RFR: 8325495: C2: implement optimization for series of Add of unique value [v2]

[Kangcheng Xu]

On Tue, 17 Sep 2024 09:39:35 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> Kangcheng Xu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 22 additional commits since the last revision:
>> 
>>  - Merge branch 'openjdk:master' into arithmetic-canonicalization
>>  - Merge pull request #1 from tabjy/arithmetic-canonicalization-v2
>>    
>>    Arithmetic canonicalization v2
>>  - remove dead code
>>  - fix potential void type const nodes
>>  - refactor and cleanup
>>  - add more test cases
>>  - re-implement depth limit on recursion
>>  - passes TestIRLShiftIdeal_XPlusX_LShiftC
>>  - passes AddI[L]NodeIdealizationTests
>>  - revert depth limits
>>  - ... and 12 more: https://git.openjdk.org/jdk/compare/71681c74...c8fdb74c
>
> src/hotspot/share/opto/addnode.cpp line 490:
> 
>> 488:     if (bt == T_INT || bt == T_LONG) { // const could potentially be void type
>> 489:       Node* mul_base;
>> 490:       jlong multiplier = extract_base_operand_from_serial_additions(phase, operand_node, &mul_base, depth_limit - 1);
> 
> Do you need to recurse at all here?

I believe so. Consider the case `(a + a) * 3`. Recurse here allows us to extract `a` and factor `2 * 3 => 6`

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PR Review Comment: https://git.openjdk.org/jdk/pull/20754#discussion_r1769185209