RFR: 8303970: C2 can not merge homogeneous adjacent two If [v3]

[Yi Yang]

On Fri, 17 Mar 2023 15:38:01 GMT, Cesar Soares Lucas <cslucas at openjdk.org> wrote:

>> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review from tobias
>
> src/hotspot/share/opto/subnode.cpp line 1488:
> 
>> 1486: 
>> 1487: static bool is_arithmetic_cmp(Node* cmp) {
>> 1488:   if (!cmp->is_Cmp()) {
> 
> Perhaps just merge this if with the next one.

Hi Cesar, I receive feedback from Roland in #13039 that suggested extending identical_backtoback_ifs instead of adding Ideal for BoolNode and CmpNode. 

Before making any modifications based on your review comment, I would first like to reach a consensus on whether we should add idealization for bool and cmp or extend identical_backtoback_ifs. Do you have any comments in this regard? Perhaps @TobiHartmann could also chime in.

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PR: https://git.openjdk.org/jdk/pull/12978