llvm/lib/Target/AMDGPU/R600EmitClauseMarkers.cpp

   1 //===-- R600EmitClauseMarkers.cpp - Emit CF_ALU ---------------------------===//
   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 /// \file
  10 /// Add CF_ALU. R600 Alu instructions are grouped in clause which can hold
  11 /// 128 Alu instructions ; these instructions can access up to 4 prefetched
  12 /// 4 lines of 16 registers from constant buffers. Such ALU clauses are
  13 /// initiated by CF_ALU instructions.
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "MCTargetDesc/R600MCTargetDesc.h"
  17 #include "R600.h"
  18 #include "R600Defines.h"
  19 #include "R600Subtarget.h"
  20 #include "llvm/CodeGen/MachineFunctionPass.h"
  21
  22 using namespace llvm;
  23
  24 namespace llvm {
  25
  26   void initializeR600EmitClauseMarkersPass(PassRegistry&);
  27
  28 } // end namespace llvm
  29
  30 namespace {
  31
  32 class R600EmitClauseMarkers : public MachineFunctionPass {
  33 private:
  34   const R600InstrInfo *TII = nullptr;
  35   int Address = 0;
  36
  37   unsigned OccupiedDwords(MachineInstr &MI) const {
  38     switch (MI.getOpcode()) {
  39     case R600::INTERP_PAIR_XY:
  40     case R600::INTERP_PAIR_ZW:
  41     case R600::INTERP_VEC_LOAD:
  42     case R600::DOT_4:
  43       return 4;
  44     case R600::KILL:
  45       return 0;
  46     default:
  47       break;
  48     }
  49
  50     // These will be expanded to two ALU instructions in the
  51     // ExpandSpecialInstructions pass.
  52     if (TII->isLDSRetInstr(MI.getOpcode()))
  53       return 2;
  54
  55     if (TII->isVector(MI) || TII->isCubeOp(MI.getOpcode()) ||
  56         TII->isReductionOp(MI.getOpcode()))
  57       return 4;
  58
  59     unsigned NumLiteral = 0;
  60     for (MachineInstr::mop_iterator It = MI.operands_begin(),
  61                                     E = MI.operands_end();
  62          It != E; ++It) {
  63       MachineOperand &MO = *It;
  64       if (MO.isReg() && MO.getReg() == R600::ALU_LITERAL_X)
  65         ++NumLiteral;
  66     }
  67     return 1 + NumLiteral;
  68   }
  69
  70   bool isALU(const MachineInstr &MI) const {
  71     if (TII->isALUInstr(MI.getOpcode()))
  72       return true;
  73     if (TII->isVector(MI) || TII->isCubeOp(MI.getOpcode()))
  74       return true;
  75     switch (MI.getOpcode()) {
  76     case R600::PRED_X:
  77     case R600::INTERP_PAIR_XY:
  78     case R600::INTERP_PAIR_ZW:
  79     case R600::INTERP_VEC_LOAD:
  80     case R600::COPY:
  81     case R600::DOT_4:
  82       return true;
  83     default:
  84       return false;
  85     }
  86   }
  87
  88   bool IsTrivialInst(MachineInstr &MI) const {
  89     switch (MI.getOpcode()) {
  90     case R600::KILL:
  91     case R600::RETURN:
  92     case R600::IMPLICIT_DEF:
  93       return true;
  94     default:
  95       return false;
  96     }
  97   }
  98
  99   std::pair<unsigned, unsigned> getAccessedBankLine(unsigned Sel) const {
 100     // Sel is (512 + (kc_bank << 12) + ConstIndex) << 2
 101     // (See also R600ISelLowering.cpp)
 102     // ConstIndex value is in [0, 4095];
 103     return std::pair<unsigned, unsigned>(
 104         ((Sel >> 2) - 512) >> 12, // KC_BANK
 105         // Line Number of ConstIndex
 106         // A line contains 16 constant registers however KCX bank can lock
 107         // two line at the same time ; thus we want to get an even line number.
 108         // Line number can be retrieved with (>>4), using (>>5) <<1 generates
 109         // an even number.
 110         ((((Sel >> 2) - 512) & 4095) >> 5) << 1);
 111   }
 112
 113   bool
 114   SubstituteKCacheBank(MachineInstr &MI,
 115                        std::vector<std::pair<unsigned, unsigned>> &CachedConsts,
 116                        bool UpdateInstr = true) const {
 117     std::vector<std::pair<unsigned, unsigned>> UsedKCache;
 118
 119     if (!TII->isALUInstr(MI.getOpcode()) && MI.getOpcode() != R600::DOT_4)
 120       return true;
 121
 122     const SmallVectorImpl<std::pair<MachineOperand *, int64_t>> &Consts =
 123         TII->getSrcs(MI);
 124     assert(
 125         (TII->isALUInstr(MI.getOpcode()) || MI.getOpcode() == R600::DOT_4) &&
 126         "Can't assign Const");
 127     for (auto &[Op, Sel] : Consts) {
 128       if (Op->getReg() != R600::ALU_CONST)
 129         continue;
 130       unsigned Chan = Sel & 3, Index = ((Sel >> 2) - 512) & 31;
 131       unsigned KCacheIndex = Index * 4 + Chan;
 132       const std::pair<unsigned, unsigned> &BankLine = getAccessedBankLine(Sel);
 133       if (CachedConsts.empty()) {
 134         CachedConsts.push_back(BankLine);
 135         UsedKCache.emplace_back(0, KCacheIndex);
 136         continue;
 137       }
 138       if (CachedConsts[0] == BankLine) {
 139         UsedKCache.emplace_back(0, KCacheIndex);
 140         continue;
 141       }
 142       if (CachedConsts.size() == 1) {
 143         CachedConsts.push_back(BankLine);
 144         UsedKCache.emplace_back(1, KCacheIndex);
 145         continue;
 146       }
 147       if (CachedConsts[1] == BankLine) {
 148         UsedKCache.emplace_back(1, KCacheIndex);
 149         continue;
 150       }
 151       return false;
 152     }
 153
 154     if (!UpdateInstr)
 155       return true;
 156
 157     unsigned j = 0;
 158     for (auto &[Op, Sel] : Consts) {
 159       if (Op->getReg() != R600::ALU_CONST)
 160         continue;
 161       switch (UsedKCache[j].first) {
 162       case 0:
 163         Op->setReg(R600::R600_KC0RegClass.getRegister(UsedKCache[j].second));
 164         break;
 165       case 1:
 166         Op->setReg(R600::R600_KC1RegClass.getRegister(UsedKCache[j].second));
 167         break;
 168       default:
 169         llvm_unreachable("Wrong Cache Line");
 170       }
 171       j++;
 172     }
 173     return true;
 174   }
 175
 176   bool canClauseLocalKillFitInClause(
 177                         unsigned AluInstCount,
 178                         std::vector<std::pair<unsigned, unsigned>> KCacheBanks,
 179                         MachineBasicBlock::iterator Def,
 180                         MachineBasicBlock::iterator BBEnd) {
 181     const R600RegisterInfo &TRI = TII->getRegisterInfo();
 182     //TODO: change this to defs?
 183     for (MachineOperand &MO : Def->all_defs()) {
 184       if (TRI.isPhysRegLiveAcrossClauses(MO.getReg()))
 185         continue;
 186
 187       // Def defines a clause local register, so check that its use will fit
 188       // in the clause.
 189       unsigned LastUseCount = 0;
 190       for (MachineBasicBlock::iterator UseI = Def; UseI != BBEnd; ++UseI) {
 191         AluInstCount += OccupiedDwords(*UseI);
 192         // Make sure we won't need to end the clause due to KCache limitations.
 193         if (!SubstituteKCacheBank(*UseI, KCacheBanks, false))
 194           return false;
 195
 196         // We have reached the maximum instruction limit before finding the
 197         // use that kills this register, so we cannot use this def in the
 198         // current clause.
 199         if (AluInstCount >= TII->getMaxAlusPerClause())
 200           return false;
 201
 202         // TODO: Is this true? kill flag appears to work OK below
 203         // Register kill flags have been cleared by the time we get to this
 204         // pass, but it is safe to assume that all uses of this register
 205         // occur in the same basic block as its definition, because
 206         // it is illegal for the scheduler to schedule them in
 207         // different blocks.
 208         if (UseI->readsRegister(MO.getReg(), &TRI))
 209           LastUseCount = AluInstCount;
 210
 211         // Exit early if the current use kills the register
 212         if (UseI != Def && UseI->killsRegister(MO.getReg(), &TRI))
 213           break;
 214       }
 215       if (LastUseCount)
 216         return LastUseCount <= TII->getMaxAlusPerClause();
 217       llvm_unreachable("Clause local register live at end of clause.");
 218     }
 219     return true;
 220   }
 221
 222   MachineBasicBlock::iterator
 223   MakeALUClause(MachineBasicBlock &MBB, MachineBasicBlock::iterator I) {
 224     MachineBasicBlock::iterator ClauseHead = I;
 225     std::vector<std::pair<unsigned, unsigned>> KCacheBanks;
 226     bool PushBeforeModifier = false;
 227     unsigned AluInstCount = 0;
 228     for (MachineBasicBlock::iterator E = MBB.end(); I != E; ++I) {
 229       if (IsTrivialInst(*I))
 230         continue;
 231       if (!isALU(*I))
 232         break;
 233       if (AluInstCount > TII->getMaxAlusPerClause())
 234         break;
 235       if (I->getOpcode() == R600::PRED_X) {
 236         // We put PRED_X in its own clause to ensure that ifcvt won't create
 237         // clauses with more than 128 insts.
 238         // IfCvt is indeed checking that "then" and "else" branches of an if
 239         // statement have less than ~60 insts thus converted clauses can't be
 240         // bigger than ~121 insts (predicate setter needs to be in the same
 241         // clause as predicated alus).
 242         if (AluInstCount > 0)
 243           break;
 244         if (TII->getFlagOp(*I).getImm() & MO_FLAG_PUSH)
 245           PushBeforeModifier = true;
 246         AluInstCount ++;
 247         continue;
 248       }
 249       // XXX: GROUP_BARRIER instructions cannot be in the same ALU clause as:
 250       //
 251       // * KILL or INTERP instructions
 252       // * Any instruction that sets UPDATE_EXEC_MASK or UPDATE_PRED bits
 253       // * Uses waterfalling (i.e. INDEX_MODE = AR.X)
 254       //
 255       // XXX: These checks have not been implemented yet.
 256       if (TII->mustBeLastInClause(I->getOpcode())) {
 257         I++;
 258         break;
 259       }
 260
 261       // If this instruction defines a clause local register, make sure
 262       // its use can fit in this clause.
 263       if (!canClauseLocalKillFitInClause(AluInstCount, KCacheBanks, I, E))
 264         break;
 265
 266       if (!SubstituteKCacheBank(*I, KCacheBanks))
 267         break;
 268       AluInstCount += OccupiedDwords(*I);
 269     }
 270     unsigned Opcode = PushBeforeModifier ?
 271         R600::CF_ALU_PUSH_BEFORE : R600::CF_ALU;
 272     BuildMI(MBB, ClauseHead, MBB.findDebugLoc(ClauseHead), TII->get(Opcode))
 273     // We don't use the ADDR field until R600ControlFlowFinalizer pass, where
 274     // it is safe to assume it is 0. However if we always put 0 here, the ifcvt
 275     // pass may assume that identical ALU clause starter at the beginning of a
 276     // true and false branch can be factorized which is not the case.
 277         .addImm(Address++) // ADDR
 278         .addImm(KCacheBanks.empty()?0:KCacheBanks[0].first) // KB0
 279         .addImm((KCacheBanks.size() < 2)?0:KCacheBanks[1].first) // KB1
 280         .addImm(KCacheBanks.empty()?0:2) // KM0
 281         .addImm((KCacheBanks.size() < 2)?0:2) // KM1
 282         .addImm(KCacheBanks.empty()?0:KCacheBanks[0].second) // KLINE0
 283         .addImm((KCacheBanks.size() < 2)?0:KCacheBanks[1].second) // KLINE1
 284         .addImm(AluInstCount) // COUNT
 285         .addImm(1); // Enabled
 286     return I;
 287   }
 288
 289 public:
 290   static char ID;
 291
 292   R600EmitClauseMarkers() : MachineFunctionPass(ID) {
 293     initializeR600EmitClauseMarkersPass(*PassRegistry::getPassRegistry());
 294   }
 295
 296   bool runOnMachineFunction(MachineFunction &MF) override {
 297     const R600Subtarget &ST = MF.getSubtarget<R600Subtarget>();
 298     TII = ST.getInstrInfo();
 299
 300     for (MachineBasicBlock &MBB : MF) {
 301       MachineBasicBlock::iterator I = MBB.begin();
 302       if (I != MBB.end() && I->getOpcode() == R600::CF_ALU)
 303         continue; // BB was already parsed
 304       for (MachineBasicBlock::iterator E = MBB.end(); I != E;) {
 305         if (isALU(*I)) {
 306           auto next = MakeALUClause(MBB, I);
 307           assert(next != I);
 308           I = next;
 309         } else
 310           ++I;
 311       }
 312     }
 313     return false;
 314   }
 315
 316   StringRef getPassName() const override {
 317     return "R600 Emit Clause Markers Pass";
 318   }
 319 };
 320
 321 char R600EmitClauseMarkers::ID = 0;
 322
 323 } // end anonymous namespace
 324
 325 INITIALIZE_PASS_BEGIN(R600EmitClauseMarkers, "emitclausemarkers",
 326                       "R600 Emit Clause Markers", false, false)
 327 INITIALIZE_PASS_END(R600EmitClauseMarkers, "emitclausemarkers",
 328                     "R600 Emit Clause Markers", false, false)
 329
 330 FunctionPass *llvm::createR600EmitClauseMarkers() {
 331   return new R600EmitClauseMarkers();
 332 }