SME: incorrect DCE for LUTI operations

[aemerson]

See https://godbolt.org/z/KfzKqjs8e

It looks like as we select one of the LUTIs we end up somehow causing a sequence of incorrect DCEs.

[aemerson]

@sdesmalen-arm @davemgreen @MacDue

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: Amara Emerson (aemerson)

See https://godbolt.org/z/KfzKqjs8e

It looks like as we select one of the LUTIs we end up somehow causing a sequence of incorrect DCEs.