StackColoring.cpp revision 0b8c9a80f20772c3793201ab5b251d3520b9cea3
1//===-- StackColoring.cpp -------------------------------------------------===// 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 pass implements the stack-coloring optimization that looks for 11// lifetime markers machine instructions (LIFESTART_BEGIN and LIFESTART_END), 12// which represent the possible lifetime of stack slots. It attempts to 13// merge disjoint stack slots and reduce the used stack space. 14// NOTE: This pass is not StackSlotColoring, which optimizes spill slots. 15// 16// TODO: In the future we plan to improve stack coloring in the following ways: 17// 1. Allow merging multiple small slots into a single larger slot at different 18// offsets. 19// 2. Merge this pass with StackSlotColoring and allow merging of allocas with 20// spill slots. 21// 22//===----------------------------------------------------------------------===// 23 24#define DEBUG_TYPE "stackcoloring" 25#include "llvm/CodeGen/Passes.h" 26#include "MachineTraceMetrics.h" 27#include "llvm/ADT/BitVector.h" 28#include "llvm/ADT/DepthFirstIterator.h" 29#include "llvm/ADT/PostOrderIterator.h" 30#include "llvm/ADT/SetVector.h" 31#include "llvm/ADT/SmallPtrSet.h" 32#include "llvm/ADT/SparseSet.h" 33#include "llvm/ADT/Statistic.h" 34#include "llvm/Analysis/Dominators.h" 35#include "llvm/Analysis/ValueTracking.h" 36#include "llvm/CodeGen/LiveInterval.h" 37#include "llvm/CodeGen/MachineBasicBlock.h" 38#include "llvm/CodeGen/MachineBranchProbabilityInfo.h" 39#include "llvm/CodeGen/MachineDominators.h" 40#include "llvm/CodeGen/MachineFrameInfo.h" 41#include "llvm/CodeGen/MachineFunctionPass.h" 42#include "llvm/CodeGen/MachineLoopInfo.h" 43#include "llvm/CodeGen/MachineMemOperand.h" 44#include "llvm/CodeGen/MachineModuleInfo.h" 45#include "llvm/CodeGen/MachineRegisterInfo.h" 46#include "llvm/CodeGen/SlotIndexes.h" 47#include "llvm/DebugInfo.h" 48#include "llvm/IR/Function.h" 49#include "llvm/IR/Instructions.h" 50#include "llvm/IR/Module.h" 51#include "llvm/MC/MCInstrItineraries.h" 52#include "llvm/Support/CommandLine.h" 53#include "llvm/Support/Debug.h" 54#include "llvm/Support/raw_ostream.h" 55#include "llvm/Target/TargetInstrInfo.h" 56#include "llvm/Target/TargetRegisterInfo.h" 57 58using namespace llvm; 59 60static cl::opt<bool> 61DisableColoring("no-stack-coloring", 62 cl::init(false), cl::Hidden, 63 cl::desc("Disable stack coloring")); 64 65/// The user may write code that uses allocas outside of the declared lifetime 66/// zone. This can happen when the user returns a reference to a local 67/// data-structure. We can detect these cases and decide not to optimize the 68/// code. If this flag is enabled, we try to save the user. 69static cl::opt<bool> 70ProtectFromEscapedAllocas("protect-from-escaped-allocas", 71 cl::init(false), cl::Hidden, 72 cl::desc("Do not optimize lifetime zones that are broken")); 73 74STATISTIC(NumMarkerSeen, "Number of lifetime markers found."); 75STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots."); 76STATISTIC(StackSlotMerged, "Number of stack slot merged."); 77STATISTIC(EscapedAllocas, 78 "Number of allocas that escaped the lifetime region"); 79 80//===----------------------------------------------------------------------===// 81// StackColoring Pass 82//===----------------------------------------------------------------------===// 83 84namespace { 85/// StackColoring - A machine pass for merging disjoint stack allocations, 86/// marked by the LIFETIME_START and LIFETIME_END pseudo instructions. 87class StackColoring : public MachineFunctionPass { 88 MachineFrameInfo *MFI; 89 MachineFunction *MF; 90 91 /// A class representing liveness information for a single basic block. 92 /// Each bit in the BitVector represents the liveness property 93 /// for a different stack slot. 94 struct BlockLifetimeInfo { 95 /// Which slots BEGINs in each basic block. 96 BitVector Begin; 97 /// Which slots ENDs in each basic block. 98 BitVector End; 99 /// Which slots are marked as LIVE_IN, coming into each basic block. 100 BitVector LiveIn; 101 /// Which slots are marked as LIVE_OUT, coming out of each basic block. 102 BitVector LiveOut; 103 }; 104 105 /// Maps active slots (per bit) for each basic block. 106 DenseMap<MachineBasicBlock*, BlockLifetimeInfo> BlockLiveness; 107 108 /// Maps serial numbers to basic blocks. 109 DenseMap<MachineBasicBlock*, int> BasicBlocks; 110 /// Maps basic blocks to a serial number. 111 SmallVector<MachineBasicBlock*, 8> BasicBlockNumbering; 112 113 /// Maps liveness intervals for each slot. 114 SmallVector<LiveInterval*, 16> Intervals; 115 /// VNInfo is used for the construction of LiveIntervals. 116 VNInfo::Allocator VNInfoAllocator; 117 /// SlotIndex analysis object. 118 SlotIndexes *Indexes; 119 120 /// The list of lifetime markers found. These markers are to be removed 121 /// once the coloring is done. 122 SmallVector<MachineInstr*, 8> Markers; 123 124 /// SlotSizeSorter - A Sort utility for arranging stack slots according 125 /// to their size. 126 struct SlotSizeSorter { 127 MachineFrameInfo *MFI; 128 SlotSizeSorter(MachineFrameInfo *mfi) : MFI(mfi) { } 129 bool operator()(int LHS, int RHS) { 130 // We use -1 to denote a uninteresting slot. Place these slots at the end. 131 if (LHS == -1) return false; 132 if (RHS == -1) return true; 133 // Sort according to size. 134 return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS); 135 } 136}; 137 138public: 139 static char ID; 140 StackColoring() : MachineFunctionPass(ID) { 141 initializeStackColoringPass(*PassRegistry::getPassRegistry()); 142 } 143 void getAnalysisUsage(AnalysisUsage &AU) const; 144 bool runOnMachineFunction(MachineFunction &MF); 145 146private: 147 /// Debug. 148 void dump(); 149 150 /// Removes all of the lifetime marker instructions from the function. 151 /// \returns true if any markers were removed. 152 bool removeAllMarkers(); 153 154 /// Scan the machine function and find all of the lifetime markers. 155 /// Record the findings in the BEGIN and END vectors. 156 /// \returns the number of markers found. 157 unsigned collectMarkers(unsigned NumSlot); 158 159 /// Perform the dataflow calculation and calculate the lifetime for each of 160 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and 161 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming 162 /// in and out blocks. 163 void calculateLocalLiveness(); 164 165 /// Construct the LiveIntervals for the slots. 166 void calculateLiveIntervals(unsigned NumSlots); 167 168 /// Go over the machine function and change instructions which use stack 169 /// slots to use the joint slots. 170 void remapInstructions(DenseMap<int, int> &SlotRemap); 171 172 /// The input program may contain intructions which are not inside lifetime 173 /// markers. This can happen due to a bug in the compiler or due to a bug in 174 /// user code (for example, returning a reference to a local variable). 175 /// This procedure checks all of the instructions in the function and 176 /// invalidates lifetime ranges which do not contain all of the instructions 177 /// which access that frame slot. 178 void removeInvalidSlotRanges(); 179 180 /// Map entries which point to other entries to their destination. 181 /// A->B->C becomes A->C. 182 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots); 183}; 184} // end anonymous namespace 185 186char StackColoring::ID = 0; 187char &llvm::StackColoringID = StackColoring::ID; 188 189INITIALIZE_PASS_BEGIN(StackColoring, 190 "stack-coloring", "Merge disjoint stack slots", false, false) 191INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) 192INITIALIZE_PASS_DEPENDENCY(SlotIndexes) 193INITIALIZE_PASS_END(StackColoring, 194 "stack-coloring", "Merge disjoint stack slots", false, false) 195 196void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const { 197 AU.addRequired<MachineDominatorTree>(); 198 AU.addPreserved<MachineDominatorTree>(); 199 AU.addRequired<SlotIndexes>(); 200 MachineFunctionPass::getAnalysisUsage(AU); 201} 202 203void StackColoring::dump() { 204 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF); 205 FI != FE; ++FI) { 206 unsigned Num = BasicBlocks[*FI]; 207 DEBUG(dbgs()<<"Inspecting block #"<<Num<<" ["<<FI->getName()<<"]\n"); 208 Num = 0; 209 DEBUG(dbgs()<<"BEGIN : {"); 210 for (unsigned i=0; i < BlockLiveness[*FI].Begin.size(); ++i) 211 DEBUG(dbgs()<<BlockLiveness[*FI].Begin.test(i)<<" "); 212 DEBUG(dbgs()<<"}\n"); 213 214 DEBUG(dbgs()<<"END : {"); 215 for (unsigned i=0; i < BlockLiveness[*FI].End.size(); ++i) 216 DEBUG(dbgs()<<BlockLiveness[*FI].End.test(i)<<" "); 217 218 DEBUG(dbgs()<<"}\n"); 219 220 DEBUG(dbgs()<<"LIVE_IN: {"); 221 for (unsigned i=0; i < BlockLiveness[*FI].LiveIn.size(); ++i) 222 DEBUG(dbgs()<<BlockLiveness[*FI].LiveIn.test(i)<<" "); 223 224 DEBUG(dbgs()<<"}\n"); 225 DEBUG(dbgs()<<"LIVEOUT: {"); 226 for (unsigned i=0; i < BlockLiveness[*FI].LiveOut.size(); ++i) 227 DEBUG(dbgs()<<BlockLiveness[*FI].LiveOut.test(i)<<" "); 228 DEBUG(dbgs()<<"}\n"); 229 } 230} 231 232unsigned StackColoring::collectMarkers(unsigned NumSlot) { 233 unsigned MarkersFound = 0; 234 // Scan the function to find all lifetime markers. 235 // NOTE: We use the a reverse-post-order iteration to ensure that we obtain a 236 // deterministic numbering, and because we'll need a post-order iteration 237 // later for solving the liveness dataflow problem. 238 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF); 239 FI != FE; ++FI) { 240 241 // Assign a serial number to this basic block. 242 BasicBlocks[*FI] = BasicBlockNumbering.size(); 243 BasicBlockNumbering.push_back(*FI); 244 245 BlockLiveness[*FI].Begin.resize(NumSlot); 246 BlockLiveness[*FI].End.resize(NumSlot); 247 248 for (MachineBasicBlock::iterator BI = (*FI)->begin(), BE = (*FI)->end(); 249 BI != BE; ++BI) { 250 251 if (BI->getOpcode() != TargetOpcode::LIFETIME_START && 252 BI->getOpcode() != TargetOpcode::LIFETIME_END) 253 continue; 254 255 Markers.push_back(BI); 256 257 bool IsStart = BI->getOpcode() == TargetOpcode::LIFETIME_START; 258 MachineOperand &MI = BI->getOperand(0); 259 unsigned Slot = MI.getIndex(); 260 261 MarkersFound++; 262 263 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot); 264 if (Allocation) { 265 DEBUG(dbgs()<<"Found a lifetime marker for slot #"<<Slot<< 266 " with allocation: "<< Allocation->getName()<<"\n"); 267 } 268 269 if (IsStart) { 270 BlockLiveness[*FI].Begin.set(Slot); 271 } else { 272 if (BlockLiveness[*FI].Begin.test(Slot)) { 273 // Allocas that start and end within a single block are handled 274 // specially when computing the LiveIntervals to avoid pessimizing 275 // the liveness propagation. 276 BlockLiveness[*FI].Begin.reset(Slot); 277 } else { 278 BlockLiveness[*FI].End.set(Slot); 279 } 280 } 281 } 282 } 283 284 // Update statistics. 285 NumMarkerSeen += MarkersFound; 286 return MarkersFound; 287} 288 289void StackColoring::calculateLocalLiveness() { 290 // Perform a standard reverse dataflow computation to solve for 291 // global liveness. The BEGIN set here is equivalent to KILL in the standard 292 // formulation, and END is equivalent to GEN. The result of this computation 293 // is a map from blocks to bitvectors where the bitvectors represent which 294 // allocas are live in/out of that block. 295 SmallPtrSet<MachineBasicBlock*, 8> BBSet(BasicBlockNumbering.begin(), 296 BasicBlockNumbering.end()); 297 unsigned NumSSMIters = 0; 298 bool changed = true; 299 while (changed) { 300 changed = false; 301 ++NumSSMIters; 302 303 SmallPtrSet<MachineBasicBlock*, 8> NextBBSet; 304 305 for (SmallVector<MachineBasicBlock*, 8>::iterator 306 PI = BasicBlockNumbering.begin(), PE = BasicBlockNumbering.end(); 307 PI != PE; ++PI) { 308 309 MachineBasicBlock *BB = *PI; 310 if (!BBSet.count(BB)) continue; 311 312 BitVector LocalLiveIn; 313 BitVector LocalLiveOut; 314 315 // Forward propagation from begins to ends. 316 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), 317 PE = BB->pred_end(); PI != PE; ++PI) 318 LocalLiveIn |= BlockLiveness[*PI].LiveOut; 319 LocalLiveIn |= BlockLiveness[BB].End; 320 LocalLiveIn.reset(BlockLiveness[BB].Begin); 321 322 // Reverse propagation from ends to begins. 323 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), 324 SE = BB->succ_end(); SI != SE; ++SI) 325 LocalLiveOut |= BlockLiveness[*SI].LiveIn; 326 LocalLiveOut |= BlockLiveness[BB].Begin; 327 LocalLiveOut.reset(BlockLiveness[BB].End); 328 329 LocalLiveIn |= LocalLiveOut; 330 LocalLiveOut |= LocalLiveIn; 331 332 // After adopting the live bits, we need to turn-off the bits which 333 // are de-activated in this block. 334 LocalLiveOut.reset(BlockLiveness[BB].End); 335 LocalLiveIn.reset(BlockLiveness[BB].Begin); 336 337 // If we have both BEGIN and END markers in the same basic block then 338 // we know that the BEGIN marker comes after the END, because we already 339 // handle the case where the BEGIN comes before the END when collecting 340 // the markers (and building the BEGIN/END vectore). 341 // Want to enable the LIVE_IN and LIVE_OUT of slots that have both 342 // BEGIN and END because it means that the value lives before and after 343 // this basic block. 344 BitVector LocalEndBegin = BlockLiveness[BB].End; 345 LocalEndBegin &= BlockLiveness[BB].Begin; 346 LocalLiveIn |= LocalEndBegin; 347 LocalLiveOut |= LocalEndBegin; 348 349 if (LocalLiveIn.test(BlockLiveness[BB].LiveIn)) { 350 changed = true; 351 BlockLiveness[BB].LiveIn |= LocalLiveIn; 352 353 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), 354 PE = BB->pred_end(); PI != PE; ++PI) 355 NextBBSet.insert(*PI); 356 } 357 358 if (LocalLiveOut.test(BlockLiveness[BB].LiveOut)) { 359 changed = true; 360 BlockLiveness[BB].LiveOut |= LocalLiveOut; 361 362 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), 363 SE = BB->succ_end(); SI != SE; ++SI) 364 NextBBSet.insert(*SI); 365 } 366 } 367 368 BBSet = NextBBSet; 369 }// while changed. 370} 371 372void StackColoring::calculateLiveIntervals(unsigned NumSlots) { 373 SmallVector<SlotIndex, 16> Starts; 374 SmallVector<SlotIndex, 16> Finishes; 375 376 // For each block, find which slots are active within this block 377 // and update the live intervals. 378 for (MachineFunction::iterator MBB = MF->begin(), MBBe = MF->end(); 379 MBB != MBBe; ++MBB) { 380 Starts.clear(); 381 Starts.resize(NumSlots); 382 Finishes.clear(); 383 Finishes.resize(NumSlots); 384 385 // Create the interval for the basic blocks with lifetime markers in them. 386 for (SmallVector<MachineInstr*, 8>::iterator it = Markers.begin(), 387 e = Markers.end(); it != e; ++it) { 388 MachineInstr *MI = *it; 389 if (MI->getParent() != MBB) 390 continue; 391 392 assert((MI->getOpcode() == TargetOpcode::LIFETIME_START || 393 MI->getOpcode() == TargetOpcode::LIFETIME_END) && 394 "Invalid Lifetime marker"); 395 396 bool IsStart = MI->getOpcode() == TargetOpcode::LIFETIME_START; 397 MachineOperand &Mo = MI->getOperand(0); 398 int Slot = Mo.getIndex(); 399 assert(Slot >= 0 && "Invalid slot"); 400 401 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI); 402 403 if (IsStart) { 404 if (!Starts[Slot].isValid() || Starts[Slot] > ThisIndex) 405 Starts[Slot] = ThisIndex; 406 } else { 407 if (!Finishes[Slot].isValid() || Finishes[Slot] < ThisIndex) 408 Finishes[Slot] = ThisIndex; 409 } 410 } 411 412 // Create the interval of the blocks that we previously found to be 'alive'. 413 BitVector Alive = BlockLiveness[MBB].LiveIn; 414 Alive |= BlockLiveness[MBB].LiveOut; 415 416 if (Alive.any()) { 417 for (int pos = Alive.find_first(); pos != -1; 418 pos = Alive.find_next(pos)) { 419 if (!Starts[pos].isValid()) 420 Starts[pos] = Indexes->getMBBStartIdx(MBB); 421 if (!Finishes[pos].isValid()) 422 Finishes[pos] = Indexes->getMBBEndIdx(MBB); 423 } 424 } 425 426 for (unsigned i = 0; i < NumSlots; ++i) { 427 assert(Starts[i].isValid() == Finishes[i].isValid() && "Unmatched range"); 428 if (!Starts[i].isValid()) 429 continue; 430 431 assert(Starts[i] && Finishes[i] && "Invalid interval"); 432 VNInfo *ValNum = Intervals[i]->getValNumInfo(0); 433 SlotIndex S = Starts[i]; 434 SlotIndex F = Finishes[i]; 435 if (S < F) { 436 // We have a single consecutive region. 437 Intervals[i]->addRange(LiveRange(S, F, ValNum)); 438 } else { 439 // We have two non consecutive regions. This happens when 440 // LIFETIME_START appears after the LIFETIME_END marker. 441 SlotIndex NewStart = Indexes->getMBBStartIdx(MBB); 442 SlotIndex NewFin = Indexes->getMBBEndIdx(MBB); 443 Intervals[i]->addRange(LiveRange(NewStart, F, ValNum)); 444 Intervals[i]->addRange(LiveRange(S, NewFin, ValNum)); 445 } 446 } 447 } 448} 449 450bool StackColoring::removeAllMarkers() { 451 unsigned Count = 0; 452 for (unsigned i = 0; i < Markers.size(); ++i) { 453 Markers[i]->eraseFromParent(); 454 Count++; 455 } 456 Markers.clear(); 457 458 DEBUG(dbgs()<<"Removed "<<Count<<" markers.\n"); 459 return Count; 460} 461 462void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) { 463 unsigned FixedInstr = 0; 464 unsigned FixedMemOp = 0; 465 unsigned FixedDbg = 0; 466 MachineModuleInfo *MMI = &MF->getMMI(); 467 468 // Remap debug information that refers to stack slots. 469 MachineModuleInfo::VariableDbgInfoMapTy &VMap = MMI->getVariableDbgInfo(); 470 for (MachineModuleInfo::VariableDbgInfoMapTy::iterator VI = VMap.begin(), 471 VE = VMap.end(); VI != VE; ++VI) { 472 const MDNode *Var = VI->first; 473 if (!Var) continue; 474 std::pair<unsigned, DebugLoc> &VP = VI->second; 475 if (SlotRemap.count(VP.first)) { 476 DEBUG(dbgs()<<"Remapping debug info for ["<<Var->getName()<<"].\n"); 477 VP.first = SlotRemap[VP.first]; 478 FixedDbg++; 479 } 480 } 481 482 // Keep a list of *allocas* which need to be remapped. 483 DenseMap<const AllocaInst*, const AllocaInst*> Allocas; 484 for (DenseMap<int, int>::iterator it = SlotRemap.begin(), 485 e = SlotRemap.end(); it != e; ++it) { 486 const AllocaInst *From = MFI->getObjectAllocation(it->first); 487 const AllocaInst *To = MFI->getObjectAllocation(it->second); 488 assert(To && From && "Invalid allocation object"); 489 Allocas[From] = To; 490 } 491 492 // Remap all instructions to the new stack slots. 493 MachineFunction::iterator BB, BBE; 494 MachineBasicBlock::iterator I, IE; 495 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB) 496 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) { 497 498 // Skip lifetime markers. We'll remove them soon. 499 if (I->getOpcode() == TargetOpcode::LIFETIME_START || 500 I->getOpcode() == TargetOpcode::LIFETIME_END) 501 continue; 502 503 // Update the MachineMemOperand to use the new alloca. 504 for (MachineInstr::mmo_iterator MM = I->memoperands_begin(), 505 E = I->memoperands_end(); MM != E; ++MM) { 506 MachineMemOperand *MMO = *MM; 507 508 const Value *V = MMO->getValue(); 509 510 if (!V) 511 continue; 512 513 // Climb up and find the original alloca. 514 V = GetUnderlyingObject(V); 515 // If we did not find one, or if the one that we found is not in our 516 // map, then move on. 517 if (!V || !isa<AllocaInst>(V)) { 518 // Clear mem operand since we don't know for sure that it doesn't 519 // alias a merged alloca. 520 MMO->setValue(0); 521 continue; 522 } 523 const AllocaInst *AI= cast<AllocaInst>(V); 524 if (!Allocas.count(AI)) 525 continue; 526 527 MMO->setValue(Allocas[AI]); 528 FixedMemOp++; 529 } 530 531 // Update all of the machine instruction operands. 532 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) { 533 MachineOperand &MO = I->getOperand(i); 534 535 if (!MO.isFI()) 536 continue; 537 int FromSlot = MO.getIndex(); 538 539 // Don't touch arguments. 540 if (FromSlot<0) 541 continue; 542 543 // Only look at mapped slots. 544 if (!SlotRemap.count(FromSlot)) 545 continue; 546 547 // In a debug build, check that the instruction that we are modifying is 548 // inside the expected live range. If the instruction is not inside 549 // the calculated range then it means that the alloca usage moved 550 // outside of the lifetime markers, or that the user has a bug. 551 // NOTE: Alloca address calculations which happen outside the lifetime 552 // zone are are okay, despite the fact that we don't have a good way 553 // for validating all of the usages of the calculation. 554#ifndef NDEBUG 555 bool TouchesMemory = I->mayLoad() || I->mayStore(); 556 // If we *don't* protect the user from escaped allocas, don't bother 557 // validating the instructions. 558 if (!I->isDebugValue() && TouchesMemory && ProtectFromEscapedAllocas) { 559 SlotIndex Index = Indexes->getInstructionIndex(I); 560 LiveInterval *Interval = Intervals[FromSlot]; 561 assert(Interval->find(Index) != Interval->end() && 562 "Found instruction usage outside of live range."); 563 } 564#endif 565 566 // Fix the machine instructions. 567 int ToSlot = SlotRemap[FromSlot]; 568 MO.setIndex(ToSlot); 569 FixedInstr++; 570 } 571 } 572 573 DEBUG(dbgs()<<"Fixed "<<FixedMemOp<<" machine memory operands.\n"); 574 DEBUG(dbgs()<<"Fixed "<<FixedDbg<<" debug locations.\n"); 575 DEBUG(dbgs()<<"Fixed "<<FixedInstr<<" machine instructions.\n"); 576} 577 578void StackColoring::removeInvalidSlotRanges() { 579 MachineFunction::iterator BB, BBE; 580 MachineBasicBlock::iterator I, IE; 581 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB) 582 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) { 583 584 if (I->getOpcode() == TargetOpcode::LIFETIME_START || 585 I->getOpcode() == TargetOpcode::LIFETIME_END || I->isDebugValue()) 586 continue; 587 588 // Some intervals are suspicious! In some cases we find address 589 // calculations outside of the lifetime zone, but not actual memory 590 // read or write. Memory accesses outside of the lifetime zone are a clear 591 // violation, but address calculations are okay. This can happen when 592 // GEPs are hoisted outside of the lifetime zone. 593 // So, in here we only check instructions which can read or write memory. 594 if (!I->mayLoad() && !I->mayStore()) 595 continue; 596 597 // Check all of the machine operands. 598 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) { 599 MachineOperand &MO = I->getOperand(i); 600 601 if (!MO.isFI()) 602 continue; 603 604 int Slot = MO.getIndex(); 605 606 if (Slot<0) 607 continue; 608 609 if (Intervals[Slot]->empty()) 610 continue; 611 612 // Check that the used slot is inside the calculated lifetime range. 613 // If it is not, warn about it and invalidate the range. 614 LiveInterval *Interval = Intervals[Slot]; 615 SlotIndex Index = Indexes->getInstructionIndex(I); 616 if (Interval->find(Index) == Interval->end()) { 617 Intervals[Slot]->clear(); 618 DEBUG(dbgs()<<"Invalidating range #"<<Slot<<"\n"); 619 EscapedAllocas++; 620 } 621 } 622 } 623} 624 625void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap, 626 unsigned NumSlots) { 627 // Expunge slot remap map. 628 for (unsigned i=0; i < NumSlots; ++i) { 629 // If we are remapping i 630 if (SlotRemap.count(i)) { 631 int Target = SlotRemap[i]; 632 // As long as our target is mapped to something else, follow it. 633 while (SlotRemap.count(Target)) { 634 Target = SlotRemap[Target]; 635 SlotRemap[i] = Target; 636 } 637 } 638 } 639} 640 641bool StackColoring::runOnMachineFunction(MachineFunction &Func) { 642 DEBUG(dbgs() << "********** Stack Coloring **********\n" 643 << "********** Function: " 644 << ((const Value*)Func.getFunction())->getName() << '\n'); 645 MF = &Func; 646 MFI = MF->getFrameInfo(); 647 Indexes = &getAnalysis<SlotIndexes>(); 648 BlockLiveness.clear(); 649 BasicBlocks.clear(); 650 BasicBlockNumbering.clear(); 651 Markers.clear(); 652 Intervals.clear(); 653 VNInfoAllocator.Reset(); 654 655 unsigned NumSlots = MFI->getObjectIndexEnd(); 656 657 // If there are no stack slots then there are no markers to remove. 658 if (!NumSlots) 659 return false; 660 661 SmallVector<int, 8> SortedSlots; 662 663 SortedSlots.reserve(NumSlots); 664 Intervals.reserve(NumSlots); 665 666 unsigned NumMarkers = collectMarkers(NumSlots); 667 668 unsigned TotalSize = 0; 669 DEBUG(dbgs()<<"Found "<<NumMarkers<<" markers and "<<NumSlots<<" slots\n"); 670 DEBUG(dbgs()<<"Slot structure:\n"); 671 672 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) { 673 DEBUG(dbgs()<<"Slot #"<<i<<" - "<<MFI->getObjectSize(i)<<" bytes.\n"); 674 TotalSize += MFI->getObjectSize(i); 675 } 676 677 DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n"); 678 679 // Don't continue because there are not enough lifetime markers, or the 680 // stack is too small, or we are told not to optimize the slots. 681 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) { 682 DEBUG(dbgs()<<"Will not try to merge slots.\n"); 683 return removeAllMarkers(); 684 } 685 686 for (unsigned i=0; i < NumSlots; ++i) { 687 LiveInterval *LI = new LiveInterval(i, 0); 688 Intervals.push_back(LI); 689 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator); 690 SortedSlots.push_back(i); 691 } 692 693 // Calculate the liveness of each block. 694 calculateLocalLiveness(); 695 696 // Propagate the liveness information. 697 calculateLiveIntervals(NumSlots); 698 699 // Search for allocas which are used outside of the declared lifetime 700 // markers. 701 if (ProtectFromEscapedAllocas) 702 removeInvalidSlotRanges(); 703 704 // Maps old slots to new slots. 705 DenseMap<int, int> SlotRemap; 706 unsigned RemovedSlots = 0; 707 unsigned ReducedSize = 0; 708 709 // Do not bother looking at empty intervals. 710 for (unsigned I = 0; I < NumSlots; ++I) { 711 if (Intervals[SortedSlots[I]]->empty()) 712 SortedSlots[I] = -1; 713 } 714 715 // This is a simple greedy algorithm for merging allocas. First, sort the 716 // slots, placing the largest slots first. Next, perform an n^2 scan and look 717 // for disjoint slots. When you find disjoint slots, merge the samller one 718 // into the bigger one and update the live interval. Remove the small alloca 719 // and continue. 720 721 // Sort the slots according to their size. Place unused slots at the end. 722 // Use stable sort to guarantee deterministic code generation. 723 std::stable_sort(SortedSlots.begin(), SortedSlots.end(), 724 SlotSizeSorter(MFI)); 725 726 bool Chanded = true; 727 while (Chanded) { 728 Chanded = false; 729 for (unsigned I = 0; I < NumSlots; ++I) { 730 if (SortedSlots[I] == -1) 731 continue; 732 733 for (unsigned J=I+1; J < NumSlots; ++J) { 734 if (SortedSlots[J] == -1) 735 continue; 736 737 int FirstSlot = SortedSlots[I]; 738 int SecondSlot = SortedSlots[J]; 739 LiveInterval *First = Intervals[FirstSlot]; 740 LiveInterval *Second = Intervals[SecondSlot]; 741 assert (!First->empty() && !Second->empty() && "Found an empty range"); 742 743 // Merge disjoint slots. 744 if (!First->overlaps(*Second)) { 745 Chanded = true; 746 First->MergeRangesInAsValue(*Second, First->getValNumInfo(0)); 747 SlotRemap[SecondSlot] = FirstSlot; 748 SortedSlots[J] = -1; 749 DEBUG(dbgs()<<"Merging #"<<FirstSlot<<" and slots #"<< 750 SecondSlot<<" together.\n"); 751 unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot), 752 MFI->getObjectAlignment(SecondSlot)); 753 754 assert(MFI->getObjectSize(FirstSlot) >= 755 MFI->getObjectSize(SecondSlot) && 756 "Merging a small object into a larger one"); 757 758 RemovedSlots+=1; 759 ReducedSize += MFI->getObjectSize(SecondSlot); 760 MFI->setObjectAlignment(FirstSlot, MaxAlignment); 761 MFI->RemoveStackObject(SecondSlot); 762 } 763 } 764 } 765 }// While changed. 766 767 // Record statistics. 768 StackSpaceSaved += ReducedSize; 769 StackSlotMerged += RemovedSlots; 770 DEBUG(dbgs()<<"Merge "<<RemovedSlots<<" slots. Saved "<< 771 ReducedSize<<" bytes\n"); 772 773 // Scan the entire function and update all machine operands that use frame 774 // indices to use the remapped frame index. 775 expungeSlotMap(SlotRemap, NumSlots); 776 remapInstructions(SlotRemap); 777 778 // Release the intervals. 779 for (unsigned I = 0; I < NumSlots; ++I) { 780 delete Intervals[I]; 781 } 782 783 return removeAllMarkers(); 784} 785