[11] RFR(S) 8206265: assert in TestOptionsWithRanges on aarch64

[Boris Ulasevich]

Hi all,

please review bugfix for openjdk-11 and 12:

   http://cr.openjdk.java.net/~bulasevich/8206265/webrev.04/
   https://bugs.openjdk.java.net/browse/JDK-8206265

Currently, TestOptionsWithRanges which tries different combinations of 
maximum option values fails with assert if SoftwarePrefetchHintDistance 
option limit is 32K (prfm gets imm12<<3) when using its maximum value in 
cmp instruction (which fits only 12-bit immediate).

A new instruction cmp(rscratch, Rn, imm) alias is introduced to use it 
when immediate value can not fit in 12 bit. I believe it's cleaner than 
using subs.

Alternatively, if someone believes this looks risky for 11 I can propose 
to just limit SoftwarePrefetchHintDistance. It seems unreasonable to 
prefetch more than a few cache lines ahead anyway.

thanks,
Boris