SFX and address cloning problem

[Roman Kennke]

>> diff -r 6fa068615a94 src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp
>> --- a/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp  Wed Jul 03 17:19:16 2019 +0200
>> +++ b/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp  Fri Jul 05 11:51:13 2019 +0200
>> @@ -1530,6 +1530,12 @@
>>      } else {
>>        addr = phase->igvn().zerocon(T_OBJECT);
>>      }
>> +    if (addr->Opcode() == Op_AddP) {
>> +      addr = addr->clone();
>> +      addr->set_req(0, ctrl); // Critical? Bad generated code without it...
>> +      phase->register_new_node(addr, ctrl);
>> +    }
>> +
>>      call_lrb_stub(ctrl, fwd, addr, result_mem, raw_mem, phase);
>>      region->init_req(_evac_path, ctrl);
>>      val_phi->init_req(_evac_path, fwd);
>>
> 
> I don't think setting the control on the the AddPNode can be made to
> work. There are several solutin to this:
> 
> One is to not push the cloned AddP on the IGVN worklist: call
> phase->igvn()._worklist.yank(addr) after register_new_node(). That one
> is not 100% robust to work as the node could be transformed later as a
> side effect of something else.
> 
> Clone the addr and change the base input so it's a CheckCastPPNode of
> the previous base input to the current type of the base input but with
> carry_dependency set. Set the control of the CheckCastPPNode.

This version sounds most feasible (if it works). Do I also need to treat
the address input of the cloned AddP the same way?

Roman


> Do the cloning at graph final reshaping time. There's nothing that
> should common identical nodes then.
> 
> Do the cloning as part of matching by changing
> Matcher::clone_address_expressions().
> 
> Roland.
>