1 //===-- StackColoring.cpp -------------------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
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
19 // 2. Merge this pass with StackSlotColoring and allow merging of allocas with
22 //===----------------------------------------------------------------------===//
24 #define DEBUG_TYPE "stackcoloring"
25 #include "llvm/CodeGen/Passes.h"
26 #include "llvm/ADT/BitVector.h"
27 #include "llvm/ADT/DepthFirstIterator.h"
28 #include "llvm/ADT/PostOrderIterator.h"
29 #include "llvm/ADT/SetVector.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/SparseSet.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Analysis/ValueTracking.h"
34 #include "llvm/CodeGen/LiveInterval.h"
35 #include "llvm/CodeGen/MachineBasicBlock.h"
36 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
37 #include "llvm/CodeGen/MachineDominators.h"
38 #include "llvm/CodeGen/MachineFrameInfo.h"
39 #include "llvm/CodeGen/MachineFunctionPass.h"
40 #include "llvm/CodeGen/MachineLoopInfo.h"
41 #include "llvm/CodeGen/MachineMemOperand.h"
42 #include "llvm/CodeGen/MachineModuleInfo.h"
43 #include "llvm/CodeGen/MachineRegisterInfo.h"
44 #include "llvm/CodeGen/PseudoSourceValue.h"
45 #include "llvm/CodeGen/SlotIndexes.h"
46 #include "llvm/CodeGen/StackProtector.h"
47 #include "llvm/IR/DebugInfo.h"
48 #include "llvm/IR/Dominators.h"
49 #include "llvm/IR/Function.h"
50 #include "llvm/IR/Instructions.h"
51 #include "llvm/IR/Module.h"
52 #include "llvm/MC/MCInstrItineraries.h"
53 #include "llvm/Support/CommandLine.h"
54 #include "llvm/Support/Debug.h"
55 #include "llvm/Support/raw_ostream.h"
56 #include "llvm/Target/TargetInstrInfo.h"
57 #include "llvm/Target/TargetRegisterInfo.h"
62 DisableColoring("no-stack-coloring",
63 cl::init(false), cl::Hidden,
64 cl::desc("Disable stack coloring"));
66 /// The user may write code that uses allocas outside of the declared lifetime
67 /// zone. This can happen when the user returns a reference to a local
68 /// data-structure. We can detect these cases and decide not to optimize the
69 /// code. If this flag is enabled, we try to save the user.
71 ProtectFromEscapedAllocas("protect-from-escaped-allocas",
72 cl::init(false), cl::Hidden,
73 cl::desc("Do not optimize lifetime zones that "
76 STATISTIC(NumMarkerSeen, "Number of lifetime markers found.");
77 STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots.");
78 STATISTIC(StackSlotMerged, "Number of stack slot merged.");
79 STATISTIC(EscapedAllocas, "Number of allocas that escaped the lifetime region");
81 //===----------------------------------------------------------------------===//
83 //===----------------------------------------------------------------------===//
86 /// StackColoring - A machine pass for merging disjoint stack allocations,
87 /// marked by the LIFETIME_START and LIFETIME_END pseudo instructions.
88 class StackColoring : public MachineFunctionPass {
89 MachineFrameInfo *MFI;
92 /// A class representing liveness information for a single basic block.
93 /// Each bit in the BitVector represents the liveness property
94 /// for a different stack slot.
95 struct BlockLifetimeInfo {
96 /// Which slots BEGINs in each basic block.
98 /// Which slots ENDs in each basic block.
100 /// Which slots are marked as LIVE_IN, coming into each basic block.
102 /// Which slots are marked as LIVE_OUT, coming out of each basic block.
106 /// Maps active slots (per bit) for each basic block.
107 typedef DenseMap<const MachineBasicBlock*, BlockLifetimeInfo> LivenessMap;
108 LivenessMap BlockLiveness;
110 /// Maps serial numbers to basic blocks.
111 DenseMap<const MachineBasicBlock*, int> BasicBlocks;
112 /// Maps basic blocks to a serial number.
113 SmallVector<const MachineBasicBlock*, 8> BasicBlockNumbering;
115 /// Maps liveness intervals for each slot.
116 SmallVector<std::unique_ptr<LiveInterval>, 16> Intervals;
117 /// VNInfo is used for the construction of LiveIntervals.
118 VNInfo::Allocator VNInfoAllocator;
119 /// SlotIndex analysis object.
120 SlotIndexes *Indexes;
121 /// The stack protector object.
124 /// The list of lifetime markers found. These markers are to be removed
125 /// once the coloring is done.
126 SmallVector<MachineInstr*, 8> Markers;
130 StackColoring() : MachineFunctionPass(ID) {
131 initializeStackColoringPass(*PassRegistry::getPassRegistry());
133 void getAnalysisUsage(AnalysisUsage &AU) const override;
134 bool runOnMachineFunction(MachineFunction &MF) override;
140 /// Removes all of the lifetime marker instructions from the function.
141 /// \returns true if any markers were removed.
142 bool removeAllMarkers();
144 /// Scan the machine function and find all of the lifetime markers.
145 /// Record the findings in the BEGIN and END vectors.
146 /// \returns the number of markers found.
147 unsigned collectMarkers(unsigned NumSlot);
149 /// Perform the dataflow calculation and calculate the lifetime for each of
150 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and
151 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming
152 /// in and out blocks.
153 void calculateLocalLiveness();
155 /// Construct the LiveIntervals for the slots.
156 void calculateLiveIntervals(unsigned NumSlots);
158 /// Go over the machine function and change instructions which use stack
159 /// slots to use the joint slots.
160 void remapInstructions(DenseMap<int, int> &SlotRemap);
162 /// The input program may contain instructions which are not inside lifetime
163 /// markers. This can happen due to a bug in the compiler or due to a bug in
164 /// user code (for example, returning a reference to a local variable).
165 /// This procedure checks all of the instructions in the function and
166 /// invalidates lifetime ranges which do not contain all of the instructions
167 /// which access that frame slot.
168 void removeInvalidSlotRanges();
170 /// Map entries which point to other entries to their destination.
171 /// A->B->C becomes A->C.
172 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots);
174 } // end anonymous namespace
176 char StackColoring::ID = 0;
177 char &llvm::StackColoringID = StackColoring::ID;
179 INITIALIZE_PASS_BEGIN(StackColoring,
180 "stack-coloring", "Merge disjoint stack slots", false, false)
181 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
182 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
183 INITIALIZE_PASS_DEPENDENCY(StackProtector)
184 INITIALIZE_PASS_END(StackColoring,
185 "stack-coloring", "Merge disjoint stack slots", false, false)
187 void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const {
188 AU.addRequired<MachineDominatorTree>();
189 AU.addPreserved<MachineDominatorTree>();
190 AU.addRequired<SlotIndexes>();
191 AU.addRequired<StackProtector>();
192 MachineFunctionPass::getAnalysisUsage(AU);
195 void StackColoring::dump() const {
196 for (MachineBasicBlock *MBB : depth_first(MF)) {
197 DEBUG(dbgs() << "Inspecting block #" << BasicBlocks.lookup(MBB) << " ["
198 << MBB->getName() << "]\n");
200 LivenessMap::const_iterator BI = BlockLiveness.find(MBB);
201 assert(BI != BlockLiveness.end() && "Block not found");
202 const BlockLifetimeInfo &BlockInfo = BI->second;
204 DEBUG(dbgs()<<"BEGIN : {");
205 for (unsigned i=0; i < BlockInfo.Begin.size(); ++i)
206 DEBUG(dbgs()<<BlockInfo.Begin.test(i)<<" ");
207 DEBUG(dbgs()<<"}\n");
209 DEBUG(dbgs()<<"END : {");
210 for (unsigned i=0; i < BlockInfo.End.size(); ++i)
211 DEBUG(dbgs()<<BlockInfo.End.test(i)<<" ");
213 DEBUG(dbgs()<<"}\n");
215 DEBUG(dbgs()<<"LIVE_IN: {");
216 for (unsigned i=0; i < BlockInfo.LiveIn.size(); ++i)
217 DEBUG(dbgs()<<BlockInfo.LiveIn.test(i)<<" ");
219 DEBUG(dbgs()<<"}\n");
220 DEBUG(dbgs()<<"LIVEOUT: {");
221 for (unsigned i=0; i < BlockInfo.LiveOut.size(); ++i)
222 DEBUG(dbgs()<<BlockInfo.LiveOut.test(i)<<" ");
223 DEBUG(dbgs()<<"}\n");
227 unsigned StackColoring::collectMarkers(unsigned NumSlot) {
228 unsigned MarkersFound = 0;
229 // Scan the function to find all lifetime markers.
230 // NOTE: We use the a reverse-post-order iteration to ensure that we obtain a
231 // deterministic numbering, and because we'll need a post-order iteration
232 // later for solving the liveness dataflow problem.
233 for (MachineBasicBlock *MBB : depth_first(MF)) {
235 // Assign a serial number to this basic block.
236 BasicBlocks[MBB] = BasicBlockNumbering.size();
237 BasicBlockNumbering.push_back(MBB);
239 // Keep a reference to avoid repeated lookups.
240 BlockLifetimeInfo &BlockInfo = BlockLiveness[MBB];
242 BlockInfo.Begin.resize(NumSlot);
243 BlockInfo.End.resize(NumSlot);
245 for (MachineInstr &MI : *MBB) {
246 if (MI.getOpcode() != TargetOpcode::LIFETIME_START &&
247 MI.getOpcode() != TargetOpcode::LIFETIME_END)
250 Markers.push_back(&MI);
252 bool IsStart = MI.getOpcode() == TargetOpcode::LIFETIME_START;
253 const MachineOperand &MO = MI.getOperand(0);
254 unsigned Slot = MO.getIndex();
258 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot);
260 DEBUG(dbgs()<<"Found a lifetime marker for slot #"<<Slot<<
261 " with allocation: "<< Allocation->getName()<<"\n");
265 BlockInfo.Begin.set(Slot);
267 if (BlockInfo.Begin.test(Slot)) {
268 // Allocas that start and end within a single block are handled
269 // specially when computing the LiveIntervals to avoid pessimizing
270 // the liveness propagation.
271 BlockInfo.Begin.reset(Slot);
273 BlockInfo.End.set(Slot);
279 // Update statistics.
280 NumMarkerSeen += MarkersFound;
284 void StackColoring::calculateLocalLiveness() {
285 // Perform a standard reverse dataflow computation to solve for
286 // global liveness. The BEGIN set here is equivalent to KILL in the standard
287 // formulation, and END is equivalent to GEN. The result of this computation
288 // is a map from blocks to bitvectors where the bitvectors represent which
289 // allocas are live in/out of that block.
290 SmallPtrSet<const MachineBasicBlock*, 8> BBSet(BasicBlockNumbering.begin(),
291 BasicBlockNumbering.end());
292 unsigned NumSSMIters = 0;
298 SmallPtrSet<const MachineBasicBlock*, 8> NextBBSet;
300 for (const MachineBasicBlock *BB : BasicBlockNumbering) {
301 if (!BBSet.count(BB)) continue;
303 // Use an iterator to avoid repeated lookups.
304 LivenessMap::iterator BI = BlockLiveness.find(BB);
305 assert(BI != BlockLiveness.end() && "Block not found");
306 BlockLifetimeInfo &BlockInfo = BI->second;
308 BitVector LocalLiveIn;
309 BitVector LocalLiveOut;
311 // Forward propagation from begins to ends.
312 for (MachineBasicBlock::const_pred_iterator PI = BB->pred_begin(),
313 PE = BB->pred_end(); PI != PE; ++PI) {
314 LivenessMap::const_iterator I = BlockLiveness.find(*PI);
315 assert(I != BlockLiveness.end() && "Predecessor not found");
316 LocalLiveIn |= I->second.LiveOut;
318 LocalLiveIn |= BlockInfo.End;
319 LocalLiveIn.reset(BlockInfo.Begin);
321 // Reverse propagation from ends to begins.
322 for (MachineBasicBlock::const_succ_iterator SI = BB->succ_begin(),
323 SE = BB->succ_end(); SI != SE; ++SI) {
324 LivenessMap::const_iterator I = BlockLiveness.find(*SI);
325 assert(I != BlockLiveness.end() && "Successor not found");
326 LocalLiveOut |= I->second.LiveIn;
328 LocalLiveOut |= BlockInfo.Begin;
329 LocalLiveOut.reset(BlockInfo.End);
331 LocalLiveIn |= LocalLiveOut;
332 LocalLiveOut |= LocalLiveIn;
334 // After adopting the live bits, we need to turn-off the bits which
335 // are de-activated in this block.
336 LocalLiveOut.reset(BlockInfo.End);
337 LocalLiveIn.reset(BlockInfo.Begin);
339 // If we have both BEGIN and END markers in the same basic block then
340 // we know that the BEGIN marker comes after the END, because we already
341 // handle the case where the BEGIN comes before the END when collecting
342 // the markers (and building the BEGIN/END vectore).
343 // Want to enable the LIVE_IN and LIVE_OUT of slots that have both
344 // BEGIN and END because it means that the value lives before and after
346 BitVector LocalEndBegin = BlockInfo.End;
347 LocalEndBegin &= BlockInfo.Begin;
348 LocalLiveIn |= LocalEndBegin;
349 LocalLiveOut |= LocalEndBegin;
351 if (LocalLiveIn.test(BlockInfo.LiveIn)) {
353 BlockInfo.LiveIn |= LocalLiveIn;
355 NextBBSet.insert(BB->pred_begin(), BB->pred_end());
358 if (LocalLiveOut.test(BlockInfo.LiveOut)) {
360 BlockInfo.LiveOut |= LocalLiveOut;
362 NextBBSet.insert(BB->succ_begin(), BB->succ_end());
370 void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
371 SmallVector<SlotIndex, 16> Starts;
372 SmallVector<SlotIndex, 16> Finishes;
374 // For each block, find which slots are active within this block
375 // and update the live intervals.
376 for (const MachineBasicBlock &MBB : *MF) {
378 Starts.resize(NumSlots);
380 Finishes.resize(NumSlots);
382 // Create the interval for the basic blocks with lifetime markers in them.
383 for (const MachineInstr *MI : Markers) {
384 if (MI->getParent() != &MBB)
387 assert((MI->getOpcode() == TargetOpcode::LIFETIME_START ||
388 MI->getOpcode() == TargetOpcode::LIFETIME_END) &&
389 "Invalid Lifetime marker");
391 bool IsStart = MI->getOpcode() == TargetOpcode::LIFETIME_START;
392 const MachineOperand &Mo = MI->getOperand(0);
393 int Slot = Mo.getIndex();
394 assert(Slot >= 0 && "Invalid slot");
396 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI);
399 if (!Starts[Slot].isValid() || Starts[Slot] > ThisIndex)
400 Starts[Slot] = ThisIndex;
402 if (!Finishes[Slot].isValid() || Finishes[Slot] < ThisIndex)
403 Finishes[Slot] = ThisIndex;
407 // Create the interval of the blocks that we previously found to be 'alive'.
408 BlockLifetimeInfo &MBBLiveness = BlockLiveness[&MBB];
409 for (int pos = MBBLiveness.LiveIn.find_first(); pos != -1;
410 pos = MBBLiveness.LiveIn.find_next(pos)) {
411 Starts[pos] = Indexes->getMBBStartIdx(&MBB);
413 for (int pos = MBBLiveness.LiveOut.find_first(); pos != -1;
414 pos = MBBLiveness.LiveOut.find_next(pos)) {
415 Finishes[pos] = Indexes->getMBBEndIdx(&MBB);
418 for (unsigned i = 0; i < NumSlots; ++i) {
419 assert(Starts[i].isValid() == Finishes[i].isValid() && "Unmatched range");
420 if (!Starts[i].isValid())
423 assert(Starts[i] && Finishes[i] && "Invalid interval");
424 VNInfo *ValNum = Intervals[i]->getValNumInfo(0);
425 SlotIndex S = Starts[i];
426 SlotIndex F = Finishes[i];
428 // We have a single consecutive region.
429 Intervals[i]->addSegment(LiveInterval::Segment(S, F, ValNum));
431 // We have two non-consecutive regions. This happens when
432 // LIFETIME_START appears after the LIFETIME_END marker.
433 SlotIndex NewStart = Indexes->getMBBStartIdx(&MBB);
434 SlotIndex NewFin = Indexes->getMBBEndIdx(&MBB);
435 Intervals[i]->addSegment(LiveInterval::Segment(NewStart, F, ValNum));
436 Intervals[i]->addSegment(LiveInterval::Segment(S, NewFin, ValNum));
442 bool StackColoring::removeAllMarkers() {
444 for (MachineInstr *MI : Markers) {
445 MI->eraseFromParent();
450 DEBUG(dbgs()<<"Removed "<<Count<<" markers.\n");
454 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
455 unsigned FixedInstr = 0;
456 unsigned FixedMemOp = 0;
457 unsigned FixedDbg = 0;
458 MachineModuleInfo *MMI = &MF->getMMI();
460 // Remap debug information that refers to stack slots.
461 for (auto &VI : MMI->getVariableDbgInfo()) {
464 if (SlotRemap.count(VI.Slot)) {
465 DEBUG(dbgs()<<"Remapping debug info for ["<<VI.Var->getName()<<"].\n");
466 VI.Slot = SlotRemap[VI.Slot];
471 // Keep a list of *allocas* which need to be remapped.
472 DenseMap<const AllocaInst*, const AllocaInst*> Allocas;
473 for (const std::pair<int, int> &SI : SlotRemap) {
474 const AllocaInst *From = MFI->getObjectAllocation(SI.first);
475 const AllocaInst *To = MFI->getObjectAllocation(SI.second);
476 assert(To && From && "Invalid allocation object");
479 // AA might be used later for instruction scheduling, and we need it to be
480 // able to deduce the correct aliasing releationships between pointers
481 // derived from the alloca being remapped and the target of that remapping.
482 // The only safe way, without directly informing AA about the remapping
483 // somehow, is to directly update the IR to reflect the change being made
485 Instruction *Inst = const_cast<AllocaInst *>(To);
486 if (From->getType() != To->getType()) {
487 BitCastInst *Cast = new BitCastInst(Inst, From->getType());
488 Cast->insertAfter(Inst);
492 // Allow the stack protector to adjust its value map to account for the
493 // upcoming replacement.
494 SP->adjustForColoring(From, To);
496 // Note that this will not replace uses in MMOs (which we'll update below),
497 // or anywhere else (which is why we won't delete the original
499 const_cast<AllocaInst *>(From)->replaceAllUsesWith(Inst);
502 // Remap all instructions to the new stack slots.
503 for (MachineBasicBlock &BB : *MF)
504 for (MachineInstr &I : BB) {
505 // Skip lifetime markers. We'll remove them soon.
506 if (I.getOpcode() == TargetOpcode::LIFETIME_START ||
507 I.getOpcode() == TargetOpcode::LIFETIME_END)
510 // Update the MachineMemOperand to use the new alloca.
511 for (MachineMemOperand *MMO : I.memoperands()) {
512 // FIXME: In order to enable the use of TBAA when using AA in CodeGen,
513 // we'll also need to update the TBAA nodes in MMOs with values
514 // derived from the merged allocas. When doing this, we'll need to use
515 // the same variant of GetUnderlyingObjects that is used by the
516 // instruction scheduler (that can look through ptrtoint/inttoptr
519 // We've replaced IR-level uses of the remapped allocas, so we only
520 // need to replace direct uses here.
521 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(MMO->getValue());
525 if (!Allocas.count(AI))
528 MMO->setValue(Allocas[AI]);
532 // Update all of the machine instruction operands.
533 for (MachineOperand &MO : I.operands()) {
536 int FromSlot = MO.getIndex();
538 // Don't touch arguments.
542 // Only look at mapped slots.
543 if (!SlotRemap.count(FromSlot))
546 // In a debug build, check that the instruction that we are modifying is
547 // inside the expected live range. If the instruction is not inside
548 // the calculated range then it means that the alloca usage moved
549 // outside of the lifetime markers, or that the user has a bug.
550 // NOTE: Alloca address calculations which happen outside the lifetime
551 // zone are are okay, despite the fact that we don't have a good way
552 // for validating all of the usages of the calculation.
554 bool TouchesMemory = I.mayLoad() || I.mayStore();
555 // If we *don't* protect the user from escaped allocas, don't bother
556 // validating the instructions.
557 if (!I.isDebugValue() && TouchesMemory && ProtectFromEscapedAllocas) {
558 SlotIndex Index = Indexes->getInstructionIndex(&I);
559 const LiveInterval *Interval = &*Intervals[FromSlot];
560 assert(Interval->find(Index) != Interval->end() &&
561 "Found instruction usage outside of live range.");
565 // Fix the machine instructions.
566 int ToSlot = SlotRemap[FromSlot];
572 DEBUG(dbgs()<<"Fixed "<<FixedMemOp<<" machine memory operands.\n");
573 DEBUG(dbgs()<<"Fixed "<<FixedDbg<<" debug locations.\n");
574 DEBUG(dbgs()<<"Fixed "<<FixedInstr<<" machine instructions.\n");
577 void StackColoring::removeInvalidSlotRanges() {
578 for (MachineBasicBlock &BB : *MF)
579 for (MachineInstr &I : BB) {
580 if (I.getOpcode() == TargetOpcode::LIFETIME_START ||
581 I.getOpcode() == TargetOpcode::LIFETIME_END || I.isDebugValue())
584 // Some intervals are suspicious! In some cases we find address
585 // calculations outside of the lifetime zone, but not actual memory
586 // read or write. Memory accesses outside of the lifetime zone are a clear
587 // violation, but address calculations are okay. This can happen when
588 // GEPs are hoisted outside of the lifetime zone.
589 // So, in here we only check instructions which can read or write memory.
590 if (!I.mayLoad() && !I.mayStore())
593 // Check all of the machine operands.
594 for (const MachineOperand &MO : I.operands()) {
598 int Slot = MO.getIndex();
603 if (Intervals[Slot]->empty())
606 // Check that the used slot is inside the calculated lifetime range.
607 // If it is not, warn about it and invalidate the range.
608 LiveInterval *Interval = &*Intervals[Slot];
609 SlotIndex Index = Indexes->getInstructionIndex(&I);
610 if (Interval->find(Index) == Interval->end()) {
612 DEBUG(dbgs()<<"Invalidating range #"<<Slot<<"\n");
619 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap,
621 // Expunge slot remap map.
622 for (unsigned i=0; i < NumSlots; ++i) {
623 // If we are remapping i
624 if (SlotRemap.count(i)) {
625 int Target = SlotRemap[i];
626 // As long as our target is mapped to something else, follow it.
627 while (SlotRemap.count(Target)) {
628 Target = SlotRemap[Target];
629 SlotRemap[i] = Target;
635 bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
636 if (skipOptnoneFunction(*Func.getFunction()))
639 DEBUG(dbgs() << "********** Stack Coloring **********\n"
640 << "********** Function: "
641 << ((const Value*)Func.getFunction())->getName() << '\n');
643 MFI = MF->getFrameInfo();
644 Indexes = &getAnalysis<SlotIndexes>();
645 SP = &getAnalysis<StackProtector>();
646 BlockLiveness.clear();
648 BasicBlockNumbering.clear();
651 VNInfoAllocator.Reset();
653 unsigned NumSlots = MFI->getObjectIndexEnd();
655 // If there are no stack slots then there are no markers to remove.
659 SmallVector<int, 8> SortedSlots;
661 SortedSlots.reserve(NumSlots);
662 Intervals.reserve(NumSlots);
664 unsigned NumMarkers = collectMarkers(NumSlots);
666 unsigned TotalSize = 0;
667 DEBUG(dbgs()<<"Found "<<NumMarkers<<" markers and "<<NumSlots<<" slots\n");
668 DEBUG(dbgs()<<"Slot structure:\n");
670 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) {
671 DEBUG(dbgs()<<"Slot #"<<i<<" - "<<MFI->getObjectSize(i)<<" bytes.\n");
672 TotalSize += MFI->getObjectSize(i);
675 DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n");
677 // Don't continue because there are not enough lifetime markers, or the
678 // stack is too small, or we are told not to optimize the slots.
679 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
680 DEBUG(dbgs()<<"Will not try to merge slots.\n");
681 return removeAllMarkers();
684 for (unsigned i=0; i < NumSlots; ++i) {
685 std::unique_ptr<LiveInterval> LI(new LiveInterval(i, 0));
686 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator);
687 Intervals.push_back(std::move(LI));
688 SortedSlots.push_back(i);
691 // Calculate the liveness of each block.
692 calculateLocalLiveness();
694 // Propagate the liveness information.
695 calculateLiveIntervals(NumSlots);
697 // Search for allocas which are used outside of the declared lifetime
699 if (ProtectFromEscapedAllocas)
700 removeInvalidSlotRanges();
702 // Maps old slots to new slots.
703 DenseMap<int, int> SlotRemap;
704 unsigned RemovedSlots = 0;
705 unsigned ReducedSize = 0;
707 // Do not bother looking at empty intervals.
708 for (unsigned I = 0; I < NumSlots; ++I) {
709 if (Intervals[SortedSlots[I]]->empty())
713 // This is a simple greedy algorithm for merging allocas. First, sort the
714 // slots, placing the largest slots first. Next, perform an n^2 scan and look
715 // for disjoint slots. When you find disjoint slots, merge the samller one
716 // into the bigger one and update the live interval. Remove the small alloca
719 // Sort the slots according to their size. Place unused slots at the end.
720 // Use stable sort to guarantee deterministic code generation.
721 std::stable_sort(SortedSlots.begin(), SortedSlots.end(),
722 [this](int LHS, int RHS) {
723 // We use -1 to denote a uninteresting slot. Place these slots at the end.
724 if (LHS == -1) return false;
725 if (RHS == -1) return true;
726 // Sort according to size.
727 return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS);
733 for (unsigned I = 0; I < NumSlots; ++I) {
734 if (SortedSlots[I] == -1)
737 for (unsigned J=I+1; J < NumSlots; ++J) {
738 if (SortedSlots[J] == -1)
741 int FirstSlot = SortedSlots[I];
742 int SecondSlot = SortedSlots[J];
743 LiveInterval *First = &*Intervals[FirstSlot];
744 LiveInterval *Second = &*Intervals[SecondSlot];
745 assert (!First->empty() && !Second->empty() && "Found an empty range");
747 // Merge disjoint slots.
748 if (!First->overlaps(*Second)) {
750 First->MergeSegmentsInAsValue(*Second, First->getValNumInfo(0));
751 SlotRemap[SecondSlot] = FirstSlot;
753 DEBUG(dbgs()<<"Merging #"<<FirstSlot<<" and slots #"<<
754 SecondSlot<<" together.\n");
755 unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot),
756 MFI->getObjectAlignment(SecondSlot));
758 assert(MFI->getObjectSize(FirstSlot) >=
759 MFI->getObjectSize(SecondSlot) &&
760 "Merging a small object into a larger one");
763 ReducedSize += MFI->getObjectSize(SecondSlot);
764 MFI->setObjectAlignment(FirstSlot, MaxAlignment);
765 MFI->RemoveStackObject(SecondSlot);
771 // Record statistics.
772 StackSpaceSaved += ReducedSize;
773 StackSlotMerged += RemovedSlots;
774 DEBUG(dbgs()<<"Merge "<<RemovedSlots<<" slots. Saved "<<
775 ReducedSize<<" bytes\n");
777 // Scan the entire function and update all machine operands that use frame
778 // indices to use the remapped frame index.
779 expungeSlotMap(SlotRemap, NumSlots);
780 remapInstructions(SlotRemap);
782 return removeAllMarkers();