All the statements starting with OACC_ represent directives and
clauses used by the OpenACC API http://www.openacc.org/.
     
OACC_CACHE#pragma acc cache (var ...).
     OACC_DATA#pragma acc data [clause1 ... clauseN].
     OACC_DECLARE#pragma acc declare [clause1 ... clauseN].
     OACC_ENTER_DATA#pragma acc enter data [clause1 ... clauseN].
     OACC_EXIT_DATA#pragma acc exit data [clause1 ... clauseN].
     OACC_HOST_DATA#pragma acc host_data [clause1 ... clauseN].
     OACC_KERNELS#pragma acc kernels [clause1 ... clauseN].
     OACC_LOOP#pragma acc loop [clause1 ... clauseN].
     See the description of the OMP_FOR code.
     
OACC_PARALLEL#pragma acc parallel [clause1 ... clauseN].
     OACC_UPDATE#pragma acc update [clause1 ... clauseN].