[String] Fix corner case in comparison fast-path. #20937
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When in a post-binary-prefix-scan fast-path, we need to make sure we are comparing a full-segment scalar, otherwise we miss situations where a combining end-of-segment scalar would be reordered with a prior combining scalar in the same segment under normalization in one string but not the other. This was hidden by the fact that many combining scalars are not NFC_QC=maybe, but those which are not present in any precomposed form have NFC_QC=yes. Added tests.
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This regresses performance of some code that hits this fast-path, but I have improvements coming soon that compensates for this fact. |
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@swift-ci please benchmark |
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@swift-ci please test |
Build comment file:Performance: -O
Performance: -Osize
Performance: -Onone
How to read the dataThe tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.If you see any unexpected regressions, you should consider fixing the Noise: Sometimes the performance results (not code size!) contain false Hardware Overview |
milseman
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When in a post-binary-prefix-scan fast-path, we need to make sure we are comparing a full-segment scalar, otherwise we miss situations where a combining end-of-segment scalar would be reordered with a prior combining scalar in the same segment under normalization in one string but not the other. This was hidden by the fact that many combining scalars are not NFC_QC=maybe, but those which are not present in any precomposed form have NFC_QC=yes. Added tests.
airspeedswift
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Dec 5, 2018
* [String] Fix corner case in comparison fast-path. (#20937) When in a post-binary-prefix-scan fast-path, we need to make sure we are comparing a full-segment scalar, otherwise we miss situations where a combining end-of-segment scalar would be reordered with a prior combining scalar in the same segment under normalization in one string but not the other. This was hidden by the fact that many combining scalars are not NFC_QC=maybe, but those which are not present in any precomposed form have NFC_QC=yes. Added tests. * [String] Normalization-boundary-before UTF-8 fast path. All latiny (<0x300) scalars have normalization boundaries before them, so when asking if memory containing a scalar encoded in valid UTF-8 has a boundary before it, check if the leading byte definitely encodes a scalar less than 0x300. * [String] Refactor and fast-path normalization Refactor some normalization queries into StringNormalization.swift, and add more latiny (<0x300) fast-paths. * [String] Speed up constant factors on comparison. Include some tuning and tweaking to reduce the constant factors involved in string comparison. This yields considerable improvement on our micro-benchmarks, and allows us to make less inlinable code and have a smaller ABI surface area. Adds more extensive testing of corner cases in our existing fast-paths. * [String] Hand-increment loop variable for perf. Hand-incrementing the loop variable allows us to skip overflow detection, and will permit more vectorization improvements in the future. For now, it gives us perf improvements in nano-benchmarks.
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When in a post-binary-prefix-scan fast-path, we need to make sure we
are comparing a full-segment scalar, otherwise we miss situations
where a combining end-of-segment scalar would be reordered with a
prior combining scalar in the same segment under normalization in one
string but not the other.
This was hidden by the fact that many combining scalars are
NFC_QC=maybe, but those which are not present in any precomposed form
have NFC_QC=yes. Added tests.