1 //===-- MLxExpansionPass.cpp - Expand MLx instrs to avoid hazards ---------===// 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 // Expand VFP / NEON floating point MLA / MLS instructions (each to a pair of 10 // multiple and add / sub instructions) when special VMLx hazards are detected. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "ARM.h" 15 #include "ARMBaseInstrInfo.h" 16 #include "ARMSubtarget.h" 17 #include "llvm/ADT/SmallPtrSet.h" 18 #include "llvm/ADT/Statistic.h" 19 #include "llvm/CodeGen/MachineFunctionPass.h" 20 #include "llvm/CodeGen/MachineInstr.h" 21 #include "llvm/CodeGen/MachineInstrBuilder.h" 22 #include "llvm/CodeGen/MachineRegisterInfo.h" 23 #include "llvm/CodeGen/TargetRegisterInfo.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Support/Debug.h" 26 #include "llvm/Support/raw_ostream.h" 27 using namespace llvm; 28 29 #define DEBUG_TYPE "mlx-expansion" 30 31 static cl::opt<bool> 32 ForceExapnd("expand-all-fp-mlx", cl::init(false), cl::Hidden); 33 static cl::opt<unsigned> 34 ExpandLimit("expand-limit", cl::init(~0U), cl::Hidden); 35 36 STATISTIC(NumExpand, "Number of fp MLA / MLS instructions expanded"); 37 38 namespace { 39 struct MLxExpansion : public MachineFunctionPass { 40 static char ID; 41 MLxExpansion() : MachineFunctionPass(ID) {} 42 43 bool runOnMachineFunction(MachineFunction &Fn) override; 44 45 StringRef getPassName() const override { 46 return "ARM MLA / MLS expansion pass"; 47 } 48 49 private: 50 const ARMBaseInstrInfo *TII; 51 const TargetRegisterInfo *TRI; 52 MachineRegisterInfo *MRI; 53 54 bool isLikeA9; 55 bool isSwift; 56 unsigned MIIdx; 57 MachineInstr* LastMIs[4]; 58 SmallPtrSet<MachineInstr*, 4> IgnoreStall; 59 60 void clearStack(); 61 void pushStack(MachineInstr *MI); 62 MachineInstr *getAccDefMI(MachineInstr *MI) const; 63 unsigned getDefReg(MachineInstr *MI) const; 64 bool hasLoopHazard(MachineInstr *MI) const; 65 bool hasRAWHazard(unsigned Reg, MachineInstr *MI) const; 66 bool FindMLxHazard(MachineInstr *MI); 67 void ExpandFPMLxInstruction(MachineBasicBlock &MBB, MachineInstr *MI, 68 unsigned MulOpc, unsigned AddSubOpc, 69 bool NegAcc, bool HasLane); 70 bool ExpandFPMLxInstructions(MachineBasicBlock &MBB); 71 }; 72 char MLxExpansion::ID = 0; 73 } 74 75 void MLxExpansion::clearStack() { 76 std::fill(LastMIs, LastMIs + 4, nullptr); 77 MIIdx = 0; 78 } 79 80 void MLxExpansion::pushStack(MachineInstr *MI) { 81 LastMIs[MIIdx] = MI; 82 if (++MIIdx == 4) 83 MIIdx = 0; 84 } 85 86 MachineInstr *MLxExpansion::getAccDefMI(MachineInstr *MI) const { 87 // Look past COPY and INSERT_SUBREG instructions to find the 88 // real definition MI. This is important for _sfp instructions. 89 Register Reg = MI->getOperand(1).getReg(); 90 if (Reg.isPhysical()) 91 return nullptr; 92 93 MachineBasicBlock *MBB = MI->getParent(); 94 MachineInstr *DefMI = MRI->getVRegDef(Reg); 95 while (true) { 96 if (DefMI->getParent() != MBB) 97 break; 98 if (DefMI->isCopyLike()) { 99 Reg = DefMI->getOperand(1).getReg(); 100 if (Reg.isVirtual()) { 101 DefMI = MRI->getVRegDef(Reg); 102 continue; 103 } 104 } else if (DefMI->isInsertSubreg()) { 105 Reg = DefMI->getOperand(2).getReg(); 106 if (Reg.isVirtual()) { 107 DefMI = MRI->getVRegDef(Reg); 108 continue; 109 } 110 } 111 break; 112 } 113 return DefMI; 114 } 115 116 unsigned MLxExpansion::getDefReg(MachineInstr *MI) const { 117 Register Reg = MI->getOperand(0).getReg(); 118 if (Reg.isPhysical() || !MRI->hasOneNonDBGUse(Reg)) 119 return Reg; 120 121 MachineBasicBlock *MBB = MI->getParent(); 122 MachineInstr *UseMI = &*MRI->use_instr_nodbg_begin(Reg); 123 if (UseMI->getParent() != MBB) 124 return Reg; 125 126 while (UseMI->isCopy() || UseMI->isInsertSubreg()) { 127 Reg = UseMI->getOperand(0).getReg(); 128 if (Reg.isPhysical() || !MRI->hasOneNonDBGUse(Reg)) 129 return Reg; 130 UseMI = &*MRI->use_instr_nodbg_begin(Reg); 131 if (UseMI->getParent() != MBB) 132 return Reg; 133 } 134 135 return Reg; 136 } 137 138 /// hasLoopHazard - Check whether an MLx instruction is chained to itself across 139 /// a single-MBB loop. 140 bool MLxExpansion::hasLoopHazard(MachineInstr *MI) const { 141 Register Reg = MI->getOperand(1).getReg(); 142 if (Reg.isPhysical()) 143 return false; 144 145 MachineBasicBlock *MBB = MI->getParent(); 146 MachineInstr *DefMI = MRI->getVRegDef(Reg); 147 while (true) { 148 outer_continue: 149 if (DefMI->getParent() != MBB) 150 break; 151 152 if (DefMI->isPHI()) { 153 for (unsigned i = 1, e = DefMI->getNumOperands(); i < e; i += 2) { 154 if (DefMI->getOperand(i + 1).getMBB() == MBB) { 155 Register SrcReg = DefMI->getOperand(i).getReg(); 156 if (SrcReg.isVirtual()) { 157 DefMI = MRI->getVRegDef(SrcReg); 158 goto outer_continue; 159 } 160 } 161 } 162 } else if (DefMI->isCopyLike()) { 163 Reg = DefMI->getOperand(1).getReg(); 164 if (Reg.isVirtual()) { 165 DefMI = MRI->getVRegDef(Reg); 166 continue; 167 } 168 } else if (DefMI->isInsertSubreg()) { 169 Reg = DefMI->getOperand(2).getReg(); 170 if (Reg.isVirtual()) { 171 DefMI = MRI->getVRegDef(Reg); 172 continue; 173 } 174 } 175 176 break; 177 } 178 179 return DefMI == MI; 180 } 181 182 bool MLxExpansion::hasRAWHazard(unsigned Reg, MachineInstr *MI) const { 183 // FIXME: Detect integer instructions properly. 184 const MCInstrDesc &MCID = MI->getDesc(); 185 unsigned Domain = MCID.TSFlags & ARMII::DomainMask; 186 if (MI->mayStore()) 187 return false; 188 unsigned Opcode = MCID.getOpcode(); 189 if (Opcode == ARM::VMOVRS || Opcode == ARM::VMOVRRD) 190 return false; 191 if ((Domain & ARMII::DomainVFP) || (Domain & ARMII::DomainNEON)) 192 return MI->readsRegister(Reg, TRI); 193 return false; 194 } 195 196 static bool isFpMulInstruction(unsigned Opcode) { 197 switch (Opcode) { 198 case ARM::VMULS: 199 case ARM::VMULfd: 200 case ARM::VMULfq: 201 case ARM::VMULD: 202 case ARM::VMULslfd: 203 case ARM::VMULslfq: 204 return true; 205 default: 206 return false; 207 } 208 } 209 210 bool MLxExpansion::FindMLxHazard(MachineInstr *MI) { 211 if (NumExpand >= ExpandLimit) 212 return false; 213 214 if (ForceExapnd) 215 return true; 216 217 MachineInstr *DefMI = getAccDefMI(MI); 218 if (TII->isFpMLxInstruction(DefMI->getOpcode())) { 219 // r0 = vmla 220 // r3 = vmla r0, r1, r2 221 // takes 16 - 17 cycles 222 // 223 // r0 = vmla 224 // r4 = vmul r1, r2 225 // r3 = vadd r0, r4 226 // takes about 14 - 15 cycles even with vmul stalling for 4 cycles. 227 IgnoreStall.insert(DefMI); 228 return true; 229 } 230 231 // On Swift, we mostly care about hazards from multiplication instructions 232 // writing the accumulator and the pipelining of loop iterations by out-of- 233 // order execution. 234 if (isSwift) 235 return isFpMulInstruction(DefMI->getOpcode()) || hasLoopHazard(MI); 236 237 if (IgnoreStall.count(MI)) 238 return false; 239 240 // If a VMLA.F is followed by an VADD.F or VMUL.F with no RAW hazard, the 241 // VADD.F or VMUL.F will stall 4 cycles before issue. The 4 cycle stall 242 // preserves the in-order retirement of the instructions. 243 // Look at the next few instructions, if *most* of them can cause hazards, 244 // then the scheduler can't *fix* this, we'd better break up the VMLA. 245 unsigned Limit1 = isLikeA9 ? 1 : 4; 246 unsigned Limit2 = isLikeA9 ? 1 : 4; 247 for (unsigned i = 1; i <= 4; ++i) { 248 int Idx = ((int)MIIdx - i + 4) % 4; 249 MachineInstr *NextMI = LastMIs[Idx]; 250 if (!NextMI) 251 continue; 252 253 if (TII->canCauseFpMLxStall(NextMI->getOpcode())) { 254 if (i <= Limit1) 255 return true; 256 } 257 258 // Look for VMLx RAW hazard. 259 if (i <= Limit2 && hasRAWHazard(getDefReg(MI), NextMI)) 260 return true; 261 } 262 263 return false; 264 } 265 266 /// ExpandFPMLxInstructions - Expand a MLA / MLS instruction into a pair 267 /// of MUL + ADD / SUB instructions. 268 void 269 MLxExpansion::ExpandFPMLxInstruction(MachineBasicBlock &MBB, MachineInstr *MI, 270 unsigned MulOpc, unsigned AddSubOpc, 271 bool NegAcc, bool HasLane) { 272 Register DstReg = MI->getOperand(0).getReg(); 273 bool DstDead = MI->getOperand(0).isDead(); 274 Register AccReg = MI->getOperand(1).getReg(); 275 Register Src1Reg = MI->getOperand(2).getReg(); 276 Register Src2Reg = MI->getOperand(3).getReg(); 277 bool Src1Kill = MI->getOperand(2).isKill(); 278 bool Src2Kill = MI->getOperand(3).isKill(); 279 unsigned LaneImm = HasLane ? MI->getOperand(4).getImm() : 0; 280 unsigned NextOp = HasLane ? 5 : 4; 281 ARMCC::CondCodes Pred = (ARMCC::CondCodes)MI->getOperand(NextOp).getImm(); 282 Register PredReg = MI->getOperand(++NextOp).getReg(); 283 284 const MCInstrDesc &MCID1 = TII->get(MulOpc); 285 const MCInstrDesc &MCID2 = TII->get(AddSubOpc); 286 const MachineFunction &MF = *MI->getParent()->getParent(); 287 Register TmpReg = 288 MRI->createVirtualRegister(TII->getRegClass(MCID1, 0, TRI, MF)); 289 290 MachineInstrBuilder MIB = BuildMI(MBB, MI, MI->getDebugLoc(), MCID1, TmpReg) 291 .addReg(Src1Reg, getKillRegState(Src1Kill)) 292 .addReg(Src2Reg, getKillRegState(Src2Kill)); 293 if (HasLane) 294 MIB.addImm(LaneImm); 295 MIB.addImm(Pred).addReg(PredReg); 296 297 MIB = BuildMI(MBB, MI, MI->getDebugLoc(), MCID2) 298 .addReg(DstReg, getDefRegState(true) | getDeadRegState(DstDead)); 299 300 if (NegAcc) { 301 bool AccKill = MRI->hasOneNonDBGUse(AccReg); 302 MIB.addReg(TmpReg, getKillRegState(true)) 303 .addReg(AccReg, getKillRegState(AccKill)); 304 } else { 305 MIB.addReg(AccReg).addReg(TmpReg, getKillRegState(true)); 306 } 307 MIB.addImm(Pred).addReg(PredReg); 308 309 LLVM_DEBUG({ 310 dbgs() << "Expanding: " << *MI; 311 dbgs() << " to:\n"; 312 MachineBasicBlock::iterator MII = MI; 313 MII = std::prev(MII); 314 MachineInstr &MI2 = *MII; 315 MII = std::prev(MII); 316 MachineInstr &MI1 = *MII; 317 dbgs() << " " << MI1; 318 dbgs() << " " << MI2; 319 }); 320 321 MI->eraseFromParent(); 322 ++NumExpand; 323 } 324 325 bool MLxExpansion::ExpandFPMLxInstructions(MachineBasicBlock &MBB) { 326 bool Changed = false; 327 328 clearStack(); 329 IgnoreStall.clear(); 330 331 unsigned Skip = 0; 332 MachineBasicBlock::reverse_iterator MII = MBB.rbegin(), E = MBB.rend(); 333 while (MII != E) { 334 MachineInstr *MI = &*MII++; 335 336 if (MI->isPosition() || MI->isImplicitDef() || MI->isCopy()) 337 continue; 338 339 const MCInstrDesc &MCID = MI->getDesc(); 340 if (MI->isBarrier()) { 341 clearStack(); 342 Skip = 0; 343 continue; 344 } 345 346 unsigned Domain = MCID.TSFlags & ARMII::DomainMask; 347 if (Domain == ARMII::DomainGeneral) { 348 if (++Skip == 2) 349 // Assume dual issues of non-VFP / NEON instructions. 350 pushStack(nullptr); 351 } else { 352 Skip = 0; 353 354 unsigned MulOpc, AddSubOpc; 355 bool NegAcc, HasLane; 356 if (!TII->isFpMLxInstruction(MCID.getOpcode(), 357 MulOpc, AddSubOpc, NegAcc, HasLane) || 358 !FindMLxHazard(MI)) 359 pushStack(MI); 360 else { 361 ExpandFPMLxInstruction(MBB, MI, MulOpc, AddSubOpc, NegAcc, HasLane); 362 Changed = true; 363 } 364 } 365 } 366 367 return Changed; 368 } 369 370 bool MLxExpansion::runOnMachineFunction(MachineFunction &Fn) { 371 if (skipFunction(Fn.getFunction())) 372 return false; 373 374 TII = static_cast<const ARMBaseInstrInfo *>(Fn.getSubtarget().getInstrInfo()); 375 TRI = Fn.getSubtarget().getRegisterInfo(); 376 MRI = &Fn.getRegInfo(); 377 const ARMSubtarget *STI = &Fn.getSubtarget<ARMSubtarget>(); 378 if (!STI->expandMLx()) 379 return false; 380 isLikeA9 = STI->isLikeA9() || STI->isSwift(); 381 isSwift = STI->isSwift(); 382 383 bool Modified = false; 384 for (MachineBasicBlock &MBB : Fn) 385 Modified |= ExpandFPMLxInstructions(MBB); 386 387 return Modified; 388 } 389 390 FunctionPass *llvm::createMLxExpansionPass() { 391 return new MLxExpansion(); 392 } 393