RFR(XS): 8078113: 8011102 changes may cause incorrect results

[Viswanathan, Sandhya]

Hi Vladimir,

I verified the fix using the code from our customer that I got under NDA, so unable to share that.

Best Regards,
Sandhya


-----Original Message-----
From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com] 
Sent: Friday, April 17, 2015 3:13 PM
To: Viswanathan, Sandhya; hotspot-compiler-dev at openjdk.java.net
Subject: Re: RFR(XS): 8078113: 8011102 changes may cause incorrect results

Looks good. How your verified the fix?

Thanks,
Vladimir

On 4/17/15 3:05 PM, Viswanathan, Sandhya wrote:
> Hi All,
>
> We would like to contribute a patch for bug 8078113 from Intel.
>
> RFE: https://bugs.openjdk.java.net/browse/JDK-8078113
>
> webrev: http://cr.openjdk.java.net/~kvn/8078113/webrev.00/
>
> With 32 byte width vectorization the JVM produces wrong results under
> certain circumstances for x86_64.
>
> The Vzeroupper instruction introduced in String.equals, String.compareTo
> and OptimizeFill intrinsic/stubs in the following change set is the
> cause of the bug:
>
> http://hg.openjdk.java.net/jdk7u/jdk7u/hotspot/rev/d59ed8d47aed
>
> For 32 byte vectorization, YMM registers are used by the hotspot
> compiler and the register allocator can allocate these across intrinsic
> methods.
>
> Vzeroupper in the intrinsic is clobbering upper 16 bytes in all the
> other YMM registers that are not touched in these methods and so our
> customers are
>
> seeing unexpected results.
>
> This patch fixes the problem on Linux.
>
> Best Regards,
>
> Sandhya
>