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 "stackslotcoloring"
15 #include "llvm/CodeGen/Passes.h"
16 #include "llvm/ADT/BitVector.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
20 #include "llvm/CodeGen/LiveStackAnalysis.h"
21 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
22 #include "llvm/CodeGen/MachineFrameInfo.h"
23 #include "llvm/CodeGen/MachineInstrBuilder.h"
24 #include "llvm/CodeGen/MachineMemOperand.h"
25 #include "llvm/CodeGen/MachineRegisterInfo.h"
26 #include "llvm/CodeGen/PseudoSourceValue.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/Support/CommandLine.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/Target/TargetInstrInfo.h"
32 #include "llvm/Target/TargetMachine.h"
37 DisableSharing("no-stack-slot-sharing",
38 cl::init(false), cl::Hidden,
39 cl::desc("Suppress slot sharing during stack coloring"));
41 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
43 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
44 STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
47 class StackSlotColoring : public MachineFunctionPass {
49 MachineFrameInfo *MFI;
50 const TargetInstrInfo *TII;
51 const MachineBlockFrequencyInfo *MBFI;
53 // SSIntervals - Spill slot intervals.
54 std::vector<LiveInterval*> SSIntervals;
56 // SSRefs - Keep a list of MachineMemOperands for each spill slot.
57 // MachineMemOperands can be shared between instructions, so we need
58 // to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not
59 // become FI0 -> FI1 -> FI2.
60 SmallVector<SmallVector<MachineMemOperand *, 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), NextColor(-1) {
87 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
90 void getAnalysisUsage(AnalysisUsage &AU) const override {
92 AU.addRequired<SlotIndexes>();
93 AU.addPreserved<SlotIndexes>();
94 AU.addRequired<LiveStacks>();
95 AU.addRequired<MachineBlockFrequencyInfo>();
96 AU.addPreserved<MachineBlockFrequencyInfo>();
97 AU.addPreservedID(MachineDominatorsID);
98 MachineFunctionPass::getAnalysisUsage(AU);
101 bool runOnMachineFunction(MachineFunction &MF) override;
104 void InitializeSlots();
105 void ScanForSpillSlotRefs(MachineFunction &MF);
106 bool OverlapWithAssignments(LiveInterval *li, int Color) const;
107 int ColorSlot(LiveInterval *li);
108 bool ColorSlots(MachineFunction &MF);
109 void RewriteInstruction(MachineInstr *MI, SmallVectorImpl<int> &SlotMapping,
110 MachineFunction &MF);
111 bool RemoveDeadStores(MachineBasicBlock* MBB);
113 } // end anonymous namespace
115 char StackSlotColoring::ID = 0;
116 char &llvm::StackSlotColoringID = StackSlotColoring::ID;
118 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
119 "Stack Slot Coloring", false, false)
120 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
121 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
122 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
123 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
124 "Stack Slot Coloring", false, false)
127 // IntervalSorter - Comparison predicate that sort live intervals by
129 struct IntervalSorter {
130 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
131 return LHS->weight > RHS->weight;
136 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
137 /// references and update spill slot weights.
138 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
139 SSRefs.resize(MFI->getObjectIndexEnd());
141 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
142 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
144 MachineBasicBlock *MBB = &*MBBI;
145 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
147 MachineInstr *MI = &*MII;
148 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
149 MachineOperand &MO = MI->getOperand(i);
152 int FI = MO.getIndex();
155 if (!LS->hasInterval(FI))
157 LiveInterval &li = LS->getInterval(FI);
158 if (!MI->isDebugValue())
159 li.weight += LiveIntervals::getSpillWeight(false, true, MBFI, MI);
161 for (MachineInstr::mmo_iterator MMOI = MI->memoperands_begin(),
162 EE = MI->memoperands_end(); MMOI != EE; ++MMOI) {
163 MachineMemOperand *MMO = *MMOI;
164 if (const FixedStackPseudoSourceValue *FSV =
165 dyn_cast_or_null<FixedStackPseudoSourceValue>(
166 MMO->getPseudoValue())) {
167 int FI = FSV->getFrameIndex();
169 SSRefs[FI].push_back(MMO);
176 /// InitializeSlots - Process all spill stack slot liveintervals and add them
177 /// to a sorted (by weight) list.
178 void StackSlotColoring::InitializeSlots() {
179 int LastFI = MFI->getObjectIndexEnd();
180 OrigAlignments.resize(LastFI);
181 OrigSizes.resize(LastFI);
182 AllColors.resize(LastFI);
183 UsedColors.resize(LastFI);
184 Assignments.resize(LastFI);
186 // Gather all spill slots into a list.
187 DEBUG(dbgs() << "Spill slot intervals:\n");
188 for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
189 LiveInterval &li = i->second;
191 int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
192 if (MFI->isDeadObjectIndex(FI))
194 SSIntervals.push_back(&li);
195 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
196 OrigSizes[FI] = MFI->getObjectSize(FI);
199 DEBUG(dbgs() << '\n');
201 // Sort them by weight.
202 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
204 // Get first "color".
205 NextColor = AllColors.find_first();
208 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
209 /// LiveIntervals that have already been assigned to the specified color.
211 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
212 const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color];
213 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
214 LiveInterval *OtherLI = OtherLIs[i];
215 if (OtherLI->overlaps(*li))
221 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
223 int StackSlotColoring::ColorSlot(LiveInterval *li) {
226 if (!DisableSharing) {
227 // Check if it's possible to reuse any of the used colors.
228 Color = UsedColors.find_first();
229 while (Color != -1) {
230 if (!OverlapWithAssignments(li, Color)) {
235 Color = UsedColors.find_next(Color);
239 // Assign it to the first available color (assumed to be the best) if it's
240 // not possible to share a used color with other objects.
242 assert(NextColor != -1 && "No more spill slots?");
244 UsedColors.set(Color);
245 NextColor = AllColors.find_next(NextColor);
248 // Record the assignment.
249 Assignments[Color].push_back(li);
250 int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
251 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
253 // Change size and alignment of the allocated slot. If there are multiple
254 // objects sharing the same slot, then make sure the size and alignment
255 // are large enough for all.
256 unsigned Align = OrigAlignments[FI];
257 if (!Share || Align > MFI->getObjectAlignment(Color))
258 MFI->setObjectAlignment(Color, Align);
259 int64_t Size = OrigSizes[FI];
260 if (!Share || Size > MFI->getObjectSize(Color))
261 MFI->setObjectSize(Color, Size);
265 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
266 /// operands in the function.
267 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
268 unsigned NumObjs = MFI->getObjectIndexEnd();
269 SmallVector<int, 16> SlotMapping(NumObjs, -1);
270 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
271 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
272 BitVector UsedColors(NumObjs);
274 DEBUG(dbgs() << "Color spill slot intervals:\n");
275 bool Changed = false;
276 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
277 LiveInterval *li = SSIntervals[i];
278 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
279 int NewSS = ColorSlot(li);
280 assert(NewSS >= 0 && "Stack coloring failed?");
281 SlotMapping[SS] = NewSS;
282 RevMap[NewSS].push_back(SS);
283 SlotWeights[NewSS] += li->weight;
284 UsedColors.set(NewSS);
285 Changed |= (SS != NewSS);
288 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
289 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
290 LiveInterval *li = SSIntervals[i];
291 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
292 li->weight = SlotWeights[SS];
294 // Sort them by new weight.
295 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
298 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
299 DEBUG(SSIntervals[i]->dump());
300 DEBUG(dbgs() << '\n');
306 // Rewrite all MachineMemOperands.
307 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
308 int NewFI = SlotMapping[SS];
309 if (NewFI == -1 || (NewFI == (int)SS))
312 const PseudoSourceValue *NewSV = PseudoSourceValue::getFixedStack(NewFI);
313 SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
314 for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
315 RefMMOs[i]->setValue(NewSV);
318 // Rewrite all MO_FrameIndex operands. Look for dead stores.
319 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
321 MachineBasicBlock *MBB = &*MBBI;
322 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
324 RewriteInstruction(MII, SlotMapping, MF);
325 RemoveDeadStores(MBB);
328 // Delete unused stack slots.
329 while (NextColor != -1) {
330 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
331 MFI->RemoveStackObject(NextColor);
332 NextColor = AllColors.find_next(NextColor);
338 /// RewriteInstruction - Rewrite specified instruction by replacing references
339 /// to old frame index with new one.
340 void StackSlotColoring::RewriteInstruction(MachineInstr *MI,
341 SmallVectorImpl<int> &SlotMapping,
342 MachineFunction &MF) {
343 // Update the operands.
344 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
345 MachineOperand &MO = MI->getOperand(i);
348 int OldFI = MO.getIndex();
351 int NewFI = SlotMapping[OldFI];
352 if (NewFI == -1 || NewFI == OldFI)
357 // The MachineMemOperands have already been updated.
361 /// RemoveDeadStores - Scan through a basic block and look for loads followed
362 /// by stores. If they're both using the same stack slot, then the store is
363 /// definitely dead. This could obviously be much more aggressive (consider
364 /// pairs with instructions between them), but such extensions might have a
365 /// considerable compile time impact.
366 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
367 // FIXME: This could be much more aggressive, but we need to investigate
368 // the compile time impact of doing so.
369 bool changed = false;
371 SmallVector<MachineInstr*, 4> toErase;
373 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
375 if (DCELimit != -1 && (int)NumDead >= DCELimit)
378 int FirstSS, SecondSS;
379 if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
380 FirstSS == SecondSS &&
384 toErase.push_back(I);
388 MachineBasicBlock::iterator NextMI = std::next(I);
389 if (NextMI == MBB->end()) continue;
391 unsigned LoadReg = 0;
392 unsigned StoreReg = 0;
393 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
394 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
395 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
400 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) {
402 toErase.push_back(I);
405 toErase.push_back(NextMI);
409 for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(),
410 E = toErase.end(); I != E; ++I)
411 (*I)->eraseFromParent();
417 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
419 dbgs() << "********** Stack Slot Coloring **********\n"
420 << "********** Function: " << MF.getName() << '\n';
423 MFI = MF.getFrameInfo();
424 TII = MF.getTarget().getInstrInfo();
425 LS = &getAnalysis<LiveStacks>();
426 MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
428 bool Changed = false;
430 unsigned NumSlots = LS->getNumIntervals();
435 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
436 // coloring. The stack could be modified before the longjmp is executed,
437 // resulting in the wrong value being used afterwards. (See
438 // <rdar://problem/8007500>.)
439 if (MF.exposesReturnsTwice())
442 // Gather spill slot references
443 ScanForSpillSlotRefs(MF);
445 Changed = ColorSlots(MF);
449 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
452 OrigAlignments.clear();
456 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
457 Assignments[i].clear();