Add triage 2021-05-25

triage/2021-05-25.md

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+# 2021-05-25 Triage Log
+
+A somewhat quiet week. Some PRs had performance runs performed on them, but the changes were merged despite this. Also, we still have issues with certain benchmarks being noisy. 
+
+Triage done by **@rylev**.
+Revision range: [25a277f03df7e44643ddfcc240d034409cb2f505..cdbe2888979bb8797b05f0d58a6f6e60753983d2](https://perf.rust-lang.org/?start=25a277f03df7e44643ddfcc240d034409cb2f505&end=cdbe2888979bb8797b05f0d58a6f6e60753983d2&absolute=false&stat=instructions%3Au)
+
+2 Regressions, 2 Improvements, 1 Mixed
+0 of them in rollups
+
+#### Regressions
+
+Make building THIR a stealable query [#85273](https://github.com/rust-lang/rust/issues/85273)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=126561cb31e8ebe1e2dd9dfd0d3ca621308dc56f&end=d568d63b1f9f5fc47e4202e2a2a84142ff6202d8&stat=instructions:u) (up to 3.7% on `incr-full` builds of `tuple-stress-check`)
+- Work needed for other work to land. A performance run was performed, but still the change was allowed to land. I've asked [why](https://github.com/rust-lang/rust/pull/85273#issuecomment-848017988).
+
+Implement the new desugaring from `try_trait_v2` [#84767](https://github.com/rust-lang/rust/issues/84767)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=491cf5561efb1f5ff33c3234ccd0bc5cacbebe3e&end=4e3e6db011c5b482d2bef8ba02274657f93b5e0d&stat=instructions:u) (up to 2.9% on `full` builds of `cranelift-codegen-check`)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=491cf5561efb1f5ff33c3234ccd0bc5cacbebe3e&end=4e3e6db011c5b482d2bef8ba02274657f93b5e0d&stat=instructions:u) (up to -1.8% on `full` builds of `deeply-nested-async-check`)
+- A much larger performance hit than when the performance suite was run while the pull request was open. This is largely a performance regression with only one non-volatile benchmark showing improvement. 
+- Biggest change seems to be in the `mir_built` query which seems to make sense given that probably more mir will be produced by this change.
+- Follow-up happening [here](https://github.com/rust-lang/rust/pull/84767#issuecomment-848036325).
+
+#### Improvements
+
+fix deallocation of immutable allocations [#85599](https://github.com/rust-lang/rust/issues/85599)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=6e92fb409816c65cd0a78a1fbcc71e2fbabdf50a&end=0f8cd43ee8c3614e04b5c624dd8a45758d7023da&stat=instructions:u) (up to -1.9% on `full` builds of `deeply-nested-async-check`)
+
+std: Attempt again to inline thread-local-init across crates [#84876](https://github.com/rust-lang/rust/issues/84876)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=3e827cc21e0734edd26170e8d1481f0d66a1426b&end=3bcaeb0bf9e1c29d18abc32928fd2f23d1bed0bd&stat=instructions:u) (up to -1.8% on `incr-full` builds of `externs-debug`)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=3e827cc21e0734edd26170e8d1481f0d66a1426b&end=3bcaeb0bf9e1c29d18abc32928fd2f23d1bed0bd&stat=instructions:u) (up to 1.3% on `full` builds of `regex-opt`)
+
+#### Mixed
+
+Avoid zero-length memcpy in formatting [#85391](https://github.com/rust-lang/rust/issues/85391)
+- Moderate regression in [instruction counts](https://perf.rust-lang.org/compare.html?start=df70463ea5d701489d6f53dc780a2c16294d6143&end=a426fc37f2269093ef1a4dbb3e31b3247980fccc&stat=instructions:u) (up to 3.8% on `incr-patched: println` builds of `cargo-opt`)
+- Moderate improvement in [instruction counts](https://perf.rust-lang.org/compare.html?start=df70463ea5d701489d6f53dc780a2c16294d6143&end=a426fc37f2269093ef1a4dbb3e31b3247980fccc&stat=instructions:u) (up to -1.8% on `full` builds of `deeply-nested-async-debug`)
+- This seems to have some interactions with LLVM codegen that cause certain benchmarks to fluctuate in performance. These largely cancel each other out.
+
+#### Nags requiring follow up
+
+- Follow-up:
+    [#84767](https://github.com/rust-lang/rust/pull/84767#issuecomment-848036325).
+
+