 4 %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           38: start: 
check:12'0     ~~~~~~~
           39:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           40: } 
check:12'0     ~~
           41:  
check:12'0     ~
           42: attributes #0 = { nounwind "target-cpu"="generic" } 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           43:  
check:12'0     ~
           44: !llvm.ident = !{!0} 
check:12'0     ~~~~~~~~~~~~~~~~~~~~
           45:  
check:12'0     ~
           46: !0 = !{!"rustc version 1.96.0-nightly (257af5fcb 2026-03-03)"} 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>

------------------------------------------

error: verification with 'FileCheck' failed
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/ci-llvm/bin/FileCheck" "--input-file" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll" "/checkout/tests/codegen-llvm/maybe_dangling_refs.rs" "--check-prefix=CHECK" "--allow-unused-prefixes" "--dump-input-context" "100"
stdout: none
--- stderr -------------------------------
/checkout/tests/codegen-llvm/maybe_dangling_refs.rs:12:11: error: CHECK: expected string not found in input
// CHECK: define noundef nonnull ptr @f(ptr noundef nonnull %x) unnamed_addr
          ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll:1:1: note: scanning from here
; ModuleID = 'maybe_dangling_refs.9ac11b7eb2eadbaf-cgu.0'
^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll:7:11: note: possible intended match here
define dso_local noundef nonnull ptr @f(ptr noundef nonnull %x) unnamed_addr #0 {
          ^

Input file: /checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/maybe_dangling_refs/maybe_dangling_refs.ll
Check file: /checkout/tests/codegen-llvm/maybe_dangling_refs.rs

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            1: ; ModuleID = 'maybe_dangling_refs.9ac11b7eb2eadbaf-cgu.0' 
check:12'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
            2: source_filename = "maybe_dangling_refs.9ac11b7eb2eadbaf-cgu.0" 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            3: target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-i128:128-n32:64-S128-ni:1:10:20" 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            4: target triple = "wasm32-unknown-wasip1" 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            5:  
check:12'0     ~
            6: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
            7: define dso_local noundef nonnull ptr @f(ptr noundef nonnull %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:12'1               ?                                                                        possible intended match
            8: start: 
check:12'0     ~~~~~~~
            9:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           10: } 
check:12'0     ~~
           11:  
check:12'0     ~
           12: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           13: define dso_local noundef nonnull ptr @g(ptr noundef nonnull %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           14: start: 
check:12'0     ~~~~~~~
           15:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           16: } 
check:12'0     ~~
           17:  
check:12'0     ~
           18: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           19: define dso_local noundef nonnull ptr @h(ptr noundef nonnull %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           20: start: 
check:12'0     ~~~~~~~
           21:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           22: } 
check:12'0     ~~
           23:  
check:12'0     ~
           24: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           25: define dso_local noundef nonnull align 4 ptr @i(ptr noundef nonnull align 4 %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           26: start: 
check:12'0     ~~~~~~~
           27:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           28: } 
check:12'0     ~~
           29:  
check:12'0     ~
           30: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           31: define dso_local noundef nonnull align 4 ptr @j(ptr noundef nonnull align 4 %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           32: start: 
check:12'0     ~~~~~~~
           33:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           34: } 
check:12'0     ~~
           35:  
check:12'0     ~
           36: ; Function Attrs: nounwind 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
           37: define dso_local noundef nonnull align 4 ptr @k(ptr noundef nonnull align 4 %x) unnamed_addr #0 { 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           38: start: 
check:12'0     ~~~~~~~
           39:  ret ptr %x 
check:12'0     ~~~~~~~~~~~~
           40: } 
check:12'0     ~~
           41:  
check:12'0     ~
           42: attributes #0 = { nounwind "target-cpu"="generic" } 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           43:  
check:12'0     ~
           44: !llvm.ident = !{!0} 
check:12'0     ~~~~~~~~~~~~~~~~~~~~
           45:  
check:12'0     ~
           46: !0 = !{!"rustc version 1.96.0-nightly (257af5fcb 2026-03-03)"} 
check:12'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>
------------------------------------------

---- [codegen] tests/codegen-llvm/maybe_dangling_refs.rs stdout end ----

WaffleLapkin force-pushed the maybe-dangling-semantics branch 2 times, most recently from aebfd56 to 63e07cf Compare December 27, 2025 21:28

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RalfJung reviewed Dec 28, 2025

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miri/const eval: support MaybeDangling #150446

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WaffleLapkin force-pushed the maybe-dangling-semantics branch from 63e07cf to c40ca7d Compare February 19, 2026 14:35

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rustbot added the A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. label Feb 19, 2026

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WaffleLapkin force-pushed the maybe-dangling-semantics branch from 6d96bdb to d71787d Compare February 19, 2026 18:35

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WaffleLapkin force-pushed the maybe-dangling-semantics branch from baa9118 to c135ac1 Compare February 23, 2026 16:07

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WaffleLapkin force-pushed the maybe-dangling-semantics branch from c135ac1 to f399322 Compare February 25, 2026 23:07

rustbot added the PG-exploit-mitigations Project group: Exploit mitigations label Feb 25, 2026

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WaffleLapkin force-pushed the maybe-dangling-semantics branch from a72a3f3 to 42ce338 Compare February 26, 2026 12:26

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WaffleLapkin force-pushed the maybe-dangling-semantics branch 2 times, most recently from 51a5c77 to efc351d Compare February 26, 2026 13:52

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RalfJung requested changes Mar 1, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 1, 2026

add an adt flag for MaybeDangling

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WaffleLapkin force-pushed the maybe-dangling-semantics branch from efc351d to 8102f65 Compare March 2, 2026 13:43

WaffleLapkin force-pushed the maybe-dangling-semantics branch from 395a073 to 62cbdee Compare March 2, 2026 15:48

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WaffleLapkin added 2 commits March 3, 2026 11:07

refactor PointeeInfo

9082178

Make `size`/`align` always correct rather than conditionally on the `safe` field. This makes it less error prone and easier to work with for `MaybeDangling` / potential future pointer kinds like `Aligned<_>`.

WaffleLapkin force-pushed the maybe-dangling-semantics branch from 62cbdee to 24012bc Compare March 3, 2026 10:07

WaffleLapkin added 3 commits March 3, 2026 11:54

add a codegen-llvm test for ManuallyDrop

0bb3056

add semantics to MaybeDangling

faf532a

strip readonly/captures from MaybeDangling<&T>

f308311

WaffleLapkin force-pushed the maybe-dangling-semantics branch from 24012bc to f308311 Compare March 3, 2026 10:54

rust-bors bot pushed a commit that referenced this pull request Mar 3, 2026

Auto merge of #150447 - WaffleLapkin:maybe-dangling-semantics, r=<try>

e147e93

Implement `MaybeDangling` compiler support

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 3, 2026

	/// `drop_target_pointee` is used to special-case the argument of `ptr::drop_in_place`,
	/// `drop_target_pointee`, if set, causes the scalar, if it is a pointer, to be treated as a mutable
	/// reference to the given type. This is used to special-case the argument of `ptr::drop_in_place`,

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