RFR: 8303970: C2 can not merge homogeneous adjacent two If [v2]

[Yi Yang]

On Tue, 14 Mar 2023 10:41:38 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   dont apply Identity for dead bool
>
> src/hotspot/share/opto/subnode.cpp line 1487:
> 
>> 1485:   if (cop == Op_FastLock || cop == Op_FastUnlock ||
>> 1486:       cop == Op_SubTypeCheck || cop == Op_VectorTest ||
>> 1487:       cmp->is_Overflow()) {
> 
> Why is this check now needed?

For safety considerations through I dont really touch it. I checked the remaining transformation patterns in BoolNode::Ideal, and none of them applied on Overflow input, so I think it's okay to do so..

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