> I'm requesting comments and, hopefully, some help with this patch to replace > `StringCoding.hasNegatives` with `countPositives`. The new method does a very > similar pass, but alters the intrinsic to return the number of leading bytes > in the `byte[]` range which only has positive bytes. This allows for dealing > much more efficiently with those `byte[]`s that has a ASCII prefix, with no > measurable cost on ASCII-only or latin1/UTF16-mostly input. > > Microbenchmark results: > https://jmh.morethan.io/?gists=428b487e92e3e47ccb7f169501600a88,3c585de7435506d3a3bdb32160fe8904 > > - Only implemented on x86 for now, but I want to verify that implementations > of `countPositives` can be implemented with similar efficiency on all > platforms that today implement a `hasNegatives` intrinsic (aarch64, ppc etc) > before moving ahead. This pretty much means holding up this until it's > implemented on all platforms, which can either contributed to this PR or as > dependent follow-ups. > > - An alternative to holding up until all platforms are on board is to allow > the implementation of `StringCoding.hasNegatives` and `countPositives` to be > implemented so that the non-intrinsified method calls into the intrinsified. > This requires structuring the implementations differently based on which > intrinsic - if any - is actually implemented. One way to do this could be to > mimic how `java.nio` handles unaligned accesses and expose which intrinsic is > available via `Unsafe` into a `static final` field. > > - There are a few minor regressions (~5%) in the x86 implementation on > `encode-/decodeLatin1Short`. Those regressions disappear when mixing inputs, > for example `encode-/decodeShortMixed` even see a minor improvement, which > makes me consider those corner case regressions with little real world > implications (if you have latin1 Strings, you're likely to also have > ASCII-only strings in your mix).
Claes Redestad has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 25 additional commits since the last revision: - Revert micro changes, split out to #7516 - Merge branch 'master' of https://github.com/cl4es/jdk into count_positives - Merge branch 'master' into count_positives - Restore partial vector checks in AVX2 and SSE intrinsic variants - Let countPositives use hasNegatives to allow ports not implementing the countPositives intrinsic to stay neutral - Simplify changes to encodeUTF8 - Fix little-endian error caught by testing - Reduce jumps in the ascii path - Remove unused tail_mask - Remove has_negatives intrinsic on x86 (and hook up 32-bit x86 to use count_positives) - ... and 15 more: https://git.openjdk.java.net/jdk/compare/1ca44ef9...531139a1 ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/7231/files - new: https://git.openjdk.java.net/jdk/pull/7231/files/c4bb3612..531139a1 Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7231&range=02 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7231&range=01-02 Stats: 10910 lines in 329 files changed: 7340 ins; 2150 del; 1420 mod Patch: https://git.openjdk.java.net/jdk/pull/7231.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/7231/head:pull/7231 PR: https://git.openjdk.java.net/jdk/pull/7231
