RFR (M): 8087198: G1 card refinement: batching, sorting

[Kim Barrett]

> On Nov 19, 2019, at 3:02 PM, Man Cao <manc at google.com> wrote:
> 
> Thanks for the feedback. I will address them soon.
> 
> One question about casting:
> I would prefer leaving the type alone here and instead using
>   static_cast<CardTable::CardValue*>(_node_buffer[i])
> (maybe packaged in a little helper here).
> But I have a strong dislike for reinterpret_cast (with whatever
> spelling) where it can reasonably be avoided.
> 
> There is a problem with G1RemSet::clean_card_before_refine(CardValue*& card_ptr),
> that it needs to modify the card_ptr. In order to make the code clean for Edward's
> two-finger compaction, the code needs to call
> clean_card_before_refine(_node_buffer[i]) and able to modify _node_buffer[i] in-place.
> 
> If we have "void** _node_buffer", then it cannot do
> static_cast<CardValue*&>(_node_buffer[i])
> or
> static_cast<CardValue**>(&_node_buffer[i]).
> 
> I found a workaround:
> Change to:
> G1RemSet::clean_card_before_refine(CardValue** card_ptr_addr); 
> Then:
> void* card_addr = &_node_buffer[i];
> clean_card_before_refine(static_cast<CardValue**>(card_addr))
> 
> However, I think this is basically reinterpret_cast<CardValue**>(&_node_buffer[i]).
> Any suggestion on a better casting approach?
> 
> -Man

Ick!  I forgot about clean_card_before_refine possibly updating.
Given that, I think the various cures are worse; just go with the
reinterpret_cast you had originally.