Adjust wording for forward progress guarantees

Author: Mark-Simulacrum

posts/2021-05-06-Rust-1.52.0.md

@@ -27,7 +27,14 @@ from the appropriate page on our website, and check out the
 
 This release is fairly small, primarily containing stabilizations of various APIs in the standard library.
 
-This release also closes out a long-standing bug in the Rust compiler: forward progress is no longer assumed by LLVM, which means that some programs which used to compile incorrectly are now properly handled. This is due to changes in LLVM IR semantics, which no longer assume forward progress is guaranteed and optimize for that.
+This release also closes out a long-standing [bug] in the Rust compiler. Previously, LLVM assumed that the program would make progress, and used this to optimize. This meant that certain constructs in safe Rust were removed or otherwise miscompiled, such as infinite loops (`loop {}`) or recursion which didn't terminate.
+
+In Rust 1.49.0, we landed a [partial fix] to this bug specifically targeting
+`loop {}`, but this fix brings an LLVM upgrade which avoids needing workarounds
+for these cases, fixing the larger class of bug.
+
+[bug]: https://github.com/rust-lang/rust/issues/28728
+[partial fix]: https://github.com/rust-lang/rust/pull/77972
 
 ### Stabilized APIs
 
@@ -86,4 +93,4 @@ There are other changes in the Rust 1.52.0 release: check out what changed in [R
 
 ### Contributors to 1.52.0
 
-Many people came together to create Rust 1.52.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.52.0/)
+Many people came together to create Rust 1.52.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.52.0/)