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/Dominators.h"
34 #include "llvm/Analysis/ValueTracking.h"
35 #include "llvm/CodeGen/LiveInterval.h"
36 #include "llvm/CodeGen/MachineBasicBlock.h"
37 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
38 #include "llvm/CodeGen/MachineDominators.h"
39 #include "llvm/CodeGen/MachineFrameInfo.h"
40 #include "llvm/CodeGen/MachineFunctionPass.h"
41 #include "llvm/CodeGen/MachineLoopInfo.h"
42 #include "llvm/CodeGen/MachineMemOperand.h"
43 #include "llvm/CodeGen/MachineModuleInfo.h"
44 #include "llvm/CodeGen/MachineRegisterInfo.h"
45 #include "llvm/CodeGen/SlotIndexes.h"
46 #include "llvm/DebugInfo.h"
47 #include "llvm/IR/Function.h"
48 #include "llvm/IR/Instructions.h"
49 #include "llvm/IR/Module.h"
50 #include "llvm/MC/MCInstrItineraries.h"
51 #include "llvm/Support/CommandLine.h"
52 #include "llvm/Support/Debug.h"
53 #include "llvm/Support/raw_ostream.h"
54 #include "llvm/Target/TargetInstrInfo.h"
55 #include "llvm/Target/TargetRegisterInfo.h"
60 DisableColoring("no-stack-coloring",
61 cl::init(false), cl::Hidden,
62 cl::desc("Disable stack coloring"));
64 /// The user may write code that uses allocas outside of the declared lifetime
65 /// zone. This can happen when the user returns a reference to a local
66 /// data-structure. We can detect these cases and decide not to optimize the
67 /// code. If this flag is enabled, we try to save the user.
69 ProtectFromEscapedAllocas("protect-from-escaped-allocas",
70 cl::init(false), cl::Hidden,
71 cl::desc("Do not optimize lifetime zones that are broken"));
73 STATISTIC(NumMarkerSeen, "Number of lifetime markers found.");
74 STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots.");
75 STATISTIC(StackSlotMerged, "Number of stack slot merged.");
76 STATISTIC(EscapedAllocas,
77 "Number of allocas that escaped the lifetime region");
79 //===----------------------------------------------------------------------===//
81 //===----------------------------------------------------------------------===//
84 /// StackColoring - A machine pass for merging disjoint stack allocations,
85 /// marked by the LIFETIME_START and LIFETIME_END pseudo instructions.
86 class StackColoring : public MachineFunctionPass {
87 MachineFrameInfo *MFI;
90 /// A class representing liveness information for a single basic block.
91 /// Each bit in the BitVector represents the liveness property
92 /// for a different stack slot.
93 struct BlockLifetimeInfo {
94 /// Which slots BEGINs in each basic block.
96 /// Which slots ENDs in each basic block.
98 /// Which slots are marked as LIVE_IN, coming into each basic block.
100 /// Which slots are marked as LIVE_OUT, coming out of each basic block.
104 /// Maps active slots (per bit) for each basic block.
105 DenseMap<MachineBasicBlock*, BlockLifetimeInfo> BlockLiveness;
107 /// Maps serial numbers to basic blocks.
108 DenseMap<MachineBasicBlock*, int> BasicBlocks;
109 /// Maps basic blocks to a serial number.
110 SmallVector<MachineBasicBlock*, 8> BasicBlockNumbering;
112 /// Maps liveness intervals for each slot.
113 SmallVector<LiveInterval*, 16> Intervals;
114 /// VNInfo is used for the construction of LiveIntervals.
115 VNInfo::Allocator VNInfoAllocator;
116 /// SlotIndex analysis object.
117 SlotIndexes *Indexes;
119 /// The list of lifetime markers found. These markers are to be removed
120 /// once the coloring is done.
121 SmallVector<MachineInstr*, 8> Markers;
123 /// SlotSizeSorter - A Sort utility for arranging stack slots according
125 struct SlotSizeSorter {
126 MachineFrameInfo *MFI;
127 SlotSizeSorter(MachineFrameInfo *mfi) : MFI(mfi) { }
128 bool operator()(int LHS, int RHS) {
129 // We use -1 to denote a uninteresting slot. Place these slots at the end.
130 if (LHS == -1) return false;
131 if (RHS == -1) return true;
132 // Sort according to size.
133 return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS);
139 StackColoring() : MachineFunctionPass(ID) {
140 initializeStackColoringPass(*PassRegistry::getPassRegistry());
142 void getAnalysisUsage(AnalysisUsage &AU) const;
143 bool runOnMachineFunction(MachineFunction &MF);
149 /// Removes all of the lifetime marker instructions from the function.
150 /// \returns true if any markers were removed.
151 bool removeAllMarkers();
153 /// Scan the machine function and find all of the lifetime markers.
154 /// Record the findings in the BEGIN and END vectors.
155 /// \returns the number of markers found.
156 unsigned collectMarkers(unsigned NumSlot);
158 /// Perform the dataflow calculation and calculate the lifetime for each of
159 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and
160 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming
161 /// in and out blocks.
162 void calculateLocalLiveness();
164 /// Construct the LiveIntervals for the slots.
165 void calculateLiveIntervals(unsigned NumSlots);
167 /// Go over the machine function and change instructions which use stack
168 /// slots to use the joint slots.
169 void remapInstructions(DenseMap<int, int> &SlotRemap);
171 /// The input program may contain intructions which are not inside lifetime
172 /// markers. This can happen due to a bug in the compiler or due to a bug in
173 /// user code (for example, returning a reference to a local variable).
174 /// This procedure checks all of the instructions in the function and
175 /// invalidates lifetime ranges which do not contain all of the instructions
176 /// which access that frame slot.
177 void removeInvalidSlotRanges();
179 /// Map entries which point to other entries to their destination.
180 /// A->B->C becomes A->C.
181 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots);
183 } // end anonymous namespace
185 char StackColoring::ID = 0;
186 char &llvm::StackColoringID = StackColoring::ID;
188 INITIALIZE_PASS_BEGIN(StackColoring,
189 "stack-coloring", "Merge disjoint stack slots", false, false)
190 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
191 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
192 INITIALIZE_PASS_END(StackColoring,
193 "stack-coloring", "Merge disjoint stack slots", false, false)
195 void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const {
196 AU.addRequired<MachineDominatorTree>();
197 AU.addPreserved<MachineDominatorTree>();
198 AU.addRequired<SlotIndexes>();
199 MachineFunctionPass::getAnalysisUsage(AU);
202 void StackColoring::dump() const {
203 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
205 DEBUG(dbgs()<<"Inspecting block #"<<BasicBlocks.lookup(*FI)<<
206 " ["<<FI->getName()<<"]\n");
208 DenseMap<MachineBasicBlock*, BlockLifetimeInfo>::const_iterator BI =
209 BlockLiveness.find(*FI);
210 assert(BI != BlockLiveness.end() && "Block not found");
211 const BlockLifetimeInfo &BlockInfo = BI->second;
213 DEBUG(dbgs()<<"BEGIN : {");
214 for (unsigned i=0; i < BlockInfo.Begin.size(); ++i)
215 DEBUG(dbgs()<<BlockInfo.Begin.test(i)<<" ");
216 DEBUG(dbgs()<<"}\n");
218 DEBUG(dbgs()<<"END : {");
219 for (unsigned i=0; i < BlockInfo.End.size(); ++i)
220 DEBUG(dbgs()<<BlockInfo.End.test(i)<<" ");
222 DEBUG(dbgs()<<"}\n");
224 DEBUG(dbgs()<<"LIVE_IN: {");
225 for (unsigned i=0; i < BlockInfo.LiveIn.size(); ++i)
226 DEBUG(dbgs()<<BlockInfo.LiveIn.test(i)<<" ");
228 DEBUG(dbgs()<<"}\n");
229 DEBUG(dbgs()<<"LIVEOUT: {");
230 for (unsigned i=0; i < BlockInfo.LiveOut.size(); ++i)
231 DEBUG(dbgs()<<BlockInfo.LiveOut.test(i)<<" ");
232 DEBUG(dbgs()<<"}\n");
236 unsigned StackColoring::collectMarkers(unsigned NumSlot) {
237 unsigned MarkersFound = 0;
238 // Scan the function to find all lifetime markers.
239 // NOTE: We use the a reverse-post-order iteration to ensure that we obtain a
240 // deterministic numbering, and because we'll need a post-order iteration
241 // later for solving the liveness dataflow problem.
242 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
245 // Assign a serial number to this basic block.
246 BasicBlocks[*FI] = BasicBlockNumbering.size();
247 BasicBlockNumbering.push_back(*FI);
249 // Keep a reference to avoid repeated lookups.
250 BlockLifetimeInfo &BlockInfo = BlockLiveness[*FI];
252 BlockInfo.Begin.resize(NumSlot);
253 BlockInfo.End.resize(NumSlot);
255 for (MachineBasicBlock::iterator BI = (*FI)->begin(), BE = (*FI)->end();
258 if (BI->getOpcode() != TargetOpcode::LIFETIME_START &&
259 BI->getOpcode() != TargetOpcode::LIFETIME_END)
262 Markers.push_back(BI);
264 bool IsStart = BI->getOpcode() == TargetOpcode::LIFETIME_START;
265 MachineOperand &MI = BI->getOperand(0);
266 unsigned Slot = MI.getIndex();
270 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot);
272 DEBUG(dbgs()<<"Found a lifetime marker for slot #"<<Slot<<
273 " with allocation: "<< Allocation->getName()<<"\n");
277 BlockInfo.Begin.set(Slot);
279 if (BlockInfo.Begin.test(Slot)) {
280 // Allocas that start and end within a single block are handled
281 // specially when computing the LiveIntervals to avoid pessimizing
282 // the liveness propagation.
283 BlockInfo.Begin.reset(Slot);
285 BlockInfo.End.set(Slot);
291 // Update statistics.
292 NumMarkerSeen += MarkersFound;
296 void StackColoring::calculateLocalLiveness() {
297 // Perform a standard reverse dataflow computation to solve for
298 // global liveness. The BEGIN set here is equivalent to KILL in the standard
299 // formulation, and END is equivalent to GEN. The result of this computation
300 // is a map from blocks to bitvectors where the bitvectors represent which
301 // allocas are live in/out of that block.
302 SmallPtrSet<MachineBasicBlock*, 8> BBSet(BasicBlockNumbering.begin(),
303 BasicBlockNumbering.end());
304 unsigned NumSSMIters = 0;
310 SmallPtrSet<MachineBasicBlock*, 8> NextBBSet;
312 for (SmallVector<MachineBasicBlock*, 8>::iterator
313 PI = BasicBlockNumbering.begin(), PE = BasicBlockNumbering.end();
316 MachineBasicBlock *BB = *PI;
317 if (!BBSet.count(BB)) continue;
319 BitVector LocalLiveIn;
320 BitVector LocalLiveOut;
322 // Forward propagation from begins to ends.
323 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
324 PE = BB->pred_end(); PI != PE; ++PI)
325 LocalLiveIn |= BlockLiveness[*PI].LiveOut;
326 LocalLiveIn |= BlockLiveness[BB].End;
327 LocalLiveIn.reset(BlockLiveness[BB].Begin);
329 // Reverse propagation from ends to begins.
330 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
331 SE = BB->succ_end(); SI != SE; ++SI)
332 LocalLiveOut |= BlockLiveness[*SI].LiveIn;
333 LocalLiveOut |= BlockLiveness[BB].Begin;
334 LocalLiveOut.reset(BlockLiveness[BB].End);
336 LocalLiveIn |= LocalLiveOut;
337 LocalLiveOut |= LocalLiveIn;
339 // After adopting the live bits, we need to turn-off the bits which
340 // are de-activated in this block.
341 LocalLiveOut.reset(BlockLiveness[BB].End);
342 LocalLiveIn.reset(BlockLiveness[BB].Begin);
344 // If we have both BEGIN and END markers in the same basic block then
345 // we know that the BEGIN marker comes after the END, because we already
346 // handle the case where the BEGIN comes before the END when collecting
347 // the markers (and building the BEGIN/END vectore).
348 // Want to enable the LIVE_IN and LIVE_OUT of slots that have both
349 // BEGIN and END because it means that the value lives before and after
351 BitVector LocalEndBegin = BlockLiveness[BB].End;
352 LocalEndBegin &= BlockLiveness[BB].Begin;
353 LocalLiveIn |= LocalEndBegin;
354 LocalLiveOut |= LocalEndBegin;
356 if (LocalLiveIn.test(BlockLiveness[BB].LiveIn)) {
358 BlockLiveness[BB].LiveIn |= LocalLiveIn;
360 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
361 PE = BB->pred_end(); PI != PE; ++PI)
362 NextBBSet.insert(*PI);
365 if (LocalLiveOut.test(BlockLiveness[BB].LiveOut)) {
367 BlockLiveness[BB].LiveOut |= LocalLiveOut;
369 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
370 SE = BB->succ_end(); SI != SE; ++SI)
371 NextBBSet.insert(*SI);
379 void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
380 SmallVector<SlotIndex, 16> Starts;
381 SmallVector<SlotIndex, 16> Finishes;
383 // For each block, find which slots are active within this block
384 // and update the live intervals.
385 for (MachineFunction::iterator MBB = MF->begin(), MBBe = MF->end();
386 MBB != MBBe; ++MBB) {
388 Starts.resize(NumSlots);
390 Finishes.resize(NumSlots);
392 // Create the interval for the basic blocks with lifetime markers in them.
393 for (SmallVector<MachineInstr*, 8>::iterator it = Markers.begin(),
394 e = Markers.end(); it != e; ++it) {
395 MachineInstr *MI = *it;
396 if (MI->getParent() != MBB)
399 assert((MI->getOpcode() == TargetOpcode::LIFETIME_START ||
400 MI->getOpcode() == TargetOpcode::LIFETIME_END) &&
401 "Invalid Lifetime marker");
403 bool IsStart = MI->getOpcode() == TargetOpcode::LIFETIME_START;
404 MachineOperand &Mo = MI->getOperand(0);
405 int Slot = Mo.getIndex();
406 assert(Slot >= 0 && "Invalid slot");
408 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI);
411 if (!Starts[Slot].isValid() || Starts[Slot] > ThisIndex)
412 Starts[Slot] = ThisIndex;
414 if (!Finishes[Slot].isValid() || Finishes[Slot] < ThisIndex)
415 Finishes[Slot] = ThisIndex;
419 // Create the interval of the blocks that we previously found to be 'alive'.
420 BitVector Alive = BlockLiveness[MBB].LiveIn;
421 Alive |= BlockLiveness[MBB].LiveOut;
424 for (int pos = Alive.find_first(); pos != -1;
425 pos = Alive.find_next(pos)) {
426 if (!Starts[pos].isValid())
427 Starts[pos] = Indexes->getMBBStartIdx(MBB);
428 if (!Finishes[pos].isValid())
429 Finishes[pos] = Indexes->getMBBEndIdx(MBB);
433 for (unsigned i = 0; i < NumSlots; ++i) {
434 assert(Starts[i].isValid() == Finishes[i].isValid() && "Unmatched range");
435 if (!Starts[i].isValid())
438 assert(Starts[i] && Finishes[i] && "Invalid interval");
439 VNInfo *ValNum = Intervals[i]->getValNumInfo(0);
440 SlotIndex S = Starts[i];
441 SlotIndex F = Finishes[i];
443 // We have a single consecutive region.
444 Intervals[i]->addRange(LiveRange(S, F, ValNum));
446 // We have two non consecutive regions. This happens when
447 // LIFETIME_START appears after the LIFETIME_END marker.
448 SlotIndex NewStart = Indexes->getMBBStartIdx(MBB);
449 SlotIndex NewFin = Indexes->getMBBEndIdx(MBB);
450 Intervals[i]->addRange(LiveRange(NewStart, F, ValNum));
451 Intervals[i]->addRange(LiveRange(S, NewFin, ValNum));
457 bool StackColoring::removeAllMarkers() {
459 for (unsigned i = 0; i < Markers.size(); ++i) {
460 Markers[i]->eraseFromParent();
465 DEBUG(dbgs()<<"Removed "<<Count<<" markers.\n");
469 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
470 unsigned FixedInstr = 0;
471 unsigned FixedMemOp = 0;
472 unsigned FixedDbg = 0;
473 MachineModuleInfo *MMI = &MF->getMMI();
475 // Remap debug information that refers to stack slots.
476 MachineModuleInfo::VariableDbgInfoMapTy &VMap = MMI->getVariableDbgInfo();
477 for (MachineModuleInfo::VariableDbgInfoMapTy::iterator VI = VMap.begin(),
478 VE = VMap.end(); VI != VE; ++VI) {
479 const MDNode *Var = VI->first;
481 std::pair<unsigned, DebugLoc> &VP = VI->second;
482 if (SlotRemap.count(VP.first)) {
483 DEBUG(dbgs()<<"Remapping debug info for ["<<Var->getName()<<"].\n");
484 VP.first = SlotRemap[VP.first];
489 // Keep a list of *allocas* which need to be remapped.
490 DenseMap<const AllocaInst*, const AllocaInst*> Allocas;
491 for (DenseMap<int, int>::iterator it = SlotRemap.begin(),
492 e = SlotRemap.end(); it != e; ++it) {
493 const AllocaInst *From = MFI->getObjectAllocation(it->first);
494 const AllocaInst *To = MFI->getObjectAllocation(it->second);
495 assert(To && From && "Invalid allocation object");
499 // Remap all instructions to the new stack slots.
500 MachineFunction::iterator BB, BBE;
501 MachineBasicBlock::iterator I, IE;
502 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB)
503 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) {
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 (MachineInstr::mmo_iterator MM = I->memoperands_begin(),
512 E = I->memoperands_end(); MM != E; ++MM) {
513 MachineMemOperand *MMO = *MM;
515 const Value *V = MMO->getValue();
520 // Climb up and find the original alloca.
521 V = GetUnderlyingObject(V);
522 // If we did not find one, or if the one that we found is not in our
523 // map, then move on.
524 if (!V || !isa<AllocaInst>(V)) {
525 // Clear mem operand since we don't know for sure that it doesn't
526 // alias a merged alloca.
530 const AllocaInst *AI= cast<AllocaInst>(V);
531 if (!Allocas.count(AI))
534 MMO->setValue(Allocas[AI]);
538 // Update all of the machine instruction operands.
539 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) {
540 MachineOperand &MO = I->getOperand(i);
544 int FromSlot = MO.getIndex();
546 // Don't touch arguments.
550 // Only look at mapped slots.
551 if (!SlotRemap.count(FromSlot))
554 // In a debug build, check that the instruction that we are modifying is
555 // inside the expected live range. If the instruction is not inside
556 // the calculated range then it means that the alloca usage moved
557 // outside of the lifetime markers, or that the user has a bug.
558 // NOTE: Alloca address calculations which happen outside the lifetime
559 // zone are are okay, despite the fact that we don't have a good way
560 // for validating all of the usages of the calculation.
562 bool TouchesMemory = I->mayLoad() || I->mayStore();
563 // If we *don't* protect the user from escaped allocas, don't bother
564 // validating the instructions.
565 if (!I->isDebugValue() && TouchesMemory && ProtectFromEscapedAllocas) {
566 SlotIndex Index = Indexes->getInstructionIndex(I);
567 LiveInterval *Interval = Intervals[FromSlot];
568 assert(Interval->find(Index) != Interval->end() &&
569 "Found instruction usage outside of live range.");
573 // Fix the machine instructions.
574 int ToSlot = SlotRemap[FromSlot];
580 DEBUG(dbgs()<<"Fixed "<<FixedMemOp<<" machine memory operands.\n");
581 DEBUG(dbgs()<<"Fixed "<<FixedDbg<<" debug locations.\n");
582 DEBUG(dbgs()<<"Fixed "<<FixedInstr<<" machine instructions.\n");
585 void StackColoring::removeInvalidSlotRanges() {
586 MachineFunction::iterator BB, BBE;
587 MachineBasicBlock::iterator I, IE;
588 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB)
589 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) {
591 if (I->getOpcode() == TargetOpcode::LIFETIME_START ||
592 I->getOpcode() == TargetOpcode::LIFETIME_END || I->isDebugValue())
595 // Some intervals are suspicious! In some cases we find address
596 // calculations outside of the lifetime zone, but not actual memory
597 // read or write. Memory accesses outside of the lifetime zone are a clear
598 // violation, but address calculations are okay. This can happen when
599 // GEPs are hoisted outside of the lifetime zone.
600 // So, in here we only check instructions which can read or write memory.
601 if (!I->mayLoad() && !I->mayStore())
604 // Check all of the machine operands.
605 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) {
606 MachineOperand &MO = I->getOperand(i);
611 int Slot = MO.getIndex();
616 if (Intervals[Slot]->empty())
619 // Check that the used slot is inside the calculated lifetime range.
620 // If it is not, warn about it and invalidate the range.
621 LiveInterval *Interval = Intervals[Slot];
622 SlotIndex Index = Indexes->getInstructionIndex(I);
623 if (Interval->find(Index) == Interval->end()) {
624 Intervals[Slot]->clear();
625 DEBUG(dbgs()<<"Invalidating range #"<<Slot<<"\n");
632 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap,
634 // Expunge slot remap map.
635 for (unsigned i=0; i < NumSlots; ++i) {
636 // If we are remapping i
637 if (SlotRemap.count(i)) {
638 int Target = SlotRemap[i];
639 // As long as our target is mapped to something else, follow it.
640 while (SlotRemap.count(Target)) {
641 Target = SlotRemap[Target];
642 SlotRemap[i] = Target;
648 bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
649 DEBUG(dbgs() << "********** Stack Coloring **********\n"
650 << "********** Function: "
651 << ((const Value*)Func.getFunction())->getName() << '\n');
653 MFI = MF->getFrameInfo();
654 Indexes = &getAnalysis<SlotIndexes>();
655 BlockLiveness.clear();
657 BasicBlockNumbering.clear();
660 VNInfoAllocator.Reset();
662 unsigned NumSlots = MFI->getObjectIndexEnd();
664 // If there are no stack slots then there are no markers to remove.
668 SmallVector<int, 8> SortedSlots;
670 SortedSlots.reserve(NumSlots);
671 Intervals.reserve(NumSlots);
673 unsigned NumMarkers = collectMarkers(NumSlots);
675 unsigned TotalSize = 0;
676 DEBUG(dbgs()<<"Found "<<NumMarkers<<" markers and "<<NumSlots<<" slots\n");
677 DEBUG(dbgs()<<"Slot structure:\n");
679 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) {
680 DEBUG(dbgs()<<"Slot #"<<i<<" - "<<MFI->getObjectSize(i)<<" bytes.\n");
681 TotalSize += MFI->getObjectSize(i);
684 DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n");
686 // Don't continue because there are not enough lifetime markers, or the
687 // stack is too small, or we are told not to optimize the slots.
688 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
689 DEBUG(dbgs()<<"Will not try to merge slots.\n");
690 return removeAllMarkers();
693 for (unsigned i=0; i < NumSlots; ++i) {
694 LiveInterval *LI = new LiveInterval(i, 0);
695 Intervals.push_back(LI);
696 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator);
697 SortedSlots.push_back(i);
700 // Calculate the liveness of each block.
701 calculateLocalLiveness();
703 // Propagate the liveness information.
704 calculateLiveIntervals(NumSlots);
706 // Search for allocas which are used outside of the declared lifetime
708 if (ProtectFromEscapedAllocas)
709 removeInvalidSlotRanges();
711 // Maps old slots to new slots.
712 DenseMap<int, int> SlotRemap;
713 unsigned RemovedSlots = 0;
714 unsigned ReducedSize = 0;
716 // Do not bother looking at empty intervals.
717 for (unsigned I = 0; I < NumSlots; ++I) {
718 if (Intervals[SortedSlots[I]]->empty())
722 // This is a simple greedy algorithm for merging allocas. First, sort the
723 // slots, placing the largest slots first. Next, perform an n^2 scan and look
724 // for disjoint slots. When you find disjoint slots, merge the samller one
725 // into the bigger one and update the live interval. Remove the small alloca
728 // Sort the slots according to their size. Place unused slots at the end.
729 // Use stable sort to guarantee deterministic code generation.
730 std::stable_sort(SortedSlots.begin(), SortedSlots.end(),
731 SlotSizeSorter(MFI));
736 for (unsigned I = 0; I < NumSlots; ++I) {
737 if (SortedSlots[I] == -1)
740 for (unsigned J=I+1; J < NumSlots; ++J) {
741 if (SortedSlots[J] == -1)
744 int FirstSlot = SortedSlots[I];
745 int SecondSlot = SortedSlots[J];
746 LiveInterval *First = Intervals[FirstSlot];
747 LiveInterval *Second = Intervals[SecondSlot];
748 assert (!First->empty() && !Second->empty() && "Found an empty range");
750 // Merge disjoint slots.
751 if (!First->overlaps(*Second)) {
753 First->MergeRangesInAsValue(*Second, First->getValNumInfo(0));
754 SlotRemap[SecondSlot] = FirstSlot;
756 DEBUG(dbgs()<<"Merging #"<<FirstSlot<<" and slots #"<<
757 SecondSlot<<" together.\n");
758 unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot),
759 MFI->getObjectAlignment(SecondSlot));
761 assert(MFI->getObjectSize(FirstSlot) >=
762 MFI->getObjectSize(SecondSlot) &&
763 "Merging a small object into a larger one");
766 ReducedSize += MFI->getObjectSize(SecondSlot);
767 MFI->setObjectAlignment(FirstSlot, MaxAlignment);
768 MFI->RemoveStackObject(SecondSlot);
774 // Record statistics.
775 StackSpaceSaved += ReducedSize;
776 StackSlotMerged += RemovedSlots;
777 DEBUG(dbgs()<<"Merge "<<RemovedSlots<<" slots. Saved "<<
778 ReducedSize<<" bytes\n");
780 // Scan the entire function and update all machine operands that use frame
781 // indices to use the remapped frame index.
782 expungeSlotMap(SlotRemap, NumSlots);
783 remapInstructions(SlotRemap);
785 // Release the intervals.
786 for (unsigned I = 0; I < NumSlots; ++I) {
790 return removeAllMarkers();