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 "MachineTraceMetrics.h"
26 #include "llvm/Function.h"
27 #include "llvm/Module.h"
28 #include "llvm/ADT/BitVector.h"
29 #include "llvm/Analysis/Dominators.h"
30 #include "llvm/Analysis/ValueTracking.h"
31 #include "llvm/ADT/DepthFirstIterator.h"
32 #include "llvm/ADT/PostOrderIterator.h"
33 #include "llvm/ADT/SetVector.h"
34 #include "llvm/ADT/SmallPtrSet.h"
35 #include "llvm/ADT/SparseSet.h"
36 #include "llvm/ADT/Statistic.h"
37 #include "llvm/CodeGen/LiveInterval.h"
38 #include "llvm/CodeGen/MachineLoopInfo.h"
39 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
40 #include "llvm/CodeGen/MachineDominators.h"
41 #include "llvm/CodeGen/MachineBasicBlock.h"
42 #include "llvm/CodeGen/MachineFunctionPass.h"
43 #include "llvm/CodeGen/MachineLoopInfo.h"
44 #include "llvm/CodeGen/MachineModuleInfo.h"
45 #include "llvm/CodeGen/MachineRegisterInfo.h"
46 #include "llvm/CodeGen/MachineFrameInfo.h"
47 #include "llvm/CodeGen/MachineMemOperand.h"
48 #include "llvm/CodeGen/Passes.h"
49 #include "llvm/CodeGen/SlotIndexes.h"
50 #include "llvm/DebugInfo.h"
51 #include "llvm/MC/MCInstrItineraries.h"
52 #include "llvm/Target/TargetInstrInfo.h"
53 #include "llvm/Target/TargetRegisterInfo.h"
54 #include "llvm/Support/CommandLine.h"
55 #include "llvm/Support/Debug.h"
56 #include "llvm/Support/raw_ostream.h"
61 DisableColoring("no-stack-coloring",
62 cl::init(true), cl::Hidden,
63 cl::desc("Suppress stack coloring"));
65 STATISTIC(NumMarkerSeen, "Number of life markers found.");
66 STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots.");
67 STATISTIC(StackSlotMerged, "Number of stack slot merged.");
69 //===----------------------------------------------------------------------===//
71 //===----------------------------------------------------------------------===//
74 /// StackColoring - A machine pass for merging disjoint stack allocations,
75 /// marked by the LIFETIME_START and LIFETIME_END pseudo instructions.
76 class StackColoring : public MachineFunctionPass {
77 MachineFrameInfo *MFI;
80 /// A class representing liveness information for a single basic block.
81 /// Each bit in the BitVector represents the liveness property
82 /// for a different stack slot.
83 struct BlockLifetimeInfo {
84 /// Which slots BEGINs in each basic block.
86 /// Which slots ENDs in each basic block.
88 /// Which slots are marked as LIVE_IN, coming into each basic block.
90 /// Which slots are marked as LIVE_OUT, coming out of each basic block.
94 /// Maps active slots (per bit) for each basic block.
95 DenseMap<MachineBasicBlock*, BlockLifetimeInfo> BlockLiveness;
97 /// Maps serial numbers to basic blocks.
98 DenseMap<MachineBasicBlock*, int> BasicBlocks;
99 /// Maps basic blocks to a serial number.
100 SmallVector<MachineBasicBlock*, 8> BasicBlockNumbering;
102 /// Maps liveness intervals for each slot.
103 SmallVector<LiveInterval*, 16> Intervals;
104 /// VNInfo is used for the construction of LiveIntervals.
105 VNInfo::Allocator VNInfoAllocator;
106 /// SlotIndex analysis object.
107 SlotIndexes* Indexes;
109 /// The list of lifetime markers found. These markers are to be removed
110 /// once the coloring is done.
111 SmallVector<MachineInstr*, 8> Markers;
113 /// SlotSizeSorter - A Sort utility for arranging stack slots according
115 struct SlotSizeSorter {
116 MachineFrameInfo *MFI;
117 SlotSizeSorter(MachineFrameInfo *mfi) : MFI(mfi) { }
118 bool operator()(int LHS, int RHS) {
119 // We use -1 to denote a uninteresting slot. Place these slots at the end.
120 if (LHS == -1) return false;
121 if (RHS == -1) return true;
122 // Sort according to size.
123 return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS);
129 StackColoring() : MachineFunctionPass(ID) {
130 initializeStackColoringPass(*PassRegistry::getPassRegistry());
132 void getAnalysisUsage(AnalysisUsage &AU) const;
133 bool runOnMachineFunction(MachineFunction &MF);
139 /// Removes all of the lifetime marker instructions from the function.
140 /// \returns true if any markers were removed.
141 bool removeAllMarkers();
143 /// Scan the machine function and find all of the lifetime markers.
144 /// Record the findings in the BEGIN and END vectors.
145 /// \returns the number of markers found.
146 unsigned collectMarkers(unsigned NumSlot);
148 /// Perform the dataflow calculation and calculate the lifetime for each of
149 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and
150 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming
151 /// in and out blocks.
152 void calculateLocalLiveness();
154 /// Construct the LiveIntervals for the slots.
155 void calculateLiveIntervals(unsigned NumSlots);
157 /// Go over the machine function and change instructions which use stack
158 /// slots to use the joint slots.
159 void remapInstructions(DenseMap<int, int> &SlotRemap);
161 /// Map entries which point to other entries to their destination.
162 /// A->B->C becomes A->C.
163 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots);
165 } // end anonymous namespace
167 char StackColoring::ID = 0;
168 char &llvm::StackColoringID = StackColoring::ID;
170 INITIALIZE_PASS_BEGIN(StackColoring,
171 "stack-coloring", "Merge disjoint stack slots", false, false)
172 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
173 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
174 INITIALIZE_PASS_END(StackColoring,
175 "stack-coloring", "Merge disjoint stack slots", false, false)
177 void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const {
178 AU.addRequired<MachineDominatorTree>();
179 AU.addPreserved<MachineDominatorTree>();
180 AU.addRequired<SlotIndexes>();
181 MachineFunctionPass::getAnalysisUsage(AU);
184 void StackColoring::dump() {
185 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
187 unsigned Num = BasicBlocks[*FI];
188 DEBUG(dbgs()<<"Inspecting block #"<<Num<<" ["<<FI->getName()<<"]\n");
190 DEBUG(dbgs()<<"BEGIN : {");
191 for (unsigned i=0; i < BlockLiveness[*FI].Begin.size(); ++i)
192 DEBUG(dbgs()<<BlockLiveness[*FI].Begin.test(i)<<" ");
193 DEBUG(dbgs()<<"}\n");
195 DEBUG(dbgs()<<"END : {");
196 for (unsigned i=0; i < BlockLiveness[*FI].End.size(); ++i)
197 DEBUG(dbgs()<<BlockLiveness[*FI].End.test(i)<<" ");
199 DEBUG(dbgs()<<"}\n");
201 DEBUG(dbgs()<<"LIVE_IN: {");
202 for (unsigned i=0; i < BlockLiveness[*FI].LiveIn.size(); ++i)
203 DEBUG(dbgs()<<BlockLiveness[*FI].LiveIn.test(i)<<" ");
205 DEBUG(dbgs()<<"}\n");
206 DEBUG(dbgs()<<"LIVEOUT: {");
207 for (unsigned i=0; i < BlockLiveness[*FI].LiveOut.size(); ++i)
208 DEBUG(dbgs()<<BlockLiveness[*FI].LiveOut.test(i)<<" ");
209 DEBUG(dbgs()<<"}\n");
213 unsigned StackColoring::collectMarkers(unsigned NumSlot) {
214 unsigned MarkersFound = 0;
215 // Scan the function to find all lifetime markers.
216 // NOTE: We use the a reverse-post-order iteration to ensure that we obtain a
217 // deterministic numbering, and because we'll need a post-order iteration
218 // later for solving the liveness dataflow problem.
219 for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
222 // Assign a serial number to this basic block.
223 BasicBlocks[*FI] = BasicBlockNumbering.size();;
224 BasicBlockNumbering.push_back(*FI);
226 BlockLiveness[*FI].Begin.resize(NumSlot);
227 BlockLiveness[*FI].End.resize(NumSlot);
229 for (MachineBasicBlock::iterator BI = (*FI)->begin(), BE = (*FI)->end();
232 if (BI->getOpcode() != TargetOpcode::LIFETIME_START &&
233 BI->getOpcode() != TargetOpcode::LIFETIME_END)
236 Markers.push_back(BI);
238 bool IsStart = BI->getOpcode() == TargetOpcode::LIFETIME_START;
239 MachineOperand &MI = BI->getOperand(0);
240 unsigned Slot = MI.getIndex();
244 const Value* Allocation = MFI->getObjectAllocation(Slot);
246 DEBUG(dbgs()<<"Found lifetime marker for allocation: "<<
247 Allocation->getName()<<"\n");
251 BlockLiveness[*FI].Begin.set(Slot);
253 if (BlockLiveness[*FI].Begin.test(Slot)) {
254 // Allocas that start and end within a single block are handled
255 // specially when computing the LiveIntervals to avoid pessimizing
256 // the liveness propagation.
257 BlockLiveness[*FI].Begin.reset(Slot);
259 BlockLiveness[*FI].End.set(Slot);
265 // Update statistics.
266 NumMarkerSeen += MarkersFound;
270 void StackColoring::calculateLocalLiveness() {
271 // Perform a standard reverse dataflow computation to solve for
272 // global liveness. The BEGIN set here is equivalent to KILL in the standard
273 // formulation, and END is equivalent to GEN. The result of this computation
274 // is a map from blocks to bitvectors where the bitvectors represent which
275 // allocas are live in/out of that block.
276 SmallPtrSet<MachineBasicBlock*, 8> BBSet(BasicBlockNumbering.begin(),
277 BasicBlockNumbering.end());
278 unsigned NumSSMIters = 0;
284 SmallPtrSet<MachineBasicBlock*, 8> NextBBSet;
286 for (SmallVector<MachineBasicBlock*, 8>::iterator
287 PI = BasicBlockNumbering.begin(), PE = BasicBlockNumbering.end();
290 MachineBasicBlock *BB = *PI;
291 if (!BBSet.count(BB)) continue;
293 BitVector LocalLiveIn;
294 BitVector LocalLiveOut;
296 // Forward propagation from begins to ends.
297 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
298 PE = BB->pred_end(); PI != PE; ++PI)
299 LocalLiveIn |= BlockLiveness[*PI].LiveOut;
300 LocalLiveIn |= BlockLiveness[BB].End;
301 LocalLiveIn.reset(BlockLiveness[BB].Begin);
303 // Reverse propagation from ends to begins.
304 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
305 SE = BB->succ_end(); SI != SE; ++SI)
306 LocalLiveOut |= BlockLiveness[*SI].LiveIn;
307 LocalLiveOut |= BlockLiveness[BB].Begin;
308 LocalLiveOut.reset(BlockLiveness[BB].End);
310 LocalLiveIn |= LocalLiveOut;
311 LocalLiveOut |= LocalLiveIn;
313 // After adopting the live bits, we need to turn-off the bits which
314 // are de-activated in this block.
315 LocalLiveOut.reset(BlockLiveness[BB].End);
316 LocalLiveIn.reset(BlockLiveness[BB].Begin);
318 if (LocalLiveIn.test(BlockLiveness[BB].LiveIn)) {
320 BlockLiveness[BB].LiveIn |= LocalLiveIn;
322 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
323 PE = BB->pred_end(); PI != PE; ++PI)
324 NextBBSet.insert(*PI);
327 if (LocalLiveOut.test(BlockLiveness[BB].LiveOut)) {
329 BlockLiveness[BB].LiveOut |= LocalLiveOut;
331 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
332 SE = BB->succ_end(); SI != SE; ++SI)
333 NextBBSet.insert(*SI);
341 void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
342 SmallVector<SlotIndex, 16> Starts;
343 SmallVector<SlotIndex, 16> Finishes;
345 // For each block, find which slots are active within this block
346 // and update the live intervals.
347 for (MachineFunction::iterator MBB = MF->begin(), MBBe = MF->end();
348 MBB != MBBe; ++MBB) {
350 Starts.resize(NumSlots);
352 Finishes.resize(NumSlots);
354 // Create the interval for the basic blocks with lifetime markers in them.
355 for (SmallVector<MachineInstr*, 8>::iterator it = Markers.begin(),
356 e = Markers.end(); it != e; ++it) {
357 MachineInstr *MI = *it;
358 if (MI->getParent() != MBB)
361 assert((MI->getOpcode() == TargetOpcode::LIFETIME_START ||
362 MI->getOpcode() == TargetOpcode::LIFETIME_END) &&
363 "Invalid Lifetime marker");
365 bool IsStart = MI->getOpcode() == TargetOpcode::LIFETIME_START;
366 MachineOperand &Mo = MI->getOperand(0);
367 int Slot = Mo.getIndex();
368 assert(Slot >= 0 && "Invalid slot");
370 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI);
373 if (!Starts[Slot].isValid() || Starts[Slot] > ThisIndex)
374 Starts[Slot] = ThisIndex;
376 if (!Finishes[Slot].isValid() || Finishes[Slot] < ThisIndex)
377 Finishes[Slot] = ThisIndex;
381 // Create the interval of the blocks that we previously found to be 'alive'.
382 BitVector Alive = BlockLiveness[MBB].LiveIn;
383 Alive |= BlockLiveness[MBB].LiveOut;
386 for (int pos = Alive.find_first(); pos != -1;
387 pos = Alive.find_next(pos)) {
388 if (!Starts[pos].isValid())
389 Starts[pos] = Indexes->getMBBStartIdx(MBB);
390 if (!Finishes[pos].isValid())
391 Finishes[pos] = Indexes->getMBBEndIdx(MBB);
395 for (unsigned i = 0; i < NumSlots; ++i) {
396 assert(Starts[i].isValid() == Finishes[i].isValid() && "Unmatched range");
397 if (!Starts[i].isValid())
400 assert(Starts[i] && Finishes[i] && "Invalid interval");
401 VNInfo *ValNum = Intervals[i]->getValNumInfo(0);
402 SlotIndex S = Starts[i];
403 SlotIndex F = Finishes[i];
405 // We have a single consecutive region.
406 Intervals[i]->addRange(LiveRange(S, F, ValNum));
408 // We have two non consecutive regions. This happens when
409 // LIFETIME_START appears after the LIFETIME_END marker.
410 SlotIndex NewStart = Indexes->getMBBStartIdx(MBB);
411 SlotIndex NewFin = Indexes->getMBBEndIdx(MBB);
412 Intervals[i]->addRange(LiveRange(NewStart, F, ValNum));
413 Intervals[i]->addRange(LiveRange(S, NewFin, ValNum));
419 bool StackColoring::removeAllMarkers() {
421 for (unsigned i = 0; i < Markers.size(); ++i) {
422 Markers[i]->eraseFromParent();
427 DEBUG(dbgs()<<"Removed "<<Count<<" markers.\n");
431 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
432 unsigned FixedInstr = 0;
433 unsigned FixedMemOp = 0;
434 unsigned FixedDbg = 0;
435 MachineModuleInfo *MMI = &MF->getMMI();
437 // Remap debug information that refers to stack slots.
438 MachineModuleInfo::VariableDbgInfoMapTy &VMap = MMI->getVariableDbgInfo();
439 for (MachineModuleInfo::VariableDbgInfoMapTy::iterator VI = VMap.begin(),
440 VE = VMap.end(); VI != VE; ++VI) {
441 const MDNode *Var = VI->first;
443 std::pair<unsigned, DebugLoc> &VP = VI->second;
444 if (SlotRemap.count(VP.first)) {
445 DEBUG(dbgs()<<"Remapping debug info for ["<<Var->getName()<<"].\n");
446 VP.first = SlotRemap[VP.first];
451 // Keep a list of *allocas* which need to be remapped.
452 DenseMap<const Value*, const Value*> Allocas;
453 for (DenseMap<int, int>::iterator it = SlotRemap.begin(),
454 e = SlotRemap.end(); it != e; ++it) {
455 const Value* From = MFI->getObjectAllocation(it->first);
456 const Value* To = MFI->getObjectAllocation(it->second);
457 assert(To && From && "Invalid allocation object");
461 // Remap all instructions to the new stack slots.
462 MachineFunction::iterator BB, BBE;
463 MachineBasicBlock::iterator I, IE;
464 for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB)
465 for (I = BB->begin(), IE = BB->end(); I != IE; ++I) {
467 // Skip lifetime markers. We'll remove them soon.
468 if (I->getOpcode() == TargetOpcode::LIFETIME_START ||
469 I->getOpcode() == TargetOpcode::LIFETIME_END)
472 // Update the MachineMemOperand to use the new alloca.
473 for (MachineInstr::mmo_iterator MM = I->memoperands_begin(),
474 E = I->memoperands_end(); MM != E; ++MM) {
475 MachineMemOperand *MMO = *MM;
477 const Value *V = MMO->getValue();
482 // Climb up and find the original alloca.
483 V = GetUnderlyingObject(V);
484 // If we did not find one, or if the one that we found is not in our
485 // map, then move on.
486 if (!V || !Allocas.count(V))
489 MMO->setValue(Allocas[V]);
493 // Update all of the machine instruction operands.
494 for (unsigned i = 0 ; i < I->getNumOperands(); ++i) {
495 MachineOperand &MO = I->getOperand(i);
499 int FromSlot = MO.getIndex();
501 // Don't touch arguments.
505 // Only look at mapped slots.
506 if (!SlotRemap.count(FromSlot))
509 // In a debug build, check that the instruction that we are modifying is
510 // inside the expected live range. If the instruction is not inside
511 // the calculated range then it means that the alloca usage moved
512 // outside of the lifetime markers.
514 SlotIndex Index = Indexes->getInstructionIndex(I);
515 LiveInterval* Interval = Intervals[FromSlot];
516 assert(Interval->find(Index) != Interval->end() &&
517 "Found instruction usage outside of live range.");
520 // Fix the machine instructions.
521 int ToSlot = SlotRemap[FromSlot];
527 DEBUG(dbgs()<<"Fixed "<<FixedMemOp<<" machine memory operands.\n");
528 DEBUG(dbgs()<<"Fixed "<<FixedDbg<<" debug locations.\n");
529 DEBUG(dbgs()<<"Fixed "<<FixedInstr<<" machine instructions.\n");
532 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap,
534 // Expunge slot remap map.
535 for (unsigned i=0; i < NumSlots; ++i) {
536 // If we are remapping i
537 if (SlotRemap.count(i)) {
538 int Target = SlotRemap[i];
539 // As long as our target is mapped to something else, follow it.
540 while (SlotRemap.count(Target)) {
541 Target = SlotRemap[Target];
542 SlotRemap[i] = Target;
548 bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
549 DEBUG(dbgs() << "********** Stack Coloring **********\n"
550 << "********** Function: "
551 << ((const Value*)Func.getFunction())->getName() << '\n');
553 MFI = MF->getFrameInfo();
554 Indexes = &getAnalysis<SlotIndexes>();
555 BlockLiveness.clear();
557 BasicBlockNumbering.clear();
560 VNInfoAllocator.Reset();
562 unsigned NumSlots = MFI->getObjectIndexEnd();
564 // If there are no stack slots then there are no markers to remove.
568 SmallVector<int, 8> SortedSlots;
570 SortedSlots.reserve(NumSlots);
571 Intervals.reserve(NumSlots);
573 unsigned NumMarkers = collectMarkers(NumSlots);
575 unsigned TotalSize = 0;
576 DEBUG(dbgs()<<"Found "<<NumMarkers<<" markers and "<<NumSlots<<" slots\n");
577 DEBUG(dbgs()<<"Slot structure:\n");
579 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) {
580 DEBUG(dbgs()<<"Slot #"<<i<<" - "<<MFI->getObjectSize(i)<<" bytes.\n");
581 TotalSize += MFI->getObjectSize(i);
584 DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n");
586 // Don't continue because there are not enough lifetime markers, or the
587 // stack or too small, or we are told not to optimize the slots.
588 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
589 DEBUG(dbgs()<<"Will not try to merge slots.\n");
590 return removeAllMarkers();
593 for (unsigned i=0; i < NumSlots; ++i) {
594 LiveInterval *LI = new LiveInterval(i, 0);
595 Intervals.push_back(LI);
596 LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator);
597 SortedSlots.push_back(i);
600 // Calculate the liveness of each block.
601 calculateLocalLiveness();
603 // Propagate the liveness information.
604 calculateLiveIntervals(NumSlots);
606 // Maps old slots to new slots.
607 DenseMap<int, int> SlotRemap;
608 unsigned RemovedSlots = 0;
609 unsigned ReducedSize = 0;
611 // Do not bother looking at empty intervals.
612 for (unsigned I = 0; I < NumSlots; ++I) {
613 if (Intervals[SortedSlots[I]]->empty())
617 // This is a simple greedy algorithm for merging allocas. First, sort the
618 // slots, placing the largest slots first. Next, perform an n^2 scan and look
619 // for disjoint slots. When you find disjoint slots, merge the samller one
620 // into the bigger one and update the live interval. Remove the small alloca
623 // Sort the slots according to their size. Place unused slots at the end.
624 std::sort(SortedSlots.begin(), SortedSlots.end(), SlotSizeSorter(MFI));
629 for (unsigned I = 0; I < NumSlots; ++I) {
630 if (SortedSlots[I] == -1)
633 for (unsigned J=I+1; J < NumSlots; ++J) {
634 if (SortedSlots[J] == -1)
637 int FirstSlot = SortedSlots[I];
638 int SecondSlot = SortedSlots[J];
639 LiveInterval *First = Intervals[FirstSlot];
640 LiveInterval *Second = Intervals[SecondSlot];
641 assert (!First->empty() && !Second->empty() && "Found an empty range");
643 // Merge disjoint slots.
644 if (!First->overlaps(*Second)) {
646 First->MergeRangesInAsValue(*Second, First->getValNumInfo(0));
647 SlotRemap[SecondSlot] = FirstSlot;
649 DEBUG(dbgs()<<"Merging #"<<FirstSlot<<" and slots #"<<
650 SecondSlot<<" together.\n");
651 unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot),
652 MFI->getObjectAlignment(SecondSlot));
654 assert(MFI->getObjectSize(FirstSlot) >=
655 MFI->getObjectSize(SecondSlot) &&
656 "Merging a small object into a larger one");
659 ReducedSize += MFI->getObjectSize(SecondSlot);
660 MFI->setObjectAlignment(FirstSlot, MaxAlignment);
661 MFI->RemoveStackObject(SecondSlot);
667 // Record statistics.
668 StackSpaceSaved += ReducedSize;
669 StackSlotMerged += RemovedSlots;
670 DEBUG(dbgs()<<"Merge "<<RemovedSlots<<" slots. Saved "<<
671 ReducedSize<<" bytes\n");
673 // Scan the entire function and update all machine operands that use frame
674 // indices to use the remapped frame index.
675 expungeSlotMap(SlotRemap, NumSlots);
676 remapInstructions(SlotRemap);
678 // Release the intervals.
679 for (unsigned I = 0; I < NumSlots; ++I) {
683 return removeAllMarkers();