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| 1 | +# 2024-04-29 Triage Log |
| 2 | + |
| 3 | +Several non-noise changes this week, with both improvements and regresions |
| 4 | +coming as a result. Overall compiler performance is roughly neutral across the |
| 5 | +week. |
| 6 | + |
| 7 | +Triage done by **@simulacrum**. |
| 8 | +Revision range: [a77f76e2..c65b2dc9](https://perf.rust-lang.org/?start=a77f76e26302e9a084fb321817675b1dfc1dcd63&end=c65b2dc935c27c0c8c3997c6e8d8894718a2cb1a&absolute=false&stat=instructions%3Au) |
| 9 | + |
| 10 | +**Summary**: |
| 11 | + |
| 12 | +| (instructions:u) | mean | range | count | |
| 13 | +|:----------------------------------:|:-----:|:---------------:|:-----:| |
| 14 | +| Regressions ❌ <br /> (primary) | 0.4% | [0.2%, 1.4%] | 104 | |
| 15 | +| Regressions ❌ <br /> (secondary) | 2.4% | [0.2%, 23.7%] | 81 | |
| 16 | +| Improvements ✅ <br /> (primary) | -3.8% | [-26.1%, -0.3%] | 10 | |
| 17 | +| Improvements ✅ <br /> (secondary) | -1.6% | [-4.6%, -0.5%] | 12 | |
| 18 | +| All ❌✅ (primary) | 0.1% | [-26.1%, 1.4%] | 114 | |
| 19 | + |
| 20 | + |
| 21 | +2 Regressions, 2 Improvements, 3 Mixed; 1 of them in rollups |
| 22 | +51 artifact comparisons made in total |
| 23 | + |
| 24 | +#### Regressions |
| 25 | + |
| 26 | +Use fulfillment in method probe, not evaluation [#122317](https://github.com/rust-lang/rust/pull/122317) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=ad07aa12c99698f810d730d7b5a49704c729651d&end=cd90d5c03532da6f7ca7dcfb861ffabdc36a9d00&stat=instructions:u) |
| 27 | + |
| 28 | +| (instructions:u) | mean | range | count | |
| 29 | +|:----------------------------------:|:----:|:-------------:|:-----:| |
| 30 | +| Regressions ❌ <br /> (primary) | 0.5% | [0.2%, 1.3%] | 38 | |
| 31 | +| Regressions ❌ <br /> (secondary) | 4.2% | [0.5%, 23.6%] | 39 | |
| 32 | +| Improvements ✅ <br /> (primary) | - | - | 0 | |
| 33 | +| Improvements ✅ <br /> (secondary) | - | - | 0 | |
| 34 | +| All ❌✅ (primary) | 0.5% | [0.2%, 1.3%] | 38 | |
| 35 | + |
| 36 | +Some additional attempts to fix perf were done in a follow-up PR |
| 37 | +(https://github.com/rust-lang/rust/pull/124303) but did not pan out to be |
| 38 | +successful. It looks like this is a correctness fix, so we'll need to accept |
| 39 | +the regressions for now. |
| 40 | + |
| 41 | +Stabilize `Utf8Chunks` [#123909](https://github.com/rust-lang/rust/pull/123909) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=1b3a32958bb54bde45e693217e8f7469459e5865&end=4d570eea025a19564429eb52b34ec34e14659f55&stat=instructions:u) |
| 42 | + |
| 43 | +| (instructions:u) | mean | range | count | |
| 44 | +|:----------------------------------:|:----:|:------------:|:-----:| |
| 45 | +| Regressions ❌ <br /> (primary) | 0.5% | [0.2%, 1.1%] | 11 | |
| 46 | +| Regressions ❌ <br /> (secondary) | 0.8% | [0.3%, 1.2%] | 19 | |
| 47 | +| Improvements ✅ <br /> (primary) | - | - | 0 | |
| 48 | +| Improvements ✅ <br /> (secondary) | - | - | 0 | |
| 49 | +| All ❌✅ (primary) | 0.5% | [0.2%, 1.1%] | 11 | |
| 50 | + |
| 51 | +The regressions are in doc builds, but are not really expected from what is a |
| 52 | +relatively small change. Further investigation feels warranted (see |
| 53 | +https://github.com/rust-lang/rust/pull/123909#issuecomment-2082668500). |
| 54 | + |
| 55 | +#### Improvements |
| 56 | + |
| 57 | +Rollup of 5 pull requests [#124289](https://github.com/rust-lang/rust/pull/124289) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=c67277301c896857d0534f2bb7431680796833fb&end=ad07aa12c99698f810d730d7b5a49704c729651d&stat=instructions:u) |
| 58 | + |
| 59 | +| (instructions:u) | mean | range | count | |
| 60 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 61 | +| Regressions ❌ <br /> (primary) | - | - | 0 | |
| 62 | +| Regressions ❌ <br /> (secondary) | - | - | 0 | |
| 63 | +| Improvements ✅ <br /> (primary) | -0.3% | [-0.3%, -0.2%] | 7 | |
| 64 | +| Improvements ✅ <br /> (secondary) | -0.2% | [-0.2%, -0.2%] | 2 | |
| 65 | +| All ❌✅ (primary) | -0.3% | [-0.3%, -0.2%] | 7 | |
| 66 | + |
| 67 | +Unclear whether this is a genuine improvement. Performance seems to have |
| 68 | +re-regressed in #123126 (see Mixed results below), so this may just be |
| 69 | +bimodality of some kind. |
| 70 | + |
| 71 | +Set writable and dead_on_unwind attributes for sret arguments [#121298](https://github.com/rust-lang/rust/pull/121298) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=cb3752d20e0f5d24348062211102a08d46fbecff&end=284f94f9c0f77ad4ef85323a634cfda29c1a801d&stat=instructions:u) |
| 72 | + |
| 73 | +| (instructions:u) | mean | range | count | |
| 74 | +|:----------------------------------:|:-----:|:---------------:|:-----:| |
| 75 | +| Regressions ❌ <br /> (primary) | 0.5% | [0.5%, 0.5%] | 1 | |
| 76 | +| Regressions ❌ <br /> (secondary) | - | - | 0 | |
| 77 | +| Improvements ✅ <br /> (primary) | -3.1% | [-26.0%, -0.3%] | 12 | |
| 78 | +| Improvements ✅ <br /> (secondary) | -1.6% | [-4.4%, -0.5%] | 11 | |
| 79 | +| All ❌✅ (primary) | -2.8% | [-26.0%, 0.5%] | 13 | |
| 80 | + |
| 81 | +#### Mixed |
| 82 | + |
| 83 | +Enable `CrateNum` query feeding via `TyCtxt` [#123126](https://github.com/rust-lang/rust/pull/123126) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=40dcd796d094b911b8b7b55a0519fb8e3d21680f&end=244da22fabd9fa677bbd0ac601a88e5ca6917526&stat=instructions:u) |
| 84 | + |
| 85 | +| (instructions:u) | mean | range | count | |
| 86 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 87 | +| Regressions ❌ <br /> (primary) | 0.3% | [0.2%, 0.6%] | 19 | |
| 88 | +| Regressions ❌ <br /> (secondary) | 0.4% | [0.3%, 0.5%] | 5 | |
| 89 | +| Improvements ✅ <br /> (primary) | - | - | 0 | |
| 90 | +| Improvements ✅ <br /> (secondary) | -0.7% | [-0.7%, -0.7%] | 2 | |
| 91 | +| All ❌✅ (primary) | 0.3% | [0.2%, 0.6%] | 19 | |
| 92 | + |
| 93 | +This looks like it's mostly just a regression to incremental. The PR |
| 94 | +description notes this is expected and sounds like there's follow-up work |
| 95 | +planned (unclear whether it will help with performance though). |
| 96 | + |
| 97 | +Stop using LLVM struct types for alloca [#122053](https://github.com/rust-lang/rust/pull/122053) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=c1feb3eceef7d5f0126c309a87062cf413fe0a25&end=29a56a3b1c06a624c0c06728c0af756d09df6b1b&stat=instructions:u) |
| 98 | + |
| 99 | +| (instructions:u) | mean | range | count | |
| 100 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 101 | +| Regressions ❌ <br /> (primary) | 0.2% | [0.2%, 0.3%] | 8 | |
| 102 | +| Regressions ❌ <br /> (secondary) | 0.4% | [0.2%, 1.1%] | 17 | |
| 103 | +| Improvements ✅ <br /> (primary) | -1.9% | [-1.9%, -1.9%] | 1 | |
| 104 | +| Improvements ✅ <br /> (secondary) | -0.4% | [-0.4%, -0.4%] | 1 | |
| 105 | +| All ❌✅ (primary) | -0.0% | [-1.9%, 0.3%] | 9 | |
| 106 | + |
| 107 | +Instruction counts are predominantly affected by some shuffling inside LLVM, |
| 108 | +but cycles are largely unaffected. See detailed analysis in |
| 109 | +https://github.com/rust-lang/rust/pull/122053#issuecomment-2074850501. |
| 110 | + |
| 111 | +Abort a process when FD ownership is violated [#124210](https://github.com/rust-lang/rust/pull/124210) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=6c90ac8d8f4489472720fce03c338cd5d0977f33&end=cb4940645775f60d74aee2e018d6c516c5aa9ed7&stat=instructions:u) |
| 112 | + |
| 113 | +| (instructions:u) | mean | range | count | |
| 114 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 115 | +| Regressions ❌ <br /> (primary) | 0.4% | [0.4%, 0.4%] | 2 | |
| 116 | +| Regressions ❌ <br /> (secondary) | - | - | 0 | |
| 117 | +| Improvements ✅ <br /> (primary) | -0.8% | [-0.8%, -0.8%] | 1 | |
| 118 | +| Improvements ✅ <br /> (secondary) | -0.1% | [-0.1%, -0.1%] | 2 | |
| 119 | +| All ❌✅ (primary) | 0.0% | [-0.8%, 0.4%] | 3 | |
| 120 | + |
| 121 | +Based on the [self profile results](https://perf.rust-lang.org/detailed-query.html?commit=cb4940645775f60d74aee2e018d6c516c5aa9ed7&benchmark=cargo-0.60.0-opt&scenario=full&base_commit=6c90ac8d8f4489472720fce03c338cd5d0977f33&sort_idx=-12) |
| 122 | +I suspect this is caused by us generating more code in the downstream crate(s) |
| 123 | +as a result of the late-bound ub checks. |
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