Merge pull request #814 from rylev/triage-2020-12-29

Add triage for 2020-12-29

Author: Mark-Simulacrum

triage/2020-11-10.md

@@ -2,7 +2,7 @@
 
 A mixed week with improvements still outweighing regressions. Perhaps the biggest highlight was the move to compiling rustc crates [with the initial-exec TLS model](https://github.com/rust-lang/rust/pull/78201) which results in fewer calls to `_tls_get_addr` and thus faster compile times.
 
-Triage done by **@rylevick**.
+Triage done by **@rylev**.
 Revision range: [5cdf5b882da9e8b7c73b5cadeb7745cb68f6ff63..cf9cf7c923eb01146971429044f216a3ca905e06](https://perf.rust-lang.org/?start=5cdf5b882da9e8b7c73b5cadeb7745cb68f6ff63&end=cf9cf7c923eb01146971429044f216a3ca905e06&absolute=false&stat=instructions%3Au)
 
 1 Regressions, 2 Improvements, 2 Mixed

triage/2020-11-19.md

@@ -5,7 +5,7 @@ This was a relatively mixed week, with some very large performance wins balanced
 
 The winner this week for largest performance improvement was [#78826](https://github.com/rust-lang/rust/issues/78826) which saw huge gains in the relatively new derive stress benchmark.
 
-Triage done by **@rylevick**.
+Triage done by **@rylev**.
 Revision range: [cf9cf7c923eb01146971429044f216a3ca905e06..c919f490bbcd2b29b74016101f7ec71aaa24bdbb](https://perf.rust-lang.org/?start=cf9cf7c923eb01146971429044f216a3ca905e06&end=c919f490bbcd2b29b74016101f7ec71aaa24bdbb&absolute=false&stat=instructions%3Au)
 
 5 Regressions, 5 Improvements, 2 Mixed

triage/2020-12-03.md

@@ -2,7 +2,7 @@
 
 A fairly mixed week with regressions and improvements mainly washing each other out with the exception of the very large improvement to [incremental compilation](https://github.com/rust-lang/rust/issues/74967) with huge gains in a large portion of the perf test suite.
 
-Triage done by **@rylevick**.
+Triage done by **@rylev**.
 Revision range: [25a691003cf6676259ee7d4bed05b43cb6283cea..c7cff213e937c1bb301be807ce04fcf6092b9163](https://perf.rust-lang.org/?start=25a691003cf6676259ee7d4bed05b43cb6283cea&end=c7cff213e937c1bb301be807ce04fcf6092b9163&absolute=false&stat=instructions%3Au)
 
 2 Regressions, 2 Improvement, 2 Mixed

triage/2020-12-15.md

@@ -2,7 +2,7 @@
 
 A week dominated by small regressions with only 1 modest yet clear performance gain. None of the regressions are large enough to cause concern, but there should be a followup to some to ensure that those regressions are at least examined.
 
-Triage done by **@rylevick**.
+Triage done by **@rylev**.
 Revision range: [4fd4a98d4788bc987d7f7add9df5f5ead6a1c15e..e1cce06e4ff5206daf397e1dcf91ed53653be171](https://perf.rust-lang.org/?start=4fd4a98d4788bc987d7f7add9df5f5ead6a1c15e&end=e1cce06e4ff5206daf397e1dcf91ed53653be171&absolute=false&stat=instructions%3Au)
 
 6 Regressions, 1 Improvements, 2 Mixed

triage/2020-12-29.md

@@ -0,0 +1,36 @@
+2020-12-29 Triage Log
+
+This was a quite week as many were on winter holidays. The regressions and improvements were all minor and mostly balanced each other out.
+
+Triage done by **@rylev**.
+Revision range: [c34c015fe2710caf53ba7ae9d1644f9ba65a6f74..e2a2592885539ca97bfb1232669e7519a0c0703b](https://perf.rust-lang.org/?start=c34c015fe2710caf53ba7ae9d1644f9ba65a6f74&end=e2a2592885539ca97bfb1232669e7519a0c0703b&absolute=false&stat=instructions%3Au)
+
+2 Regressions, 2 Improvements, 0 Mixed
+0 of them in rollups
+
+#### Regressions
+
+validate promoteds [#80235](https://github.com/rust-lang/rust/issues/80235)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=1832bdd7de93573464e1536e3ea17d5fd7d2888b&end=bb178237c5539c75e1b85ab78a8ab902b1f333d5&stat=instructions:u) (up to 4.8% on `full` builds of `ucd-check`)
+- Turn on const-value validation for promoteds.
+- In the PR there is a discussion if this change should instead only be a debug assertion. This should be discussed after a crater run happens. 
+
+BTreeMap: respect pointer provenance rules in split_off [#79347](https://github.com/rust-lang/rust/issues/79347)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=0edce6f4bbb4514482537f569f0b8ef48e71e0a0&end=2c308b9a2a9b9d531cafa3f11cb1000ee5362e63&stat=instructions:u) (up to 2.9% on `full` builds of `cranelift-codegen-opt`)
+- The minor perf regressions introduced here seemed to be gained back by [#79520](https://github.com/rust-lang/rust/issues/79520)
+
+#### Improvements
+
+Remove pointer comparison from slice equality [#80209](https://github.com/rust-lang/rust/issues/80209)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=d30dac2d839293f2c48e18ebfea1082819115d08&end=780b094d767b6720c11b1bf145dac2cf2643b89e&stat=instructions:u) (up to -3.1% on `incr-full` builds of `encoding-opt`)
+- Removed eagerly testing pointer equality in slices since most of the time slices won't be compared with themselves. This leads to an improvement in the code gen.
+
+BTreeMap: clean up access to MaybeUninit arrays [#79520](https://github.com/rust-lang/rust/issues/79520)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=30a42735a0ff678172f66f63aca746096a717293&end=89524d0f8e28080197a85e06d143b7d6f131b67e&stat=instructions:u) (up to -3.1% on `full` builds of `cranelift-codegen-opt`)
+- The minor perf gains seem to be regaining perfomance lossed by [#79347](https://github.com/rust-lang/rust/issues/79347)
+
+
+#### Nags requiring follow up
+
+- stdarch is still a major contributor to libcore compile times.
+

triage/README.md

@@ -7,6 +7,7 @@ usage.
 
 - ecstatic-morse
 - Mark-Simulacrum
+- rylev
 
 Monday evening in North America is a good time to do it because This Week in Rust (see below) is usually
 published on Tuesday, US time, and so it means the PR to include the triage
@@ -17,7 +18,7 @@ at.
 ## Instructions
 
 First, check the previous triage log entry. Look for responses in PRs, and
-follow up on any promised actions. (I.e. nag people!)
+follow up on any promised actions. (i.e. nag people!)
 
 Start the new triage log entry in a new file using a `YYYY-MM-DD.md`-form name.
 Follow the format of the previous entries.