RFR: 8331126: [s390x] secondary_super_cache does not scale well [v4]

[Lutz Schmidt]

On Mon, 24 Jun 2024 18:44:29 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Amit Kumar has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Update src/hotspot/cpu/s390/macroAssembler_s390.cpp
>>  - rename: r_scratch to r_result in repne_scan method
>
> src/hotspot/cpu/s390/macroAssembler_s390.cpp line 3171:
> 
>> 3169: 
>> 3170:   bind(L_loop);
>> 3171:   z_cg(r_value, Address(r_addr));
> 
> Idea: I think it is possible to use z_xg to do both at once: Set to 0 iff equal and CC to equal. (Like PPC64.)

Good idea. But will have no benefit. When using z_xg, r_value will be altered. Subsequent iterations will then compare against a modified value. To use the triadic register instruction (XGRK), we first have to load the value int a scratch register.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19544#discussion_r1652830658