src/llvm/lib/CodeGen/StackColoring.cpp

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