Implement unstable trait impl #140399
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Implement unstable trait impl #140399
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BoxyUwU
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Jun 10, 2025
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☔ The latest upstream changes (presumably #142299) made this pull request unmergeable. Please resolve the merge conflicts. |
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[Perf] Remove call to hir_attrs in predicates_of
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Test how much regression we still have if we remove the call to ``hir_attrs`` in ``predicates_of`` for #140399
r? ghost
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looks like the cost is from just the new While I think changing Unless you want to try something to reduce the perf impact, r=me |
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@bors r=lcnr rollup=never I would really like to get this perf back but also supporting stability of |
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@bors r=lcnr,BoxyUwU |
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💡 This pull request was already approved, no need to approve it again.
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I am happy to send a follow-up PR to try more stuff to claw back the perf Thanks for all the reviews ❤️ |
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☀️ Test successful - checks-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 fd2eb39 (parent) -> 014bd82 (this PR) Test differencesShow 292 test diffsStage 1
Stage 2
(and 140 additional test diffs) Additionally, 52 doctest diffs were found. These are ignored, as they are noisy. Job group index
Test dashboardRun cargo run --manifest-path src/ci/citool/Cargo.toml -- \
test-dashboard 014bd8290f084c714995205a9116e6c035419ae6 --output-dir test-dashboardAnd then open Job duration changes
How to interpret the job duration changes?Job durations can vary a lot, based on the actual runner instance |
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Finished benchmarking commit (014bd82): comparison URL. Overall result: ❌ regressions - please read the text belowOur benchmarks found a performance regression caused by this PR. Next Steps:
@rustbot label: +perf-regression Instruction countOur most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.
Max RSS (memory usage)Results (secondary -1.2%)A less reliable metric. May be of interest, but not used to determine the overall result above.
CyclesResults (primary 2.3%, secondary 0.6%)A less reliable metric. May be of interest, but not used to determine the overall result above.
Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 467.109s -> 462.752s (-0.93%) |
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The perf regressions were deemed to be acceptable for the time being, to avoid delaying this feature. Interestingly this was a solid win on bootstrap time, maybe because of some refactoring/restructuring of code? @rustbot label: +perf-regression-triaged |
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It’s just that bootstrap times are more unstable on the new benchmark machine. |
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Really? I haven't seen that large swings recently. Usually it's ~2.5s at most (https://perf.rust-lang.org/bootstrap.html), so 4.5s seemed like it could be an actual change to me. But it could also be noise ofc, as you say, doesn't really matter. |
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Hmm, unattended upgrades or anything similar doesn't seem to be it, per logs. I wonder if it might have been datadog, that seems like the only thing that consumes a bunch of CPU there. |
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This PR allows marking impls of stable trait with stable type as unstable.
Approach
In std/core, an impl can be marked as unstable by annotating it with
#[unstable_feature_bound(feat_name)]. This will add aClauseKind::Unstable_Feature(feat_name)to the list of predicates inpredicates_of.When an unstable impl's function is called, we will first iterate through all the goals in
param_envto check if there is anyClauseKind::UnstableFeature(feat_name)inparam_env.The existence of
ClauseKind::Unstable_Feature(feat_name)inparam_envmeans an#[unstable_feature_bound(feat_name)]is present at the call site of the function, so we allow the check to succeed in this case.If
ClauseKind::UnstableFeature(feat_name)does not exist inparam_env, we will still allow the check to succeed for either of the cases below:#[feature(feat_name)]outside of std / core.For the rest of the case, it will fail with ambiguity.
Limitation
In this PR, we do not support:
#[unstable_feature_bound]within stable APIs#[unstable_feature_bound]#[unstable_feature_bound]on items other than free function and implAcknowledgement
The design and mentoring are done by @BoxyUwU