[aarch64-port-dev ] RFR: JDK-8205004: AArch64: fix failures in jtreg ArraysEqCmpTest

[Joshua Zhu]

Hi Dmitrij,

I saw the below comments in original codes.
    5137     // on most CPUs a2 is still "locked"(surprisingly) in ldrw and it's
    5138     // faster to perform another branch before comparing a1 and a2
before 
    5139     cmp(cnt1, elem_per_word);
    5140     br(LE, SHORT); // short or same

and if as the comments say, I think we can move
    5141     cmpoop(a1, a2);
    5142     br(EQ, SAME);
before 
    5132     cbz(a1, A_IS_NULL);
    5133     ldrw(cnt1, Address(a1, length_offset));
    5134     cbz(a2, A_IS_NULL);
    5135     ldrw(cnt2, Address(a2, length_offset));

and add additional code:
    cmp(cnt2, cnt1);
    br(NE, DONE);
in the SHORT path just as my patch did after 
    5209     bind(SHORT);

and label LEN_IS_ZERO and its path can also be deleted like below:
    bind(SHORT);
    cmp(cnt2, cnt1);
    br(NE, DONE);
    cbz(cnt1, SAME);

Best Regards,
Joshua

> Hi,
> 
> I think you can just move existing checks:
> 
> 5148     cmp(cnt2, cnt1);
> 5149     br(NE, DONE);
> 
> and
> 
> 5141     cmpoop(a1, a2);
> 5142     br(EQ, SAME);
> 
> before jump to short case: 5140 br(LE, SHORT); // short or same
> 
> Then you don't need to add any additional code.
> 
> (cmpoop(a1, a2) check should go first, because cnt1 and cnt2 loads are
> possibly still executed)
> 
> Thanks,
> Dmitrij
> 
> On 14.06.2018 16:26, Joshua Zhu wrote:
> > Hi,
> >
> > Please review the following change.
> >
> > Bug: https://bugs.openjdk.java.net/browse/JDK-8205004
> > Webrev: http://cr.openjdk.java.net/~zyao/8205004/
> >
> > This bug causes three failures in Jtreg ArraysEqCmpTest.
> > test ArraysEqCmpTest.testArray(byte[]) test
> > ArraysEqCmpTest.testArray(unsigned byte[]) test
> > ArraysEqCmpTest.testArray(char[])
> >
> > Array length needs to be compared for short arrays.
> > Please see detailed description in JBS.
> >
> > Best Regards,
> > Joshua
> >