[11u] RFR 8245512: CRC32 optimization using AVX512 instructions

[Viswanathan, Sandhya]

I would like to backport the CRC32 optimization using AVX512 instructions to JDK 11u.
This optimization was introduced in JDK 15.

JBS: https://bugs.openjdk.java.net/browse/JDK-8245512
Webrev: http://cr.openjdk.java.net/~sviswanathan/8245512/webrev.00/

Only one change was needed to the original patch in src/hotspot/cpu/x86/assembler_x86.cpp.

The following in Assembler::blendvpb(), line 7908:

 emit_int24(0x4C, (0xC0 | encode), (0xF0 & src2_enc << 4));
was replaced by equivalent:
  emit_int8((unsigned char)0x4C);
emit_int8((unsigned char)(0xC0 | encode));
emit_int8((unsigned char)(0xF0 & src2_enc<<4));

The patch applies cleanly otherwise.

Please review this backport to 11u.

Best Regards,
Sandhya