fd2e1e743a
The benchmarks added in this change revealed that ValidString runs ~17% faster than Valid([]byte) on the ASCII prefix of the input. Inspection of the assembly revealed that the code generated for p[8:] required recomputing the slice capacity to handle the cap=0 special case, which added an ADD -8 instruction. By making len=cap, the capacity becomes a common subexpression with the length, saving the ADD instruction. (Thanks to khr for the tip.) Incidentally, I tried a number of other optimizations but was unable to make consistent gains across all benchmarks. The most promising was to retain the bitmask of non-ASCII bytes from the fast loop; the slow loop would shift it, and when it becomes zero, return to the fast loop. This made the MostlyASCII benchmark 4x faster, but made the other cases slower by up to 10%. cpu: Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz benchmark old ns/op new ns/op delta BenchmarkValidTenASCIIChars-16 4.09 4.06 -0.85% BenchmarkValid100KASCIIChars-16 9325 7747 -16.92% BenchmarkValidTenJapaneseChars-16 27.0 27.2 +0.85% BenchmarkValidLongMostlyASCII-16 57277 58361 +1.89% BenchmarkValidLongJapanese-16 94002 93131 -0.93% BenchmarkValidStringTenASCIIChars-16 4.15 4.07 -1.74% BenchmarkValidString100KASCIIChars-16 7980 8019 +0.49% BenchmarkValidStringTenJapaneseChars-16 26.0 25.9 -0.38% BenchmarkValidStringLongMostlyASCII-16 58550 58006 -0.93% BenchmarkValidStringLongJapanese-16 97964 100038 +2.12% Change-Id: Ic9d585dedd9af83c27dd791ecd805150ac949f15 Reviewed-on: https://go-review.googlesource.com/c/go/+/375594 Reviewed-by: Keith Randall <khr@golang.org> Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gopher Robot <gobot@golang.org> Trust: Alex Rakoczy <alex@golang.org>
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