RFR: 8286104: use aggressive liveness for unstable_if traps [v10]

[Xin Liu]

On Sat, 4 Jun 2022 16:17:19 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> 2 tests failed so far. I put information into RFE.
>
>> 2 tests failed so far. I put information into RFE.
> 
> No other new failures in my tier1-7 testing. I think after you address found issue it will be ready to integrate (after second review by other Reviewer). But I would suggest to push it into JDK 20 after 19 is forked in one week to get more testing  before release.

hi, @vnkozlov, 

I file a new issue JDK-8287840([PR](https://github.com/openjdk/jdk/pull/9035)) for the new regression. It will allow some IfNodes carry out fold-compares in 1st IterGVN. 

Back to this PR, for safety, I added a mechanism to guarantee that fold-compares gives up if its dominating trap has been modified. This is a guardrail and should not happen frequent. 

I also add a regression test to cover fold-compare cases. for `testEnumValues`,  c2 would prefer fold-compares if we merged JDK-8287840.

> But I would suggest to push it into JDK 20 after 19 is forked in one week to get more testing before release.

sure. no problem. 

thanks,
--lx

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PR: https://git.openjdk.java.net/jdk/pull/8545