RFR: 8286104: use aggressive liveness for unstable_if traps [v7]

[Xin Liu]

On Wed, 1 Jun 2022 19:58:51 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Xin Liu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove useless flag. if jdwp is on, liveness_at_bci() marks all local
>>   variables live.
>
> src/hotspot/share/opto/compile.cpp line 1877:
> 
>> 1875: uint unstable_ifs_all              = 0;
>> 1876: 
>> 1877: void Compile::preprocess_unstable_ifs() {
> 
> I assume it will be used in product VM  by next changes 8287385.
> Otherwise counters and method should be under `#ifndef PRODUCT` because they used only for statistics.

Yes, this is for 8287385. I will remove preprocessing logic from this PR. 

Because we can determine a unstable_if trap is trivial after parsing.  My idea is to do the leftover parsing job in this preprocess function. That's why I think preprocess should before `PhaseRemoveUseless`.

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