RFR: 8325495: C2: implement optimization for series of Add of unique value [v8]

[Christian Hagedorn]

On Mon, 7 Oct 2024 18:44:41 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

>> src/hotspot/share/opto/addnode.cpp line 567:
>> 
>>> 565: 
>>> 566:     // We can't simply return the lshift node even if ((a << CON) - a) + a cancels out. Ideal() must return a new node.
>>> 567:     *multiplier = ((jlong) 1 << con->get_int()) - 1;
>> 
>> Can't this be an `Identity()` transformation where you can return existing nodes?
>
> Good point. I realized `(x - y) + y => x` is already handled by `AddINode::Identity` and `AddLNode::Identify`. I don't need to repeat here.

That's great!

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PR Review Comment: https://git.openjdk.org/jdk/pull/20754#discussion_r1791317004