Add triage for this week

triage/2025/2025-08-18.md

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+# 2025-08-18 Triage Log
+
+Lots of noise/bimodality this week. Overall though no major performance impacting changes landed.
+
+Triage done by **@simulacrum**.
+Revision range: [6355cd39..239e8b1b](https://perf.rust-lang.org/?start=6355cd39c81e9699b1925c58d2ed3165bcab1715&end=239e8b1b47b34120287ec36b33228c1e177f0c38&absolute=false&stat=instructions%3Au)
+
+**Summary**:
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3%  | [0.2%, 1.2%]   | 94    |
+| Regressions ❌ <br /> (secondary)  | 0.4%  | [0.1%, 1.1%]   | 48    |
+| Improvements ✅ <br /> (primary)   | -1.2% | [-3.2%, -0.2%] | 16    |
+| Improvements ✅ <br /> (secondary) | -0.3% | [-0.5%, -0.2%] | 5     |
+| All ❌✅ (primary)                 | 0.1%  | [-3.2%, 1.2%]  | 110   |
+
+1 Regressions, 3 Improvements, 7 Mixed; 4 of them in rollups
+27 artifact comparisons made in total
+
+#### Regressions
+
+Make no_mangle on foreign items explicit instead of implicit [#144678](https://github.com/rust-lang/rust/pull/144678) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d9dba3a55476ae2da5d4e5bce8a81b341c675750&end=8e62bfd311791bfd9dca886abdfbab07ec54d8b4&stat=instructions:u)
+
+| (instructions:u)                   | mean | range        | count |
+|:----------------------------------:|:----:|:------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3% | [0.2%, 0.6%] | 8     |
+| Regressions ❌ <br /> (secondary)  | 0.2% | [0.1%, 0.5%] | 8     |
+| Improvements ✅ <br /> (primary)   | -    | -            | 0     |
+| Improvements ✅ <br /> (secondary) | -    | -            | 0     |
+| All ❌✅ (primary)                 | 0.3% | [0.2%, 0.6%] | 8     |
+
+One extra query introduced, possibly to be removed at a future date with
+additional validation on attributes in an earlier stage of the compiler.
+
+#### Improvements
+
+Rollup of 13 pull requests [#145388](https://github.com/rust-lang/rust/pull/145388) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=2c1ac85679678dfe5cce7ea8037735b0349ceaf3&end=30017c36d6b5e3382ee7cf018d330a6a4a937d39&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.7%  | [0.7%, 0.7%]   | 1     |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.2%, 0.4%]   | 3     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.4%, -0.2%] | 68    |
+| Improvements ✅ <br /> (secondary) | -0.4% | [-1.8%, -0.2%] | 24    |
+| All ❌✅ (primary)                 | -0.2% | [-0.4%, 0.7%]  | 69    |
+
+
+Rework target checking for built-in attributes [#145085](https://github.com/rust-lang/rust/pull/145085) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=be00ea1968d8d5afb5d93d2dedeb97a8bba300cb&end=898aff704d6f0d00343f21d31b8b9bfac8e43007&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.4% | [-0.9%, -0.1%] | 13    |
+| All ❌✅ (primary)                 | -     | -              | 0     |
+
+
+Rollup of 10 pull requests [#145551](https://github.com/rust-lang/rust/pull/145551) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=425a9c0a0e365c0b8c6cfd00c2ded83a73bed9a0&end=239e8b1b47b34120287ec36b33228c1e177f0c38&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -1.2% | [-1.5%, -0.8%] | 2     |
+| Improvements ✅ <br /> (secondary) | -0.6% | [-1.5%, -0.1%] | 3     |
+| All ❌✅ (primary)                 | -1.2% | [-1.5%, -0.8%] | 2     |
+
+
+#### Mixed
+
+Fix parallel rustc not being reproducible due to unstable sorts of items [#144722](https://github.com/rust-lang/rust/pull/144722) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=1c9952f4dd6e0947ee91f07130c03813a088a894&end=350d0ef0ec0493e6d21cfb265cb8211a0e74d766&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3%  | [0.2%, 0.5%]   | 5     |
+| Regressions ❌ <br /> (secondary)  | 0.2%  | [0.2%, 0.3%]   | 7     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.6%, -0.1%] | 12    |
+| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
+| All ❌✅ (primary)                 | -0.1% | [-0.6%, 0.5%]  | 17    |
+
+[#145358](https://github.com/rust-lang/rust/pull/145358) claws back some of the performance impact from this PR.
+
+Update to LLVM 21.1.0 rc3 [#145298](https://github.com/rust-lang/rust/pull/145298) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=350d0ef0ec0493e6d21cfb265cb8211a0e74d766&end=f5b8a11fecf23cb669f6d1feae81aafc2930aeb9&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.2%  | [0.1%, 0.2%]   | 8     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.2%, -0.2%] | 1     |
+| Improvements ✅ <br /> (secondary) | -0.7% | [-1.8%, -0.2%] | 3     |
+| All ❌✅ (primary)                 | 0.1%  | [-0.2%, 0.2%]  | 9     |
+
+I'm not convinced the changes are real here, but they're certainly not
+significant enough to investigate deeply for an LLVM upgrade.
+
+Rollup of 9 pull requests [#145366](https://github.com/rust-lang/rust/pull/145366) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=f5b8a11fecf23cb669f6d1feae81aafc2930aeb9&end=3672a55b7cfd0a12e7097197b6242872473ffaa7&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.2%  | [0.1%, 0.7%]   | 43    |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.1%, 0.6%]   | 20    |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.5% | [-0.5%, -0.5%] | 1     |
+| All ❌✅ (primary)                 | 0.2%  | [0.1%, 0.7%]   | 43    |
+
+Caused by
+[#145153](https://github.com/rust-lang/rust/pull/145153#issuecomment-3189567116).
+In general regressions across the board aren't great, but this is headed
+towards introduction of new functionality, so perhaps required. Some profiling
+of the PR may yield interesting results given how wide spread the regression is
+for some micro-opt work.
+
+resolve: Split extern prelude into two scopes [#144793](https://github.com/rust-lang/rust/pull/144793) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=3672a55b7cfd0a12e7097197b6242872473ffaa7&end=8e7795415acaa9471b5eeb2301915d6996d289ec&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.2%  | [0.2%, 0.2%]   | 2     |
+| Regressions ❌ <br /> (secondary)  | 0.7%  | [0.3%, 1.9%]   | 4     |
+| Improvements ✅ <br /> (primary)   | -0.4% | [-0.7%, -0.2%] | 5     |
+| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
+| All ❌✅ (primary)                 | -0.2% | [-0.7%, 0.2%]  | 7     |
+
+Looks like it's only a real regression for the secondary externs scenario, and
+even there only significant in incr-unchanged. I'm not worried enough to merit
+further poking, especially as it seems plausible this is a natural (if slight)
+regression from tracking at finer granularity.
+
+Rollup of 11 pull requests [#145407](https://github.com/rust-lang/rust/pull/145407) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=898aff704d6f0d00343f21d31b8b9bfac8e43007&end=3507a749b365aae4eefa96ab700a9315d3280ee7&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3%  | [0.2%, 0.4%]   | 39    |
+| Regressions ❌ <br /> (secondary)  | 0.4%  | [0.2%, 0.9%]   | 18    |
+| Improvements ✅ <br /> (primary)   | -1.4% | [-3.7%, -0.2%] | 3     |
+| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
+| All ❌✅ (primary)                 | 0.1%  | [-3.7%, 0.4%]  | 42    |
+
+Regression caused by
+[#145233](https://github.com/rust-lang/rust/pull/145233#issuecomment-3191062342),
+based on granular perf run, but there's some suspicion that it might still be
+just noise. Further investigation seems unwarranted at this time.
+
+Patterns: represent constants as valtrees [#144591](https://github.com/rust-lang/rust/pull/144591) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=3507a749b365aae4eefa96ab700a9315d3280ee7&end=8800ec16657b24ad8a2f443c133bf0b56ae76033&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 5.3%  | [5.3%, 5.3%]   | 1     |
+| Regressions ❌ <br /> (secondary)  | 0.7%  | [0.2%, 1.0%]   | 9     |
+| Improvements ✅ <br /> (primary)   | -2.7% | [-3.2%, -2.2%] | 6     |
+| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
+| All ❌✅ (primary)                 | -1.5% | [-3.2%, 5.3%]  | 7     |
+
+The match-stress regression seems real, but probably not important to look into
+given the context of this PR. Other regressions look like noise.
+
+Rollup of 21 pull requests [#145423](https://github.com/rust-lang/rust/pull/145423) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=8800ec16657b24ad8a2f443c133bf0b56ae76033&end=ba412a6e70ac84641be7764d088acabd0eb3fa39&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 1.2%  | [0.2%, 3.2%]   | 4     |
+| Regressions ❌ <br /> (secondary)  | 0.4%  | [0.0%, 0.5%]   | 3     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.2%, -0.2%] | 1     |
+| Improvements ✅ <br /> (secondary) | -1.5% | [-2.0%, -0.9%] | 2     |
+| All ❌✅ (primary)                 | 0.9%  | [-0.2%, 3.2%]  | 5     |
+
+Most regressions are noise but ripgrep regression looks real, seems to be
+caused by [#122661](https://github.com/rust-lang/rust/pull/122661). See
+[writeup](https://github.com/rust-lang/rust/pull/122661#issuecomment-3199007696)
+for some brief investigation.