[llvm] [Attributor] Support nested conditional branches (PR #168532)

[Cullen Rhodes via llvm-commits]

c-rhodes wrote:

> Hey, I started seeing some unexpected crashes with the flang runtime on AMD GPUs last week and through binary search landed on this patch. It looks like a branch is being taken when it should not (#170211), and the problem seems to go away when I revert this patch.
> 
> But I'm not familiar with attributor at all and don't really know what this patch does. Does it make sense that this could be the source of this problem?

thanks for reporting, it could now be incorrectly inferring an attribute like `nonnull` perhaps. I'll revert for now whilst I look into it.

https://github.com/llvm/llvm-project/pull/168532