Add triage for this week

Author: Mark-Simulacrum

triage/2024-08-19.md

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+# 2024-08-19 Triage Log
+
+A fairly noisy week (though most of that has been dropped from this report).
+Overall we saw several improvements, and ended the week on a net positive.
+Memory usage is done around 1.5-3% over the course of the week, primarily due
+to [RawVec polymorphization](https://github.com/rust-lang/rust/pull/126793) and
+[CloneToUninit impl expansion](https://github.com/rust-lang/rust/pull/126877).
+
+Triage done by **@simulacrum**.
+Revision range: [9cb1998e..4fe1e2bd](https://perf.rust-lang.org/?start=9cb1998ea15e179482504e07cad8fa121e169a32&end=4fe1e2bd5bf5a6f1cb245f161a5e9d315766f103&absolute=false&stat=instructions%3Au)
+
+**Summary**:
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.4%  | [0.2%, 1.7%]   | 124   |
+| Regressions ❌ <br /> (secondary)  | 0.5%  | [0.1%, 1.4%]   | 103   |
+| Improvements ✅ <br /> (primary)   | -1.3% | [-4.3%, -0.2%] | 50    |
+| Improvements ✅ <br /> (secondary) | -1.4% | [-3.3%, -0.2%] | 15    |
+| All ❌✅ (primary)                 | -0.1% | [-4.3%, 1.7%]  | 174   |
+
+1 Regressions, 1 Improvements, 3 Mixed; 1 of them in rollups
+53 artifact comparisons made in total
+
+#### Regressions
+
+Fix problems with assoc expr token collection [#128725](https://github.com/rust-lang/rust/pull/128725) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=4b7d074d766d00a32fa8b2e4fa3813dd7d4d64e6&end=be0ea0c99a00bc365d9f80f1c90f747967a2e152&stat=instructions:u)
+
+| (instructions:u)                   | mean | range        | count |
+|:----------------------------------:|:----:|:------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3% | [0.2%, 0.3%] | 5     |
+| Regressions ❌ <br /> (secondary)  | 0.3% | [0.2%, 0.5%] | 5     |
+| Improvements ✅ <br /> (primary)   | -    | -            | 0     |
+| Improvements ✅ <br /> (secondary) | -    | -            | 0     |
+| All ❌✅ (primary)                 | 0.3% | [0.2%, 0.3%] | 5     |
+
+Appears to be a real change in behavior (pre-merge showed fewer regressions)
+but this is a correctness fix, so accepting them. 
+
+#### Improvements
+
+Rework MIR inlining debuginfo so function parameters show up in debuggers. [#128861](https://github.com/rust-lang/rust/pull/128861) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=026e9ed3f0c5b3ee6233fd23b5e497cb94cf6434&end=3139ff09e9d07f7700f8d15ed25a231e29c43627&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | 2.3%  | [2.3%, 2.3%]   | 1     |
+| Improvements ✅ <br /> (primary)   | -1.2% | [-1.4%, -1.1%] | 6     |
+| Improvements ✅ <br /> (secondary) | -1.2% | [-1.3%, -1.2%] | 2     |
+| All ❌✅ (primary)                 | -1.2% | [-1.4%, -1.1%] | 6     |
+
+An improvement on many current benchmarks; the one regression is a spurious change.
+
+#### Mixed
+
+Apply "polymorphization at home" to RawVec [#126793](https://github.com/rust-lang/rust/pull/126793) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=41dd149fd6a6a06795fc6b9f54cb49af2f61775f&end=13f8a57cfb57d527abe797230beabb64758bb888&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.5%  | [0.2%, 1.5%]   | 89    |
+| Regressions ❌ <br /> (secondary)  | 0.4%  | [0.1%, 1.3%]   | 96    |
+| Improvements ✅ <br /> (primary)   | -1.1% | [-3.8%, -0.2%] | 54    |
+| Improvements ✅ <br /> (secondary) | -1.2% | [-2.9%, -0.3%] | 13    |
+| All ❌✅ (primary)                 | -0.1% | [-3.8%, 1.5%]  | 143   |
+
+An improvement on many current benchmarks, though some regressions. Overall a
+net positive. Also reduced memory usage by about 1% for many of our benchmarks,
+which is a great win!
+
+Support reading thin archives in ArArchiveBuilder [#128936](https://github.com/rust-lang/rust/pull/128936) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=3139ff09e9d07f7700f8d15ed25a231e29c43627&end=d2b5aa6552c8acf67f38a2ad92062a32ec542f08&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | 0.3%  | [0.2%, 0.4%]   | 14    |
+| Regressions ❌ <br /> (secondary)  | 0.4%  | [0.4%, 0.4%]   | 1     |
+| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
+| Improvements ✅ <br /> (secondary) | -2.3% | [-2.3%, -2.3%] | 1     |
+| All ❌✅ (primary)                 | 0.3%  | [0.2%, 0.4%]   | 14    |
+
+Regressions looks genuine, though relatively rare in our benchmark suite. It
+might be worth doing some profiling of the Rust archive writer to see if
+there's opportunities for optimization since it presumably hasn't received much
+attention so far.
+
+Rollup of 6 pull requests [#129202](https://github.com/rust-lang/rust/pull/129202) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=9b318d2e93ce35e7ba32d8cfa96a1dbe63a7bed1&end=0f26ee4fd95a1c046582dfb18892f520788e2c2c&stat=instructions:u)
+
+| (instructions:u)                   | mean  | range          | count |
+|:----------------------------------:|:-----:|:--------------:|:-----:|
+| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
+| Regressions ❌ <br /> (secondary)  | 0.6%  | [0.1%, 2.2%]   | 5     |
+| Improvements ✅ <br /> (primary)   | -0.9% | [-1.7%, -0.3%] | 4     |
+| Improvements ✅ <br /> (secondary) | -1.4% | [-2.2%, -0.6%] | 2     |
+| All ❌✅ (primary)                 | -0.9% | [-1.7%, -0.3%] | 4     |
+
+Regression on match-stress looks genuine but likely doesn't merit deeper
+investigation given that this is in a rollup (and I don't see obvious
+match-stress-implicating PRs in the list).