Merge pull request #812 from rylev/triage-2020-12-15-update

Update triage-2020-12-15

Author: Mark-Simulacrum

triage/2020-12-15.md

@@ -27,7 +27,7 @@ Accept arbitrary expressions in key-value attributes at parse time[#78837](https
 Capture precise paths in THIR and MIR[#79553](https://github.com/rust-lang/rust/issues/79553)
 - Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=9eb3a7ceafd1e2c1924177caa18c7cc0c25b413e&end=5bd9b60333b3dc0a51e7a5607cd1e0d537a9f718&stat=instructions:u) (up to 4.5% on `incr-unchanged` builds of `clap-rs-check`)
 - While this change powers a feature behind a feature flag (`capture_disjoint_fields`), it looks like it's still causing perf regressions in workloads not using this feature.
-- [Pinged in the PR about this issue](https://github.com/rust-lang/rust/pull/79553#issuecomment-745435558)
+- This is a known issue with [a plan](https://github.com/rust-lang/rust/pull/79553#issuecomment-745437806) for how to recover the performance loss.
 
 Create `rustc_type_ir`[#79169](https://github.com/rust-lang/rust/issues/79169)
 - Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=c3ed6681ff8d446e68ce272be4bf66f4145f6e29&end=3f2088aa603d2cd3f43c20795872de9cd6ec7735&stat=instructions:u) (up to 3.1% on `full` builds of `ctfe-stress-4-check`)
@@ -37,6 +37,7 @@ Create `rustc_type_ir`[#79169](https://github.com/rust-lang/rust/issues/79169)
 Update stdarch submodule[#79938](https://github.com/rust-lang/rust/issues/79938)
 - Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=fa416394275d2468d104b8f72ac31b1ddf7ee52e&end=8b3ee82eb68cb35030bb745c23f8aa76d9de5bee&stat=instructions:u) (up to 1.4% on `incr-unchanged` builds of `deeply-nested-debug`)
 - This was a wholesale update of the stdarch submodule. 
+- stdarch is using const arguments that would benefit from const generics. This might explain why compilation suffers.
 * [Pinged in the PR about this issue](https://github.com/rust-lang/rust/pull/79938#issuecomment-745393740)
 
 #### Improvements
@@ -61,5 +62,4 @@ Lower `discriminant_value` intrinsic[#79922](https://github.com/rust-lang/rust/i
 #### Nags requiring follow up
 
 - Several regressions need followup investigations. See their respective entries above for the issue.
-- As mentioned last week, stdarch expansion causing a 40% libcore compile time regression is still not
-  resolved, and resolution is unclear. 
+- As mentioned last week, stdarch expansion causing a 40% libcore compile time regression is still not resolved, and resolution is unclear. This is likely a related issue to the stdarch regression listed above.