[FlattenCFG] Fixup Phi nodes during CFG flattening#143766

HighW4y2H3ll wants to merge 4 commits intollvm:mainllvm/llvm-project:mainfrom

HighW4y2H3ll:fix_cfg_flattenHighW4y2H3ll/llvm-project:fix_cfg_flattenCopy head branch name to clipboard