[llvm] [InstSimplify] Fold `getelementptr inbounds null, idx -> null` (PR #130742)

[Nikita Popov via llvm-commits]

nikic wrote:

> > > > If this is causing a lot of issues can we possibly revert it while the fixes make their way through review, and then re-merge it with the fixes?
> > > 
> > > 
> > > @efriedma-quic @nikic I am ok to just add a ubsan check in clang 21. Then we can reland this patch in llvm 22/23.
> > 
> > 
> > I'm probably missing something, but don't we already have a ubsan check for this for a long time? https://clang.godbolt.org/z/vGr7qYYjr
> 
> We have a check for pointer arithmetic, but not for member access.

Right, but are any of the problematic cases (beyond the ones we already catch directly in clang) related to member access?

https://github.com/llvm/llvm-project/pull/130742