Optimized memcmp
This is an optimized memcmp for AArch64. This is a complete rewrite
using a different algorithm. The previous version split into cases
where both inputs were aligned, the inputs were mutually aligned and
unaligned using a byte loop. The new version combines all these cases,
while small inputs of less than 8 bytes are handled separately.
This allows the main code to be sped up using unaligned loads since
there are now at least 8 bytes to be compared. After the first 8 bytes,
align the first input. This ensures each iteration does at most one
unaligned access and mutually aligned inputs behave as aligned.
After the main loop, process the last 8 bytes using unaligned accesses.
This improves performance of (mutually) aligned cases by 25% and
unaligned by >500% (yes >6 times faster) on large inputs.
ChangeLog:
2017-06-28 Wilco Dijkstra <wdijkstr@arm.com>
* newlib/libc/machine/aarch64/memcmp.S (memcmp):
Rewrite of optimized memcmp.
GLIBC benchtests/bench-memcmp.c performance comparison for Cortex-A53:
Length 1, alignment 1/ 1: 153%
Length 1, alignment 1/ 1: 119%
Length 1, alignment 1/ 1: 154%
Length 2, alignment 2/ 2: 121%
Length 2, alignment 2/ 2: 140%
Length 2, alignment 2/ 2: 121%
Length 3, alignment 3/ 3: 105%
Length 3, alignment 3/ 3: 105%
Length 3, alignment 3/ 3: 105%
Length 4, alignment 4/ 4: 155%
Length 4, alignment 4/ 4: 154%
Length 4, alignment 4/ 4: 161%
Length 5, alignment 5/ 5: 173%
Length 5, alignment 5/ 5: 173%
Length 5, alignment 5/ 5: 173%
Length 6, alignment 6/ 6: 145%
Length 6, alignment 6/ 6: 145%
Length 6, alignment 6/ 6: 145%
Length 7, alignment 7/ 7: 125%
Length 7, alignment 7/ 7: 125%
Length 7, alignment 7/ 7: 125%
Length 8, alignment 8/ 8: 111%
Length 8, alignment 8/ 8: 130%
Length 8, alignment 8/ 8: 124%
Length 9, alignment 9/ 9: 160%
Length 9, alignment 9/ 9: 160%
Length 9, alignment 9/ 9: 150%
Length 10, alignment 10/10: 170%
Length 10, alignment 10/10: 137%
Length 10, alignment 10/10: 150%
Length 11, alignment 11/11: 160%
Length 11, alignment 11/11: 160%
Length 11, alignment 11/11: 160%
Length 12, alignment 12/12: 146%
Length 12, alignment 12/12: 168%
Length 12, alignment 12/12: 156%
Length 13, alignment 13/13: 167%
Length 13, alignment 13/13: 167%
Length 13, alignment 13/13: 173%
Length 14, alignment 14/14: 167%
Length 14, alignment 14/14: 168%
Length 14, alignment 14/14: 168%
Length 15, alignment 15/15: 168%
Length 15, alignment 15/15: 173%
Length 15, alignment 15/15: 173%
Length 1, alignment 0/ 0: 134%
Length 1, alignment 0/ 0: 127%
Length 1, alignment 0/ 0: 119%
Length 2, alignment 0/ 0: 94%
Length 2, alignment 0/ 0: 94%
Length 2, alignment 0/ 0: 106%
Length 3, alignment 0/ 0: 82%
Length 3, alignment 0/ 0: 87%
Length 3, alignment 0/ 0: 82%
Length 4, alignment 0/ 0: 115%
Length 4, alignment 0/ 0: 115%
Length 4, alignment 0/ 0: 122%
Length 5, alignment 0/ 0: 127%
Length 5, alignment 0/ 0: 119%
Length 5, alignment 0/ 0: 127%
Length 6, alignment 0/ 0: 103%
Length 6, alignment 0/ 0: 100%
Length 6, alignment 0/ 0: 100%
Length 7, alignment 0/ 0: 82%
Length 7, alignment 0/ 0: 91%
Length 7, alignment 0/ 0: 87%
Length 8, alignment 0/ 0: 111%
Length 8, alignment 0/ 0: 124%
Length 8, alignment 0/ 0: 124%
Length 9, alignment 0/ 0: 136%
Length 9, alignment 0/ 0: 136%
Length 9, alignment 0/ 0: 136%
Length 10, alignment 0/ 0: 136%
Length 10, alignment 0/ 0: 135%
Length 10, alignment 0/ 0: 136%
Length 11, alignment 0/ 0: 136%
Length 11, alignment 0/ 0: 136%
Length 11, alignment 0/ 0: 135%
Length 12, alignment 0/ 0: 136%
Length 12, alignment 0/ 0: 136%
Length 12, alignment 0/ 0: 136%
Length 13, alignment 0/ 0: 135%
Length 13, alignment 0/ 0: 136%
Length 13, alignment 0/ 0: 136%
Length 14, alignment 0/ 0: 136%
Length 14, alignment 0/ 0: 136%
Length 14, alignment 0/ 0: 136%
Length 15, alignment 0/ 0: 136%
Length 15, alignment 0/ 0: 136%
Length 15, alignment 0/ 0: 136%
Length 4, alignment 0/ 0: 115%
Length 4, alignment 0/ 0: 115%
Length 4, alignment 0/ 0: 115%
Length 32, alignment 0/ 0: 127%
Length 32, alignment 7/ 2: 395%
Length 32, alignment 0/ 0: 127%
Length 32, alignment 0/ 0: 127%
Length 8, alignment 0/ 0: 111%
Length 8, alignment 0/ 0: 124%
Length 8, alignment 0/ 0: 124%
Length 64, alignment 0/ 0: 128%
Length 64, alignment 6/ 4: 475%
Length 64, alignment 0/ 0: 131%
Length 64, alignment 0/ 0: 134%
Length 16, alignment 0/ 0: 128%
Length 16, alignment 0/ 0: 119%
Length 16, alignment 0/ 0: 128%
Length 128, alignment 0/ 0: 129%
Length 128, alignment 5/ 6: 475%
Length 128, alignment 0/ 0: 130%
Length 128, alignment 0/ 0: 129%
Length 32, alignment 0/ 0: 126%
Length 32, alignment 0/ 0: 126%
Length 32, alignment 0/ 0: 126%
Length 256, alignment 0/ 0: 127%
Length 256, alignment 4/ 8: 545%
Length 256, alignment 0/ 0: 126%
Length 256, alignment 0/ 0: 128%
Length 64, alignment 0/ 0: 171%
Length 64, alignment 0/ 0: 171%
Length 64, alignment 0/ 0: 174%
Length 512, alignment 0/ 0: 126%
Length 512, alignment 3/10: 585%
Length 512, alignment 0/ 0: 126%
Length 512, alignment 0/ 0: 127%
Length 128, alignment 0/ 0: 129%
Length 128, alignment 0/ 0: 128%
Length 128, alignment 0/ 0: 129%
Length 1024, alignment 0/ 0: 125%
Length 1024, alignment 2/12: 611%
Length 1024, alignment 0/ 0: 126%
Length 1024, alignment 0/ 0: 126%
Length 256, alignment 0/ 0: 128%
Length 256, alignment 0/ 0: 127%
Length 256, alignment 0/ 0: 128%
Length 2048, alignment 0/ 0: 125%
Length 2048, alignment 1/14: 625%
Length 2048, alignment 0/ 0: 125%
Length 2048, alignment 0/ 0: 125%
Length 512, alignment 0/ 0: 126%
Length 512, alignment 0/ 0: 127%
Length 512, alignment 0/ 0: 127%
Length 4096, alignment 0/ 0: 125%
Length 4096, alignment 0/16: 125%
Length 4096, alignment 0/ 0: 125%
Length 4096, alignment 0/ 0: 125%
Length 1024, alignment 0/ 0: 126%
Length 1024, alignment 0/ 0: 126%
Length 1024, alignment 0/ 0: 126%
Length 8192, alignment 0/ 0: 125%
Length 8192, alignment 63/18: 636%
Length 8192, alignment 0/ 0: 125%
Length 8192, alignment 0/ 0: 125%
Length 16, alignment 1/ 2: 317%
Length 16, alignment 1/ 2: 317%
Length 16, alignment 1/ 2: 317%
Length 32, alignment 2/ 4: 395%
Length 32, alignment 2/ 4: 395%
Length 32, alignment 2/ 4: 398%
Length 64, alignment 3/ 6: 475%
Length 64, alignment 3/ 6: 475%
Length 64, alignment 3/ 6: 477%
Length 128, alignment 4/ 8: 479%
Length 128, alignment 4/ 8: 479%
Length 128, alignment 4/ 8: 479%
Length 256, alignment 5/10: 543%
Length 256, alignment 5/10: 539%
Length 256, alignment 5/10: 543%
Length 512, alignment 6/12: 585%
Length 512, alignment 6/12: 585%
Length 512, alignment 6/12: 585%
Length 1024, alignment 7/14: 611%
Length 1024, alignment 7/14: 611%
Length 1024, alignment 7/14: 611%
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