1 //===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements the stack slot coloring pass. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/CodeGen/Passes.h" 15 #include "llvm/ADT/BitVector.h" 16 #include "llvm/ADT/SmallVector.h" 17 #include "llvm/ADT/Statistic.h" 18 #include "llvm/CodeGen/LiveIntervalAnalysis.h" 19 #include "llvm/CodeGen/LiveStackAnalysis.h" 20 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 21 #include "llvm/CodeGen/MachineFrameInfo.h" 22 #include "llvm/CodeGen/MachineInstrBuilder.h" 23 #include "llvm/CodeGen/MachineMemOperand.h" 24 #include "llvm/CodeGen/MachineRegisterInfo.h" 25 #include "llvm/CodeGen/PseudoSourceValue.h" 26 #include "llvm/IR/Module.h" 27 #include "llvm/Support/CommandLine.h" 28 #include "llvm/Support/Debug.h" 29 #include "llvm/Support/raw_ostream.h" 30 #include "llvm/Target/TargetInstrInfo.h" 31 #include "llvm/Target/TargetSubtargetInfo.h" 32 #include <vector> 33 using namespace llvm; 34 35 #define DEBUG_TYPE "stackslotcoloring" 36 37 static cl::opt<bool> 38 DisableSharing("no-stack-slot-sharing", 39 cl::init(false), cl::Hidden, 40 cl::desc("Suppress slot sharing during stack coloring")); 41 42 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden); 43 44 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring"); 45 STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated"); 46 47 namespace { 48 class StackSlotColoring : public MachineFunctionPass { 49 LiveStacks* LS; 50 MachineFrameInfo *MFI; 51 const TargetInstrInfo *TII; 52 const MachineBlockFrequencyInfo *MBFI; 53 54 // SSIntervals - Spill slot intervals. 55 std::vector<LiveInterval*> SSIntervals; 56 57 // SSRefs - Keep a list of MachineMemOperands for each spill slot. 58 // MachineMemOperands can be shared between instructions, so we need 59 // to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not 60 // become FI0 -> FI1 -> FI2. 61 SmallVector<SmallVector<MachineMemOperand *, 8>, 16> SSRefs; 62 63 // OrigAlignments - Alignments of stack objects before coloring. 64 SmallVector<unsigned, 16> OrigAlignments; 65 66 // OrigSizes - Sizess of stack objects before coloring. 67 SmallVector<unsigned, 16> OrigSizes; 68 69 // AllColors - If index is set, it's a spill slot, i.e. color. 70 // FIXME: This assumes PEI locate spill slot with smaller indices 71 // closest to stack pointer / frame pointer. Therefore, smaller 72 // index == better color. 73 BitVector AllColors; 74 75 // NextColor - Next "color" that's not yet used. 76 int NextColor; 77 78 // UsedColors - "Colors" that have been assigned. 79 BitVector UsedColors; 80 81 // Assignments - Color to intervals mapping. 82 SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments; 83 84 public: 85 static char ID; // Pass identification 86 StackSlotColoring() : 87 MachineFunctionPass(ID), NextColor(-1) { 88 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry()); 89 } 90 91 void getAnalysisUsage(AnalysisUsage &AU) const override { 92 AU.setPreservesCFG(); 93 AU.addRequired<SlotIndexes>(); 94 AU.addPreserved<SlotIndexes>(); 95 AU.addRequired<LiveStacks>(); 96 AU.addRequired<MachineBlockFrequencyInfo>(); 97 AU.addPreserved<MachineBlockFrequencyInfo>(); 98 AU.addPreservedID(MachineDominatorsID); 99 MachineFunctionPass::getAnalysisUsage(AU); 100 } 101 102 bool runOnMachineFunction(MachineFunction &MF) override; 103 104 private: 105 void InitializeSlots(); 106 void ScanForSpillSlotRefs(MachineFunction &MF); 107 bool OverlapWithAssignments(LiveInterval *li, int Color) const; 108 int ColorSlot(LiveInterval *li); 109 bool ColorSlots(MachineFunction &MF); 110 void RewriteInstruction(MachineInstr *MI, SmallVectorImpl<int> &SlotMapping, 111 MachineFunction &MF); 112 bool RemoveDeadStores(MachineBasicBlock* MBB); 113 }; 114 } // end anonymous namespace 115 116 char StackSlotColoring::ID = 0; 117 char &llvm::StackSlotColoringID = StackSlotColoring::ID; 118 119 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring", 120 "Stack Slot Coloring", false, false) 121 INITIALIZE_PASS_DEPENDENCY(SlotIndexes) 122 INITIALIZE_PASS_DEPENDENCY(LiveStacks) 123 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo) 124 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring", 125 "Stack Slot Coloring", false, false) 126 127 namespace { 128 // IntervalSorter - Comparison predicate that sort live intervals by 129 // their weight. 130 struct IntervalSorter { 131 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const { 132 return LHS->weight > RHS->weight; 133 } 134 }; 135 } 136 137 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot 138 /// references and update spill slot weights. 139 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) { 140 SSRefs.resize(MFI->getObjectIndexEnd()); 141 142 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands. 143 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); 144 MBBI != E; ++MBBI) { 145 MachineBasicBlock *MBB = &*MBBI; 146 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end(); 147 MII != EE; ++MII) { 148 MachineInstr *MI = &*MII; 149 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { 150 MachineOperand &MO = MI->getOperand(i); 151 if (!MO.isFI()) 152 continue; 153 int FI = MO.getIndex(); 154 if (FI < 0) 155 continue; 156 if (!LS->hasInterval(FI)) 157 continue; 158 LiveInterval &li = LS->getInterval(FI); 159 if (!MI->isDebugValue()) 160 li.weight += LiveIntervals::getSpillWeight(false, true, MBFI, MI); 161 } 162 for (MachineInstr::mmo_iterator MMOI = MI->memoperands_begin(), 163 EE = MI->memoperands_end(); MMOI != EE; ++MMOI) { 164 MachineMemOperand *MMO = *MMOI; 165 if (const FixedStackPseudoSourceValue *FSV = 166 dyn_cast_or_null<FixedStackPseudoSourceValue>( 167 MMO->getPseudoValue())) { 168 int FI = FSV->getFrameIndex(); 169 if (FI >= 0) 170 SSRefs[FI].push_back(MMO); 171 } 172 } 173 } 174 } 175 } 176 177 /// InitializeSlots - Process all spill stack slot liveintervals and add them 178 /// to a sorted (by weight) list. 179 void StackSlotColoring::InitializeSlots() { 180 int LastFI = MFI->getObjectIndexEnd(); 181 OrigAlignments.resize(LastFI); 182 OrigSizes.resize(LastFI); 183 AllColors.resize(LastFI); 184 UsedColors.resize(LastFI); 185 Assignments.resize(LastFI); 186 187 typedef std::iterator_traits<LiveStacks::iterator>::value_type Pair; 188 SmallVector<Pair *, 16> Intervals; 189 Intervals.reserve(LS->getNumIntervals()); 190 for (auto &I : *LS) 191 Intervals.push_back(&I); 192 std::sort(Intervals.begin(), Intervals.end(), 193 [](Pair *LHS, Pair *RHS) { return LHS->first < RHS->first; }); 194 195 // Gather all spill slots into a list. 196 DEBUG(dbgs() << "Spill slot intervals:\n"); 197 for (auto *I : Intervals) { 198 LiveInterval &li = I->second; 199 DEBUG(li.dump()); 200 int FI = TargetRegisterInfo::stackSlot2Index(li.reg); 201 if (MFI->isDeadObjectIndex(FI)) 202 continue; 203 SSIntervals.push_back(&li); 204 OrigAlignments[FI] = MFI->getObjectAlignment(FI); 205 OrigSizes[FI] = MFI->getObjectSize(FI); 206 AllColors.set(FI); 207 } 208 DEBUG(dbgs() << '\n'); 209 210 // Sort them by weight. 211 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter()); 212 213 // Get first "color". 214 NextColor = AllColors.find_first(); 215 } 216 217 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any 218 /// LiveIntervals that have already been assigned to the specified color. 219 bool 220 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const { 221 const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color]; 222 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) { 223 LiveInterval *OtherLI = OtherLIs[i]; 224 if (OtherLI->overlaps(*li)) 225 return true; 226 } 227 return false; 228 } 229 230 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot. 231 /// 232 int StackSlotColoring::ColorSlot(LiveInterval *li) { 233 int Color = -1; 234 bool Share = false; 235 if (!DisableSharing) { 236 // Check if it's possible to reuse any of the used colors. 237 Color = UsedColors.find_first(); 238 while (Color != -1) { 239 if (!OverlapWithAssignments(li, Color)) { 240 Share = true; 241 ++NumEliminated; 242 break; 243 } 244 Color = UsedColors.find_next(Color); 245 } 246 } 247 248 // Assign it to the first available color (assumed to be the best) if it's 249 // not possible to share a used color with other objects. 250 if (!Share) { 251 assert(NextColor != -1 && "No more spill slots?"); 252 Color = NextColor; 253 UsedColors.set(Color); 254 NextColor = AllColors.find_next(NextColor); 255 } 256 257 // Record the assignment. 258 Assignments[Color].push_back(li); 259 int FI = TargetRegisterInfo::stackSlot2Index(li->reg); 260 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n"); 261 262 // Change size and alignment of the allocated slot. If there are multiple 263 // objects sharing the same slot, then make sure the size and alignment 264 // are large enough for all. 265 unsigned Align = OrigAlignments[FI]; 266 if (!Share || Align > MFI->getObjectAlignment(Color)) 267 MFI->setObjectAlignment(Color, Align); 268 int64_t Size = OrigSizes[FI]; 269 if (!Share || Size > MFI->getObjectSize(Color)) 270 MFI->setObjectSize(Color, Size); 271 return Color; 272 } 273 274 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine 275 /// operands in the function. 276 bool StackSlotColoring::ColorSlots(MachineFunction &MF) { 277 unsigned NumObjs = MFI->getObjectIndexEnd(); 278 SmallVector<int, 16> SlotMapping(NumObjs, -1); 279 SmallVector<float, 16> SlotWeights(NumObjs, 0.0); 280 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs); 281 BitVector UsedColors(NumObjs); 282 283 DEBUG(dbgs() << "Color spill slot intervals:\n"); 284 bool Changed = false; 285 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) { 286 LiveInterval *li = SSIntervals[i]; 287 int SS = TargetRegisterInfo::stackSlot2Index(li->reg); 288 int NewSS = ColorSlot(li); 289 assert(NewSS >= 0 && "Stack coloring failed?"); 290 SlotMapping[SS] = NewSS; 291 RevMap[NewSS].push_back(SS); 292 SlotWeights[NewSS] += li->weight; 293 UsedColors.set(NewSS); 294 Changed |= (SS != NewSS); 295 } 296 297 DEBUG(dbgs() << "\nSpill slots after coloring:\n"); 298 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) { 299 LiveInterval *li = SSIntervals[i]; 300 int SS = TargetRegisterInfo::stackSlot2Index(li->reg); 301 li->weight = SlotWeights[SS]; 302 } 303 // Sort them by new weight. 304 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter()); 305 306 #ifndef NDEBUG 307 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) 308 DEBUG(SSIntervals[i]->dump()); 309 DEBUG(dbgs() << '\n'); 310 #endif 311 312 if (!Changed) 313 return false; 314 315 // Rewrite all MachineMemOperands. 316 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) { 317 int NewFI = SlotMapping[SS]; 318 if (NewFI == -1 || (NewFI == (int)SS)) 319 continue; 320 321 const PseudoSourceValue *NewSV = MF.getPSVManager().getFixedStack(NewFI); 322 SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS]; 323 for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i) 324 RefMMOs[i]->setValue(NewSV); 325 } 326 327 // Rewrite all MO_FrameIndex operands. Look for dead stores. 328 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); 329 MBBI != E; ++MBBI) { 330 MachineBasicBlock *MBB = &*MBBI; 331 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end(); 332 MII != EE; ++MII) 333 RewriteInstruction(MII, SlotMapping, MF); 334 RemoveDeadStores(MBB); 335 } 336 337 // Delete unused stack slots. 338 while (NextColor != -1) { 339 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n"); 340 MFI->RemoveStackObject(NextColor); 341 NextColor = AllColors.find_next(NextColor); 342 } 343 344 return true; 345 } 346 347 /// RewriteInstruction - Rewrite specified instruction by replacing references 348 /// to old frame index with new one. 349 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, 350 SmallVectorImpl<int> &SlotMapping, 351 MachineFunction &MF) { 352 // Update the operands. 353 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) { 354 MachineOperand &MO = MI->getOperand(i); 355 if (!MO.isFI()) 356 continue; 357 int OldFI = MO.getIndex(); 358 if (OldFI < 0) 359 continue; 360 int NewFI = SlotMapping[OldFI]; 361 if (NewFI == -1 || NewFI == OldFI) 362 continue; 363 MO.setIndex(NewFI); 364 } 365 366 // The MachineMemOperands have already been updated. 367 } 368 369 370 /// RemoveDeadStores - Scan through a basic block and look for loads followed 371 /// by stores. If they're both using the same stack slot, then the store is 372 /// definitely dead. This could obviously be much more aggressive (consider 373 /// pairs with instructions between them), but such extensions might have a 374 /// considerable compile time impact. 375 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) { 376 // FIXME: This could be much more aggressive, but we need to investigate 377 // the compile time impact of doing so. 378 bool changed = false; 379 380 SmallVector<MachineInstr*, 4> toErase; 381 382 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); 383 I != E; ++I) { 384 if (DCELimit != -1 && (int)NumDead >= DCELimit) 385 break; 386 387 int FirstSS, SecondSS; 388 if (TII->isStackSlotCopy(I, FirstSS, SecondSS) && 389 FirstSS == SecondSS && 390 FirstSS != -1) { 391 ++NumDead; 392 changed = true; 393 toErase.push_back(I); 394 continue; 395 } 396 397 MachineBasicBlock::iterator NextMI = std::next(I); 398 if (NextMI == MBB->end()) continue; 399 400 unsigned LoadReg = 0; 401 unsigned StoreReg = 0; 402 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue; 403 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue; 404 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue; 405 406 ++NumDead; 407 changed = true; 408 409 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) { 410 ++NumDead; 411 toErase.push_back(I); 412 } 413 414 toErase.push_back(NextMI); 415 ++I; 416 } 417 418 for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(), 419 E = toErase.end(); I != E; ++I) 420 (*I)->eraseFromParent(); 421 422 return changed; 423 } 424 425 426 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) { 427 DEBUG({ 428 dbgs() << "********** Stack Slot Coloring **********\n" 429 << "********** Function: " << MF.getName() << '\n'; 430 }); 431 432 MFI = MF.getFrameInfo(); 433 TII = MF.getSubtarget().getInstrInfo(); 434 LS = &getAnalysis<LiveStacks>(); 435 MBFI = &getAnalysis<MachineBlockFrequencyInfo>(); 436 437 bool Changed = false; 438 439 unsigned NumSlots = LS->getNumIntervals(); 440 if (NumSlots == 0) 441 // Nothing to do! 442 return false; 443 444 // If there are calls to setjmp or sigsetjmp, don't perform stack slot 445 // coloring. The stack could be modified before the longjmp is executed, 446 // resulting in the wrong value being used afterwards. (See 447 // <rdar://problem/8007500>.) 448 if (MF.exposesReturnsTwice()) 449 return false; 450 451 // Gather spill slot references 452 ScanForSpillSlotRefs(MF); 453 InitializeSlots(); 454 Changed = ColorSlots(MF); 455 456 NextColor = -1; 457 SSIntervals.clear(); 458 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i) 459 SSRefs[i].clear(); 460 SSRefs.clear(); 461 OrigAlignments.clear(); 462 OrigSizes.clear(); 463 AllColors.clear(); 464 UsedColors.clear(); 465 for (unsigned i = 0, e = Assignments.size(); i != e; ++i) 466 Assignments[i].clear(); 467 Assignments.clear(); 468 469 return Changed; 470 } 471