Loop Blocking for fn GPU Backend #1379

Job	Run time
perftests (gcc-8, release)	1m 35s
perftests (gcc-9, release)	1m 25s
perftests (gcc-10, release)	1m 36s
perftests (gcc-11, release)	1m 34s
perftests (gcc-12, debug)	2m 8s
perftests (gcc-12, release)	1m 38s
perftests (gcc-13, debug)	2m 1s
perftests (gcc-13, release)	1m 33s
perftests (clang-11, debug)	1m 56s
perftests (clang-11, release)	1m 54s
perftests (clang-12, debug)	1m 57s
perftests (clang-12, release)	1m 57s
perftests (clang-13, release)	2m 3s
perftests (clang-14, release)	2m 5s
perftests (clang-15, debug)	1m 52s
perftests (clang-15, release)	1m 55s
perftests (clang-16, debug)	1m 49s
perftests (clang-16, release)	1m 58s
perftests (clang-14-cuda-11, debug)	6m 12s
perftests (clang-14-cuda-11, release)	5m 15s
perftests (gcc-10-cuda-11.8, debug)	6m 6s
perftests (gcc-10-cuda-11.8, release)	5m 11s
perftests (gcc-11-cuda-12.0, debug)	5m 46s
perftests (gcc-11-cuda-12.0, release)	5m 7s
perftests (gcc-12-cuda-12.3, debug)	6m 21s
perftests (gcc-12-cuda-12.3, release)	5m 24s
perftests (gcc-12-cuda-12.4, debug)	5m 48s
perftests (gcc-12-cuda-12.4, release)	5m 9s
perftests (base-hip, debug)	7m 44s
perftests (base-hip, release)	6m 19s
perftests (gcc-10-hpx, release)	3m 27s
perftests (nvhpc-23.3, debug)	8m 49s
perftests (nvhpc-23.3, release)	11m 30s
perftests (nvhpc-23.9, debug)	12m 29s
perftests (nvhpc-23.9, release)	10m 38s
	2h 30m 11s

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