This PR fixes incorrect LCSSA PHI node generation when splitting critical edges with both `PreserveLCSSA` and `MergeIdenticalEdges` enabled. The bug caused PHI nodes in the split block to miss predecessors when multiple identical edges were merged.
This PR fixes incorrect LCSSA PHI node generation when splitting critical edges with both `PreserveLCSSA` and `MergeIdenticalEdges` enabled. The bug caused PHI nodes in the split block to miss predecessors when multiple identical edges were merged.