displs in struct ucg_collective should be outside of union, but triggers assert

[csehydrogen]

xucg/api/ucg.h

Lines 326 to 333 in 9aa43b4

	union {
	/* only in "send" (see @ref UCG_PARAM_TYPE ) */
	ucg_collective_type_t type; /**< type and root of the collective */
	/* only in "recv" (see @ref UCG_PARAM_OP , @ref UCG_PARAM_DISPLS ) */
	void *op; /**< external reduce operation handle */
	const int *displs; /**< item displacement array */
	};

The comment says that displs is only used in "recv". However, collective communications, such as scatterv, alltoallw, and neighbor_alltoallw defined in ucg_mpi.h, require both type and displs fields.

Simple solution would be putting displs outside of union:

union {
ucg_collective_type_t type;
void *op;
};
const int *displs;

which unfortunately triggers assert

ucg_group.c: UCS_STATIC_ASSERT(sizeof(ucg_collective_params_t) == UCS_SYS_CACHE_LINE_SIZE)

due to struct size change.

Any suggestion?