llvm/tools/llvm-mca/RetireControlUnit.cpp

#include "Dispatch.h"
#include "RetireControlUnit.h"
#include "llvm/MC/MCSchedule.h"
#include "llvm/Support/Debug.h"

using namespace llvm;

#define DEBUG_TYPE "llvm-mca"

namespace mca {

RetireControlUnit::RetireControlUnit(const llvm::MCSchedModel &SM,
                                     DispatchUnit *DU)
    : NextAvailableSlotIdx(0), CurrentInstructionSlotIdx(0),
      AvailableSlots(SM.MicroOpBufferSize), MaxRetirePerCycle(0), Owner(DU) {
  // Check if the scheduling model provides extra information about the machine
  // processor. If so, then use that information to set the reorder buffer size
  // and the maximum number of instructions retired per cycle.
  if (SM.hasExtraProcessorInfo()) {
    const MCExtraProcessorInfo &EPI = SM.getExtraProcessorInfo();
    if (EPI.ReorderBufferSize)
      AvailableSlots = EPI.ReorderBufferSize;
    MaxRetirePerCycle = EPI.MaxRetirePerCycle;
  }

  assert(AvailableSlots && "Invalid reorder buffer size!");
  Queue.resize(AvailableSlots);
}

// Reserves a number of slots, and returns a new token.
unsigned RetireControlUnit::reserveSlot(const InstRef &IR, unsigned NumMicroOps) {
  assert(isAvailable(NumMicroOps));
  unsigned NormalizedQuantity =
      std::min(NumMicroOps, static_cast<unsigned>(Queue.size()));
  // Zero latency instructions may have zero mOps. Artificially bump this
  // value to 1. Although zero latency instructions don't consume scheduler
  // resources, they still consume one slot in the retire queue.
  NormalizedQuantity = std::max(NormalizedQuantity, 1U);
  unsigned TokenID = NextAvailableSlotIdx;
  Queue[NextAvailableSlotIdx] = {IR, NormalizedQuantity, false};
  NextAvailableSlotIdx += NormalizedQuantity;
  NextAvailableSlotIdx %= Queue.size();
  AvailableSlots -= NormalizedQuantity;
  return TokenID;
}

void RetireControlUnit::cycleEvent() {
  if (isEmpty())
    return;

  unsigned NumRetired = 0;
  while (!isEmpty()) {
    if (MaxRetirePerCycle != 0 && NumRetired == MaxRetirePerCycle)
      break;
    RUToken &Current = Queue[CurrentInstructionSlotIdx];
    assert(Current.NumSlots && "Reserved zero slots?");
    assert(Current.IR.isValid() && "Invalid RUToken in the RCU queue.");
    if (!Current.Executed)
      break;
    Owner->notifyInstructionRetired(Current.IR);
    CurrentInstructionSlotIdx += Current.NumSlots;
    CurrentInstructionSlotIdx %= Queue.size();
    AvailableSlots += Current.NumSlots;
    NumRetired++;
  }
}

void RetireControlUnit::onInstructionExecuted(unsigned TokenID) {
  assert(Queue.size() > TokenID);
  assert(Queue[TokenID].Executed == false && Queue[TokenID].IR.isValid());
  Queue[TokenID].Executed = true;
}

#ifndef NDEBUG
void RetireControlUnit::dump() const {
  dbgs() << "Retire Unit: { Total Slots=" << Queue.size()
         << ", Available Slots=" << AvailableSlots << " }\n";
}
#endif

} // namespace mca