Merge pull request #995 from pnkfelix/triage-2021-09-07

triage report for 2021-09-07.

Author: pnkfelix

triage/2021-09-07.md

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+# 2021-09-07 Triage Log
+
+A busy week, with lots of mixed changes, though in the end only a few were deemed significant enough to report here.
+
+Triage done by **@pnkfelix**.
+Revision range: [fe37929e4cba2c5c21e6805805769630c736bc3d..69c4aa2901ffadf69deaf91b2f90604bcbc2eb36](https://perf.rust-lang.org/?start=fe37929e4cba2c5c21e6805805769630c736bc3d&end=69c4aa2901ffadf69deaf91b2f90604bcbc2eb36&absolute=false&stat=instructions%3Au)
+
+3 Regressions, 1 Improvements, 3 Mixed; 0 of them in rollups
+57 comparisons made in total
+
+#### Regressions
+
+Shrink Session a bit [#88530](https://github.com/rust-lang/rust/issues/88530)
+- Large regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=64929313f53181636e4dd37e25836973205477e4&end=fcce644119cf4e8e36001368e514bb5ed67cb855&stat=instructions:u) (up to 2.6% on `full` builds of `deeply-nested-async`)
+
+Concrete regions can show up in mir borrowck if the originated from there [#88533](https://github.com/rust-lang/rust/issues/88533)
+- Very small regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=29ef6cf1637aa8317f8911f93f14e18d404c1b0e&end=a3956106d12cebec91be0637759e29ab6908b4cd&stat=instructions:u) (up to 1.0% on `incr-patched: add static arr item` builds of `coercions`)
+- This is a small regression to `coercions` and that may be noise. However, there are many others that are over 0.4% regression to instruction counts. The combination of those two factors led pnkfelix to think that we may want to take a second look at the effects of this PR.
+
+Introduce `let...else` [#87688](https://github.com/rust-lang/rust/issues/87688)
+- Small improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=a3956106d12cebec91be0637759e29ab6908b4cd&end=c2a408840ad18f74280805535f0b7193528ff3df&stat=instructions:u) (up to -0.3% on `incr-unchanged` builds of `deeply-nested-closures`)
+- Small regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=a3956106d12cebec91be0637759e29ab6908b4cd&end=c2a408840ad18f74280805535f0b7193528ff3df&stat=instructions:u) (up to 0.4% on `full` builds of `issue-46449`)
+- Small regression (approximately 1%) in instruction counts on several of the *-doc tests, found via human eye.
+
+#### Improvements
+
+Move global analyses from lowering to resolution [#88597](https://github.com/rust-lang/rust/issues/88597)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=c5799b2a73bd03d1d7b4a432fa0a0cb93e7288db&end=577a76f0031f727735410b99a5cc5f0b61b92eef&stat=instructions:u) (up to -1.6% on `incr-unchanged` builds of `keccak`)
+
+
+#### Mixed
+
+Preserve most sub-obligations in the projection cache [#85868](https://github.com/rust-lang/rust/issues/85868)
+- Very large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=b834c4c1bad7521af47f38f44a4048be0a1fe2ee&end=371f3cd3fe523d0b398ed1db1620667c53ba7d02&stat=instructions:u) (up to -6.9% on `incr-unchanged` builds of `deeply-nested`)
+- Very large regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=b834c4c1bad7521af47f38f44a4048be0a1fe2ee&end=371f3cd3fe523d0b398ed1db1620667c53ba7d02&stat=instructions:u) (up to 9.4% on `full` builds of `deeply-nested`)
+
+
+BTreeMap/BTreeSet::from_iter: use bulk building to improve the performance [#88448](https://github.com/rust-lang/rust/issues/88448)
+- Large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=11bbb5231349a0a144d86d5c0c21061a06d1969d&end=ffaf857045f4f4d8bb563e0a5077f9b065f42916&stat=instructions:u) (up to -3.0% on `full` builds of `inflate`)
+- Large regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=11bbb5231349a0a144d86d5c0c21061a06d1969d&end=ffaf857045f4f4d8bb563e0a5077f9b065f42916&stat=instructions:u) (up to 4.5% on `incr-patched: println` builds of `clap-rs`)
+
+Avoid invoking the hir_crate query to traverse the HIR [#88435](https://github.com/rust-lang/rust/issues/88435)
+- Small improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=e30b68353fe22b00f40d021e7914eeb78473b3c1&end=7849e3e9dda60e8ec826ee245c6b180e73911b37&stat=instructions:u) (up to -1.2% on `incr-patched: add static arr item` builds of `coercions`)
+- Small regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=e30b68353fe22b00f40d021e7914eeb78473b3c1&end=7849e3e9dda60e8ec826ee245c6b180e73911b37&stat=instructions:u) (up to 0.5% on `incr-unchanged` builds of `helloworld`)
+- pnkfelix included this one as notable largely because the expected perf changes from [the actual PR](https://github.com/rust-lang/rust/pull/88435#issuecomment-907700333) largely showed slight improvements across the board, while after it landed on nightly, it is best categorized as "Mixed"
+
+#### Untriaged Pull Requests
+
+- [#88597 Move global analyses from lowering to resolution](https://github.com/rust-lang/rust/pull/88597)
+- [#88552 Stop allocating vtable entries for non-object-safe methods](https://github.com/rust-lang/rust/pull/88552)
+- [#88312 Treat types in unnormalized function signatures as well-formed](https://github.com/rust-lang/rust/pull/88312)
+- [#87815 encode `generics_of` for fields and ty params](https://github.com/rust-lang/rust/pull/87815)
+- [#87781 Remove box syntax from compiler and tools](https://github.com/rust-lang/rust/pull/87781)
+- [#87640 Rollup of 9 pull requests](https://github.com/rust-lang/rust/pull/87640)
+- [#87587 Various refactorings of the TAIT infrastructure](https://github.com/rust-lang/rust/pull/87587)
+- [#87570 Upgrade to LLVM 13](https://github.com/rust-lang/rust/pull/87570)
+- [#87244 Better diagnostics with mismatched types due to implicit static lifetime](https://github.com/rust-lang/rust/pull/87244)
+- [#86898 Add fast path for Path::cmp that skips over long shared prefixes](https://github.com/rust-lang/rust/pull/86898)
+- [#86777 Include terminators in instance size estimate](https://github.com/rust-lang/rust/pull/86777)
+- [#86698 Move OnDiskCache to rustc_query_impl.](https://github.com/rust-lang/rust/pull/86698)
+- [#86588 Rollup of 8 pull requests](https://github.com/rust-lang/rust/pull/86588)
+- [#86034 Change entry point to 🛡️ against 💥 💥-payloads](https://github.com/rust-lang/rust/pull/86034)
+- [#85556 Warn about unreachable code following an expression with an uninhabited type](https://github.com/rust-lang/rust/pull/85556)
+- [#84560 Inline Iterator as IntoIterator.](https://github.com/rust-lang/rust/pull/84560)
+- [#83302 Get piece unchecked in `write`](https://github.com/rust-lang/rust/pull/83302)