RFR 8076276 support for AVX512

[Roland Westrelin]

> http://cr.openjdk.java.net/~kvn/8076276/webrev.02

This looks good to me. A few minor remarks:

Shouldn’t the #ifdef _LP64 new instruct be in x86_64.ad? I see there are already other #ifdef _LP64 in x86.ad so I’m not sure what the guideline is.

In vm_version_x86.hpp, os_supports_avx_vectors(), you could have a single copy of the loop with different parameters.

Not sure why you dropped:

3463 // Float register operands
3473 // Double register operands

in x86_64.ad

In chaitin.hpp:

144   uint16_t _num_regs;            // 2 for Longs and Doubles, 1 for all else

comment is not aligned with the one below anymore.

Roland.