RFR: 8252964: [vectorIntrinsics] jdk/incubator/vector/Short64VectorTests.java crashes on AVX512 machines

[jiefu(傅杰)]

Hi all,

JBS:    https://bugs.openjdk.java.net/browse/JDK-8252964
Webrev: http://cr.openjdk.java.net/~jiefu/8252964/webrev.00/

Short64VectorTests.java was observed crashed on AVX512 machines.
The reason is that the vtmp1 [1] register which will be used by Assembler::phaddw should be legVec.

The fix changes src2/vtmp1/vtmp2 [1] from vec to legVec just as reduction32S [2].

Testing:
    jdk/incubator/vector on AVX512 machines

Thanks.
Best regards,
Jie

[1] http://hg.openjdk.java.net/panama/dev/file/34b4be5c12d4/src/hotspot/cpu/x86/x86.ad#l4640
[2] http://hg.openjdk.java.net/panama/dev/file/34b4be5c12d4/src/hotspot/cpu/x86/x86.ad#l4660