[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,

Sorry for late reply. I just came back from vacation.
Your feedback is helpful for me.
I will continue to improve this patch.

Best Regards,
Joshua
 
> -----Original Message-----
> From: Vladimir Ivanov <vladimir.x.ivanov at oracle.com>
> Sent: Thursday, April 4, 2019 3:26 AM
> To: Joshua Zhu (Arm Technology China) <Joshua.Zhu at arm.com>; panama-
> dev at openjdk.java.net
> Cc: nd <nd at arm.com>
> Subject: Re: [vector] RFR 8221816: IndexOutOfBoundsException for
> fromArray/intoArray with unset mask lanes - was: RE:
> IndexOutOfBoundsException with unset mask lanes
> 
> Hi Joshua,
> 
> What kind of performance testing have you done on it?
> 
> Having a conditional branch with forEach() call on slow path will cause
> problems to C2 if it can't prove access is always in-bounds and prune the
> slow path.
> 
> Overall, I don't see an acceptable way to fix it purely on JDK side.
> I like how you optimize for common case with a stricter bounds check, but
> more work is needed to reliably turn slow path into an uncommon trap.
> 
> +        if (ax + LENGTH <= a.length) {
> 
> VectorIntrinsics.checkIndex() has a more optimal implementation: it uses
> Objects.checkIndex() which internally relies on VM intrinsic.
> 
> 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.
> 
> Best regards,
> Vladimir Ivanov
> 
> [1]
> http://hg.openjdk.java.net/panama/dev/file/ccfafe96478e/src/java.base/sh
> are/classes/java/lang/invoke/MethodHandleImpl.java#l695
> 
> On 03/04/2019 03:03, Joshua Zhu (Arm Technology China) wrote:
> > Hi,
> >
> > JBS: https://bugs.openjdk.java.net/browse/JDK-8221816
> > Webrev:
> > http://cr.openjdk.java.net/~jzhu/vectorapi/8221816.OOB/webrev.00/
> >
> > (This is a rebase of original webrev [1].)
> >
> > I have a patch to fix IndexOutOfBoundsException for
> > fromArray/intoArray/gather/scatter API with unset mask lanes.
> > To align with API doc, IndexOutOfBoundsException should only be thrown
> > for any illegal vector lane index where the mask at lane is set.
> >
> > Also I write a template to generate test cases to cover this kind of exception
> testing.
> >
> > This patch has been verified by testing.
> >
> > [1]
> > http://mail.openjdk.java.net/pipermail/panama-dev/2019-
> March/004812.ht
> > ml
> >
> > Best Regards,
> > Joshua Zhu
> >