RFR: 8325467: Support methods with many arguments in C2 [v27]

[Daniel Lundén]

On Tue, 16 Sep 2025 12:02:13 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Daniel Lundén has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 39 commits:
>> 
>>  - Clarify comments in regmask.hpp
>>  - Merge remote-tracking branch 'upstream/master' into many-arguments-8325467+pr-updates
>>  - Address review comments (renaming on the way in a separate PR)
>>  - Update src/hotspot/share/opto/regmask.hpp
>>    
>>    Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>
>>  - Restore modified java/lang/invoke tests
>>  - Sort includes (new requirement)
>>  - Merge remote-tracking branch 'upstream/master' into many-arguments-8325467+pr-updates
>>  - Add clarifying comments at definitions of register mask sizes
>>  - Fix implicit zero and nullptr checks
>>  - Add deep copy comment
>>  - ... and 29 more: https://git.openjdk.org/jdk/compare/60930a3e...c1f41288
>
> src/hotspot/share/opto/chaitin.cpp line 1663:
> 
>> 1661:     if (!OptoReg::is_valid(reg) && is_infinite_stack) {
>> 1662:       // Bump register mask up to next stack chunk
>> 1663:       bool success = lrg->rollover();
> 
> Can you add a comment that explains what this does / means? Do we start spilling to the stack slots instead of using registers?

Sure, I'll expand on the existing comment.

> src/hotspot/share/opto/regmask.hpp line 837:
> 
>> 835:   // ----------------------------------------------------------------------
>> 836:   // The methods below are only for testing purposes (see test_regmask.cpp)
>> 837:   // ----------------------------------------------------------------------
> 
> I wonder if it could be solved with `friend` instead, so it does not have to be public and get accidentally used somehow.
> 
> Or maybe some `gtest_` prefix? Not sure.

I like adding a `gtest_` prefix, I'll do that. Not sure how to make gtests work with `friend`.

> test/hotspot/jtreg/compiler/arguments/TestMethodArguments.java line 51:
> 
>> 49:     static final int INPUT_SIZE = 100;
>> 50: 
>> 51:     public static Template.ZeroArgs generateTest(PrimitiveType t, int numberOfArguments) {
> 
> You should write out `type` instead of `t`, would make it consistent with your `let` below.

Thanks, I'll fix it

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PR Review Comment: https://git.openjdk.org/jdk/pull/20404#discussion_r2354938220
PR Review Comment: https://git.openjdk.org/jdk/pull/20404#discussion_r2354945861
PR Review Comment: https://git.openjdk.org/jdk/pull/20404#discussion_r2354946296