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

[Afanasyev Ivan via llvm-commits]

ivafanas wrote:

> Missing test

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> 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.

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If test is a mandatory requirement for this PR, it is ok for me to reject PR.

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