[llvm] [GlobalOpt] Do not fold away addrspacecasts which may be runtime operations (PR #153753)

[Nikita Popov via llvm-commits]

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nikic wrote:

Also please update the test so it shows an actually incorrect transform without your patch. The current test just removes all instructions, which is a legal thing to do.

https://github.com/llvm/llvm-project/pull/153753