[aarch64-port-dev ] RFR(S): 8239914: AArch64: Combine add/sub with comparison against zero

[Pengfei Li]

Hi,

Thanks for your review.
 
> This looks good, but it's hard to say without JMH tests. We really can't say
> very much about performance enhancements without measurements.

Here's a JMH for this pattern.
http://cr.openjdk.java.net/~pli/rfr/8239914/CmnCmp.java

 [Before]
  Benchmark           Mode  Cnt    Score    Error  Units
  CmnCmp.testCmnInt   avgt   15  136.047 ± 13.069  us/op
  CmnCmp.testCmnLong  avgt   15  136.046 ± 13.072  us/op
  CmnCmp.testCmpInt   avgt   15  136.061 ± 13.063  us/op
  CmnCmp.testCmpLong  avgt   15  136.051 ± 13.067  us/op

[After]
  Benchmark           Mode  Cnt    Score    Error  Units
  CmnCmp.testCmnInt   avgt   15  117.773 ± 10.327  us/op
  CmnCmp.testCmnLong  avgt   15  117.766 ± 10.334  us/op
  CmnCmp.testCmpInt   avgt   15  117.778 ± 10.316  us/op
  CmnCmp.testCmpLong  avgt   15  117.778 ± 10.315  us/op

I don't expect to see obvious performance enhancements in real workloads.
This just helps to save one instruction. Ok to push?

--
Thanks,
Pengfei