[LLVMdev] Out of tree targets: Possibly additional API to implement for out of tree targets using the IfConverter

[Arnold Schwaighofer]

Hi all,

If you have an out of tree target and use the IfConverter be aware of a new API call "getPredictationCost“ that you might want to implement:

After commit r191671:

    IfConverter: Use TargetSchedule for instruction latencies
    
    For targets that have instruction itineraries this means no change. Targets
    that move over to the new schedule model will be able to use the new schedule
    module for instruction latencies in the if-converter (the logic is such that if
    there is no itinerary we will use the new sched model for the latencies).
    
    Before, we queried "TTI->getInstructionLatency()" for the instruction latency
    and the extra prediction cost. Now, we query the TargetSchedule abstraction for
    the instruction latency and TargetInstrInfo for the extra predictation cost. The
    TargetSchedule abstraction will internally call "TTI->getInstructionLatency" if
    an itinerary exists, otherwise it will use the new schedule model.
    
    ATTENTION: Out of tree targets!
    
    (I will also send out an email later to LLVMDev)
    
    This means, if your target implements
    
     unsigned getInstrLatency(const InstrItineraryData *ItinData,
                              const MachineInstr *MI,
                              unsigned *PredCost);
    
    and returns a value for "PredCost", you now also need to implement
    
     unsigned getPredictationCost(const MachineInstr *MI);
    
    (if your target uses the IfConversion.cpp pass)


Best,
Arnold