[llvm] [IndVarSimplify] Allow predicateLoopExit on some loops with local writes (PR #155901)

[Florian Mayer via llvm-commits]

fmayer wrote:

PTAL. I changed it to use `inaccessiblemem`. I also generalized it to include non-alloca writes, because what really matters is that it is not observable in another thread. I made sure that the trap handler cannot read any values.

https://github.com/llvm/llvm-project/pull/155901