// Returns a failure if a cycle prevents the merge from happening correctly
// without breaking dominance. The IR is left in invalid state in case of
// failure.
void CollectCandidateIslands(
    llvm::function_ref<bool(llvm::StringRef, Operation*)>
        is_op_calling_func_for_cluster,
    Operation* op, StringRef cluster_name,
    SmallPtrSet<Operation*, 16>& islands_set,