[CodeGen] TailDuplicator should remove PHI when single predecessor block remains #158533
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If tail block has only single predecessor after tail duplication,
TailDuplicatorsaves PHI instructions with single block input.MIR after
TailDuplicatorlooks like:Fix proposal is to replace PHI instruction with single input by COPY instruction.
Similar to #158265, bug appears only in the scenario of pre-ra partial tail duplication and does not affect in-tree backends.