— GIMPLE function: gimple gimple_build_omp_single (gimple_seq body, tree clauses)

构建一个GIMPLE_OMP_SINGLE语句。BODY为只被执行一次的语句序列。CLAUSES为任何OMP单结构的从句：private, firstprivate, copyprivate, nowait。

— GIMPLE function: tree gimple_omp_single_clauses (gimple g)

返回OMP_SINGLE G关联的从句。

— GIMPLE function: tree *gimple_omp_single_clauses_ptr (gimple g)

返回一个指针，指向OMP_SINGLE G关联的从句。

— GIMPLE function: void gimple_omp_single_set_clauses (gimple g, tree clauses)

将CLAUSES设置为OMP_SINGLE G关联的从句。