[14] RFR (L): 8235719: C2: Merge AD instructions for ShiftV, AbsV, and NegV nodes

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/jbhateja/8235719/webrev.00/all
https://bugs.openjdk.java.net/browse/JDK-8235719

Merge AD instructions for the following vector nodes:
   - LShiftV*, RShiftV*, URShiftV*
   - AbsV*
   - NegV*

Individual patches:
 
http://cr.openjdk.java.net/~vlivanov/jbhateja/8235719/webrev.00/individual

As Jatin described, merging is applied only to AD instructions of 
similar shape. There are some more opportunities for reduction/merging 
left, but they are deliberately left out for future work.

The patch is derived from the initial version of generic vector support 
[1]. Generic vector support was reviewed earlier [2].

Testing: tier1-4, test run on different CPU flavors (KNL, SKL, etc)

Contributed-by: Jatin Bhateja <jatin.bhateja at intel.com>
Reviewed-by: vlivanov, sviswanathan, ?

Best regards,
Vladimir Ivanov

[1] 
https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2019-August/034822.html

[2] 
https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2019-November/036016.html