Add triage for the week of 2020-11-02.

Author: Mark-Simulacrum

triage/2020-11-03.md

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+# 2020-11-03 Triage Log
+
+A number of improvements on various benchmarks. The most notable news this week
+in compiler performance is the progress on instruction metric collection on a
+per-query level; see
+[measureme#143](https://github.com/rust-lang/measureme/pull/143) for the latest.
+
+Otherwise, this week was an excellent one for performance (though mostly on
+stress tests rather than commonly seen code).
+
+Triage done by **@simulacrum**.
+Revision range: [824f900a96d752da2d882863c65f9736e5f2b347..5cdf5b882da9e8b7c73b5cadeb7745cb68f6ff63](https://perf.rust-lang.org/?start=824f900a96d752da2d882863c65f9736e5f2b347&end=5cdf5b882da9e8b7c73b5cadeb7745cb68f6ff63&absolute=false&stat=instructions%3Au)
+
+0 Regressions, 5 Improvements, 0 Mixed
+
+#### Improvements
+
+[#78323](https://github.com/rust-lang/rust/issues/78323)
+- Slight improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=db241bb0c8d257e13c1560f6250e49879477039e&end=2eb4fc800aaf5006f89af3af591e2aa34f469d81&stat=instructions:u) (up to -1.3% on `incr-unchanged` builds of `packed-simd-check`)
+- Possibly within noise; unclear.
+
+[#78508](https://github.com/rust-lang/rust/issues/78508)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=a53fb30e3bf2655b0563da6d561c23cda5f3ec11&end=6bdae9edd0cc099daa6038bca469dc09b6fc078a&stat=instructions:u) (up to -2.0% on `incr-unchanged` builds of `packed-simd-check`)
+
+[#78432](https://github.com/rust-lang/rust/issues/78432)
+- Large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=c792f03379617efa7deb6ab8c20709c45e81670a&end=0d33ab7af4aebe786410b4c10367eb6ddf13af0b&stat=instructions:u) (up to -5.7% on `full` builds of `match-stress-enum-check`)
+- An unexpected improvement for a seemingly bugfix PR; would be good to verify
+  this is not an unintentional behavior change (nag left).
+
+[#78553](https://github.com/rust-lang/rust/issues/78553)
+- Very large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=e8cbaf2ae7fc5c564cacedbe55664797dc62d920&end=1899c489d4c30b2640d30b77ac04f0a548834d81&stat=instructions:u) (up to -10.1% on `full` builds of `match-stress-enum-check`)
+
+[#78448](https://github.com/rust-lang/rust/issues/78448)
+- Very large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=4c0c5e099a3b1f1c6ad53115189c2710495588b3&end=7b5a9e9cd27f01311b5e19cefa1fb574d086d3da&stat=instructions:u) (up to -95.4% on `full` builds of `externs-debug`)
+- Notable case of adding a new benchmark to perf; this is much appreciated and
+  illustrates that perf does not yet have full coverage of Rust code (though
+  this is not really expected either, though is always a goal).
+
+[#78430](https://github.com/rust-lang/rust/issues/78430)
+- Very large improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=31ee872db5aae4750e3da1ca4ed1523c4356947f&end=f9187adaef2005b903f666bf323ac675cadf8407&stat=instructions:u) (up to -23.6% on `incr-patched: println` builds of `unicode_normalization-check`)
+- Fairly large refactor to the match checking infrastructure, with a
+  correspondigly large performance improvement. There does appear to be a slight
+  regression on #58319, but this is in the "Improvements" category since it seem
+  categorically a win.
+
+#### Nags requiring follow up
+
+Compiler team attention requested:
+
+- <https://github.com/rust-lang/rust/pull/78432#issuecomment-721388323>