Add notes for compiler team triage meeting on 2019-12-12

content/minutes/triage-meeting/2019-12-12.md

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+---
+title: 2019.12.12
+type: docs
+---
+
+# 2019-12-12
+
+## Announcements
+
+- [@pnkfelix] posted an RFC about future-incompat lints [RFC 2834]
+
+- [@eddyb] landed some additional caching for trait selection which gives some nice speedups [#66821]
+
+- Const eval now has support for `if`/`match` and a PR for `loop`/`while` is open.
+
+- [@eddyb] is resurrecting their SROA MIR optimization [#48300]
+
+## Backport nominations
+
+- resolve: Always resolve visibilities on impl items [#67236]
+  - Approved for beta backport
+
+- resolve: Resolve visibilities on fields with non-builtin attributes [#67106]
+  - Approved for beta backport
+
+## Working group sync
+
+### [wg-meta]
+
+- Work has generally slowed down since the launch of the ICE breakers group.
+
+- Some planning for a new "reducer" group has begun.
+
+### [wg-mir-opt]
+
+- MIR does not know about static items anymore.
+Instead we just have a constant whose value is `&YOUR_STATIC`, `&raw mut YOUR_MUT_STATIC` or `&raw YOUR_EXTERN_STATIC`.
+This simplifies a lot of logic in the MIR and will (together with the next bullet point) allow `PlaceBase` to just be a `Local` (so a u32 index for a local to be accessed). [#66587]
+
+- [@spastorino] is about to finish a PR that removes promoteds from the list of things that are `Place`s in MIR
+
+- `mir::Body` does not contain interior mutability components anymore.
+It used to have a cache of some information on the MIR CFG that could get cleared and reinitialized as required.
+This is abstracted away in the `BodyCache` type.
+
+- Promoteds inside constants and statics are now actually separated from their constant's `mir::Body` instead of having a scheme around removing `StorageDead` statements [#66642]
+
+- Cross crate inlining now preserves debug info [#66789]
+
+- There is a new MIR optimization eliminating basic blocks that are unreachable because they are match arms of uninhabited variants [#65694]
+
+- There is a new MIR optimization to work around the problem that LLVM can't figure out trivial match arms like `Ok(x) => Ok(x)` [#66282]
+
+- The const prop optimization now runs on all builds (even debug builds) because this gives quite some nice build time improvements [#66074]
+
+- We had a mir-opt room at RustFest, which was a total success and people loved it.
+
+[@eddyb]: https://github.com/eddyb
+[@pnkfelix]: https://github.com/pnkfelix
+[@spastorino]: https://github.com/spastorino
+[#48300]: https://github.com/rust-lang/rust/pull/48300
+[#65694]: https://github.com/rust-lang/rust/pull/65694
+[#66074]: https://github.com/rust-lang/rust/pull/66074
+[#66282]: https://github.com/rust-lang/rust/pull/66282
+[#66587]: https://github.com/rust-lang/rust/pull/66587
+[#66642]: https://github.com/rust-lang/rust/pull/66642
+[#66789]: https://github.com/rust-lang/rust/pull/66789
+[#66821]: https://github.com/rust-lang/rust/pull/66821
+[#67106]: https://github.com/rust-lang/rust/pull/67106
+[#67236]: https://github.com/rust-lang/rust/pull/67236
+[RFC 2834]: https://github.com/rust-lang/rfcs/pull/2834
+[wg-meta]: https://rust-lang.github.io/compiler-team/working-groups/meta/
+[wg-mir-opt]: https://rust-lang.github.io/compiler-team/working-groups/mir-opt/