perf experiment: give noalias back to refs in closures by RalfJung · Pull Request #162361 · rust-lang/rust

RalfJung · 2026-09-06T08:58:14Z

More #160745 perf experiments.

RalfJung · 2026-09-06T08:58:36Z

perf experiment: give noalias back to refs in closures

rust-log-analyzer · 2026-09-06T09:50:22Z

The job x86_64-gnu-miri failed! Check out the build log: (web) (plain enhanced) (plain)

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

tests/pass/shims/x86/rounding-error.rs ... ok
tests/pass/shims/x86/intrinsics-x86-gfni.rs ... ok

FAILED TEST: tests/pass/generators.rs (revision `stack`)
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass" "tests/pass/generators.rs" "--edition" "2024" "--cfg=stack" "-Cextra-filename=stack"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/generators.stack.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: trying to retag from <1438> for Unique permission at alloc623[0x0], but that tag does not exist in the borrow stack for this location
##[error]  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   |                 |
   |                 this error occurs as part of retag at alloc623[0x0..0x1]
   |                 while retagging field .<coroutine-state(3)>.<captured-var(r)>
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <1438> was created by a Unique retag at offsets [0x0..0x1]
  --> tests/pass/generators.rs:73:21
   |
LL |             let a = r;
   |                     ^
help: <1438> was later invalidated at offsets [0x0..0x1] by a Unique retag
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   = note: stack backtrace:
           0: movable_gen
               at tests/pass/generators.rs:83:17: 83:18
           1: main
---



full stderr:
error: Undefined Behavior: trying to retag from <1438> for Unique permission at alloc623[0x0], but that tag does not exist in the borrow stack for this location
##[error]  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   |                 |
   |                 this error occurs as part of retag at alloc623[0x0..0x1]
   |                 while retagging field .<coroutine-state(3)>.<captured-var(r)>
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <1438> was created by a Unique retag at offsets [0x0..0x1]
  --> tests/pass/generators.rs:73:21
   |
LL |             let a = r;
   |                     ^
help: <1438> was later invalidated at offsets [0x0..0x1] by a Unique retag
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   = note: stack backtrace:
           0: movable_gen
               at tests/pass/generators.rs:83:17: 83:18
           1: main
---



FAILED TEST: tests/pass/generators.rs (revision `tree`)
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass" "tests/pass/generators.rs" "-Zmiri-tree-borrows" "--edition" "2024" "--cfg=tree" "-Cextra-filename=tree"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/generators.tree.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: write access through <1441> at alloc623[0x0] is forbidden
##[error]  --> tests/pass/generators.rs:76:13
   |
LL |             *a = 2;
   |             ^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
   = help: the accessed tag <1441> is a child of the conflicting tag <1412>
   = help: the conflicting tag <1412> has state Frozen which forbids this child write access
help: the accessed tag <1441> was created here
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
help: the conflicting tag <1412> was created here, in the initial state Reserved
  --> tests/pass/generators.rs:73:21
   |
LL |             let a = r;
   |                     ^
help: the conflicting tag <1412> later transitioned to Unique due to a child write access at offsets [0x0..0x1]
  --> tests/pass/generators.rs:74:13
   |
LL |             *a = 1;
   |             ^^^^^^
   = help: this transition corresponds to the first write to a 2-phase borrowed mutable reference
help: the conflicting tag <1412> later transitioned to Frozen due to a reborrow (acting as a foreign read access) at offsets [0x0..0x1]
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   = help: this transition corresponds to a loss of write permissions
   = note: stack backtrace:
           0: movable_gen::make_gen::{closure#0}
               at tests/pass/generators.rs:76:13: 76:19
---



full stderr:
error: Undefined Behavior: write access through <1441> at alloc623[0x0] is forbidden
##[error]  --> tests/pass/generators.rs:76:13
   |
LL |             *a = 2;
   |             ^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
   = help: the accessed tag <1441> is a child of the conflicting tag <1412>
   = help: the conflicting tag <1412> has state Frozen which forbids this child write access
help: the accessed tag <1441> was created here
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
help: the conflicting tag <1412> was created here, in the initial state Reserved
  --> tests/pass/generators.rs:73:21
   |
LL |             let a = r;
   |                     ^
help: the conflicting tag <1412> later transitioned to Unique due to a child write access at offsets [0x0..0x1]
  --> tests/pass/generators.rs:74:13
   |
LL |             *a = 1;
   |             ^^^^^^
   = help: this transition corresponds to the first write to a 2-phase borrowed mutable reference
help: the conflicting tag <1412> later transitioned to Frozen due to a reborrow (acting as a foreign read access) at offsets [0x0..0x1]
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   = help: this transition corresponds to a loss of write permissions
   = note: stack backtrace:
           0: movable_gen::make_gen::{closure#0}
               at tests/pass/generators.rs:76:13: 76:19
---



FAILED TEST: tests/pass/generators.rs (revision `tree_implicit_writes`)
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass" "tests/pass/generators.rs" "-Zmiri-tree-borrows" "-Zmiri-tree-borrows-implicit-writes" "--edition" "2024" "--cfg=tree_implicit_writes" "-Cextra-filename=tree_implicit_writes"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/generators.tree_implicit_writes.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: write access through <1441> at alloc623[0x0] is forbidden
##[error]  --> tests/pass/generators.rs:76:13
   |
LL |             *a = 2;
   |             ^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
   = help: the accessed tag <1441> is a child of the conflicting tag <1412>
   = help: the conflicting tag <1412> has state Frozen which forbids this child write access
help: the accessed tag <1441> was created here
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
help: the conflicting tag <1412> was created here, in the initial state Reserved
  --> tests/pass/generators.rs:73:21
   |
LL |             let a = r;
   |                     ^
help: the conflicting tag <1412> later transitioned to Unique due to a child write access at offsets [0x0..0x1]
  --> tests/pass/generators.rs:74:13
   |
LL |             *a = 1;
   |             ^^^^^^
   = help: this transition corresponds to the first write to a 2-phase borrowed mutable reference
help: the conflicting tag <1412> later transitioned to Frozen due to a reborrow (acting as a foreign read access) at offsets [0x0..0x1]
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   = help: this transition corresponds to a loss of write permissions
   = note: stack backtrace:
           0: movable_gen::make_gen::{closure#0}
               at tests/pass/generators.rs:76:13: 76:19
---



full stderr:
error: Undefined Behavior: write access through <1441> at alloc623[0x0] is forbidden
##[error]  --> tests/pass/generators.rs:76:13
   |
LL |             *a = 2;
   |             ^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
   = help: the accessed tag <1441> is a child of the conflicting tag <1412>
   = help: the conflicting tag <1412> has state Frozen which forbids this child write access
help: the accessed tag <1441> was created here
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
help: the conflicting tag <1412> was created here, in the initial state Reserved
  --> tests/pass/generators.rs:73:21
   |
LL |             let a = r;
   |                     ^
help: the conflicting tag <1412> later transitioned to Unique due to a child write access at offsets [0x0..0x1]
  --> tests/pass/generators.rs:74:13
   |
LL |             *a = 1;
   |             ^^^^^^
   = help: this transition corresponds to the first write to a 2-phase borrowed mutable reference
help: the conflicting tag <1412> later transitioned to Frozen due to a reborrow (acting as a foreign read access) at offsets [0x0..0x1]
  --> tests/pass/generators.rs:83:17
   |
LL |     let mut j = i;
   |                 ^
   = help: this transition corresponds to a loss of write permissions
   = note: stack backtrace:
           0: movable_gen::make_gen::{closure#0}
               at tests/pass/generators.rs:76:13: 76:19
---



FAILED TEST: tests/pass/both_borrows/maybe_dangling.rs (revision `stack`)
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass/both_borrows" "tests/pass/both_borrows/maybe_dangling.rs" "--edition" "2021" "--cfg=stack" "-Cextra-filename=stack"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/both_borrows/maybe_dangling.stack.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: deallocating while item [Unique for <557>] is strongly protected
##[error]  --> /checkout/library/alloc/src/boxed.rs:2045:17
   |
LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
---
           2: std::mem::drop::<std::boxed::Box<i32>>
               at /checkout/library/core/src/mem/mod.rs:1049:1: 1049:2
           3: closure::{closure#0}
               at tests/pass/both_borrows/maybe_dangling.rs:78:9: 78:42
           4: closure::invoke::<{closure@tests/pass/both_borrows/maybe_dangling.rs:77:12: 77:19}>
               at tests/pass/both_borrows/maybe_dangling.rs:73:9: 73:12
           5: closure
               at tests/pass/both_borrows/maybe_dangling.rs:77:5: 79:7
           6: main
               at tests/pass/both_borrows/maybe_dangling.rs:17:5: 17:14
---



full stderr:
error: Undefined Behavior: deallocating while item [Unique for <557>] is strongly protected
##[error]  --> /checkout/library/alloc/src/boxed.rs:2045:17
   |
LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
---
           2: std::mem::drop::<std::boxed::Box<i32>>
               at /checkout/library/core/src/mem/mod.rs:1049:1: 1049:2
           3: closure::{closure#0}
               at tests/pass/both_borrows/maybe_dangling.rs:78:9: 78:42
           4: closure::invoke::<{closure@tests/pass/both_borrows/maybe_dangling.rs:77:12: 77:19}>
               at tests/pass/both_borrows/maybe_dangling.rs:73:9: 73:12
           5: closure
               at tests/pass/both_borrows/maybe_dangling.rs:77:5: 79:7
           6: main
               at tests/pass/both_borrows/maybe_dangling.rs:17:5: 17:14
---



FAILED TEST: tests/pass/both_borrows/maybe_dangling.rs (revision `tree`)
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass/both_borrows" "tests/pass/both_borrows/maybe_dangling.rs" "-Zmiri-tree-borrows" "--edition" "2021" "--cfg=tree" "-Cextra-filename=tree"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/both_borrows/maybe_dangling.tree.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: deallocation through <550> at alloc300[0x0] is forbidden
##[error]  --> /checkout/library/alloc/src/boxed.rs:2045:17
   |
LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
---
           2: std::mem::drop::<std::boxed::Box<i32>>
               at /checkout/library/core/src/mem/mod.rs:1049:1: 1049:2
           3: closure::{closure#0}
               at tests/pass/both_borrows/maybe_dangling.rs:78:9: 78:42
           4: closure::invoke::<{closure@tests/pass/both_borrows/maybe_dangling.rs:77:12: 77:19}>
               at tests/pass/both_borrows/maybe_dangling.rs:73:9: 73:12
           5: closure
               at tests/pass/both_borrows/maybe_dangling.rs:77:5: 79:7
           6: main
               at tests/pass/both_borrows/maybe_dangling.rs:17:5: 17:14
---



full stderr:
error: Undefined Behavior: deallocation through <550> at alloc300[0x0] is forbidden
##[error]  --> /checkout/library/alloc/src/boxed.rs:2045:17
   |
LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
---
           2: std::mem::drop::<std::boxed::Box<i32>>
               at /checkout/library/core/src/mem/mod.rs:1049:1: 1049:2
           3: closure::{closure#0}
               at tests/pass/both_borrows/maybe_dangling.rs:78:9: 78:42
           4: closure::invoke::<{closure@tests/pass/both_borrows/maybe_dangling.rs:77:12: 77:19}>
               at tests/pass/both_borrows/maybe_dangling.rs:73:9: 73:12
           5: closure
               at tests/pass/both_borrows/maybe_dangling.rs:77:5: 79:7
           6: main
               at tests/pass/both_borrows/maybe_dangling.rs:17:5: 17:14
---



FAILED TEST: tests/pass/both_borrows/maybe_dangling.rs (revision `tree_implicit_writes`)
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass/both_borrows" "tests/pass/both_borrows/maybe_dangling.rs" "-Zmiri-tree-borrows" "-Zmiri-tree-borrows-implicit-writes" "--edition" "2021" "--cfg=tree_implicit_writes" "-Cextra-filename=tree_implicit_writes"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/both_borrows/maybe_dangling.tree_implicit_writes.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: deallocation through <550> at alloc300[0x0] is forbidden
##[error]  --> /checkout/library/alloc/src/boxed.rs:2045:17
   |
LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
---
           2: std::mem::drop::<std::boxed::Box<i32>>
               at /checkout/library/core/src/mem/mod.rs:1049:1: 1049:2
           3: closure::{closure#0}
               at tests/pass/both_borrows/maybe_dangling.rs:78:9: 78:42
           4: closure::invoke::<{closure@tests/pass/both_borrows/maybe_dangling.rs:77:12: 77:19}>
               at tests/pass/both_borrows/maybe_dangling.rs:73:9: 73:12
           5: closure
               at tests/pass/both_borrows/maybe_dangling.rs:77:5: 79:7
           6: main
               at tests/pass/both_borrows/maybe_dangling.rs:17:5: 17:14
---



full stderr:
error: Undefined Behavior: deallocation through <550> at alloc300[0x0] is forbidden
##[error]  --> /checkout/library/alloc/src/boxed.rs:2045:17
   |
LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
---
           2: std::mem::drop::<std::boxed::Box<i32>>
               at /checkout/library/core/src/mem/mod.rs:1049:1: 1049:2
           3: closure::{closure#0}
               at tests/pass/both_borrows/maybe_dangling.rs:78:9: 78:42
           4: closure::invoke::<{closure@tests/pass/both_borrows/maybe_dangling.rs:77:12: 77:19}>
               at tests/pass/both_borrows/maybe_dangling.rs:73:9: 73:12
           5: closure
               at tests/pass/both_borrows/maybe_dangling.rs:77:5: 79:7
           6: main
               at tests/pass/both_borrows/maybe_dangling.rs:17:5: 17:14
---



FAILED TEST: tests/pass/concurrency/scope.rs
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-IsU3Vt" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/miri" "--error-format=json" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass/concurrency" "tests/pass/concurrency/scope.rs" "--edition" "2021"

error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/concurrency/scope.stderr` to the actual output
+++ <stderr output>
error: Undefined Behavior: not granting access to tag <10582> because that would remove [SharedReadOnly for <5756>] which is strongly protected
##[error]  --> /checkout/library/alloc/src/vec/mod.rs:1003:17
   |
LL |     pub fn push(&mut self, value: T) {
   |                 ^^^^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <10582> was created by a SharedReadWrite retag at offsets [0x0..0x18]
  --> tests/pass/concurrency/scope.rs:22:5
   |
LL |     a.push(4);
   |     ^
help: <5756> is this argument
  --> /checkout/library/std/src/thread/lifecycle.rs:61:22
   |
LL |       let rust_start = move || {
   |  ______________________^
LL | |         let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
LL | |             crate::sys::backtrace::__rust_begin_short_backtrace(|| hooks.inherit_and_run());
LL | |             crate::sys::backtrace::__rust_begin_short_backtrace(f)
...  |
LL | |     };
   | |_____^
   = note: this is on thread `main`
   = note: stack backtrace:
---



full stderr:
error: Undefined Behavior: not granting access to tag <10582> because that would remove [SharedReadOnly for <5756>] which is strongly protected
##[error]  --> /checkout/library/alloc/src/vec/mod.rs:1003:17
   |
LL |     pub fn push(&mut self, value: T) {
   |                 ^^^^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <10582> was created by a SharedReadWrite retag at offsets [0x0..0x18]
  --> tests/pass/concurrency/scope.rs:22:5
   |
LL |     a.push(4);
   |     ^
help: <5756> is this argument
  --> /checkout/library/std/src/thread/lifecycle.rs:61:22
   |
LL |       let rust_start = move || {
   |  ______________________^
LL | |         let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
LL | |             crate::sys::backtrace::__rust_begin_short_backtrace(|| hooks.inherit_and_run());
LL | |             crate::sys::backtrace::__rust_begin_short_backtrace(f)
...  |
LL | |     };
   | |_____^
   = note: this is on thread `main`
   = note: stack backtrace:
---

Location:
   /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.30.7/src/lib.rs:365

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.
error: test failed, to rerun pass `--test ui`

Caused by:
  process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/build/miri/54d3518e03e017c2/out/ui-54d3518e03e017c2` (exit status: 1)
Bootstrap failed while executing `test --stage 2 miri cargo-miri`
Currently active steps:
test::Miri { target: x86_64-unknown-linux-gnu } at src/bootstrap/src/core/build_steps/test.rs:716
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo test --target x86_64-unknown-linux-gnu -Zbinary-dep-depinfo -j 4 -Zroot-dir=/checkout -Zembed-metadata=no --locked --color=always --profile=release --manifest-path /checkout/src/tools/miri/Cargo.toml -- [workdir=/checkout]` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:208:21
Executed at: src/bootstrap/src/core/build_steps/test.rs:790:19

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:46:03
  local time: Sun Sep  6 09:50:08 UTC 2026
  network time: Sun, 06 Sep 2026 09:50:08 GMT
##[error]Process completed with exit code 1.
##[group]Run echo "disk usage:"

rust-bors · 2026-09-06T09:59:04Z

☀️ Try build successful (CI)
Build commit: 53adad8 (53adad86ea8dd1518c719893cfc8f19dc743b965)
Base parent: 46a266b (46a266b9fb0fb75e05fa4c9132f7355fcb62d4a4)

rust-timer · 2026-09-06T13:57:34Z

Finished benchmarking commit (53adad8): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never rustc-perf
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.3%	[0.3%, 0.4%]	4
Improvements ✅ (primary)	-0.3%	[-0.7%, -0.2%]	67
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.2%]	19
All ❌✅ (primary)	-0.3%	[-0.7%, -0.2%]	67

Max RSS (memory usage)

Results (primary -4.5%, secondary 1.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.5%	[2.5%, 4.5%]	2
Improvements ✅ (primary)	-4.5%	[-4.5%, -4.5%]	1
Improvements ✅ (secondary)	-3.5%	[-3.5%, -3.5%]	1
All ❌✅ (primary)	-4.5%	[-4.5%, -4.5%]	1

Cycles

Results (primary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.2%	[3.2%, 3.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-2.4%, 3.2%]	2

Binary size

Results (primary 0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.0%]	2

Bootstrap: 478.283s -> 476.002s (-0.48%)
Artifact size: 403.38 MiB -> 403.31 MiB (-0.02%)

perf experiment: give noalias back to refs in closures

d5af325

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. labels Sep 6, 2026

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 6, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 6, 2026

Auto merge of #162361 - RalfJung:maybe-dangling-perf2, r=<try>

53adad8

perf experiment: give noalias back to refs in closures

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Sep 6, 2026

RalfJung mentioned this pull request Sep 6, 2026

make closures act like MaybeDangling #160745

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perf experiment: give noalias back to refs in closures - #162361

perf experiment: give noalias back to refs in closures#162361
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rust-timer commented Sep 6, 2026

Overall result: ❌✅ regressions and improvements - please read:

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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