RFR(S):8242429:Better implementation for signed extract

[Eric Liu]

Hi Vladimir,

Thanks for your review.

> One comment:
> 
>   (i >> 31) >>> 31 ==> i >>> 31
>
> The shift count value is irrelevant here, isn't it?
> 
> So, the transformation can be generalized to:
> 
>   (i >> n) >>> 31 ==> i >>> 31

Yes. This match rule exactly could be more general.

JBS: https://bugs.openjdk.java.net/browse/JDK-8242429
Webrev: http://cr.openjdk.java.net/~yzhang/ericliu/8242429/webrev.01/

[Tests]
Jtreg hotspot::hotspot_all_no_apps, jdk::jdk_core and langtools::tier1. 
No new failure found. 

JMH: A simple JMH case [1] on AArch64 and AMD64 machines. 

For AArch64, one platform has no obvious improvement, but on others the
performance gain is 7.3%~32.7%. 

For AMD64, one platform has no obvious improvement, but on others the
performance gain is 13.7%~32.4%. 

A simple test case [2] has checked the correctness for some corner
cases.

[1] https://bugs.openjdk.java.net/secure/attachment/87712/IdealNegate.java
[2] https://bugs.openjdk.java.net/secure/attachment/87713/SignExtractTest.java


Thanks,
Eric