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triage/2021-02-24.md

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+# 2021-02-24 Triage Log
+
+Overall, a positive week for compiler performance with only one moderate regression. The change that introduced the regression leads to significantly improved [bootstrap speed](https://github.com/rust-lang/rust/pull/70951#issuecomment-766292996) of the compiler as well as easier maintainability.
+
+Triage done by **@rylev**.
+Revision range: [f1c47c79fe8438ed241630f885797eebef3a6cab..301ad8a4fa3ea56fb980443b7997c8f9d72dd717](https://perf.rust-lang.org/?start=f1c47c79fe8438ed241630f885797eebef3a6cab&end=301ad8a4fa3ea56fb980443b7997c8f9d72dd717&absolute=false&stat=instructions%3Au)
+
+1 Regression, 5 Improvements, 0 Mixed
+0 of them in rollups
+
+#### Regressions
+
+Move the query engine out of rustc_middle [#70951](https://github.com/rust-lang/rust/issues/70951)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=e7c23ab933ebc1f205c3b59f4ebc85d40f67d404&end=83b30a639d5abd1270ade35d9bd92271f5a5ba18&stat=instructions:u) (up to 4.9% on `full` builds of `deeply-nested-check`)
+- While this does somewhat hurt compiler performance, it is a huge gain in bootstrap speed. The performance impact was deemed acceptable, but perhaps an investigation in if the remaining performance regressions can be eliminated, should be looked into.
+- Added a nag to [the pull request](https://github.com/rust-lang/rust/pull/70951#issuecomment-785044935).
+
+#### Improvements
+
+Only store a LocalDefId in some HIR nodes [#81611](https://github.com/rust-lang/rust/issues/81611)
+- Very large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=a143517d44cac50b20cbd3a0b579addab40dd399&end=8fe989dd768f5dfdb0fc90933f3f74fa4579fefd&stat=instructions:u) (up to -9.6% on `incr-unchanged` builds of `many-assoc-items-check`)
+- Large improvements in the associated_item query which naturally led to improvements in the stress test related to associated items.
+
+Inline try_get_cached [#82197](https://github.com/rust-lang/rust/issues/82197)
+- Very large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=8fe989dd768f5dfdb0fc90933f3f74fa4579fefd&end=ee88f46bb5e27c4d9f30326e69ff2298dcbeecb1&stat=instructions:u) (up to -10.4% on `full` builds of `externs-debug`)
+- This change shows improvements originally expected from [#81855](https://github.com/rust-lang/rust/issues/81855), which based query fast path on try_get_cached. In-between the initial successful perf run of #81855 and merging, another PR [#81892](https://github.com/rust-lang/rust/issues/81892) removed an inline hint from the function, which was soon to be on the fast path.
+
+Reduce size of InterpErrorInfo to 8 bytes [#82116](https://github.com/rust-lang/rust/issues/82116)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=ee88f46bb5e27c4d9f30326e69ff2298dcbeecb1&end=5ef21063f0c0fd5b973bfa8cb88c0b70982da977&stat=instructions:u) (up to -4.1% on `full` builds of `ctfe-stress-4-check`)
+- Small improvements in ctfe stress tests. We'll take it though.
+
+Make the `Query` enum a simple struct. [#80891](https://github.com/rust-lang/rust/issues/80891)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=fe1bf8e05c39bdcc73fc09e246b7209444e389bc&end=301ad8a4fa3ea56fb980443b7997c8f9d72dd717&stat=instructions:u) (up to -1.5% on `full` builds of `externs-debug`)
+- Largely a code quality refactoring which originally had poor perf results but was fine tuned to lead to a small improvement. Good job!
+
+Improve assert_eq! and assert_ne! [#79100](https://github.com/rust-lang/rust/issues/79100)
+- Large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=a31c16212d70fcae3ad9d073b00d883951e573ee&end=ed58a2b03b6284b070fae2349898b16df98b7765&stat=instructions:u) (up to -8.4% on `full` builds of `packed-simd-check`)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=a31c16212d70fcae3ad9d073b00d883951e573ee&end=ed58a2b03b6284b070fae2349898b16df98b7765&stat=instructions:u) (up to 1.2% on `incr-patched: b9b3e592dd cherry picked` builds of `style-servo-debug`)
+- The regression is fairly small. It is servo which seems to have regressed in codegen queries. I imagine this would be the case if there are a lot of monomorphized instances of the new `assert_failed` function but this could was probably being generated before so I'm not entirely sure. The codegen query seems to be noisy this week and has caused other (clearly non-perf sensitive changes) to show changes in codegen times.
+
+Nags requiring follow up
+
+- One nag for the only regression for the week.