RFR: 8346280: C2: implement late barrier elision for G1 [v2]

[Thomas Schatzl]

On Fri, 31 Jan 2025 08:48:52 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Roberto Castañeda Lozano has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:
>> 
>>  - Merge commit 'afcc2b0' into JDK-8346280-late-barrier-elision
>>  - Add new test case (store after exception)
>>  - Remove unused includes
>>  - Remove temporary UseNewCode guard
>>  - Use clearer names and document access API interface
>>  - Move ZGC-specific barrier elision code to BarrierSetC2
>>  - Set UseNewCode to true temporarily
>>  - Make elide_mach_barrier virtual
>>  - Move late barrier elision analysis from G1BarrierSetC2 to BarrierSetC2
>>  - Initial implementation
>>  - ... and 1 more: https://git.openjdk.org/jdk/compare/afcc2b03...ab47d7f8
>
> src/hotspot/share/gc/shared/c2/barrierSetC2.cpp line 956:
> 
>> 954: static bool is_unknown(intptr_t offset) {
>> 955:   return offset == Type::OffsetBot;
>> 956: }
> 
> pre-existing: these two predicates would be nice to have elsewhere in C2 code too (i.e. there's quite a lot of these predicates inlined elsewhere).

Maybe something for another RFE of course.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23235#discussion_r1936890465