CR for RFR 8129376

[Berg, Michael C]

Hi Folks,

Performance on client x86 targets was hampered in two SPECjvm98 metrics (mpegaudio and  mtrt) for 32-bit since we added AVX512.  I also checked to make sure only client on x86-32 was affected.  I have mitigated this by altering the xmm pad modeling in the x86-32-bit machine description so that register allocation cannot see the dummy definitions, enabling the desired performance while retaining correctness for 32-bit on AVX512.

This code was tested as follows: hotspot jreg, SPECjvm2008, SPECjvm98 on hsw, skx and knl targets complete with no issues on 32-bit.  These changes do not alter behavior on x86-64.

Bug-id: https://bugs.openjdk.java.net/browse/JDK-8129376

webrev:
http://cr.openjdk.java.net/~mcberg/8129376/webrev.01

Regards,
Michael
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/attachments/20160920/3a868d27/attachment.html>