[clang] [Clang] Add release note for pointer overflow optimization change (PR #122462)

[Nikita Popov via cfe-commits]

================
@@ -58,6 +58,26 @@ code bases.
   containing strict-aliasing violations. The new default behavior can be
   disabled using ``-fno-pointer-tbaa``.
 
+- Clang will now more aggressively use undefined behavior on pointer addition
----------------
nikic wrote:

I think it's hard to add an example that is small and simple enough for a release note. After all, the distinguishing feature between a desirable and an undesirable optimization in this context is just how many layers of abstraction there are. (This is Schrödinger's programmer: Doesn't want the compiler to optimize trivial cases because its "obviously wrong". Does want it to optimize complex cases.)

E.g. one of the motivating cases I have lying around is https://godbolt.org/z/3Y5bTxzqq, and that is both too large for a release note and too reduced to be really meaningful :)

https://github.com/llvm/llvm-project/pull/122462