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

[Xin Liu]

On Wed, 1 Jun 2022 21:00:15 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> 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`.
>
>> Yes, this is for 8287385. I will remove preprocessing logic from this PR.
> 
> Okay.
> 
>> 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`.
> 
> Then you should consider my proposal about cleaning the list and update counters in `Compile::remove_useless_nodes()`. Let discuss it in next changes.

I move preprocess after PhaseRemoveUseless phase. I think it's reasonable to count only useful nodes.

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