On Fri, 13 May 2022 01:35:40 GMT, Xiaohong Gong <xg...@openjdk.org> wrote:
>> Checking whether the indexes of masked lanes are inside of the valid memory >> boundary is necessary for masked vector memory access. However, this could >> be saved if the given offset is inside of the vector range that could make >> sure no IOOBE (IndexOutOfBoundaryException) happens. The masked load APIs >> have saved this kind of check for common cases. And this patch did the >> similar optimization for the masked vector store. >> >> The performance for the new added store masked benchmarks improves about >> `1.83x ~ 2.62x` on a x86 system: >> >> Benchmark Before After Gain Units >> StoreMaskedBenchmark.byteStoreArrayMask 12757.936 23291.118 1.826 ops/ms >> StoreMaskedBenchmark.doubleStoreArrayMask 1520.932 3921.616 2.578 ops/ms >> StoreMaskedBenchmark.floatStoreArrayMask 2713.031 7122.535 2.625 ops/ms >> StoreMaskedBenchmark.intStoreArrayMask 4113.772 8220.206 1.998 ops/ms >> StoreMaskedBenchmark.longStoreArrayMask 1993.986 4874.148 2.444 ops/ms >> StoreMaskedBenchmark.shortStoreArrayMask 8543.593 17821.086 2.086 ops/ms >> >> Similar performane gain can also be observed on ARM hardware. > > Xiaohong Gong has updated the pull request incrementally with one additional > commit since the last revision: > > Wrap the offset check into a static method However, we seem to lack the ability to do an unsigned comparison reliably. C2 can transform `x + MIN_VALUE <=> y + MIN_VALUE` into `x u<=> y` but it will fail if `x` or `y` is an addition with constant in such cases the constants will be merged together. As a result, I think we need an intrinsic for this. `Integer.compareUnsigned` may fit but it manifests the result into an integer register which may lead to suboptimal materialisation of flags, another approach would be to have a separate method `Integer.lessThanUnsigned` which only returns `boolean` and C2 can have better time splitting the boolean comparison through `IfNode`, which will prevent the materialisation of `boolean` values. What do you two think? I.e, after splitting if through merge point, the shape of `if (Integer.lessThanUnsigned(a, b))` would be transformed from a b \ / CmpU | Bool | If / \ IfTrue IfFalse \ / Region 1 0 \ | / Phi 0 \ / CmpI into a b \ / CmpU Thanks. ------------- PR: https://git.openjdk.java.net/jdk/pull/8620