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() {
203 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
205 unsigned Num = BasicBlocks[*FI];
206 DEBUG(dbgs()<<"Inspecting block #"<<Num<<" ["<<FI->getName()<<"]\n");
208 DEBUG(dbgs()<<"BEGIN : {");
209 for (unsigned i=0; i < BlockLiveness[*FI].Begin.size(); ++i)
210 DEBUG(dbgs()<<BlockLiveness[*FI].Begin.test(i)<<" ");
211 DEBUG(dbgs()<<"}\n");
213 DEBUG(dbgs()<<"END : {");
214 for (unsigned i=0; i < BlockLiveness[*FI].End.size(); ++i)
215 DEBUG(dbgs()<<BlockLiveness[*FI].End.test(i)<<" ");
217 DEBUG(dbgs()<<"}\n");
219 DEBUG(dbgs()<<"LIVE_IN: {");
220 for (unsigned i=0; i < BlockLiveness[*FI].LiveIn.size(); ++i)
221 DEBUG(dbgs()<<BlockLiveness[*FI].LiveIn.test(i)<<" ");
223 DEBUG(dbgs()<<"}\n");
224 DEBUG(dbgs()<<"LIVEOUT: {");
225 for (unsigned i=0; i < BlockLiveness[*FI].LiveOut.size(); ++i)
226 DEBUG(dbgs()<<BlockLiveness[*FI].LiveOut.test(i)<<" ");
227 DEBUG(dbgs()<<"}\n");
231 unsigned StackColoring::collectMarkers(unsigned NumSlot) {
232 unsigned MarkersFound = 0;
233 // Scan the function to find all lifetime markers.
234 // NOTE: We use the a reverse-post-order iteration to ensure that we obtain a
235 // deterministic numbering, and because we'll need a post-order iteration
236 // later for solving the liveness dataflow problem.
237 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
240 // Assign a serial number to this basic block.
241 BasicBlocks[*FI] = BasicBlockNumbering.size();
242 BasicBlockNumbering.push_back(*FI);
244 BlockLiveness[*FI].Begin.resize(NumSlot);
245 BlockLiveness[*FI].End.resize(NumSlot);
247 for (MachineBasicBlock::iterator BI = (*FI)->begin(), BE = (*FI)->end();
250 if (BI->getOpcode() != TargetOpcode::LIFETIME_START &&
251 BI->getOpcode() != TargetOpcode::LIFETIME_END)
254 Markers.push_back(BI);
256 bool IsStart = BI->getOpcode() == TargetOpcode::LIFETIME_START;
257 MachineOperand &MI = BI->getOperand(0);
258 unsigned Slot = MI.getIndex();
262 const AllocaInst *Allocation = MFI->getObjectAllocation(Slot);
264 DEBUG(dbgs()<<"Found a lifetime marker for slot #"<<Slot<<
265 " with allocation: "<< Allocation->getName()<<"\n");
269 BlockLiveness[*FI].Begin.set(Slot);
271 if (BlockLiveness[*FI].Begin.test(Slot)) {
272 // Allocas that start and end within a single block are handled
273 // specially when computing the LiveIntervals to avoid pessimizing
274 // the liveness propagation.
275 BlockLiveness[*FI].Begin.reset(Slot);
277 BlockLiveness[*FI].End.set(Slot);
283 // Update statistics.
284 NumMarkerSeen += MarkersFound;
288 void StackColoring::calculateLocalLiveness() {
289 // Perform a standard reverse dataflow computation to solve for
290 // global liveness. The BEGIN set here is equivalent to KILL in the standard
291 // formulation, and END is equivalent to GEN. The result of this computation
292 // is a map from blocks to bitvectors where the bitvectors represent which
293 // allocas are live in/out of that block.
294 SmallPtrSet<MachineBasicBlock*, 8> BBSet(BasicBlockNumbering.begin(),
295 BasicBlockNumbering.end());
296 unsigned NumSSMIters = 0;
302 SmallPtrSet<MachineBasicBlock*, 8> NextBBSet;
304 for (SmallVector<MachineBasicBlock*, 8>::iterator
305 PI = BasicBlockNumbering.begin(), PE = BasicBlockNumbering.end();
308 MachineBasicBlock *BB = *PI;
309 if (!BBSet.count(BB)) continue;
311 BitVector LocalLiveIn;
312 BitVector LocalLiveOut;
314 // Forward propagation from begins to ends.
315 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
316 PE = BB->pred_end(); PI != PE; ++PI)
317 LocalLiveIn |= BlockLiveness[*PI].LiveOut;
318 LocalLiveIn |= BlockLiveness[BB].End;
319 LocalLiveIn.reset(BlockLiveness[BB].Begin);
321 // Reverse propagation from ends to begins.
322 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
323 SE = BB->succ_end(); SI != SE; ++SI)
324 LocalLiveOut |= BlockLiveness[*SI].LiveIn;
325 LocalLiveOut |= BlockLiveness[BB].Begin;
326 LocalLiveOut.reset(BlockLiveness[BB].End);
328 LocalLiveIn |= LocalLiveOut;
329 LocalLiveOut |= LocalLiveIn;
331 // After adopting the live bits, we need to turn-off the bits which
332 // are de-activated in this block.
333 LocalLiveOut.reset(BlockLiveness[BB].End);
334 LocalLiveIn.reset(BlockLiveness[BB].Begin);
336 // If we have both BEGIN and END markers in the same basic block then
337 // we know that the BEGIN marker comes after the END, because we already
338 // handle the case where the BEGIN comes before the END when collecting
339 // the markers (and building the BEGIN/END vectore).
340 // Want to enable the LIVE_IN and LIVE_OUT of slots that have both
341 // BEGIN and END because it means that the value lives before and after
343 BitVector LocalEndBegin = BlockLiveness[BB].End;
344 LocalEndBegin &= BlockLiveness[BB].Begin;
345 LocalLiveIn |= LocalEndBegin;
346 LocalLiveOut |= LocalEndBegin;
348 if (LocalLiveIn.test(BlockLiveness[BB].LiveIn)) {
350 BlockLiveness[BB].LiveIn |= LocalLiveIn;
352 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
353 PE = BB->pred_end(); PI != PE; ++PI)
354 NextBBSet.insert(*PI);
357 if (LocalLiveOut.test(BlockLiveness[BB].LiveOut)) {
359 BlockLiveness[BB].LiveOut |= LocalLiveOut;
361 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
362 SE = BB->succ_end(); SI != SE; ++SI)
363 NextBBSet.insert(*SI);
371 void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
372 SmallVector<SlotIndex, 16> Starts;
373 SmallVector<SlotIndex, 16> Finishes;
375 // For each block, find which slots are active within this block
376 // and update the live intervals.
377 for (MachineFunction::iterator MBB = MF->begin(), MBBe = MF->end();
378 MBB != MBBe; ++MBB) {
380 Starts.resize(NumSlots);
382 Finishes.resize(NumSlots);
384 // Create the interval for the basic blocks with lifetime markers in them.
385 for (SmallVector<MachineInstr*, 8>::iterator it = Markers.begin(),
386 e = Markers.end(); it != e; ++it) {
387 MachineInstr *MI = *it;
388 if (MI->getParent() != MBB)
391 assert((MI->getOpcode() == TargetOpcode::LIFETIME_START ||
392 MI->getOpcode() == TargetOpcode::LIFETIME_END) &&
393 "Invalid Lifetime marker");
395 bool IsStart = MI->getOpcode() == TargetOpcode::LIFETIME_START;
396 MachineOperand &Mo = MI->getOperand(0);
397 int Slot = Mo.getIndex();
398 assert(Slot >= 0 && "Invalid slot");
400 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI);
403 if (!Starts[Slot].isValid() || Starts[Slot] > ThisIndex)
404 Starts[Slot] = ThisIndex;
406 if (!Finishes[Slot].isValid() || Finishes[Slot] < ThisIndex)
407 Finishes[Slot] = ThisIndex;
411 // Create the interval of the blocks that we previously found to be 'alive'.
412 BitVector Alive = BlockLiveness[MBB].LiveIn;
413 Alive |= BlockLiveness[MBB].LiveOut;
416 for (int pos = Alive.find_first(); pos != -1;
417 pos = Alive.find_next(pos)) {
418 if (!Starts[pos].isValid())
419 Starts[pos] = Indexes->getMBBStartIdx(MBB);
420 if (!Finishes[pos].isValid())
421 Finishes[pos] = Indexes->getMBBEndIdx(MBB);
425 for (unsigned i = 0; i < NumSlots; ++i) {
426 assert(Starts[i].isValid() == Finishes[i].isValid() && "Unmatched range");
427 if (!Starts[i].isValid())
430 assert(Starts[i] && Finishes[i] && "Invalid interval");
431 VNInfo *ValNum = Intervals[i]->getValNumInfo(0);
432 SlotIndex S = Starts[i];
433 SlotIndex F = Finishes[i];
435 // We have a single consecutive region.
436 Intervals[i]->addRange(LiveRange(S, F, ValNum));
438 // We have two non consecutive regions. This happens when
439 // LIFETIME_START appears after the LIFETIME_END marker.
440 SlotIndex NewStart = Indexes->getMBBStartIdx(MBB);
441 SlotIndex NewFin = Indexes->getMBBEndIdx(MBB);
442 Intervals[i]->addRange(LiveRange(NewStart, F, ValNum));
443 Intervals[i]->addRange(LiveRange(S, NewFin, ValNum));
449 bool StackColoring::removeAllMarkers() {
451 for (unsigned i = 0; i < Markers.size(); ++i) {
452 Markers[i]->eraseFromParent();
457 DEBUG(dbgs()<<"Removed "<<Count<<" markers.\n");
461 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
462 unsigned FixedInstr = 0;
463 unsigned FixedMemOp = 0;
464 unsigned FixedDbg = 0;
465 MachineModuleInfo *MMI = &MF->getMMI();
467 // Remap debug information that refers to stack slots.
468 MachineModuleInfo::VariableDbgInfoMapTy &VMap = MMI->getVariableDbgInfo();
469 for (MachineModuleInfo::VariableDbgInfoMapTy::iterator VI = VMap.begin(),
470 VE = VMap.end(); VI != VE; ++VI) {
471 const MDNode *Var = VI->first;
473 std::pair<unsigned, DebugLoc> &VP = VI->second;
474 if (SlotRemap.count(VP.first)) {
475 DEBUG(dbgs()<<"Remapping debug info for ["<<Var->getName()<<"].\n");
476 VP.first = SlotRemap[VP.first];
481 // Keep a list of *allocas* which need to be remapped.
482 DenseMap<const AllocaInst*, const AllocaInst*> Allocas;
483 for (DenseMap<int, int>::iterator it = SlotRemap.begin(),
484 e = SlotRemap.end(); it != e; ++it) {
485 const AllocaInst *From = MFI->getObjectAllocation(it->first);
486 const AllocaInst *To = MFI->getObjectAllocation(it->second);
487 assert(To && From && "Invalid allocation object");
491 // Remap all instructions to the new stack slots.
492 MachineFunction::iterator BB, BBE;
493 MachineBasicBlock::iterator I, IE;
494 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB)
495 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) {
497 // Skip lifetime markers. We'll remove them soon.
498 if (I->getOpcode() == TargetOpcode::LIFETIME_START ||
499 I->getOpcode() == TargetOpcode::LIFETIME_END)
502 // Update the MachineMemOperand to use the new alloca.
503 for (MachineInstr::mmo_iterator MM = I->memoperands_begin(),
504 E = I->memoperands_end(); MM != E; ++MM) {
505 MachineMemOperand *MMO = *MM;
507 const Value *V = MMO->getValue();
512 // Climb up and find the original alloca.
513 V = GetUnderlyingObject(V);
514 // If we did not find one, or if the one that we found is not in our
515 // map, then move on.
516 if (!V || !isa<AllocaInst>(V)) {
517 // Clear mem operand since we don't know for sure that it doesn't
518 // alias a merged alloca.
522 const AllocaInst *AI= cast<AllocaInst>(V);
523 if (!Allocas.count(AI))
526 MMO->setValue(Allocas[AI]);
530 // Update all of the machine instruction operands.
531 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) {
532 MachineOperand &MO = I->getOperand(i);
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 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 MachineFunction::iterator BB, BBE;
579 MachineBasicBlock::iterator I, IE;
580 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB)
581 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) {
583 if (I->getOpcode() == TargetOpcode::LIFETIME_START ||
584 I->getOpcode() == TargetOpcode::LIFETIME_END || I->isDebugValue())
587 // Some intervals are suspicious! In some cases we find address
588 // calculations outside of the lifetime zone, but not actual memory
589 // read or write. Memory accesses outside of the lifetime zone are a clear
590 // violation, but address calculations are okay. This can happen when
591 // GEPs are hoisted outside of the lifetime zone.
592 // So, in here we only check instructions which can read or write memory.
593 if (!I->mayLoad() && !I->mayStore())
596 // Check all of the machine operands.
597 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) {
598 MachineOperand &MO = I->getOperand(i);
603 int Slot = MO.getIndex();
608 if (Intervals[Slot]->empty())
611 // Check that the used slot is inside the calculated lifetime range.
612 // If it is not, warn about it and invalidate the range.
613 LiveInterval *Interval = Intervals[Slot];
614 SlotIndex Index = Indexes->getInstructionIndex(I);
615 if (Interval->find(Index) == Interval->end()) {
616 Intervals[Slot]->clear();
617 DEBUG(dbgs()<<"Invalidating range #"<<Slot<<"\n");
624 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap,
626 // Expunge slot remap map.
627 for (unsigned i=0; i < NumSlots; ++i) {
628 // If we are remapping i
629 if (SlotRemap.count(i)) {
630 int Target = SlotRemap[i];
631 // As long as our target is mapped to something else, follow it.
632 while (SlotRemap.count(Target)) {
633 Target = SlotRemap[Target];
634 SlotRemap[i] = Target;
640 bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
641 DEBUG(dbgs() << "********** Stack Coloring **********\n"
642 << "********** Function: "
643 << ((const Value*)Func.getFunction())->getName() << '\n');
645 MFI = MF->getFrameInfo();
646 Indexes = &getAnalysis<SlotIndexes>();
647 BlockLiveness.clear();
649 BasicBlockNumbering.clear();
652 VNInfoAllocator.Reset();
654 unsigned NumSlots = MFI->getObjectIndexEnd();
656 // If there are no stack slots then there are no markers to remove.
660 SmallVector<int, 8> SortedSlots;
662 SortedSlots.reserve(NumSlots);
663 Intervals.reserve(NumSlots);
665 unsigned NumMarkers = collectMarkers(NumSlots);
667 unsigned TotalSize = 0;
668 DEBUG(dbgs()<<"Found "<<NumMarkers<<" markers and "<<NumSlots<<" slots\n");
669 DEBUG(dbgs()<<"Slot structure:\n");
671 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) {
672 DEBUG(dbgs()<<"Slot #"<<i<<" - "<<MFI->getObjectSize(i)<<" bytes.\n");
673 TotalSize += MFI->getObjectSize(i);
676 DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n");
678 // Don't continue because there are not enough lifetime markers, or the
679 // stack is too small, or we are told not to optimize the slots.
680 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
681 DEBUG(dbgs()<<"Will not try to merge slots.\n");
682 return removeAllMarkers();
685 for (unsigned i=0; i < NumSlots; ++i) {
686 LiveInterval *LI = new LiveInterval(i, 0);
687 Intervals.push_back(LI);
688 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator);
689 SortedSlots.push_back(i);
692 // Calculate the liveness of each block.
693 calculateLocalLiveness();
695 // Propagate the liveness information.
696 calculateLiveIntervals(NumSlots);
698 // Search for allocas which are used outside of the declared lifetime
700 if (ProtectFromEscapedAllocas)
701 removeInvalidSlotRanges();
703 // Maps old slots to new slots.
704 DenseMap<int, int> SlotRemap;
705 unsigned RemovedSlots = 0;
706 unsigned ReducedSize = 0;
708 // Do not bother looking at empty intervals.
709 for (unsigned I = 0; I < NumSlots; ++I) {
710 if (Intervals[SortedSlots[I]]->empty())
714 // This is a simple greedy algorithm for merging allocas. First, sort the
715 // slots, placing the largest slots first. Next, perform an n^2 scan and look
716 // for disjoint slots. When you find disjoint slots, merge the samller one
717 // into the bigger one and update the live interval. Remove the small alloca
720 // Sort the slots according to their size. Place unused slots at the end.
721 // Use stable sort to guarantee deterministic code generation.
722 std::stable_sort(SortedSlots.begin(), SortedSlots.end(),
723 SlotSizeSorter(MFI));
728 for (unsigned I = 0; I < NumSlots; ++I) {
729 if (SortedSlots[I] == -1)
732 for (unsigned J=I+1; J < NumSlots; ++J) {
733 if (SortedSlots[J] == -1)
736 int FirstSlot = SortedSlots[I];
737 int SecondSlot = SortedSlots[J];
738 LiveInterval *First = Intervals[FirstSlot];
739 LiveInterval *Second = Intervals[SecondSlot];
740 assert (!First->empty() && !Second->empty() && "Found an empty range");
742 // Merge disjoint slots.
743 if (!First->overlaps(*Second)) {
745 First->MergeRangesInAsValue(*Second, First->getValNumInfo(0));
746 SlotRemap[SecondSlot] = FirstSlot;
748 DEBUG(dbgs()<<"Merging #"<<FirstSlot<<" and slots #"<<
749 SecondSlot<<" together.\n");
750 unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot),
751 MFI->getObjectAlignment(SecondSlot));
753 assert(MFI->getObjectSize(FirstSlot) >=
754 MFI->getObjectSize(SecondSlot) &&
755 "Merging a small object into a larger one");
758 ReducedSize += MFI->getObjectSize(SecondSlot);
759 MFI->setObjectAlignment(FirstSlot, MaxAlignment);
760 MFI->RemoveStackObject(SecondSlot);
766 // Record statistics.
767 StackSpaceSaved += ReducedSize;
768 StackSlotMerged += RemovedSlots;
769 DEBUG(dbgs()<<"Merge "<<RemovedSlots<<" slots. Saved "<<
770 ReducedSize<<" bytes\n");
772 // Scan the entire function and update all machine operands that use frame
773 // indices to use the remapped frame index.
774 expungeSlotMap(SlotRemap, NumSlots);
775 remapInstructions(SlotRemap);
777 // Release the intervals.
778 for (unsigned I = 0; I < NumSlots; ++I) {
782 return removeAllMarkers();