[llvm] [MachineVerifier] Fix LiveInterval verification of unwinding instructions (PR #131565)

[Reid Kleckner via llvm-commits]

rnk wrote:

Well, this verifier check *should* fire on an analogous, non-wasm test case, where a virtual register is defined after a potentially throwing call in an Itanium landingpad predecessor. In such a case, the value will be computed and the register value defined after the call, but if the call throws and we try to read the value from a landingpad, bad things will happen.

Our MIR representation is somewhat deficient because we don't have an equivalent of the LLVM IR `invoke` instruction, and this verifier check is making sure that CodeGen passes don't try to insert PHI-elimination code (and eventually possibly register fills) between the call, the terminating jump, and the landingpad.

I agree we need to relax the check for wasm and Windows asynch EH, because, as your test case points out, we no longer have the invariant that all landingpad predecessor blocks end in a potentially throwing call. They may end in seh.try.end (non-call label) or CLEANUPRET or some other runtime-mediated control transfer instruction.

https://github.com/llvm/llvm-project/pull/131565