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Implement MaybeDangling compiler support #150447

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@WaffleLapkin WaffleLapkin commented Dec 27, 2025

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Dec 27, 2025
@WaffleLapkin WaffleLapkin force-pushed the maybe-dangling-semantics branch from 24f36ff to aebfd56 Compare December 27, 2025 21:22
@WaffleLapkin WaffleLapkin force-pushed the maybe-dangling-semantics branch from aebfd56 to 63e07cf Compare December 27, 2025 21:28
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rust-log-analyzer commented Dec 27, 2025

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) 

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

------FileCheck stderr------------------------------
/checkout/tests/codegen-llvm/manually_drop_refs.rs:6:11: error: CHECK: expected string not found in input
// CHECK: define noundef nonnull ptr @f(ptr noundef nonnull readnone returned {{(captures\(ret: address, provenance\) )?}}%x) unnamed_addr
          ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/manually_drop_refs/manually_drop_refs.ll:1:1: note: scanning from here
; ModuleID = 'manually_drop_refs.f6bd3c5d90b64e2d-cgu.0'
^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/manually_drop_refs/manually_drop_refs.ll:7:11: note: possible intended match here
define dso_local noundef nonnull ptr @f(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 {
          ^

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

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

Input was:
<<<<<<
           1: ; ModuleID = 'manually_drop_refs.f6bd3c5d90b64e2d-cgu.0' 
check:6'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           2: source_filename = "manually_drop_refs.f6bd3c5d90b64e2d-cgu.0" 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           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:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           4: target triple = "wasm32-unknown-wasip1" 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           5:  
check:6'0     ~
           6: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           7: define dso_local noundef nonnull ptr @f(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 { 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:6'1               ?                                                                                                                             possible intended match
           8: start: 
check:6'0     ~~~~~~~
           9:  ret ptr %x 
check:6'0     ~~~~~~~~~~~~
          10: } 
check:6'0     ~~
          11:  
check:6'0     ~
          12: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          13: define dso_local noundef nonnull ptr @g(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 { 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          14: start: 
check:6'0     ~~~~~~~
          15:  ret ptr %x 
check:6'0     ~~~~~~~~~~~~
          16: } 
check:6'0     ~~
          17:  
check:6'0     ~
          18: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          19: define dso_local noundef nonnull ptr @h(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 { 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          20: start: 
check:6'0     ~~~~~~~
          21:  ret ptr %x 
check:6'0     ~~~~~~~~~~~~
          22: } 
check:6'0     ~~
          23:  
check:6'0     ~
          24: attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) "target-cpu"="generic" } 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          25:  
check:6'0     ~
          26: !llvm.ident = !{!0} 
check:6'0     ~~~~~~~~~~~~~~~~~~~~
          27:  
check:6'0     ~
          28: !0 = !{!"rustc version 1.94.0-nightly (5efa397c6 2025-12-27)"} 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>

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

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/manually_drop_refs/manually_drop_refs.ll" "/checkout/tests/codegen-llvm/manually_drop_refs.rs" "--check-prefix=CHECK" "--allow-unused-prefixes" "--dump-input-context" "100"
stdout: none
--- stderr -------------------------------
/checkout/tests/codegen-llvm/manually_drop_refs.rs:6:11: error: CHECK: expected string not found in input
// CHECK: define noundef nonnull ptr @f(ptr noundef nonnull readnone returned {{(captures\(ret: address, provenance\) )?}}%x) unnamed_addr
          ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/manually_drop_refs/manually_drop_refs.ll:1:1: note: scanning from here
; ModuleID = 'manually_drop_refs.f6bd3c5d90b64e2d-cgu.0'
^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen-llvm/manually_drop_refs/manually_drop_refs.ll:7:11: note: possible intended match here
define dso_local noundef nonnull ptr @f(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 {
          ^

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

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

Input was:
<<<<<<
           1: ; ModuleID = 'manually_drop_refs.f6bd3c5d90b64e2d-cgu.0' 
check:6'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           2: source_filename = "manually_drop_refs.f6bd3c5d90b64e2d-cgu.0" 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           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:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           4: target triple = "wasm32-unknown-wasip1" 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           5:  
check:6'0     ~
           6: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           7: define dso_local noundef nonnull ptr @f(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 { 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:6'1               ?                                                                                                                             possible intended match
           8: start: 
check:6'0     ~~~~~~~
           9:  ret ptr %x 
check:6'0     ~~~~~~~~~~~~
          10: } 
check:6'0     ~~
          11:  
check:6'0     ~
          12: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          13: define dso_local noundef nonnull ptr @g(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 { 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          14: start: 
check:6'0     ~~~~~~~
          15:  ret ptr %x 
check:6'0     ~~~~~~~~~~~~
          16: } 
check:6'0     ~~
          17:  
check:6'0     ~
          18: ; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          19: define dso_local noundef nonnull ptr @h(ptr noundef nonnull readnone returned captures(ret: address, provenance) %x) unnamed_addr #0 { 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          20: start: 
check:6'0     ~~~~~~~
          21:  ret ptr %x 
check:6'0     ~~~~~~~~~~~~
          22: } 
check:6'0     ~~
          23:  
check:6'0     ~
          24: attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) "target-cpu"="generic" } 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          25:  
check:6'0     ~
          26: !llvm.ident = !{!0} 
check:6'0     ~~~~~~~~~~~~~~~~~~~~
          27:  
check:6'0     ~
          28: !0 = !{!"rustc version 1.94.0-nightly (5efa397c6 2025-12-27)"} 
check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>
------------------------------------------

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

RalfJung
RalfJung reviewed Dec 28, 2025
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tests/codegen-llvm/manually_drop_refs.rs
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@RalfJung RalfJung Dec 28, 2025

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Would be good to have a comment explaining what we are checking here: the absence of dereferenceable and noalias

RalfJung
RalfJung reviewed Dec 28, 2025
View reviewed changes
compiler/rustc_middle/src/ty/layout.rs
Comment on lines +1057 to +1060
// FIXME: what is the exact effect of maybe dangling?
Self::ty_and_layout_pointee_info_at(this.field(cx, 0), cx, offset)
.map(|info| PointeeInfo { safe: None, ..info })
}
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@RalfJung RalfJung Dec 28, 2025

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This should also reset the size to 0, that's how we encode dereferenceable.

Odd that the test does not catch this...

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