This reverts commit16bd10a387. Re-applies:b3c55b7071- "[SelectionDAG] Handle more opcodes in canCreateUndefOrPoison (#84921)"8e2f6495c0- "[DAGCombiner] Do not always fold FREEZE over BUILD_VECTOR (#85932)"73472c5996- "[SelectionDAG] Treat CopyFromReg as freezing the value (#85932)" with a fix in DAGCombiner::visitFREEZE.