RFR: 8323220: Reassociate loop invariants involved in Cmps and Add/Subs [v2]

[Joshua Cao]

On Thu, 18 Jan 2024 08:25:46 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Some sort of pattern matcher could work. It would be able nice to match something like `a ADD_I b CMP_LT c`. In java this could look something like 
>> 
>> 
>> @IR(counts = {IRNode.CMP_LT[IRNode.ANY, IRNode.SUB_I, IRNode.ANY], "1"}
>> 
>> 
>> The arguments in the `[]` are the inputs. `IRNode.ANY` matches any node. (The zero'th node is ANY because its the region node).
>> 
>> Anyway, I think a `lt` test is not super-required for the coverage for this PR. The current machinery does not provide a convenient way to test it. I'd prefer to avoid something hacky. I think this work can be done separately.
>
> I agree with you there, don't do anything hacky here.
> But yes, I've also been wondering what kind of improvements to the IR framework would help us to do these sorts of graph-matching verifications.

Created https://bugs.openjdk.org/browse/JDK-8324226

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PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1459579634