Add 2025-12-16 triage

triage/2025/2025-12-16.md

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+# 2025-12-16 Triage Log
+
+This week we saw several regressions, partly from the compiler doing more work. The remaining
+regressions are being investigated.
+
+Triage done by **@kobzol**.
+Revision range: [55495234..21ff67df](https://perf.rust-lang.org/?start=554952348a7dd13851f25789f6bb1061f45c4b60&end=21ff67df15329dd7548ccba54b6c6ae9a562124f&absolute=false&stat=instructions%3Au)
+
+**Summary**:
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.5%  | [0.1%, 5.1%]   | 40    |
+| Regressions ❌ <br /> (secondary)  | 0.8%  | [0.0%, 3.0%]   | 63    |
+| Improvements ✅ <br /> (primary)   | -0.7% | [-1.5%, -0.1%] | 35    |
+| Improvements ✅ <br /> (secondary) | -1.0% | [-7.4%, -0.0%] | 73    |
+| All ❌✅ (primary)                 | -0.1% | [-1.5%, 5.1%]  | 75    |
+
+
+3 Regressions, 2 Improvements, 5 Mixed; 2 of them in rollups
+36 artifact comparisons made in total
+
+#### Regressions
+
+resolve: Preserve ambiguous glob reexports in crate metadata [#147984](https://github.com/rust-lang/rust/pull/147984) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=e2893f7c95e45f74c8bc5dbd033486c5bfaa4deb&end=c61a3a44d1a5bee35914cada6c788a05e0808f5b&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3%  | [0.1%, 0.5%]   | 24    |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.2%, 0.7%]   | 13    |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.1% | [-0.1%, -0.1%] | 1     |
+| All ❌✅ (primary)                 | 0.3%  | [0.1%, 0.5%]   | 24    |
+
+- The compiler is doing more work after this change, and this work should unblock parallelizing name resolution and macro expansion in the future.
+- Asked on the PR if something can be done about the regression.
+
+Rollup of 9 pull requests [#149891](https://github.com/rust-lang/rust/pull/149891) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=5b150d238fbd4fe7bc2cd3140d8e6fb4406099fa&end=c4dc70ee0ad7f811fb32e5bed9cd6c7b37beed4e&stat=instructions:u)
+
+| (instructions:u)                   | mean | range        | count |
+|:----------------------------------:|:----:|:------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 1.9% | [0.5%, 7.6%] | 10    |
+| Regressions ❌ <br /> (secondary)  | 1.2% | [0.2%, 2.2%] | 2     |
+| Improvements ✅ <br /> (primary)   | -    | -            | 0     |
+| Improvements ✅ <br /> (secondary) | -    | -            | 0     |
+| All ❌✅ (primary)                 | 1.9% | [0.5%, 7.6%] | 10    |
+
+- The regression in doc builds was caused by [#142380](https://github.com/rust-lang/rust/pull/142380).
+- Continuing discussion on the PR.
+
+Externally implementable items [#146348](https://github.com/rust-lang/rust/pull/146348) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=2cd4ee6bcf517345dd76d7b102d56b2e873cddbc&end=3f4dc1e02d759aa3c3807d4efc1f7f6e293536a5&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.6%  | [0.6%, 0.7%]   | 2     |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.1%, 0.8%]   | 35    |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.0% | [-0.1%, -0.0%] | 2     |
+| All ❌✅ (primary)                 | 0.6%  | [0.6%, 0.7%]   | 2     |
+
+- The regressions are only on the tiniest crates, and is quite small.
+- Marked as triaged.
+
+#### Improvements
+
+Remove unwraps from metadata decoding: introduce `BlobDecoder` [#149455](https://github.com/rust-lang/rust/pull/149455) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=03d7ad7dd67d71f1ef1a790fcb4ceb2484ced761&end=5bc345055b06dc096b01bc6d1e0cbe92d3cc630e&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.4%, -0.1%] | 8     |
+| Improvements ✅ <br /> (secondary) | -0.4% | [-1.4%, -0.1%] | 28    |
+| All ❌✅ (primary)                 | -0.2% | [-0.4%, -0.1%] | 8     |
+
+
+Don't leak sysroot crates through dependencies [#149273](https://github.com/rust-lang/rust/pull/149273) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=3f4dc1e02d759aa3c3807d4efc1f7f6e293536a5&end=08de25c4ea16d7ecc3ceeb093d4f343a2be30df5&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -2.9% | [-6.7%, -0.1%] | 11    |
+| All ❌✅ (primary)                 | -     | -              | 0     |
+
+
+#### Mixed
+
+std: Use more `unix.rs` code on WASI targets [#147572](https://github.com/rust-lang/rust/pull/147572) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=a371038013f4f3e3f1d4fdcacfaa02c3252a518b&end=018d26972e523b8d28f9579056185a1713949dfd&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.2%  | [0.2%, 0.2%]   | 3     |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.1%, 0.5%]   | 2     |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.0% | [-0.0%, -0.0%] | 1     |
+| All ❌✅ (primary)                 | 0.2%  | [0.2%, 0.2%]   | 3     |
+
+- Except for the tiny helloworld doc regression, this seems to be noise.
+- Marked as triaged.
+
+Revert "early return on duplicate span lowerings" [#149757](https://github.com/rust-lang/rust/pull/149757) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d5525a73009e2c61b09daa69df79064530bd4dcf&end=e2893f7c95e45f74c8bc5dbd033486c5bfaa4deb&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | 0.1%  | [0.1%, 0.1%]   | 1     |
+| Improvements ✅ <br /> (primary)   | -0.3% | [-0.7%, -0.1%] | 94    |
+| Improvements ✅ <br /> (secondary) | -0.4% | [-0.8%, -0.0%] | 107   |
+| All ❌✅ (primary)                 | -0.3% | [-0.7%, -0.1%] | 94    |
+
+- This revert fixed a previous performance regression from [#149060](https://github.com/rust-lang/rust/pull/149060).
+- Marked as triaged.
+
+Rollup of 5 pull requests [#149818](https://github.com/rust-lang/rust/pull/149818) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=c61a3a44d1a5bee35914cada6c788a05e0808f5b&end=5f1173bb2b0a7012640bd5383c61b433b16a452d&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.2%  | [0.1%, 0.3%]   | 18    |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.2%, 0.5%]   | 13    |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.4% | [-0.6%, -0.3%] | 3     |
+| All ❌✅ (primary)                 | 0.2%  | [0.1%, 0.3%]   | 18    |
+
+- Small regression caused by [#149664](https://github.com/rust-lang/rust/pull/149664), continuing
+  discussion on that PR.
+- Not marking as triaged yet.
+
+Port `doc` attributes to new attribute API [#149645](https://github.com/rust-lang/rust/pull/149645) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=f5209000832c9d3bc29c91f4daef4ca9f28dc797&end=5b150d238fbd4fe7bc2cd3140d8e6fb4406099fa&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.2%  | [0.2%, 0.2%]   | 1     |
+| Regressions ❌ <br /> (secondary)  | 1.4%  | [0.1%, 3.1%]   | 18    |
+| Improvements ✅ <br /> (primary)   | -0.6% | [-1.3%, -0.2%] | 36    |
+| Improvements ✅ <br /> (secondary) | -0.6% | [-1.2%, -0.1%] | 32    |
+| All ❌✅ (primary)                 | -0.6% | [-1.3%, 0.2%]  | 37    |
+
+- More improvements than regressions.
+- Already marked as triaged.
+
+Overhaul filename handling for cross-compiler consistency [#149709](https://github.com/rust-lang/rust/pull/149709) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=eb171a227f9e5de5d376b6edb56b174bc8235fb3&end=8188f6c8084bade919921457e011fa39c6bf09a4&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.7%  | [0.2%, 1.1%]   | 6     |
+| Regressions ❌ <br /> (secondary)  | 0.6%  | [0.0%, 2.2%]   | 31    |
+| Improvements ✅ <br /> (primary)   | -0.6% | [-1.5%, -0.1%] | 12    |
+| Improvements ✅ <br /> (secondary) | -0.3% | [-0.6%, -0.2%] | 4     |
+| All ❌✅ (primary)                 | -0.2% | [-1.5%, 1.1%]  | 18    |
+
+- The results are a bit all over the place, but overall it's a wash. Some tiny improvements are expected to be gained from a follow-up in [#149989](https://github.com/rust-lang/rust/pull/149989).
+- Marked as triaged.