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| 1 | +# 2023-01-03 Triage Log |
| 2 | + |
| 3 | +Fairly busy week with some massive performance improvements at the expense of some significant albeit smaller regressions. The main wins came in a long-standing PR from @cjgillot to enable encoding spans in metadata relative to their enclosing item. This causes more work in full compilation which causes some regressions up to 5% but can lead to very large wins in incremental compilation scenarios (up to ~70%). For example, the clap crate compiles 68% faster after a small 1 line change than it did previously. |
| 4 | + |
| 5 | +Triage done by **@rylev**. |
| 6 | +Revision range: [b38a6d..b43596](https://perf.rust-lang.org/?start=b38a6d373cb254697411147c0e49cd2e84864258&end=b435960c4cfd3975651c7051be56d7f5d6c201ab&absolute=false&stat=instructions%3Au) |
| 7 | + |
| 8 | +**Summary**: |
| 9 | + |
| 10 | +| (instructions:u) | mean | range | count | |
| 11 | +|:----------------------------------:|:-----:|:---------------:|:-----:| |
| 12 | +| Regressions ❌ <br /> (primary) | 1.6% | [0.3%, 4.6%] | 97 | |
| 13 | +| Regressions ❌ <br /> (secondary) | 1.8% | [0.2%, 7.6%] | 60 | |
| 14 | +| Improvements ✅ <br /> (primary) | -9.7% | [-68.7%, -0.2%] | 53 | |
| 15 | +| Improvements ✅ <br /> (secondary) | -1.7% | [-15.3%, -0.1%] | 62 | |
| 16 | +| All ❌✅ (primary) | -2.4% | [-68.7%, 4.6%] | 150 | |
| 17 | + |
| 18 | +1 Regressions, 1 Improvements, 4 Mixed; 1 of them in rollups |
| 19 | +47 artifact comparisons made in total |
| 20 | + |
| 21 | +#### Regressions |
| 22 | + |
| 23 | +Rollup of 8 pull requests [#106228](https://github.com/rust-lang/rust/pull/106228) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=270c94e484e19764a2832ef918c95224eb3f17c7&end=9709a438721d679572f0f7c389cd1fa60922fbef&stat=instructions:u) |
| 24 | + |
| 25 | +| (instructions:u) | mean | range | count | |
| 26 | +|:----------------------------------:|:----:|:------------:|:-----:| |
| 27 | +| Regressions ❌ <br /> (primary) | 0.4% | [0.2%, 0.6%] | 7 | |
| 28 | +| Regressions ❌ <br /> (secondary) | - | - | 0 | |
| 29 | +| Improvements ✅ <br /> (primary) | - | - | 0 | |
| 30 | +| Improvements ✅ <br /> (secondary) | - | - | 0 | |
| 31 | +| All ❌✅ (primary) | 0.4% | [0.2%, 0.6%] | 7 | |
| 32 | +- Kicked off a perf run on the only likely culprit. The regression is small enough that I don't think it's a big deal if we don't figure this out. |
| 33 | + |
| 34 | +Allow trait method paths to satisfy const Fn bounds [#106210](https://github.com/rust-lang/rust/pull/106210) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=2c7536eaae59b44ff5259183ca98384129d69dd0&end=973a4db8d590d1ddfa4d07bd216aeffd28ba354e&stat=instructions:u) |
| 35 | + |
| 36 | +| (instructions:u) | mean | range | count | |
| 37 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 38 | +| Regressions ❌ <br /> (primary) | 0.3% | [0.2%, 0.5%] | 16 | |
| 39 | +| Regressions ❌ <br /> (secondary) | 0.4% | [0.2%, 0.7%] | 16 | |
| 40 | +| Improvements ✅ <br /> (primary) | - | - | 0 | |
| 41 | +| Improvements ✅ <br /> (secondary) | -1.4% | [-1.4%, -1.4%] | 1 | |
| 42 | +| All ❌✅ (primary) | 0.3% | [0.2%, 0.5%] | 16 | |
| 43 | +- Massive amount of noise reversed in [#106268](https://github.com/rust-lang/rust/pull/106268). No idea where this noise comes from. |
| 44 | + |
| 45 | + |
| 46 | +#### Improvements |
| 47 | + |
| 48 | + |
| 49 | +fix comment for `TokenCursor::desugar` [#106268](https://github.com/rust-lang/rust/pull/106268) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=808be91da07c91e4d6006cca0ad78385785a741e&end=e5e5fcb0b758fcf7f149cc9206155dcfa18ec909&stat=instructions:u) |
| 50 | + |
| 51 | +| (instructions:u) | mean | range | count | |
| 52 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 53 | +| Regressions ❌ <br /> (primary) | - | - | 0 | |
| 54 | +| Regressions ❌ <br /> (secondary) | - | - | 0 | |
| 55 | +| Improvements ✅ <br /> (primary) | -0.3% | [-0.5%, -0.2%] | 17 | |
| 56 | +| Improvements ✅ <br /> (secondary) | -0.3% | [-0.7%, -0.2%] | 15 | |
| 57 | +| All ❌✅ (primary) | -0.3% | [-0.5%, -0.2%] | 17 | |
| 58 | +- Massive amount of noise coming in [#106210](https://github.com/rust-lang/rust/pull/106210) reversed here. No idea where this noise comes from. |
| 59 | + |
| 60 | + |
| 61 | +Abolish `QueryVTable` in favour of more assoc items on `QueryConfig` [#106307](https://github.com/rust-lang/rust/pull/106307) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=23b1cc197a3a6d0c1ab78a5c6e7cdad17681f1c9&end=d6f99e535a301a421dfee52a7c25bb4bdf420344&stat=instructions:u) |
| 62 | + |
| 63 | +| (instructions:u) | mean | range | count | |
| 64 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 65 | +| Regressions ❌ <br /> (primary) | - | - | 0 | |
| 66 | +| Regressions ❌ <br /> (secondary) | 0.6% | [0.4%, 1.0%] | 4 | |
| 67 | +| Improvements ✅ <br /> (primary) | -0.5% | [-1.0%, -0.2%] | 63 | |
| 68 | +| Improvements ✅ <br /> (secondary) | -0.6% | [-1.3%, -0.4%] | 60 | |
| 69 | +| All ❌✅ (primary) | -0.5% | [-1.0%, -0.2%] | 63 | |
| 70 | + |
| 71 | + |
| 72 | +#### Mixed |
| 73 | + |
| 74 | +Catch panics/unwinding in destruction of TLS values [#105426](https://github.com/rust-lang/rust/pull/105426) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=f6cc345be403d481b4518e151218118c2a9eb4bb&end=7c991868c60a4afc1ee6334b912ea96061a2c98d&stat=instructions:u) |
| 75 | + |
| 76 | +| (instructions:u) | mean | range | count | |
| 77 | +|:----------------------------------:|:-----:|:---------------:|:-----:| |
| 78 | +| Regressions ❌ <br /> (primary) | 0.7% | [0.3%, 1.9%] | 11 | |
| 79 | +| Regressions ❌ <br /> (secondary) | - | - | 0 | |
| 80 | +| Improvements ✅ <br /> (primary) | -0.3% | [-0.6%, -0.2%] | 41 | |
| 81 | +| Improvements ✅ <br /> (secondary) | -1.8% | [-14.6%, -0.2%] | 31 | |
| 82 | +| All ❌✅ (primary) | -0.1% | [-0.6%, 1.9%] | 52 | |
| 83 | +- Very much unsure where the performance changes are coming from. Some show LLVM regressions but not all. LLVM also does not explain the improvements. |
| 84 | +- Ask [in the PR](https://github.com/rust-lang/rust/pull/105426#issuecomment-1370051574) for thoughts. |
| 85 | + |
| 86 | + |
| 87 | +Use some more `const_eval_select` in pointer methods for compile times [#106275](https://github.com/rust-lang/rust/pull/106275) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=726bbfc8f0d6eb431dfa620c1c8fc3848020cd3c&end=dd01a163c1cff9461ddd85e7b3c2c0109657658f&stat=instructions:u) |
| 88 | + |
| 89 | +| (instructions:u) | mean | range | count | |
| 90 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 91 | +| Regressions ❌ <br /> (primary) | 0.4% | [0.4%, 0.4%] | 1 | |
| 92 | +| Regressions ❌ <br /> (secondary) | 0.7% | [0.6%, 0.9%] | 2 | |
| 93 | +| Improvements ✅ <br /> (primary) | -0.5% | [-0.9%, -0.2%] | 28 | |
| 94 | +| Improvements ✅ <br /> (secondary) | -0.8% | [-0.8%, -0.7%] | 3 | |
| 95 | +| All ❌✅ (primary) | -0.4% | [-0.9%, 0.4%] | 29 | |
| 96 | +- Author investigated why this might have caused a regression in `regex` and found nothing. The gains much outweigh the regressions so we should be fine keeping it. |
| 97 | + |
| 98 | + |
| 99 | +Encode spans relative to the enclosing item -- enable on nightly [#84762](https://github.com/rust-lang/rust/pull/84762) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=f89003eda8917ff99f8ee3fb5c812310a58c014b&end=fb9dfa8ceffb985105be3176d7ed2f99515ea377&stat=instructions:u) |
| 100 | + |
| 101 | +| (instructions:u) | mean | range | count | |
| 102 | +|:----------------------------------:|:------:|:---------------:|:-----:| |
| 103 | +| Regressions ❌ <br /> (primary) | 1.7% | [0.2%, 5.0%] | 108 | |
| 104 | +| Regressions ❌ <br /> (secondary) | 1.8% | [0.2%, 7.6%] | 90 | |
| 105 | +| Improvements ✅ <br /> (primary) | -20.0% | [-68.9%, -0.6%] | 25 | |
| 106 | +| Improvements ✅ <br /> (secondary) | -2.7% | [-4.8%, -1.5%] | 11 | |
| 107 | +| All ❌✅ (primary) | -2.4% | [-68.9%, 5.0%] | 133 | |
| 108 | +- There was an [FCP](https://github.com/rust-lang/rust/pull/84762#issuecomment-1327518372) to decide whether the trade off of some regressions for some huge incremental performance wins was worth it. |
| 109 | +- This FCP passed and so the PR was merged. |
| 110 | + |
| 111 | + |
| 112 | +Reenable limited top-down MIR inlining [#106364](https://github.com/rust-lang/rust/pull/106364) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d6f99e535a301a421dfee52a7c25bb4bdf420344&end=67d16171d7eebc08057a46aeed887252e7cc286b&stat=instructions:u) |
| 113 | + |
| 114 | +| (instructions:u) | mean | range | count | |
| 115 | +|:----------------------------------:|:-----:|:--------------:|:-----:| |
| 116 | +| Regressions ❌ <br /> (primary) | 0.5% | [0.3%, 1.1%] | 4 | |
| 117 | +| Regressions ❌ <br /> (secondary) | 0.6% | [0.5%, 0.6%] | 4 | |
| 118 | +| Improvements ✅ <br /> (primary) | -0.6% | [-1.2%, -0.2%] | 9 | |
| 119 | +| Improvements ✅ <br /> (secondary) | -0.9% | [-2.4%, -0.2%] | 18 | |
| 120 | +| All ❌✅ (primary) | -0.2% | [-1.2%, 1.1%] | 13 | |
| 121 | +- As pointed out [here](https://github.com/rust-lang/rust/pull/106364#issuecomment-1369111291) this was effectively a performance wash with regressions and improvements canceling themselves out. |
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