triage for 2023-12-18.

Author: pnkfelix

triage/2023-12-18.md

@@ -1,8 +1,16 @@
 # 2023-12-19 Triage Log
 
-TODO: Summary
+A lot of noise in the results this week; there was an lull in the noise
+recently, so our auto-inferred noise threshold went down, and thus five PR's
+were artificially flagged this week (and three supposed improvements were just
+reverting to the mean). Beyond that, we had three nice improvements: the first
+to debug builds in #117962 (by ceasing emission of expensive+unused
+`.debug_pubnames` and `.debug_pubtypes`), a second to diesel and serde in
+#119048 (by avoiding some unnecessary work), and a third to several benchmarks
+in #117749 (by adding some caching of an internal compiler structure).
 
-Triage done by **@???**.
+
+Triage done by **@pnkfelix**.
 Revision range: [57010939..bf9229a2](https://perf.rust-lang.org/?start=57010939ed1d00076b4af0ed06a81ec69ea5e4a8&end=bf9229a2e366b4c311f059014a4aa08af16de5d8&absolute=false&stat=instructions%3Au)
 
 **Summary**:
@@ -16,7 +24,7 @@ Revision range: [57010939..bf9229a2](https://perf.rust-lang.org/?start=57010939e
 | All ❌✅ (primary)                 | -1.6% | [-10.8%, 0.4%]  | 112   |
 
 
-6 Regressions, 9 Improvements, 3 Mixed; ??? of them in rollups
+6 Regressions, 9 Improvements, 3 Mixed; 5 of them in rollups
 67 artifact comparisons made in total
 
 #### Regressions
@@ -31,6 +39,7 @@ rustc_passes: Enforce `rustc::potential_query_instability` lint [#118870](https:
 | Improvements ✅ <br /> (secondary) | -     | -             | 0     |
 | All ❌✅ (primary)                 | 13.5% | [0.5%, 44.5%] | 8     |
 
+* already marked as triaged by lqd; this PR did not regress things, the reported change is due to a periodic "slow s3 uploads on the collector", i.e. instrument noise/bias.
 
 fix --dry-run when the change-id warning is printed [#118789](https://github.com/rust-lang/rust/pull/118789) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=1aa6aefdc92555b3fbc5ae4c99365df9845a3e31&end=529047cfc3f4f7b3ea5aaac054408f368d153727&stat=instructions:u)
 
@@ -42,6 +51,7 @@ fix --dry-run when the change-id warning is printed [#118789](https://github.com
 | Improvements ✅ <br /> (secondary) | -    | -            | 0     |
 | All ❌✅ (primary)                 | 0.9% | [0.8%, 1.0%] | 4     |
 
+* already marked as triaged by lqd; this PR did not regress things. lqd hypothesized that the inferred noise threshold was lowered (due to a period of low noisiness?), and thus normal amounts of noise are tripping the threshold.
 
 Rollup of 3 pull requests [#118982](https://github.com/rust-lang/rust/pull/118982) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=4d1bd0db7f489b22c6d8aa2385937a95412c015b&end=e6707df0de337976dce7577e68fc57adcd5e4842&stat=instructions:u)
 
@@ -54,6 +64,8 @@ Rollup of 3 pull requests [#118982](https://github.com/rust-lang/rust/pull/11898
 | All ❌✅ (primary)                 | 0.8% | [0.8%, 0.9%] | 4     |
 
 
+* already marked as triaged by lqd. We think this is another case where the inferred noise threshold was low and we are seeing regression reports as the noise ramps up again.
+
 Rollup of 5 pull requests [#119002](https://github.com/rust-lang/rust/pull/119002) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=a96d57bdb6d2bb6d233d7d5aaefc2995ab99be01&end=ca5c68a110099b17c3537e6e5840dbcc21b0e3ca&stat=instructions:u)
 
 | (instructions:u)                   | mean  | range          | count |
@@ -64,6 +76,8 @@ Rollup of 5 pull requests [#119002](https://github.com/rust-lang/rust/pull/11900
 | Improvements ✅ <br /> (secondary) | -0.1% | [-0.1%, -0.1%] | 2     |
 | All ❌✅ (primary)                 | 0.2%  | [-0.3%, 0.5%]  | 41    |
 
+* lqd identified PR #118396, "Collect lang items from AST, get rid of GenericBound::LangItemTrait" as the root cause for the regressions here.
+* not marking as triaged
 
 More unescaping cleanups [#118897](https://github.com/rust-lang/rust/pull/118897) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=1c6a06183a1452c2772db370b572e38bac9c5d86&end=3ad8e2d129a67b0dc450d6ef1100ae41d2cd4b8a&stat=instructions:u)
 
@@ -75,6 +89,8 @@ More unescaping cleanups [#118897](https://github.com/rust-lang/rust/pull/118897
 | Improvements ✅ <br /> (secondary) | -    | -            | 0     |
 | All ❌✅ (primary)                 | 0.6% | [0.1%, 0.8%] | 5     |
 
+* lqd theorized this is another instance of noise threshold wriggling
+* pnkfelix agrees and marked as triaged.
 
 coverage: Regression test for `assert!(!false)` [#119011](https://github.com/rust-lang/rust/pull/119011) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=445177724ac2beebf4faa5a3ffacb2adbe7e7846&end=9022e6a39c2714d2f447285c4ee7513bf153e3a9&stat=instructions:u)
 
@@ -86,6 +102,8 @@ coverage: Regression test for `assert!(!false)` [#119011](https://github.com/rus
 | Improvements ✅ <br /> (secondary) | -    | -            | 0     |
 | All ❌✅ (primary)                 | 0.7% | [0.7%, 0.8%] | 4     |
 
+* yet again, helloworld check is being flagged as regressing (in four scenarios), probably due to wriggling noise threshold.
+* pnkfelix marking as triaged
 
 #### Improvements
 
@@ -110,6 +128,7 @@ fix: stop emitting `.debug_pubnames` and `.debug_pubtypes` [#117962](https://git
 | Improvements ✅ <br /> (secondary) | -1.6% | [-3.1%, -0.2%] | 61    |
 | All ❌✅ (primary)                 | -2.1% | [-5.2%, -0.3%] | 24    |
 
+* nice improvement to debug builds, especially for ripgrep and serde_derive
 
 Unbreak non-unix non-windows bootstrap [#118894](https://github.com/rust-lang/rust/pull/118894) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=c3def263a44e07e09ae6d57abfc8650227fb4972&end=7176b8babdc55d68a485ab61940b10611cfa6c57&stat=instructions:u)
 
@@ -121,6 +140,7 @@ Unbreak non-unix non-windows bootstrap [#118894](https://github.com/rust-lang/ru
 | Improvements ✅ <br /> (secondary) | -      | -               | 0     |
 | All ❌✅ (primary)                 | -10.4% | [-30.8%, -0.6%] | 8     |
 
+* (don't get excited; this is just a return-to-normal after the artificial regression flagged with PR #118870 above)
 
 cache param env canonicalization [#117749](https://github.com/rust-lang/rust/pull/117749) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=e6d1b0ec9859e6f5c29aaa3b6525fb625bf354ad&end=d23e1a689426638a5146c204e09278433c509610&stat=instructions:u)
 
@@ -132,6 +152,7 @@ cache param env canonicalization [#117749](https://github.com/rust-lang/rust/pul
 | Improvements ✅ <br /> (secondary) | -1.3% | [-1.4%, -1.3%] | 2     |
 | All ❌✅ (primary)                 | -2.0% | [-4.8%, -0.2%] | 32    |
 
+* pretty solid improvement here to serde, diesel, bitmaps, hyper, image.
 
 `-Ztrait-solver=next` to `-Znext-solver` [#118937](https://github.com/rust-lang/rust/pull/118937) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=529047cfc3f4f7b3ea5aaac054408f368d153727&end=2ecba0fa00b75e7291978c50bece407f17296f45&stat=instructions:u)
 
@@ -143,6 +164,7 @@ cache param env canonicalization [#117749](https://github.com/rust-lang/rust/pul
 | Improvements ✅ <br /> (secondary) | -0.5% | [-0.8%, -0.3%] | 21    |
 | All ❌✅ (primary)                 | -0.9% | [-1.0%, -0.9%] | 4     |
 
+* (just noise)
 
 Use the LLVM option NoTrapAfterNoreturn [#110494](https://github.com/rust-lang/rust/pull/110494) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=e223c41028def5123ffd2a4a51a9109b1aae2c2e&end=02ad6676ddc7ea7bc3acd73f383180bc80185aeb&stat=instructions:u)
 
@@ -154,6 +176,7 @@ Use the LLVM option NoTrapAfterNoreturn [#110494](https://github.com/rust-lang/r
 | Improvements ✅ <br /> (secondary) | -0.5% | [-0.8%, -0.3%] | 25    |
 | All ❌✅ (primary)                 | -0.9% | [-0.9%, -0.8%] | 4     |
 
+* (just noise)
 
 Add support for `--env` on `tracked_env::var` [#118830](https://github.com/rust-lang/rust/pull/118830) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=9022e6a39c2714d2f447285c4ee7513bf153e3a9&end=5e7025419d1b1359e4cb7cd365ba5900c8299089&stat=instructions:u)
 
@@ -165,6 +188,7 @@ Add support for `--env` on `tracked_env::var` [#118830](https://github.com/rust-
 | Improvements ✅ <br /> (secondary) | -0.5% | [-0.7%, -0.3%] | 7     |
 | All ❌✅ (primary)                 | -0.7% | [-0.8%, -0.7%] | 3     |
 
+* (just noise)
 
 don't fold ParamEnv in register_predicate_obligation [#119048](https://github.com/rust-lang/rust/pull/119048) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d14e52b47ab27bcc3c3e083ed5f009a57db63eff&end=4283aeaca5c0c14864d4af3369a42c6b8b21f80f&stat=instructions:u)
 
@@ -176,6 +200,7 @@ don't fold ParamEnv in register_predicate_obligation [#119048](https://github.co
 | Improvements ✅ <br /> (secondary) | -0.3% | [-0.3%, -0.3%] | 1     |
 | All ❌✅ (primary)                 | -2.1% | [-7.3%, -0.2%] | 23    |
 
+* nice improvement to diesel and serde.
 
 resolve: Replace visibility table in resolver outputs with query feeding [#118657](https://github.com/rust-lang/rust/pull/118657) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=43dcc9b786c922251c3fbe75a0142f50f07053ca&end=321b6565a5f8ebf6f23622fc91ea1191a54f2a38&stat=instructions:u)
 
@@ -200,6 +225,7 @@ codegen_llvm: set `DW_AT_accessibility` [#115165](https://github.com/rust-lang/r
 | Improvements ✅ <br /> (secondary) | -0.4% | [-0.7%, -0.2%] | 22    |
 | All ❌✅ (primary)                 | -0.2% | [-0.7%, 0.3%]  | 8     |
 
+* the improvements are helloworld noise; the regressions are minor.
 
 Rollup of 6 pull requests [#119009](https://github.com/rust-lang/rust/pull/119009) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=5c927ab99946c312eed65f28aea15d2a035441f0&end=1c6a06183a1452c2772db370b572e38bac9c5d86&stat=instructions:u)
 
@@ -211,6 +237,8 @@ Rollup of 6 pull requests [#119009](https://github.com/rust-lang/rust/pull/11900
 | Improvements ✅ <br /> (secondary) | -     | -              | 0     |
 | All ❌✅ (primary)                 | -1.1% | [-1.9%, 0.2%]  | 9     |
 
+* The single tiny regression to exa doc full does not warrant spending time trying to tease apart this rollup, IMO.
+* marked as triaged
 
 Rollup of 5 pull requests [#119069](https://github.com/rust-lang/rust/pull/119069) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=cda4736f1eaad8af6f49388baa9b7e480df8e329&end=e004adb5561b724ac18f5b24584648ca4e42b6ad&stat=instructions:u)
 
@@ -222,41 +250,5 @@ Rollup of 5 pull requests [#119069](https://github.com/rust-lang/rust/pull/11906
 | Improvements ✅ <br /> (secondary) | -0.3% | [-0.5%, -0.2%] | 13    |
 | All ❌✅ (primary)                 | -0.2% | [-0.3%, -0.1%] | 12    |
 
-
-#### Untriaged Pull Requests
-
-- [#119069 Rollup of 5 pull requests](https://github.com/rust-lang/rust/pull/119069)
-- [#119011 coverage: Regression test for `assert!(!false)`](https://github.com/rust-lang/rust/pull/119011)
-- [#119009 Rollup of 6 pull requests](https://github.com/rust-lang/rust/pull/119009)
-- [#119002 Rollup of 5 pull requests](https://github.com/rust-lang/rust/pull/119002)
-- [#118897 More unescaping cleanups](https://github.com/rust-lang/rust/pull/118897)
-- [#118661 Restore `const PartialEq`](https://github.com/rust-lang/rust/pull/118661)
-- [#118473 Rollup of 5 pull requests](https://github.com/rust-lang/rust/pull/118473)
-- [#118420 Introduce support for `async gen` blocks](https://github.com/rust-lang/rust/pull/118420)
-- [#118405 Rollup of 7 pull requests](https://github.com/rust-lang/rust/pull/118405)
-- [#118319 Rollup of 4 pull requests](https://github.com/rust-lang/rust/pull/118319)
-- [#118308 Don't warn an empty pattern unreachable if we're not sure the data is valid](https://github.com/rust-lang/rust/pull/118308)
-- [#117769 Rollup of 6 pull requests](https://github.com/rust-lang/rust/pull/117769)
-- [#117736 Rollup of 6 pull requests](https://github.com/rust-lang/rust/pull/117736)
-- [#117180 Rollup of 7 pull requests](https://github.com/rust-lang/rust/pull/117180)
-- [#116940 Rollup of 4 pull requests](https://github.com/rust-lang/rust/pull/116940)
-- [#116915 Add an assume that the index is inbounds to slice::get_unchecked](https://github.com/rust-lang/rust/pull/116915)
-- [#116889 Eat close paren if capture_cfg to avoid unbalanced parens](https://github.com/rust-lang/rust/pull/116889)
-- [#116492 Rollup of 7 pull requests](https://github.com/rust-lang/rust/pull/116492)
-- [#116391 exhaustiveness: Rework constructor splitting](https://github.com/rust-lang/rust/pull/116391)
-- [#116183 Always preserve DebugInfo in DeadStoreElimination.](https://github.com/rust-lang/rust/pull/116183)
-- [#116033 report `unused_import` for empty reexports even it is pub](https://github.com/rust-lang/rust/pull/116033)
-- [#115762 Explain revealing of opaque types in layout_of ParamEnv](https://github.com/rust-lang/rust/pull/115762)
-- [#115751 some inspect improvements](https://github.com/rust-lang/rust/pull/115751)
-- [#115740 Cache reachable_set on disk](https://github.com/rust-lang/rust/pull/115740)
-- [#115252 Represent MIR composite debuginfo as projections instead of aggregates](https://github.com/rust-lang/rust/pull/115252)
-- [#115165 codegen_llvm: set `DW_AT_accessibility`](https://github.com/rust-lang/rust/pull/115165)
-- [#115082 Fix races conditions with `SyntaxContext` decoding](https://github.com/rust-lang/rust/pull/115082)
-- [#115025 Make subtyping explicit in MIR](https://github.com/rust-lang/rust/pull/115025)
-- [#114892 Remove conditional use of `Sharded` from query caches](https://github.com/rust-lang/rust/pull/114892)
-- [#114571 Improve `print_tts`](https://github.com/rust-lang/rust/pull/114571)
-
-#### Nags requiring follow up
-
-TODO: Nags
-
+* The two minor regressions to secondary benchmarks do not warrant spending time trying to tease apart this rollup, IMO.
+* marked as triaged