compiler: Simplify fission #776

Job	Run time
pytest-mpi (3.10)	44m 54s
pytest-mpi (pytest-mpi-docker-icx)	32m 48s
pytest-mpi (pytest-mpi-docker-gcc-arm)	19m 28s
pytest-mpi (pytest-mpi-docker-gcc)	30m 6s
pytest-mpi (3.11)	46m 23s
	2h 53m 39s

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