https://github.com/pcc created https://github.com/llvm/llvm-project/pull/99260
We can use UMAXV.4S to reduce the comparison result in a single
instruction. This improves performance by roughly 4% on Apple M1:
Summary
bin/libc.src.string.bcmp_benchmark3 --study-name="new bcmp" --sweep-mode
--sweep-max-size=128 --output=/dev/null --num-trials=10 ran
1.01 ± 0.02 times faster than bin/libc.src.string.bcmp_benchmark3
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.01 ± 0.03 times faster than bin/libc.src.string.bcmp_benchmark3
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.01 ± 0.03 times faster than bin/libc.src.string.bcmp_benchmark3
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.01 ± 0.02 times faster than bin/libc.src.string.bcmp_benchmark2
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.02 ± 0.03 times faster than bin/libc.src.string.bcmp_benchmark2
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.03 ± 0.03 times faster than bin/libc.src.string.bcmp_benchmark2
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.03 ± 0.03 times faster than bin/libc.src.string.bcmp_benchmark2
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.05 ± 0.02 times faster than bin/libc.src.string.bcmp_benchmark1
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.05 ± 0.02 times faster than bin/libc.src.string.bcmp_benchmark1
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.05 ± 0.03 times faster than bin/libc.src.string.bcmp_benchmark1
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
1.05 ± 0.02 times faster than bin/libc.src.string.bcmp_benchmark1
--study-name="new bcmp" --sweep-mode --sweep-max-size=128 --output=/dev/null
--num-trials=10
(1 = original, 2 = a variant of this patch that uses UMAXV.16B, 3 = this patch)
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