llvm/lib/Target/Hexagon/HexagonHazardRecognizer.cpp

   1 //===-- HexagonHazardRecognizer.cpp - Hexagon Post RA Hazard Recognizer ---===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the hazard recognizer for scheduling on Hexagon.
  10 // Use a DFA based hazard recognizer.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "HexagonHazardRecognizer.h"
  15 #include "llvm/CodeGen/MachineFunction.h"
  16 #include "llvm/CodeGen/MachineInstr.h"
  17 #include "llvm/CodeGen/MachineOperand.h"
  18 #include "llvm/CodeGen/ScheduleDAG.h"
  19 #include "llvm/Support/Debug.h"
  20 #include "llvm/Support/raw_ostream.h"
  21 #include <cassert>
  22
  23 using namespace llvm;
  24
  25 #define DEBUG_TYPE "post-RA-sched"
  26
  27 void HexagonHazardRecognizer::Reset() {
  28   LLVM_DEBUG(dbgs() << "Reset hazard recognizer\n");
  29   Resources->clearResources();
  30   PacketNum = 0;
  31   UsesDotCur = nullptr;
  32   DotCurPNum = -1;
  33   UsesLoad = false;
  34   PrefVectorStoreNew = nullptr;
  35   RegDefs.clear();
  36 }
  37
  38 ScheduleHazardRecognizer::HazardType
  39 HexagonHazardRecognizer::getHazardType(SUnit *SU, int stalls) {
  40   MachineInstr *MI = SU->getInstr();
  41   if (!MI || TII->isZeroCost(MI->getOpcode()))
  42     return NoHazard;
  43
  44   if (!Resources->canReserveResources(*MI)) {
  45     LLVM_DEBUG(dbgs() << "*** Hazard in cycle " << PacketNum << ", " << *MI);
  46     HazardType RetVal = Hazard;
  47     if (isNewStore(*MI)) {
  48       // The .new store version uses different resources so check if it
  49       // causes a hazard.
  50       MachineFunction *MF = MI->getParent()->getParent();
  51       MachineInstr *NewMI =
  52         MF->CreateMachineInstr(TII->get(TII->getDotNewOp(*MI)),
  53                                MI->getDebugLoc());
  54       if (Resources->canReserveResources(*NewMI))
  55         RetVal = NoHazard;
  56       LLVM_DEBUG(dbgs() << "*** Try .new version? " << (RetVal == NoHazard)
  57                         << "\n");
  58       MF->deleteMachineInstr(NewMI);
  59     }
  60     return RetVal;
  61   }
  62
  63   if (SU == UsesDotCur && DotCurPNum != (int)PacketNum) {
  64     LLVM_DEBUG(dbgs() << "*** .cur Hazard in cycle " << PacketNum << ", "
  65                       << *MI);
  66     return Hazard;
  67   }
  68
  69   return NoHazard;
  70 }
  71
  72 void HexagonHazardRecognizer::AdvanceCycle() {
  73   LLVM_DEBUG(dbgs() << "Advance cycle, clear state\n");
  74   Resources->clearResources();
  75   if (DotCurPNum != -1 && DotCurPNum != (int)PacketNum) {
  76     UsesDotCur = nullptr;
  77     DotCurPNum = -1;
  78   }
  79   UsesLoad = false;
  80   PrefVectorStoreNew = nullptr;
  81   PacketNum++;
  82   RegDefs.clear();
  83 }
  84
  85 /// Handle the cases when we prefer one instruction over another. Case 1 - we
  86 /// prefer not to generate multiple loads in the packet to avoid a potential
  87 /// bank conflict. Case 2 - if a packet contains a dot cur instruction, then we
  88 /// prefer the instruction that can use the dot cur result. However, if the use
  89 /// is not scheduled in the same packet, then prefer other instructions in the
  90 /// subsequent packet. Case 3 - we prefer a vector store that can be converted
  91 /// to a .new store. The packetizer will not generate the .new store if the
  92 /// store doesn't have resources to fit in the packet (but the .new store may
  93 /// have resources). We attempt to schedule the store as soon as possible to
  94 /// help packetize the two instructions together.
  95 bool HexagonHazardRecognizer::ShouldPreferAnother(SUnit *SU) {
  96   if (PrefVectorStoreNew != nullptr && PrefVectorStoreNew != SU)
  97     return true;
  98   if (UsesLoad && SU->isInstr() && SU->getInstr()->mayLoad())
  99     return true;
 100   return UsesDotCur && ((SU == UsesDotCur) ^ (DotCurPNum == (int)PacketNum));
 101 }
 102
 103 /// Return true if the instruction would be converted to a new value store when
 104 /// packetized.
 105 bool HexagonHazardRecognizer::isNewStore(MachineInstr &MI) {
 106   if (!TII->mayBeNewStore(MI))
 107     return false;
 108   MachineOperand &MO = MI.getOperand(MI.getNumOperands() - 1);
 109   return (MO.isReg() && RegDefs.count(MO.getReg()) != 0);
 110 }
 111
 112 void HexagonHazardRecognizer::EmitInstruction(SUnit *SU) {
 113   MachineInstr *MI = SU->getInstr();
 114   if (!MI)
 115     return;
 116
 117   // Keep the set of definitions for each packet, which is used to determine
 118   // if a .new can be used.
 119   for (const MachineOperand &MO : MI->operands())
 120     if (MO.isReg() && MO.isDef() && !MO.isImplicit())
 121       RegDefs.insert(MO.getReg());
 122
 123   if (TII->isZeroCost(MI->getOpcode()))
 124     return;
 125
 126   if (!Resources->canReserveResources(*MI) || isNewStore(*MI)) {
 127     // It must be a .new store since other instructions must be able to be
 128     // reserved at this point.
 129     assert(TII->mayBeNewStore(*MI) && "Expecting .new store");
 130     MachineFunction *MF = MI->getParent()->getParent();
 131     MachineInstr *NewMI =
 132         MF->CreateMachineInstr(TII->get(TII->getDotNewOp(*MI)),
 133                                MI->getDebugLoc());
 134     if (Resources->canReserveResources(*NewMI))
 135       Resources->reserveResources(*NewMI);
 136     else
 137       Resources->reserveResources(*MI);
 138     MF->deleteMachineInstr(NewMI);
 139   } else
 140     Resources->reserveResources(*MI);
 141   LLVM_DEBUG(dbgs() << " Add instruction " << *MI);
 142
 143   // When scheduling a dot cur instruction, check if there is an instruction
 144   // that can use the dot cur in the same packet. If so, we'll attempt to
 145   // schedule it before other instructions. We only do this if the load has a
 146   // single zero-latency use.
 147   if (TII->mayBeCurLoad(*MI))
 148     for (auto &S : SU->Succs)
 149       if (S.isAssignedRegDep() && S.getLatency() == 0 &&
 150           S.getSUnit()->NumPredsLeft == 1) {
 151         UsesDotCur = S.getSUnit();
 152         DotCurPNum = PacketNum;
 153         break;
 154       }
 155   if (SU == UsesDotCur) {
 156     UsesDotCur = nullptr;
 157     DotCurPNum = -1;
 158   }
 159
 160   UsesLoad = MI->mayLoad();
 161
 162   if (TII->isHVXVec(*MI) && !MI->mayLoad() && !MI->mayStore())
 163     for (auto &S : SU->Succs)
 164       if (S.isAssignedRegDep() && S.getLatency() == 0 &&
 165           TII->mayBeNewStore(*S.getSUnit()->getInstr()) &&
 166           Resources->canReserveResources(*S.getSUnit()->getInstr())) {
 167         PrefVectorStoreNew = S.getSUnit();
 168         break;
 169       }
 170 }