Change:
I'll leave my story here because it shows how important the information can be: We recently upgraded from rustc 1.43 to 1.47 to build Firefox (we got stuck on 1.43 for a large number of complicated reasons, and would still be stuck if we hadn't found workarounds). Anyways, consequently, we've had a bunch of regressions, one of which was performance-related and I was bisecting it. The first thing I did was to compare each rust release, and it turned out the regression started between 1.44 and 1.45. So I went to the 1.45 release notes suspecting LLVM could have been involved and saw nothing there. Now, several hours later bisecting through nightlies (because PGO and LTO being involved, testing one version takes a while), the regression appears to have started between rustc 1.45.0-nightly ( 2020-05-21) and rustc 1.45.0-nightly ( 2020-05-20) So I take my git, type and lo and behold, there it is: I'm still waiting on the results actually confirming LLVM is involved (it likely is), but it would have saved me a lot of time if the LLVM upgrade had been mentioned (which it is for LLVM 11 in 1.47, BTW, but OTOH, now that I look, it appears the last upgrade mentioned is to LLVM 6 in 1.25...)
FWIW, the LLVM 11 upgrade in 1.47 got back a lot of the performance LLVM 10 lost:
Not for the testcase I'm bisecting, but that's OT.
I agree we should be mentioning this; thank you for noting it. I would be happy to accept a PR adding those in to the release notes (just 1.45 and 1.47, or more if you have the time).
Do you have an issue for that regression?
Will have when I have more information to feed into one.

Discussion:
- [Added the `tiny` value to the `code-model` codegen flag.][72397] - [Added tier 3 support* for the `mipsel-sony-psp` target.][72062] - [Added tier 3 support for the `thumbv7a-uwp-windows-msvc` target.][72133] <ins> - [Upgraded to LLVM 10.][67759] </ins> * Refer to Rust's [platform support page][forge-platform-support] for more information on Rust's tiered platform support.

[72062]: https://github.com/rust-lang/rust/pull/72062/ [72094]: https://github.com/rust-lang/rust/pull/72094/ [72133]: https://github.com/rust-lang/rust/pull/72133/ <ins> [67759]: https://github.com/rust-lang/rust/pull/67759/ </ins> [71900]: https://github.com/rust-lang/rust/pull/71900/ [71928]: https://github.com/rust-lang/rust/pull/71928/ [71662]: https://github.com/rust-lang/rust/pull/71662/

`armv7-unknown-linux-musleabi` targets.][63107] - [Added tier 3 support for the `hexagon-unknown-linux-musl` target.][62814] - [Added tier 3 support for the `riscv32i-unknown-none-elf` target.][62784] <ins> - [Upgraded to LLVM 9.][62592] </ins> * Refer to Rust's [platform support page][forge-platform-support] for more information on Rust's tiered platform support.

[62735]: https://github.com/rust-lang/rust/pull/62735/ [62766]: https://github.com/rust-lang/rust/pull/62766/ [62784]: https://github.com/rust-lang/rust/pull/62784/ <ins> [62592]: https://github.com/rust-lang/rust/pull/62592/ </ins> [62785]: https://github.com/rust-lang/rust/issues/62785/ [62814]: https://github.com/rust-lang/rust/pull/62814/ [62896]: https://github.com/rust-lang/rust/issues/62896/

-------- - [Added the `riscv32imc-unknown-none-elf` target.][53822] - [Added the `aarch64-unknown-netbsd` target][53165] <ins> - [Upgraded to LLVM 8.][53611] </ins> Libraries ---------

[53033]: https://github.com/rust-lang/rust/pull/53033/ [53044]: https://github.com/rust-lang/rust/pull/53044/ [53165]: https://github.com/rust-lang/rust/pull/53165/ <ins> [53611]: https://github.com/rust-lang/rust/pull/53611/ </ins> [53213]: https://github.com/rust-lang/rust/pull/53213/ [53236]: https://github.com/rust-lang/rust/pull/53236/ [53272]: https://github.com/rust-lang/rust/pull/53272/

- [Bumped minimum LLVM version to 5.0.][51899] - [Added `powerpc64le-unknown-linux-musl` target.][51619] - [Added `aarch64-unknown-hermit` and `x86_64-unknown-hermit` targets.][52861] <ins> - [Upgraded to LLVM 7.][51966] </ins> Libraries ---------

[53893]: https://github.com/rust-lang/rust/pull/53893/ [52861]: https://github.com/rust-lang/rust/pull/52861/ <ins> [51966]: https://github.com/rust-lang/rust/pull/51966/ </ins> [52656]: https://github.com/rust-lang/rust/pull/52656/ [52239]: https://github.com/rust-lang/rust/pull/52239/ [52330]: https://github.com/rust-lang/rust/pull/52330/