[llvm] [CodeGen][CodeLayout] Fix segfault on access to deleted block in MBP. (PR #142357)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > Missing test
> 
> > We have caught the bug on the custom out-of-tree backend in a ~200Kb function of ~70 basic blocks with several loops, switch instructions etc.. Any attempt to reduce the test case results in bug disappearing.
> > I'm afraid, I'm not able to provide the reproducer / regression test for any in-tree backend in a reasonable time.
> 
> If test is a mandatory requirement for this PR, it is ok for me to reject PR.

Did you try llvm-reduce on it? 

https://github.com/llvm/llvm-project/pull/142357