RFR 8233500: Shenandoah: Shenandoah load barrier should save registers before calling keep alive barrier on x86

[Roman Kennke]

>>>> SATB handling is similar to G1 is doing, where's the similar code in
>>>> G1? The patch adds save/restore
>>>> at in SBSA::load_at, but there is a similar block in SBSA::store_at,
>>>> why it is not needed there?
>>>
>>> Because we do self-fixing in LRB and have to reshuffle registers.
>>
>> Okay. So AArch64 does enter()/leave(), why x86 needs the entire
>> IU_state pushed/popped?
> Roman suggested.
> 
> Roman, could you answer?

enter()/leave() sets up/tears down the stub frame for the runtime call.
push/pop_IU_state() saves/restores the registers. Aarch64 code also
saves/restores the registers via push/pop_call_clobbered_registers().

Roman


> Thanks,
> 
> -Zhengyu
> 
>>
>> My concern is that pushing/popping the entire state explodes code size
>> (we don't care about
>> performance much, but we do care about hitting the stub boundaries),
>> and probably hides some bugs
>> with register shuffles.
>>