1 //===- LiveIntervals.h - Live Interval Analysis -----------------*- C++ -*-===// 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 This file implements the LiveInterval analysis pass. Given some 10 /// numbering of each the machine instructions (in this implemention depth-first 11 /// order) an interval [i, j) is said to be a live interval for register v if 12 /// there is no instruction with number j' > j such that v is live at j' and 13 /// there is no instruction with number i' < i such that v is live at i'. In 14 /// this implementation intervals can have holes, i.e. an interval might look 15 /// like [1,20), [50,65), [1000,1001). 16 // 17 //===----------------------------------------------------------------------===// 18 19 #ifndef LLVM_CODEGEN_LIVEINTERVALS_H 20 #define LLVM_CODEGEN_LIVEINTERVALS_H 21 22 #include "llvm/ADT/ArrayRef.h" 23 #include "llvm/ADT/IndexedMap.h" 24 #include "llvm/ADT/SmallVector.h" 25 #include "llvm/CodeGen/LiveInterval.h" 26 #include "llvm/CodeGen/LiveIntervalCalc.h" 27 #include "llvm/CodeGen/MachineBasicBlock.h" 28 #include "llvm/CodeGen/MachineFunctionPass.h" 29 #include "llvm/CodeGen/MachinePassManager.h" 30 #include "llvm/CodeGen/SlotIndexes.h" 31 #include "llvm/CodeGen/TargetRegisterInfo.h" 32 #include "llvm/MC/LaneBitmask.h" 33 #include "llvm/Support/CommandLine.h" 34 #include "llvm/Support/Compiler.h" 35 #include "llvm/Support/ErrorHandling.h" 36 #include <cassert> 37 #include <cstdint> 38 #include <utility> 39 40 namespace llvm { 41 42 extern cl::opt<bool> UseSegmentSetForPhysRegs; 43 44 class BitVector; 45 class MachineBlockFrequencyInfo; 46 class MachineDominatorTree; 47 class MachineFunction; 48 class MachineInstr; 49 class MachineRegisterInfo; 50 class ProfileSummaryInfo; 51 class raw_ostream; 52 class TargetInstrInfo; 53 class VirtRegMap; 54 55 class LiveIntervals { 56 friend class LiveIntervalsAnalysis; 57 friend class LiveIntervalsWrapperPass; 58 59 MachineFunction *MF = nullptr; 60 MachineRegisterInfo *MRI = nullptr; 61 const TargetRegisterInfo *TRI = nullptr; 62 const TargetInstrInfo *TII = nullptr; 63 SlotIndexes *Indexes = nullptr; 64 MachineDominatorTree *DomTree = nullptr; 65 std::unique_ptr<LiveIntervalCalc> LICalc; 66 67 /// Special pool allocator for VNInfo's (LiveInterval val#). 68 VNInfo::Allocator VNInfoAllocator; 69 70 /// Live interval pointers for all the virtual registers. 71 IndexedMap<LiveInterval *, VirtReg2IndexFunctor> VirtRegIntervals; 72 73 /// Sorted list of instructions with register mask operands. Always use the 74 /// 'r' slot, RegMasks are normal clobbers, not early clobbers. 75 SmallVector<SlotIndex, 8> RegMaskSlots; 76 77 /// This vector is parallel to RegMaskSlots, it holds a pointer to the 78 /// corresponding register mask. This pointer can be recomputed as: 79 /// 80 /// MI = Indexes->getInstructionFromIndex(RegMaskSlot[N]); 81 /// unsigned OpNum = findRegMaskOperand(MI); 82 /// RegMaskBits[N] = MI->getOperand(OpNum).getRegMask(); 83 /// 84 /// This is kept in a separate vector partly because some standard 85 /// libraries don't support lower_bound() with mixed objects, partly to 86 /// improve locality when searching in RegMaskSlots. 87 /// Also see the comment in LiveInterval::find(). 88 SmallVector<const uint32_t *, 8> RegMaskBits; 89 90 /// For each basic block number, keep (begin, size) pairs indexing into the 91 /// RegMaskSlots and RegMaskBits arrays. 92 /// Note that basic block numbers may not be layout contiguous, that's why 93 /// we can't just keep track of the first register mask in each basic 94 /// block. 95 SmallVector<std::pair<unsigned, unsigned>, 8> RegMaskBlocks; 96 97 /// Keeps a live range set for each register unit to track fixed physreg 98 /// interference. 99 SmallVector<LiveRange *, 0> RegUnitRanges; 100 101 // Can only be created from pass manager. 102 LiveIntervals() = default; 103 LiveIntervals(MachineFunction &MF, SlotIndexes &SI, MachineDominatorTree &DT) 104 : Indexes(&SI), DomTree(&DT) { 105 analyze(MF); 106 } 107 108 void analyze(MachineFunction &MF); 109 110 void clear(); 111 112 public: 113 LiveIntervals(LiveIntervals &&) = default; 114 ~LiveIntervals(); 115 116 bool invalidate(MachineFunction &MF, const PreservedAnalyses &PA, 117 MachineFunctionAnalysisManager::Invalidator &Inv); 118 119 /// Calculate the spill weight to assign to a single instruction. 120 /// If \p PSI is provided the calculation is altered for optsize functions. 121 static float getSpillWeight(bool isDef, bool isUse, 122 const MachineBlockFrequencyInfo *MBFI, 123 const MachineInstr &MI, 124 ProfileSummaryInfo *PSI = nullptr); 125 126 /// Calculate the spill weight to assign to a single instruction. 127 /// If \p PSI is provided the calculation is altered for optsize functions. 128 static float getSpillWeight(bool isDef, bool isUse, 129 const MachineBlockFrequencyInfo *MBFI, 130 const MachineBasicBlock *MBB, 131 ProfileSummaryInfo *PSI = nullptr); 132 133 LiveInterval &getInterval(Register Reg) { 134 if (hasInterval(Reg)) 135 return *VirtRegIntervals[Reg.id()]; 136 137 return createAndComputeVirtRegInterval(Reg); 138 } 139 140 const LiveInterval &getInterval(Register Reg) const { 141 return const_cast<LiveIntervals *>(this)->getInterval(Reg); 142 } 143 144 bool hasInterval(Register Reg) const { 145 return VirtRegIntervals.inBounds(Reg.id()) && VirtRegIntervals[Reg.id()]; 146 } 147 148 /// Interval creation. 149 LiveInterval &createEmptyInterval(Register Reg) { 150 assert(!hasInterval(Reg) && "Interval already exists!"); 151 VirtRegIntervals.grow(Reg.id()); 152 VirtRegIntervals[Reg.id()] = createInterval(Reg); 153 return *VirtRegIntervals[Reg.id()]; 154 } 155 156 LiveInterval &createAndComputeVirtRegInterval(Register Reg) { 157 LiveInterval &LI = createEmptyInterval(Reg); 158 computeVirtRegInterval(LI); 159 return LI; 160 } 161 162 /// Return an existing interval for \p Reg. 163 /// If \p Reg has no interval then this creates a new empty one instead. 164 /// Note: does not trigger interval computation. 165 LiveInterval &getOrCreateEmptyInterval(Register Reg) { 166 return hasInterval(Reg) ? getInterval(Reg) : createEmptyInterval(Reg); 167 } 168 169 /// Interval removal. 170 void removeInterval(Register Reg) { 171 delete VirtRegIntervals[Reg]; 172 VirtRegIntervals[Reg] = nullptr; 173 } 174 175 /// Given a register and an instruction, adds a live segment from that 176 /// instruction to the end of its MBB. 177 LiveInterval::Segment addSegmentToEndOfBlock(Register Reg, 178 MachineInstr &startInst); 179 180 /// After removing some uses of a register, shrink its live range to just 181 /// the remaining uses. This method does not compute reaching defs for new 182 /// uses, and it doesn't remove dead defs. 183 /// Dead PHIDef values are marked as unused. New dead machine instructions 184 /// are added to the dead vector. Returns true if the interval may have been 185 /// separated into multiple connected components. 186 bool shrinkToUses(LiveInterval *li, 187 SmallVectorImpl<MachineInstr *> *dead = nullptr); 188 189 /// Specialized version of 190 /// shrinkToUses(LiveInterval *li, SmallVectorImpl<MachineInstr*> *dead) 191 /// that works on a subregister live range and only looks at uses matching 192 /// the lane mask of the subregister range. 193 /// This may leave the subrange empty which needs to be cleaned up with 194 /// LiveInterval::removeEmptySubranges() afterwards. 195 void shrinkToUses(LiveInterval::SubRange &SR, Register Reg); 196 197 /// Extend the live range \p LR to reach all points in \p Indices. The 198 /// points in the \p Indices array must be jointly dominated by the union 199 /// of the existing defs in \p LR and points in \p Undefs. 200 /// 201 /// PHI-defs are added as needed to maintain SSA form. 202 /// 203 /// If a SlotIndex in \p Indices is the end index of a basic block, \p LR 204 /// will be extended to be live out of the basic block. 205 /// If a SlotIndex in \p Indices is jointy dominated only by points in 206 /// \p Undefs, the live range will not be extended to that point. 207 /// 208 /// See also LiveRangeCalc::extend(). 209 void extendToIndices(LiveRange &LR, ArrayRef<SlotIndex> Indices, 210 ArrayRef<SlotIndex> Undefs); 211 212 void extendToIndices(LiveRange &LR, ArrayRef<SlotIndex> Indices) { 213 extendToIndices(LR, Indices, /*Undefs=*/{}); 214 } 215 216 /// If \p LR has a live value at \p Kill, prune its live range by removing 217 /// any liveness reachable from Kill. Add live range end points to 218 /// EndPoints such that extendToIndices(LI, EndPoints) will reconstruct the 219 /// value's live range. 220 /// 221 /// Calling pruneValue() and extendToIndices() can be used to reconstruct 222 /// SSA form after adding defs to a virtual register. 223 void pruneValue(LiveRange &LR, SlotIndex Kill, 224 SmallVectorImpl<SlotIndex> *EndPoints); 225 226 /// This function should not be used. Its intent is to tell you that you are 227 /// doing something wrong if you call pruneValue directly on a 228 /// LiveInterval. Indeed, you are supposed to call pruneValue on the main 229 /// LiveRange and all the LiveRanges of the subranges if any. 230 LLVM_ATTRIBUTE_UNUSED void pruneValue(LiveInterval &, SlotIndex, 231 SmallVectorImpl<SlotIndex> *) { 232 llvm_unreachable( 233 "Use pruneValue on the main LiveRange and on each subrange"); 234 } 235 236 SlotIndexes *getSlotIndexes() const { return Indexes; } 237 238 /// Returns true if the specified machine instr has been removed or was 239 /// never entered in the map. 240 bool isNotInMIMap(const MachineInstr &Instr) const { 241 return !Indexes->hasIndex(Instr); 242 } 243 244 /// Returns the base index of the given instruction. 245 SlotIndex getInstructionIndex(const MachineInstr &Instr) const { 246 return Indexes->getInstructionIndex(Instr); 247 } 248 249 /// Returns the instruction associated with the given index. 250 MachineInstr *getInstructionFromIndex(SlotIndex index) const { 251 return Indexes->getInstructionFromIndex(index); 252 } 253 254 /// Return the first index in the given basic block. 255 SlotIndex getMBBStartIdx(const MachineBasicBlock *mbb) const { 256 return Indexes->getMBBStartIdx(mbb); 257 } 258 259 /// Return the last index in the given basic block. 260 SlotIndex getMBBEndIdx(const MachineBasicBlock *mbb) const { 261 return Indexes->getMBBEndIdx(mbb); 262 } 263 264 bool isLiveInToMBB(const LiveRange &LR, const MachineBasicBlock *mbb) const { 265 return LR.liveAt(getMBBStartIdx(mbb)); 266 } 267 268 bool isLiveOutOfMBB(const LiveRange &LR, const MachineBasicBlock *mbb) const { 269 return LR.liveAt(getMBBEndIdx(mbb).getPrevSlot()); 270 } 271 272 MachineBasicBlock *getMBBFromIndex(SlotIndex index) const { 273 return Indexes->getMBBFromIndex(index); 274 } 275 276 void insertMBBInMaps(MachineBasicBlock *MBB) { 277 Indexes->insertMBBInMaps(MBB); 278 assert(unsigned(MBB->getNumber()) == RegMaskBlocks.size() && 279 "Blocks must be added in order."); 280 RegMaskBlocks.push_back(std::make_pair(RegMaskSlots.size(), 0)); 281 } 282 283 SlotIndex InsertMachineInstrInMaps(MachineInstr &MI) { 284 return Indexes->insertMachineInstrInMaps(MI); 285 } 286 287 void InsertMachineInstrRangeInMaps(MachineBasicBlock::iterator B, 288 MachineBasicBlock::iterator E) { 289 for (MachineBasicBlock::iterator I = B; I != E; ++I) 290 Indexes->insertMachineInstrInMaps(*I); 291 } 292 293 void RemoveMachineInstrFromMaps(MachineInstr &MI) { 294 Indexes->removeMachineInstrFromMaps(MI); 295 } 296 297 SlotIndex ReplaceMachineInstrInMaps(MachineInstr &MI, MachineInstr &NewMI) { 298 return Indexes->replaceMachineInstrInMaps(MI, NewMI); 299 } 300 301 VNInfo::Allocator &getVNInfoAllocator() { return VNInfoAllocator; } 302 303 /// Implement the dump method. 304 void print(raw_ostream &O) const; 305 void dump() const; 306 307 // For legacy pass to recompute liveness. 308 void reanalyze(MachineFunction &MF) { 309 clear(); 310 analyze(MF); 311 } 312 313 MachineDominatorTree &getDomTree() { return *DomTree; } 314 315 /// If LI is confined to a single basic block, return a pointer to that 316 /// block. If LI is live in to or out of any block, return NULL. 317 MachineBasicBlock *intervalIsInOneMBB(const LiveInterval &LI) const; 318 319 /// Returns true if VNI is killed by any PHI-def values in LI. 320 /// This may conservatively return true to avoid expensive computations. 321 bool hasPHIKill(const LiveInterval &LI, const VNInfo *VNI) const; 322 323 /// Add kill flags to any instruction that kills a virtual register. 324 void addKillFlags(const VirtRegMap *); 325 326 /// Call this method to notify LiveIntervals that instruction \p MI has been 327 /// moved within a basic block. This will update the live intervals for all 328 /// operands of \p MI. Moves between basic blocks are not supported. 329 /// 330 /// \param UpdateFlags Update live intervals for nonallocatable physregs. 331 void handleMove(MachineInstr &MI, bool UpdateFlags = false); 332 333 /// Update intervals of operands of all instructions in the newly 334 /// created bundle specified by \p BundleStart. 335 /// 336 /// \param UpdateFlags Update live intervals for nonallocatable physregs. 337 /// 338 /// Assumes existing liveness is accurate. 339 /// \pre BundleStart should be the first instruction in the Bundle. 340 /// \pre BundleStart should not have a have SlotIndex as one will be assigned. 341 void handleMoveIntoNewBundle(MachineInstr &BundleStart, 342 bool UpdateFlags = false); 343 344 /// Update live intervals for instructions in a range of iterators. It is 345 /// intended for use after target hooks that may insert or remove 346 /// instructions, and is only efficient for a small number of instructions. 347 /// 348 /// OrigRegs is a vector of registers that were originally used by the 349 /// instructions in the range between the two iterators. 350 /// 351 /// Currently, the only changes that are supported are simple removal 352 /// and addition of uses. 353 void repairIntervalsInRange(MachineBasicBlock *MBB, 354 MachineBasicBlock::iterator Begin, 355 MachineBasicBlock::iterator End, 356 ArrayRef<Register> OrigRegs); 357 358 // Register mask functions. 359 // 360 // Machine instructions may use a register mask operand to indicate that a 361 // large number of registers are clobbered by the instruction. This is 362 // typically used for calls. 363 // 364 // For compile time performance reasons, these clobbers are not recorded in 365 // the live intervals for individual physical registers. Instead, 366 // LiveIntervalAnalysis maintains a sorted list of instructions with 367 // register mask operands. 368 369 /// Returns a sorted array of slot indices of all instructions with 370 /// register mask operands. 371 ArrayRef<SlotIndex> getRegMaskSlots() const { return RegMaskSlots; } 372 373 /// Returns a sorted array of slot indices of all instructions with register 374 /// mask operands in the basic block numbered \p MBBNum. 375 ArrayRef<SlotIndex> getRegMaskSlotsInBlock(unsigned MBBNum) const { 376 std::pair<unsigned, unsigned> P = RegMaskBlocks[MBBNum]; 377 return getRegMaskSlots().slice(P.first, P.second); 378 } 379 380 /// Returns an array of register mask pointers corresponding to 381 /// getRegMaskSlots(). 382 ArrayRef<const uint32_t *> getRegMaskBits() const { return RegMaskBits; } 383 384 /// Returns an array of mask pointers corresponding to 385 /// getRegMaskSlotsInBlock(MBBNum). 386 ArrayRef<const uint32_t *> getRegMaskBitsInBlock(unsigned MBBNum) const { 387 std::pair<unsigned, unsigned> P = RegMaskBlocks[MBBNum]; 388 return getRegMaskBits().slice(P.first, P.second); 389 } 390 391 /// Test if \p LI is live across any register mask instructions, and 392 /// compute a bit mask of physical registers that are not clobbered by any 393 /// of them. 394 /// 395 /// Returns false if \p LI doesn't cross any register mask instructions. In 396 /// that case, the bit vector is not filled in. 397 bool checkRegMaskInterference(const LiveInterval &LI, BitVector &UsableRegs); 398 399 // Register unit functions. 400 // 401 // Fixed interference occurs when MachineInstrs use physregs directly 402 // instead of virtual registers. This typically happens when passing 403 // arguments to a function call, or when instructions require operands in 404 // fixed registers. 405 // 406 // Each physreg has one or more register units, see MCRegisterInfo. We 407 // track liveness per register unit to handle aliasing registers more 408 // efficiently. 409 410 /// Return the live range for register unit \p Unit. It will be computed if 411 /// it doesn't exist. 412 LiveRange &getRegUnit(unsigned Unit) { 413 LiveRange *LR = RegUnitRanges[Unit]; 414 if (!LR) { 415 // Compute missing ranges on demand. 416 // Use segment set to speed-up initial computation of the live range. 417 RegUnitRanges[Unit] = LR = new LiveRange(UseSegmentSetForPhysRegs); 418 computeRegUnitRange(*LR, Unit); 419 } 420 return *LR; 421 } 422 423 /// Return the live range for register unit \p Unit if it has already been 424 /// computed, or nullptr if it hasn't been computed yet. 425 LiveRange *getCachedRegUnit(unsigned Unit) { return RegUnitRanges[Unit]; } 426 427 const LiveRange *getCachedRegUnit(unsigned Unit) const { 428 return RegUnitRanges[Unit]; 429 } 430 431 /// Remove computed live range for register unit \p Unit. Subsequent uses 432 /// should rely on on-demand recomputation. 433 void removeRegUnit(unsigned Unit) { 434 delete RegUnitRanges[Unit]; 435 RegUnitRanges[Unit] = nullptr; 436 } 437 438 /// Remove associated live ranges for the register units associated with \p 439 /// Reg. Subsequent uses should rely on on-demand recomputation. \note This 440 /// method can result in inconsistent liveness tracking if multiple phyical 441 /// registers share a regunit, and should be used cautiously. 442 void removeAllRegUnitsForPhysReg(MCRegister Reg) { 443 for (MCRegUnit Unit : TRI->regunits(Reg)) 444 removeRegUnit(Unit); 445 } 446 447 /// Remove value numbers and related live segments starting at position 448 /// \p Pos that are part of any liverange of physical register \p Reg or one 449 /// of its subregisters. 450 void removePhysRegDefAt(MCRegister Reg, SlotIndex Pos); 451 452 /// Remove value number and related live segments of \p LI and its subranges 453 /// that start at position \p Pos. 454 void removeVRegDefAt(LiveInterval &LI, SlotIndex Pos); 455 456 /// Split separate components in LiveInterval \p LI into separate intervals. 457 void splitSeparateComponents(LiveInterval &LI, 458 SmallVectorImpl<LiveInterval *> &SplitLIs); 459 460 /// For live interval \p LI with correct SubRanges construct matching 461 /// information for the main live range. Expects the main live range to not 462 /// have any segments or value numbers. 463 void constructMainRangeFromSubranges(LiveInterval &LI); 464 465 private: 466 /// Compute live intervals for all virtual registers. 467 void computeVirtRegs(); 468 469 /// Compute RegMaskSlots and RegMaskBits. 470 void computeRegMasks(); 471 472 /// Walk the values in \p LI and check for dead values: 473 /// - Dead PHIDef values are marked as unused. 474 /// - Dead operands are marked as such. 475 /// - Completely dead machine instructions are added to the \p dead vector 476 /// if it is not nullptr. 477 /// Returns true if any PHI value numbers have been removed which may 478 /// have separated the interval into multiple connected components. 479 bool computeDeadValues(LiveInterval &LI, 480 SmallVectorImpl<MachineInstr *> *dead); 481 482 static LiveInterval *createInterval(Register Reg); 483 484 void printInstrs(raw_ostream &O) const; 485 void dumpInstrs() const; 486 487 void computeLiveInRegUnits(); 488 void computeRegUnitRange(LiveRange &, unsigned Unit); 489 bool computeVirtRegInterval(LiveInterval &); 490 491 using ShrinkToUsesWorkList = SmallVector<std::pair<SlotIndex, VNInfo *>, 16>; 492 void extendSegmentsToUses(LiveRange &Segments, ShrinkToUsesWorkList &WorkList, 493 Register Reg, LaneBitmask LaneMask); 494 495 /// Helper function for repairIntervalsInRange(), walks backwards and 496 /// creates/modifies live segments in \p LR to match the operands found. 497 /// Only full operands or operands with subregisters matching \p LaneMask 498 /// are considered. 499 void repairOldRegInRange(MachineBasicBlock::iterator Begin, 500 MachineBasicBlock::iterator End, 501 const SlotIndex endIdx, LiveRange &LR, Register Reg, 502 LaneBitmask LaneMask = LaneBitmask::getAll()); 503 504 class HMEditor; 505 }; 506 507 class LiveIntervalsAnalysis : public AnalysisInfoMixin<LiveIntervalsAnalysis> { 508 friend AnalysisInfoMixin<LiveIntervalsAnalysis>; 509 static AnalysisKey Key; 510 511 public: 512 using Result = LiveIntervals; 513 Result run(MachineFunction &MF, MachineFunctionAnalysisManager &MFAM); 514 }; 515 516 class LiveIntervalsPrinterPass 517 : public PassInfoMixin<LiveIntervalsPrinterPass> { 518 raw_ostream &OS; 519 520 public: 521 explicit LiveIntervalsPrinterPass(raw_ostream &OS) : OS(OS) {} 522 PreservedAnalyses run(MachineFunction &MF, 523 MachineFunctionAnalysisManager &MFAM); 524 static bool isRequired() { return true; } 525 }; 526 527 class LiveIntervalsWrapperPass : public MachineFunctionPass { 528 LiveIntervals LIS; 529 530 public: 531 static char ID; 532 533 LiveIntervalsWrapperPass(); 534 535 void getAnalysisUsage(AnalysisUsage &AU) const override; 536 void releaseMemory() override { LIS.clear(); } 537 538 /// Pass entry point; Calculates LiveIntervals. 539 bool runOnMachineFunction(MachineFunction &) override; 540 541 /// Implement the dump method. 542 void print(raw_ostream &O, const Module * = nullptr) const override { 543 LIS.print(O); 544 } 545 546 LiveIntervals &getLIS() { return LIS; } 547 }; 548 549 } // end namespace llvm 550 551 #endif 552