RFR: JDK-8213489: GC/C2 abstraction for Compile::final_graph_reshaping()

[Roman Kennke]

Hi Vladimir,

> Next
> 
> +        assert(n->is_Mem(), "");
> +        MemNode* mem  = (MemNode*)n;
> 
> could be replaced with
> 
> +        MemNode* mem  = n->as_Mem();

Right. I copied existing code from final_graph_reshaping. New changeset
fixes it.

> I don't see removal of moved ZGC code in
> Compile::final_graph_reshaping_impl()

Oops, my bad. Fixed.

> Why you skip only assert and not whole switch() (or return) ? Do you
> want to process some nodes twice: by GC first and then in main switch?

Yes. We have a case in Shenandoah where we want to process a CallNode
Shenandoah-specific and then also want to verify/reshape generically.

> May be pass nop (opcode) to final_graph_reshaping() too to avoid virtual
> call Opcode() there.

OK.

Incremental:
http://cr.openjdk.java.net/~rkennke/JDK-8213489/webrev.01.diff/
Full:
http://cr.openjdk.java.net/~rkennke/JDK-8213489/webrev.01/

Better?

Thanks for reviewing!
Roman

> Thanks,
> Vladimir
> 
> On 11/7/18 9:00 AM, Roman Kennke wrote:
>> GCs might want to do something to nodes in
>> Compile::final_graph_reshaping(). Let's put an abstraction in this place.
>>
>> The way I did it was to put a call into
>> BSC2::final_graph_reshaping(Compile*, Node*) in front of the huge switch
>> and let the caller know if the node was handled or not. This is
>> subsequently checked in the default-branch: if GC handled it, the
>> asserts are not checked. This should provide the exact same behaviour
>> that we have now, only better and nicer.
>>
>> I also took the opportunity and moved the ZGC related parts there to
>> ZBarrierSetC2.
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8213489
>> Webrev:
>> http://cr.openjdk.java.net/~rkennke/JDK-8213489/webrev.00/
>>
>> Testing: hotspot/jtreg:tier1 passes
>>
>> Thoughts? Reviews?
>>
>> Roman
>>

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