Merge pull request #750 from ecstatic-morse/triage-2019-08-24

Perf triage 2020-08-24

Author: Mark-Simulacrum

triage/2020-08-24.md

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+# 2020-08-24 Triage Log
+
+See the [README](README.md) for details on how this log was gathered.
+
+This week saw an upgrade to LLVM 11, which resulted in large speedups to
+optimized builds. This offsets the slowdown we observed as part of the [upgrade
+to LLVM 10][llvm-10-results]. Many thanks to rust-lang and LLVM contributor
+[@nikic](https://github.com/nikic) for their work to measure [LLVM
+performance][llvm-fast]. That upgrade did cause slight regressions to check and
+debug builds, but on the whole it is a significant win for compile times.
+
+Triage done by @ecstaticmorse.
+Revision range: [67e7b9b8cf776222825dbbd4cb1e39b7765ef27c..03017003c77d782cf7ed841a05d7c628a9b93f25][range]
+
+[llvm-10-results]: https://perf.rust-lang.org/compare.html?start=0aa6751c19d3ba80df5b0b02c00bf44e13c97e80&end=82911b3bba76e73afe2881b732fe6b0edb35d5d3&stat=instructions:u
+[llvm-fast]: https://nikic.github.io/2020/05/10/Make-LLVM-fast-again.html
+[range]: https://perf.rust-lang.org/?start=67e7b9b8cf776222825dbbd4cb1e39b7765ef27c&end=03017003c77d782cf7ed841a05d7c628a9b93f25&absolute=false&stat=instructions%3Au
+
+1 Regression, 4 Improvements, 0 of them in rollups.
+
+#### Regressions
+
+[#75555](https://github.com/rust-lang/rust/pull/75555) Cargo update (almost) all the things! 
+- [A very small regression](https://perf.rust-lang.org/compare.html?start=30f0a07684f6c1f5df62d69e9519d82e13d6bf2d&end=1656582822a80139d725e56f00c564f4f58f2883&stat=instructions:u)
+
+#### Improvements
+
+[#75145](https://github.com/rust-lang/rust/pull/75145) Reference lang items during AST lowering 
+- [An improvement of ~3% on `await-call-tree`](https://perf.rust-lang.org/compare.html?start=33c96b4d9782cf6364e47cb2c904e66b06c22bb4&end=792c645ca7d11a8d254df307d019c5bf01445c37&stat=instructions:u)
+- Coupled with small improvements across the board 
+
+[#75590](https://github.com/rust-lang/rust/pull/75590) Add a packed/tagged pointer abstraction and utilize it for ParamEnv 
+- [A small improvement on `keccak`/`inflate`](https://perf.rust-lang.org/compare.html?start=9900178cba95369cd5822c8ce579edcc89ffeb76&end=32c654a9795b0d88541e56ba9da4150e34f1d5f9&stat=instructions:u)
+
+[#73526](https://github.com/rust-lang/rust/pull/73526) Upgrade to LLVM 11 (rc2) 
+- [An improvement on optimized builds](https://perf.rust-lang.org/compare.html?start=e482c86b9de32c6392cb83aa97d72e22425163f9&end=7ce71c362be9a89e7897ac066aba6e3e6f747800&stat=instructions:u)
+- Tempered by a small regression on debug and check builds.
+
+[#75813](https://github.com/rust-lang/rust/pull/75813) Lazy decoding of DefPathTable from crate metadata (non-incremental case) 
+- [A major improvement on small crates, especially on check builds](https://perf.rust-lang.org/compare.html?start=7ce71c362be9a89e7897ac066aba6e3e6f747800&end=d5abc8d3b2e14c8793182b427520497a90b6de83&stat=instructions:u)
+
+#### Nags requiring follow up
+
+None