[llvm-branch-commits] [clang] release/22.x: [Clang][Coroutines] Don't emit fake uses for coroutine parameters (#194690) (PR #195869)

[Stephen Tozer via llvm-branch-commits]

SLTozer wrote:

> Is this a regression? If so, when was it introduced?

This would be a regression from Clang 20 and Clang 21 - in Clang 20, the `-fextend-variable-liveness` flag was added, which triggers the issue when enabled. in Clang 21, this flag was turned on by default at `-Og`. The issue is quite pervasive in that it will always trigger when we enable the `-fextend-variable-liveness` flag and have coroutines with at least one parameter (other than `this`), but the heap use-after-free occurs immediately after the free and the value is unused, so it is probably rare for it to actually cause a problem in practice without ASan enabled, which is why it wasn't reported until recently.

https://github.com/llvm/llvm-project/pull/195869