[llvm-dev] DFAPacketizer, Scheduling and LoadLatency

[Krzysztof Parzyszek via llvm-dev]

On 1/6/2016 1:59 PM, Rail Shafigulin wrote:
>
>
> let Itinerary = l_lwz in
>    def LWZ : LOADi32<0x1, "l.lwz", load>;
>
> My instruction itinerary data looks like the following
>
> InstrItinData<l_lwz    , [InstrStage<1, [Slot0, Slot1]>]>,
>
> and my LoadLatency is set to 2.
>
> As you can see mayLoad is never really set to 1 anywhere however it
> still seems to be using a LoadLatency of 2. What am I missing?


I'm not sure exactly what's going on in your case.  You can try to see 
if this is the function that causes the "2" to be returned.

unsigned TargetInstrInfo::
getInstrLatency(const InstrItineraryData *ItinData,
                 const MachineInstr *MI,
                 unsigned *PredCost) const {
   // Default to one cycle for no itinerary. However, an "empty" 
itinerary may
   // still have a MinLatency property, which getStageLatency checks.
   if (!ItinData)
     return MI->mayLoad() ? 2 : 1;

   return ItinData->getStageLatency(MI->getDesc().getSchedClass());
}


-Krzysztof


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