Update posts/2021-07-29-Rust-1.54.0.md

Co-authored-by: Esteban Kuber <estebank@users.noreply.github.com>

Author: Mark-Simulacrum

posts/2021-07-29-Rust-1.54.0.md

@@ -52,10 +52,26 @@ Notably, unlike the previously stabilized `x86` and `x86_64` intrinsics, these d
 
 This means that we can expose some of the intrinsics as entirely safe functions, for example [`v128_bitselect`](https://doc.rust-lang.org/beta/core/arch/wasm32/fn.v128_bitselect.html). However, there are still some intrinsics which are unsafe because they use raw pointers, such as [`v128_load`](https://doc.rust-lang.org/beta/core/arch/wasm32/fn.v128_load.html).
 
-### Incremental Compilation is XXX by default
+### Incremental Compilation is re-enabled by default
 
-TODO - Wesley is going to draft text here.
+Incremental compilation has been re-enabled by default in this release, after it being disabled by default in 1.52.
 
+In Rust 1.52, additional validation was added when loading incremental compilation data from the on-disk cache.
+This resulted in a number of pre-existing potential soundness issues being uncovered as the validation changed these silent bugs into internal compiler errors (ICEs).
+In response, the Compiler Team decided to disable incremental compilation in the 1.52.1 patch, allowing users to avoid encountering the ICEs and the underlying unsoundness, at the expense of longer compile times. [^1]
+
+Since then, we've conducted a [series of retrospectives][retros] and contributors have been hard at work resolving the reported issues, with some fixes landing in 1.53 and the majority landing in this release. [^2]
+
+There are currently still two known issues which can result in an ICE.
+Due to the lack of automated crash reporting, we can't be certain of the full extent of impact of the outstanding issues. However, based on the feedback we received from users affected by the 1.52 release, we believe these issues to be rare.
+
+Therefore, incremental compilation has been re-enabled in this release!
+
+[^1]: The [1.52.1 release notes] contain a more detailed description of these events.
+[^2]: The tracking issue for the issues is [#84970].
+[#84970]: https://github.com/rust-lang/rust/issues/84970
+[1.52.1 release notes]: https://blog.rust-lang.org/2021/05/10/Rust-1.52.1.html
+[retros]: https://github.com/rust-lang/compiler-team/issues/435
 ### Stabilized APIs
 
 The following methods and trait implementations were stabilized.