RFR: 8351994: Enable Extended EVEX to REX2/REX demotion when src and dst are the same [v27]

[Srinivas Vamsi Parasa]

On Fri, 16 May 2025 18:49:53 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update x86-asmtest.py to enable demotion by default and make test generation optional
>
> src/hotspot/cpu/x86/assembler_x86.cpp line 6935:
> 
>> 6933:   InstructionAttr attributes(AVX_128bit, /* vex_w */ false, /* legacy_mode */ false, /* no_mask_reg */ true, /* uses_vl */ false);
>> 6934:   attributes.set_address_attributes(/* tuple_type */ EVEX_NOSCALE, /* input_size_in_bits */ EVEX_32bit);
>> 6935:   evex_prefix_ndd(src, dst->encoding(), 0, VEX_SIMD_NONE, VEX_OPCODE_0F_3C /* MAP4 */, &attributes, no_flags);
> 
> To comply with existing convention like below
> https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/assembler_x86.hpp#L762
> 
> We should use eevex instead of evex as the prefix

There are some functions starting with `evex_prefix_*`; should all of those be replaced with `eevex_prefix_*` ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24431#discussion_r2098851965