Revert "Fix an ICE in the vtable iteration for a trait reference"

[workingjubilee]

The ICE fix appears to be unsound, causing a miscompilation involving dyn Trait and async {} which induces segfaults in safe Rust code. As the patch only hid an ICE, it does not seem worth the risk.

This addresses the problem in #152735 but it may still merit team discussion even if this PR is merged.

This reverts commit 8afd636, reversing changes made to 19122c0.

[rustbot]

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[lqd]

p-critical issue, straightforward reverts like this don't need reviews per se, easy r+ imho.

If you're not waiting on some wider discussion, r=me.

[mati865]

@bors r+ p=10

[rust-bors]

📌 Commit 18a707f has been approved by mati865

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: mati865
Duration: 3h 49m 21s
Pushing 3f6250a to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 1210e9f (parent) -> 3f6250a (this PR)

Test differences

Show 14 test diffs

Stage 1

• [crashes] tests/crashes/135470.rs: [missing] -> pass (J0)
• [crashes] tests/crashes/137190-2.rs: [missing] -> pass (J0)
• [crashes] tests/crashes/137190-3.rs: [missing] -> pass (J0)
• [ui] tests/ui/coercion/vtable-impossible-predicates-async.rs: pass -> [missing] (J0)
• [ui] tests/ui/coercion/vtable-unsatisfied-supertrait-generics.rs: pass -> [missing] (J0)
• [ui] tests/ui/coercion/vtable-unsatisfied-supertrait.rs: pass -> [missing] (J0)

Stage 2

• [ui] tests/ui/coercion/vtable-impossible-predicates-async.rs: pass -> [missing] (J1)
• [ui] tests/ui/coercion/vtable-unsatisfied-supertrait-generics.rs: pass -> [missing] (J1)
• [ui] tests/ui/coercion/vtable-unsatisfied-supertrait.rs: pass -> [missing] (J1)
• [crashes] tests/crashes/135470.rs: [missing] -> pass (J2)
• [crashes] tests/crashes/137190-2.rs: [missing] -> pass (J2)
• [crashes] tests/crashes/137190-3.rs: [missing] -> pass (J2)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: x86_64-gnu-llvm-20-3, x86_64-gnu-llvm-21-3
• J1: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-1, aarch64-msvc-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-gnu, x86_64-gnu-debug, x86_64-gnu-gcc, x86_64-gnu-llvm-20, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J2: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-1, aarch64-msvc-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-gnu, x86_64-gnu-gcc, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 3f6250a7bb79e600d9036bbc7c8f65af43933643 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. aarch64-apple: 3h 8m -> 3h 42m (+17.8%)
2. pr-check-1: 33m 9s -> 28m 15s (-14.8%)
3. dist-aarch64-apple: 1h 43m -> 1h 57m (+13.8%)
4. dist-apple-various: 1h 53m -> 1h 38m (-13.4%)
5. dist-aarch64-llvm-mingw: 1h 35m -> 1h 48m (+13.1%)
6. dist-aarch64-msvc: 1h 49m -> 1h 37m (-11.2%)
7. aarch64-gnu-debug: 1h 17m -> 1h 9m (-9.7%)
8. pr-check-2: 42m 27s -> 38m 41s (-8.9%)
9. i686-gnu-1: 2h 22m -> 2h 9m (-8.7%)
10. x86_64-gnu-llvm-20-3: 1h 46m -> 1h 55m (+8.7%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (3f6250a): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.2%	[0.2%, 0.3%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-1.3%, -0.5%]	16
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 2.3%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.3%	[2.3%, 2.3%]	1

Cycles

Results (secondary 0.8%)

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)	3.6%	[3.5%, 3.7%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.7%	[-4.7%, -4.7%]	1
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 482.345s -> 480.825s (-0.32%)
Artifact size: 397.85 MiB -> 395.77 MiB (-0.52%)

[lqd]

revert of #152287 which landed in the rollup #152399 and should have seen the opposite effect

@rustbot label: +perf-regression-triaged