RFR: 8254693: Add Panama feature to pass heap segments to native code [v7]

[Sidraya Jayagond]

On Thu, 19 Oct 2023 13:37:09 GMT, Lutz Schmidt <lucy at openjdk.org> wrote:

>> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   add s390 support
>
> src/hotspot/cpu/s390/downcallLinker_s390.cpp line 100:
> 
>> 98:       Address offset_addr(callerSP, FP_BIAS + reg_offset.offset());
>> 99:       __ mem2reg_opt(r_tmp1, offset_addr, true);
>> 100:       __ z_agr(reg_oop_reg, r_tmp1);
> 
> Please note that s390 is a CISC architecture. It provides instructions for almost everything. :-)
> Here, I would suggest to add the offset to reg_oop_reg directly from memory - without first loading the offset into a temp register (that is RISC style). It's shorter and faster:
> `  __ z_ag(reg_oop_reg, offset_addr);`

That's right @RealLucy. Thanks for reviewing.

> src/hotspot/cpu/s390/downcallLinker_s390.cpp line 112:
> 
>> 110:     __ mem2reg_opt(r_tmp2, oop_addr, true);
>> 111:     __ z_agr(r_tmp1, r_tmp2);
>> 112:     __ reg2mem_opt(r_tmp1, oop_addr, true);
> 
> Similar to above. You need to load only one operand into a register.
> 
>   __ mem2reg_opt(r_tmp2, oop_addr, true);
>   __ z_ag(r_tmp2, offset_addr);
>   __ reg2mem_opt(r_tmp2, oop_addr, true);

Fixed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16201#discussion_r1365916526
PR Review Comment: https://git.openjdk.org/jdk/pull/16201#discussion_r1365916660