Add 2025-11-25 triage

triage/2025/2025-11-25.md

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+# 2025-11-25 Triage Log
+
+Only a handful of performance-related changes landed this week. The largest one was changing the default name mangling scheme in nightly to the v0 version, which produces slightly larger symbol names, so it had a small negative effect on binary sizes and compilation time.
+
+Triage done by **@kobzol**.
+Revision range: [6159a440..b64df9d1](https://perf.rust-lang.org/?start=6159a44067ebce42b38f062cc7df267a1348e092&end=b64df9d1012f2482b54a4d959548cf8fc67e820c&absolute=false&stat=instructions%3Au)
+
+**Summary**:
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.9%  | [0.3%, 2.7%]   | 48    |
+| Regressions ❌ <br /> (secondary)  | 0.9%  | [0.2%, 2.1%]   | 25    |
+| Improvements ✅ <br /> (primary)   | -0.5% | [-6.8%, -0.1%] | 33    |
+| Improvements ✅ <br /> (secondary) | -0.5% | [-1.4%, -0.1%] | 53    |
+| All ❌✅ (primary)                 | 0.4%  | [-6.8%, 2.7%]  | 81    |
+
+
+1 Regression, 2 Improvements, 5 Mixed; 1 of them in rollups
+28 artifact comparisons made in total
+
+#### Regressions
+
+Turn moves into copies after copy propagation [#147804](https://github.com/rust-lang/rust/pull/147804) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=23f708107b459ed551a860ef0bf8b61bc80b48b4&end=122cbd043833a1d7540cc5f99c458bfca2d3c525&stat=instructions:u)
+
+| (instructions:u)                   | mean | range        | count |
+|:----------------------------------:|:----:|:------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.6% | [0.1%, 0.9%] | 6     |
+| Regressions ❌ <br /> (secondary)  | 0.8% | [0.8%, 0.8%] | 1     |
+| Improvements ✅ <br /> (primary)   | -    | -            | 0     |
+| Improvements ✅ <br /> (secondary) | -    | -            | 0     |
+| All ❌✅ (primary)                 | 0.6% | [0.1%, 0.9%] | 6     |
+
+- The perf. regression was deemed acceptable, as this fixes miscompilations.
+- Marked as triaged.
+
+#### Improvements
+
+Bump compiler dependencies [#148831](https://github.com/rust-lang/rust/pull/148831) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=27b076af7e3e7a363975443d81dfa9ecee5a74ec&end=5934b0655768a45aad237a704995780276b91261&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -0.3% | [-0.6%, -0.1%] | 27    |
+| Improvements ✅ <br /> (secondary) | -0.4% | [-1.3%, -0.1%] | 36    |
+| All ❌✅ (primary)                 | -0.3% | [-0.6%, -0.1%] | 27    |
+
+
+Rollup of 9 pull requests [#149222](https://github.com/rust-lang/rust/pull/149222) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=4b1b6dde0c15243857165672a1c616a4523ef32a&end=94b49fd998d6723e0a9240a7cff5f9df37b84dd8&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.2%, -0.2%] | 3     |
+| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
+| All ❌✅ (primary)                 | -0.2% | [-0.2%, -0.2%] | 3     |
+
+
+#### Mixed
+
+Update wasm-related dependencies in CI [#149037](https://github.com/rust-lang/rust/pull/149037) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=6159a44067ebce42b38f062cc7df267a1348e092&end=a591113c0a2b7755514c47bde211fdb92d1d7002&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.4%  | [0.4%, 0.4%]   | 1     |
+| Regressions ❌ <br /> (secondary)  | 0.5%  | [0.2%, 0.9%]   | 9     |
+| Improvements ✅ <br /> (primary)   | -2.8% | [-2.8%, -2.8%] | 1     |
+| Improvements ✅ <br /> (secondary) | -0.1% | [-0.1%, -0.1%] | 1     |
+| All ❌✅ (primary)                 | -1.2% | [-2.8%, 0.4%]  | 2     |
+
+- Noise.
+- Already marked as triaged.
+
+sess: default to v0 symbol mangling on nightly [#89917](https://github.com/rust-lang/rust/pull/89917) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d2f887349fe3ea079a4f89b020ce6df1993e1e06&end=683dd08db5808c41baceef49368fc82a6c4767bb&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.7%  | [0.2%, 1.5%]   | 31    |
+| Regressions ❌ <br /> (secondary)  | 0.7%  | [0.2%, 1.6%]   | 14    |
+| Improvements ✅ <br /> (primary)   | -0.4% | [-0.4%, -0.4%] | 1     |
+| Improvements ✅ <br /> (secondary) | -0.2% | [-0.6%, -0.1%] | 6     |
+| All ❌✅ (primary)                 | 0.7%  | [-0.4%, 1.5%]  | 32    |
+
+- This PR caused binary size regressions, which is expected, as the v0 mangling scheme produces larger symbols than the legacy mangling scheme, in general.
+- The compile-time regressions were likely caused by the same thing, more symbol string handling and more time spent in LLVM due to processing longer symbols.
+- Marked as triaged.
+
+See if this is the time we can remove `layout::size_align` [#149109](https://github.com/rust-lang/rust/pull/149109) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=7281a3bc4b89a010aed05528d648450feb8b69d3&end=53732d5e076329a62f71d3c6901886ce8a71e812&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | 0.4%  | [0.1%, 0.6%]   | 4     |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -0.7% | [-1.3%, -0.2%] | 8     |
+| All ❌✅ (primary)                 | -     | -              | 0     |
+
+- Just noise returning to steady state.
+- Already marked as triaged.
+
+library: upgrade to hashbrown v0.16.1 [#149159](https://github.com/rust-lang/rust/pull/149159) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=af17d59d71cd344fb34caab3e96c88b7c137f872&end=1dd43f247e6ec20a84dd017e4665266fa65e3a89&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.7%  | [0.4%, 1.4%]   | 4     |
+| Regressions ❌ <br /> (secondary)  | 1.5%  | [1.5%, 1.5%]   | 1     |
+| Improvements ✅ <br /> (primary)   | -0.2% | [-0.2%, -0.2%] | 2     |
+| Improvements ✅ <br /> (secondary) | -0.3% | [-0.5%, -0.1%] | 25    |
+| All ❌✅ (primary)                 | 0.4%  | [-0.2%, 1.4%]  | 6     |
+
+- More improvements than regressions.
+- Marked as triaged.
+
+Fix MaybeUninit codegen using GVN [#147827](https://github.com/rust-lang/rust/pull/147827) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=122cbd043833a1d7540cc5f99c458bfca2d3c525&end=e9acbd99d384280874129fb7fa0da9faeae0d051&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.1%  | [0.1%, 0.1%]   | 1     |
+| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.1%, 0.5%]   | 6     |
+| Improvements ✅ <br /> (primary)   | -7.3% | [-7.3%, -7.3%] | 1     |
+| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
+| All ❌✅ (primary)                 | -3.6% | [-7.3%, 0.1%]  | 2     |
+
+- Tiny regressions on secondary benchmarks, but a large (and real) win on the cranelift-codegen opt benchmark.
+- This should ideally produce better codegen.
+- Marked as triaged.