1 //===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
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 file implements the stack slot coloring pass.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "stackcoloring"
15 #include "VirtRegMap.h"
16 #include "llvm/Function.h"
17 #include "llvm/Module.h"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
20 #include "llvm/CodeGen/LiveStackAnalysis.h"
21 #include "llvm/CodeGen/MachineFrameInfo.h"
22 #include "llvm/CodeGen/MachineInstrBuilder.h"
23 #include "llvm/CodeGen/MachineLoopInfo.h"
24 #include "llvm/CodeGen/MachineMemOperand.h"
25 #include "llvm/CodeGen/MachineRegisterInfo.h"
26 #include "llvm/CodeGen/PseudoSourceValue.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Target/TargetInstrInfo.h"
30 #include "llvm/Target/TargetMachine.h"
31 #include "llvm/ADT/BitVector.h"
32 #include "llvm/ADT/SmallSet.h"
33 #include "llvm/ADT/SmallVector.h"
34 #include "llvm/ADT/Statistic.h"
39 DisableSharing("no-stack-slot-sharing",
40 cl::init(false), cl::Hidden,
41 cl::desc("Suppress slot sharing during stack coloring"));
43 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
45 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
46 STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
49 class StackSlotColoring : public MachineFunctionPass {
52 MachineFrameInfo *MFI;
53 const TargetInstrInfo *TII;
54 const MachineLoopInfo *loopInfo;
56 // SSIntervals - Spill slot intervals.
57 std::vector<LiveInterval*> SSIntervals;
59 // SSRefs - Keep a list of frame index references for each spill slot.
60 SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
62 // OrigAlignments - Alignments of stack objects before coloring.
63 SmallVector<unsigned, 16> OrigAlignments;
65 // OrigSizes - Sizess of stack objects before coloring.
66 SmallVector<unsigned, 16> OrigSizes;
68 // AllColors - If index is set, it's a spill slot, i.e. color.
69 // FIXME: This assumes PEI locate spill slot with smaller indices
70 // closest to stack pointer / frame pointer. Therefore, smaller
71 // index == better color.
74 // NextColor - Next "color" that's not yet used.
77 // UsedColors - "Colors" that have been assigned.
80 // Assignments - Color to intervals mapping.
81 SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
84 static char ID; // Pass identification
86 MachineFunctionPass(ID), ColorWithRegs(false), NextColor(-1) {
87 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
89 StackSlotColoring(bool RegColor) :
90 MachineFunctionPass(ID), ColorWithRegs(RegColor), NextColor(-1) {
91 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
94 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
96 AU.addRequired<SlotIndexes>();
97 AU.addPreserved<SlotIndexes>();
98 AU.addRequired<LiveStacks>();
99 AU.addRequired<VirtRegMap>();
100 AU.addPreserved<VirtRegMap>();
101 AU.addRequired<MachineLoopInfo>();
102 AU.addPreserved<MachineLoopInfo>();
103 AU.addPreservedID(MachineDominatorsID);
104 MachineFunctionPass::getAnalysisUsage(AU);
107 virtual bool runOnMachineFunction(MachineFunction &MF);
108 virtual const char* getPassName() const {
109 return "Stack Slot Coloring";
113 void InitializeSlots();
114 void ScanForSpillSlotRefs(MachineFunction &MF);
115 bool OverlapWithAssignments(LiveInterval *li, int Color) const;
116 int ColorSlot(LiveInterval *li);
117 bool ColorSlots(MachineFunction &MF);
118 void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
119 MachineFunction &MF);
120 bool RemoveDeadStores(MachineBasicBlock* MBB);
122 } // end anonymous namespace
124 char StackSlotColoring::ID = 0;
126 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
127 "Stack Slot Coloring", false, false)
128 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
129 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
130 INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
131 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
132 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
133 "Stack Slot Coloring", false, false)
135 FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
136 return new StackSlotColoring(RegColor);
140 // IntervalSorter - Comparison predicate that sort live intervals by
142 struct IntervalSorter {
143 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
144 return LHS->weight > RHS->weight;
149 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
150 /// references and update spill slot weights.
151 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
152 SSRefs.resize(MFI->getObjectIndexEnd());
154 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
155 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
157 MachineBasicBlock *MBB = &*MBBI;
158 unsigned loopDepth = loopInfo->getLoopDepth(MBB);
159 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
161 MachineInstr *MI = &*MII;
162 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
163 MachineOperand &MO = MI->getOperand(i);
166 int FI = MO.getIndex();
169 if (!LS->hasInterval(FI))
171 LiveInterval &li = LS->getInterval(FI);
172 if (!MI->isDebugValue())
173 li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
174 SSRefs[FI].push_back(MI);
180 /// InitializeSlots - Process all spill stack slot liveintervals and add them
181 /// to a sorted (by weight) list.
182 void StackSlotColoring::InitializeSlots() {
183 int LastFI = MFI->getObjectIndexEnd();
184 OrigAlignments.resize(LastFI);
185 OrigSizes.resize(LastFI);
186 AllColors.resize(LastFI);
187 UsedColors.resize(LastFI);
188 Assignments.resize(LastFI);
190 // Gather all spill slots into a list.
191 DEBUG(dbgs() << "Spill slot intervals:\n");
192 for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
193 LiveInterval &li = i->second;
195 int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
196 if (MFI->isDeadObjectIndex(FI))
198 SSIntervals.push_back(&li);
199 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
200 OrigSizes[FI] = MFI->getObjectSize(FI);
203 DEBUG(dbgs() << '\n');
205 // Sort them by weight.
206 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
208 // Get first "color".
209 NextColor = AllColors.find_first();
212 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
213 /// LiveIntervals that have already been assigned to the specified color.
215 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
216 const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
217 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
218 LiveInterval *OtherLI = OtherLIs[i];
219 if (OtherLI->overlaps(*li))
225 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
227 int StackSlotColoring::ColorSlot(LiveInterval *li) {
230 if (!DisableSharing) {
231 // Check if it's possible to reuse any of the used colors.
232 Color = UsedColors.find_first();
233 while (Color != -1) {
234 if (!OverlapWithAssignments(li, Color)) {
239 Color = UsedColors.find_next(Color);
243 // Assign it to the first available color (assumed to be the best) if it's
244 // not possible to share a used color with other objects.
246 assert(NextColor != -1 && "No more spill slots?");
248 UsedColors.set(Color);
249 NextColor = AllColors.find_next(NextColor);
252 // Record the assignment.
253 Assignments[Color].push_back(li);
254 int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
255 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
257 // Change size and alignment of the allocated slot. If there are multiple
258 // objects sharing the same slot, then make sure the size and alignment
259 // are large enough for all.
260 unsigned Align = OrigAlignments[FI];
261 if (!Share || Align > MFI->getObjectAlignment(Color))
262 MFI->setObjectAlignment(Color, Align);
263 int64_t Size = OrigSizes[FI];
264 if (!Share || Size > MFI->getObjectSize(Color))
265 MFI->setObjectSize(Color, Size);
269 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
270 /// operands in the function.
271 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
272 unsigned NumObjs = MFI->getObjectIndexEnd();
273 SmallVector<int, 16> SlotMapping(NumObjs, -1);
274 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
275 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
276 BitVector UsedColors(NumObjs);
278 DEBUG(dbgs() << "Color spill slot intervals:\n");
279 bool Changed = false;
280 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
281 LiveInterval *li = SSIntervals[i];
282 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
283 int NewSS = ColorSlot(li);
284 assert(NewSS >= 0 && "Stack coloring failed?");
285 SlotMapping[SS] = NewSS;
286 RevMap[NewSS].push_back(SS);
287 SlotWeights[NewSS] += li->weight;
288 UsedColors.set(NewSS);
289 Changed |= (SS != NewSS);
292 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
293 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
294 LiveInterval *li = SSIntervals[i];
295 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
296 li->weight = SlotWeights[SS];
298 // Sort them by new weight.
299 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
302 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
303 DEBUG(SSIntervals[i]->dump());
304 DEBUG(dbgs() << '\n');
310 // Rewrite all MO_FrameIndex operands.
311 SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
312 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
313 int NewFI = SlotMapping[SS];
314 if (NewFI == -1 || (NewFI == (int)SS))
317 SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
318 for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
319 RewriteInstruction(RefMIs[i], SS, NewFI, MF);
322 // Delete unused stack slots.
323 while (NextColor != -1) {
324 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
325 MFI->RemoveStackObject(NextColor);
326 NextColor = AllColors.find_next(NextColor);
332 /// RewriteInstruction - Rewrite specified instruction by replacing references
333 /// to old frame index with new one.
334 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
335 int NewFI, MachineFunction &MF) {
336 // Update the operands.
337 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
338 MachineOperand &MO = MI->getOperand(i);
341 int FI = MO.getIndex();
347 // Update the memory references. This changes the MachineMemOperands
348 // directly. They may be in use by multiple instructions, however all
349 // instructions using OldFI are being rewritten to use NewFI.
350 const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
351 const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
352 for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
353 E = MI->memoperands_end(); I != E; ++I)
354 if ((*I)->getValue() == OldSV)
355 (*I)->setValue(NewSV);
359 /// RemoveDeadStores - Scan through a basic block and look for loads followed
360 /// by stores. If they're both using the same stack slot, then the store is
361 /// definitely dead. This could obviously be much more aggressive (consider
362 /// pairs with instructions between them), but such extensions might have a
363 /// considerable compile time impact.
364 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
365 // FIXME: This could be much more aggressive, but we need to investigate
366 // the compile time impact of doing so.
367 bool changed = false;
369 SmallVector<MachineInstr*, 4> toErase;
371 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
373 if (DCELimit != -1 && (int)NumDead >= DCELimit)
376 MachineBasicBlock::iterator NextMI = llvm::next(I);
377 if (NextMI == MBB->end()) continue;
379 int FirstSS, SecondSS;
380 unsigned LoadReg = 0;
381 unsigned StoreReg = 0;
382 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
383 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
384 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
389 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
391 toErase.push_back(I);
394 toErase.push_back(NextMI);
398 for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
399 E = toErase.end(); I != E; ++I)
400 (*I)->eraseFromParent();
406 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
408 dbgs() << "********** Stack Slot Coloring **********\n"
409 << "********** Function: "
410 << MF.getFunction()->getName() << '\n';
413 MFI = MF.getFrameInfo();
414 TII = MF.getTarget().getInstrInfo();
415 LS = &getAnalysis<LiveStacks>();
416 loopInfo = &getAnalysis<MachineLoopInfo>();
418 bool Changed = false;
420 unsigned NumSlots = LS->getNumIntervals();
425 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
426 // coloring. The stack could be modified before the longjmp is executed,
427 // resulting in the wrong value being used afterwards. (See
428 // <rdar://problem/8007500>.)
429 if (MF.callsSetJmp())
432 // Gather spill slot references
433 ScanForSpillSlotRefs(MF);
435 Changed = ColorSlots(MF);
439 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
442 OrigAlignments.clear();
446 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
447 Assignments[i].clear();
451 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
452 Changed |= RemoveDeadStores(I);