[vector] RFR 8221816: IndexOutOfBoundsException for fromArray/intoArray with unset mask lanes - was: RE: IndexOutOfBoundsException with unset mask lanes

[Joshua Zhu (Arm Technology China)]

Hi Vladimir,

> It looks promising to introduce a variant of
> VectorIntrinsics.checkIndex() which is used to guard a fast path and is
> annotated with a JIT-compiler hint (akin to
> java.lang.invoke.MethodHandleImpl.profileBoolean() [1], but without
> profiling logic) to override bytecode profiling info, so JIT always puts an
> uncommon trap on the false branch.

Thanks for your comments.
As you suggested, I introduced VectorIntrinsics.expectTrue() in change [2].
It's used as below:
    if (expectTrue(bool condition)) {
        // fast path
    } else {
        // slow path: uncommon trap
    }

I also wrote a jmh case [3] to check the performance.
See below table for jmh test results. (In Throughput Mode, Unit: ops/ms)
                                    Base       without expectTrue (patch [1])  UncommonTrap (patch [2])
  1000 fastPath              318.228 ± 22.588       457.967 ± 12.622           457.328 ± 11.932
 10000 fastPath               21.991 ±  2.496        23.360 ±  0.070            24.744 ±  0.213
100000 fastPath                1.613 ±  0.007         1.581 ±  0.031             1.631 ±  0.003                            
  1000 fastPath + 1 slowPath        N/A              57.298 ± 11.033            55.845 ±  0.716
 10000 fastPath + 1 slowPath        N/A               4.537 ±  0.536            15.164 ±  0.098
100000 fastPath + 1 slowPath        N/A               0.577 ±  0.048             1.564 ±  0.005

[1] http://cr.openjdk.java.net/~jzhu/vectorapi/8221816.OOB/webrev.01/
[2] http://cr.openjdk.java.net/~jzhu/vectorapi/8221816.OOB/uncommontrap.webrev.00/
[3] http://cr.openjdk.java.net/~jzhu/vectorapi/8221816.OOB/IntVectorJmhTest.java

Please help review and feel free to share your comments.
Thanks.

Best Regards,
Joshua