RFR: 8343685: C2 SuperWord: refactor VPointer with MemPointer [v14]

[Emanuel Peter]

On Fri, 17 Jan 2025 12:45:02 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Batch 2 for Christian
>
> src/hotspot/share/opto/superword.hpp line 568:
> 
>> 566:     MemNode* _mem;
>> 567:     const VPointer* _vpointer;
>> 568:     int _original_index;
> 
> Can also be made const:
> Suggestion:
> 
>     const int _original_index;

That does not work sadly:

In file included from /oracle-work/jdk-fork5/open/src/hotspot/share/classfile/classLoaderData.hpp:33,
                 from /oracle-work/jdk-fork5/open/src/hotspot/share/precompiled/precompiled.hpp:34:
/oracle-work/jdk-fork5/open/src/hotspot/share/utilities/growableArray.hpp: In instantiation of 'int GrowableArrayWithAllocator<E, Derived>::append(const E&) [with E = SuperWord::MemOp; Derived = GrowableArray<SuperWord::MemOp>]':
/oracle-work/jdk-fork5/open/src/hotspot/share/opto/superword.cpp:566:20:   required from here
/oracle-work/jdk-fork5/open/src/hotspot/share/utilities/growableArray.hpp:414:22: error: use of deleted function 'SuperWord::MemOp& SuperWord::MemOp::operator=(const SuperWord::MemOp&)'
  414 |     this->_data[idx] = elem;
      |     ~~~~~~~~~~~~~~~~~^~~~~~
In file included from /oracle-work/jdk-fork5/open/src/hotspot/share/opto/superword.cpp:29:
/oracle-work/jdk-fork5/open/src/hotspot/share/opto/superword.hpp:564:9: note: 'SuperWord::MemOp& SuperWord::MemOp::operator=(const SuperWord::MemOp&)' is implicitly deleted because the default definition would be ill-formed:
  564 |   class MemOp : public StackObj {
      |         ^~~~~
/oracle-work/jdk-fork5/open/src/hotspot/share/opto/superword.hpp:564:9: error: non-static const member 'const int SuperWord::MemOp::_original_index', cannot use default assignment operator

It is a limitation with `GrowableArray`. But I think maybe more generally with sort: you need to be able to swap the values of different `MemOp`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21926#discussion_r1920967331