1 //===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the stack slot coloring pass.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/CodeGen/Passes.h"
15 #include "llvm/ADT/BitVector.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
19 #include "llvm/CodeGen/LiveStackAnalysis.h"
20 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
21 #include "llvm/CodeGen/MachineFrameInfo.h"
22 #include "llvm/CodeGen/MachineInstrBuilder.h"
23 #include "llvm/CodeGen/MachineMemOperand.h"
24 #include "llvm/CodeGen/MachineRegisterInfo.h"
25 #include "llvm/CodeGen/PseudoSourceValue.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/Target/TargetInstrInfo.h"
31 #include "llvm/Target/TargetSubtargetInfo.h"
32 #include <vector>
33 using namespace llvm;
34
35 #define DEBUG_TYPE "stackslotcoloring"
36
37 static cl::opt<bool>
38 DisableSharing("no-stack-slot-sharing",
39 cl::init(false), cl::Hidden,
40 cl::desc("Suppress slot sharing during stack coloring"));
41
42 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
43
44 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
45 STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
46
47 namespace {
48 class StackSlotColoring : public MachineFunctionPass {
49 LiveStacks* LS;
50 MachineFrameInfo *MFI;
51 const TargetInstrInfo *TII;
52 const MachineBlockFrequencyInfo *MBFI;
53
54 // SSIntervals - Spill slot intervals.
55 std::vector<LiveInterval*> SSIntervals;
56
57 // SSRefs - Keep a list of MachineMemOperands for each spill slot.
58 // MachineMemOperands can be shared between instructions, so we need
59 // to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not
60 // become FI0 -> FI1 -> FI2.
61 SmallVector<SmallVector<MachineMemOperand *, 8>, 16> SSRefs;
62
63 // OrigAlignments - Alignments of stack objects before coloring.
64 SmallVector<unsigned, 16> OrigAlignments;
65
66 // OrigSizes - Sizess of stack objects before coloring.
67 SmallVector<unsigned, 16> OrigSizes;
68
69 // AllColors - If index is set, it's a spill slot, i.e. color.
70 // FIXME: This assumes PEI locate spill slot with smaller indices
71 // closest to stack pointer / frame pointer. Therefore, smaller
72 // index == better color.
73 BitVector AllColors;
74
75 // NextColor - Next "color" that's not yet used.
76 int NextColor;
77
78 // UsedColors - "Colors" that have been assigned.
79 BitVector UsedColors;
80
81 // Assignments - Color to intervals mapping.
82 SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
83
84 public:
85 static char ID; // Pass identification
StackSlotColoring()86 StackSlotColoring() :
87 MachineFunctionPass(ID), NextColor(-1) {
88 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
89 }
90
getAnalysisUsage(AnalysisUsage & AU) const91 void getAnalysisUsage(AnalysisUsage &AU) const override {
92 AU.setPreservesCFG();
93 AU.addRequired<SlotIndexes>();
94 AU.addPreserved<SlotIndexes>();
95 AU.addRequired<LiveStacks>();
96 AU.addRequired<MachineBlockFrequencyInfo>();
97 AU.addPreserved<MachineBlockFrequencyInfo>();
98 AU.addPreservedID(MachineDominatorsID);
99 MachineFunctionPass::getAnalysisUsage(AU);
100 }
101
102 bool runOnMachineFunction(MachineFunction &MF) override;
103
104 private:
105 void InitializeSlots();
106 void ScanForSpillSlotRefs(MachineFunction &MF);
107 bool OverlapWithAssignments(LiveInterval *li, int Color) const;
108 int ColorSlot(LiveInterval *li);
109 bool ColorSlots(MachineFunction &MF);
110 void RewriteInstruction(MachineInstr *MI, SmallVectorImpl<int> &SlotMapping,
111 MachineFunction &MF);
112 bool RemoveDeadStores(MachineBasicBlock* MBB);
113 };
114 } // end anonymous namespace
115
116 char StackSlotColoring::ID = 0;
117 char &llvm::StackSlotColoringID = StackSlotColoring::ID;
118
119 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
120 "Stack Slot Coloring", false, false)
121 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
122 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
123 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
124 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
125 "Stack Slot Coloring", false, false)
126
127 namespace {
128 // IntervalSorter - Comparison predicate that sort live intervals by
129 // their weight.
130 struct IntervalSorter {
operator ()__anon6785c94b0211::IntervalSorter131 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
132 return LHS->weight > RHS->weight;
133 }
134 };
135 }
136
137 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
138 /// references and update spill slot weights.
ScanForSpillSlotRefs(MachineFunction & MF)139 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
140 SSRefs.resize(MFI->getObjectIndexEnd());
141
142 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
143 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
144 MBBI != E; ++MBBI) {
145 MachineBasicBlock *MBB = &*MBBI;
146 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
147 MII != EE; ++MII) {
148 MachineInstr *MI = &*MII;
149 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
150 MachineOperand &MO = MI->getOperand(i);
151 if (!MO.isFI())
152 continue;
153 int FI = MO.getIndex();
154 if (FI < 0)
155 continue;
156 if (!LS->hasInterval(FI))
157 continue;
158 LiveInterval &li = LS->getInterval(FI);
159 if (!MI->isDebugValue())
160 li.weight += LiveIntervals::getSpillWeight(false, true, MBFI, MI);
161 }
162 for (MachineInstr::mmo_iterator MMOI = MI->memoperands_begin(),
163 EE = MI->memoperands_end(); MMOI != EE; ++MMOI) {
164 MachineMemOperand *MMO = *MMOI;
165 if (const FixedStackPseudoSourceValue *FSV =
166 dyn_cast_or_null<FixedStackPseudoSourceValue>(
167 MMO->getPseudoValue())) {
168 int FI = FSV->getFrameIndex();
169 if (FI >= 0)
170 SSRefs[FI].push_back(MMO);
171 }
172 }
173 }
174 }
175 }
176
177 /// InitializeSlots - Process all spill stack slot liveintervals and add them
178 /// to a sorted (by weight) list.
InitializeSlots()179 void StackSlotColoring::InitializeSlots() {
180 int LastFI = MFI->getObjectIndexEnd();
181 OrigAlignments.resize(LastFI);
182 OrigSizes.resize(LastFI);
183 AllColors.resize(LastFI);
184 UsedColors.resize(LastFI);
185 Assignments.resize(LastFI);
186
187 typedef std::iterator_traits<LiveStacks::iterator>::value_type Pair;
188 SmallVector<Pair *, 16> Intervals;
189 Intervals.reserve(LS->getNumIntervals());
190 for (auto &I : *LS)
191 Intervals.push_back(&I);
192 std::sort(Intervals.begin(), Intervals.end(),
193 [](Pair *LHS, Pair *RHS) { return LHS->first < RHS->first; });
194
195 // Gather all spill slots into a list.
196 DEBUG(dbgs() << "Spill slot intervals:\n");
197 for (auto *I : Intervals) {
198 LiveInterval &li = I->second;
199 DEBUG(li.dump());
200 int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
201 if (MFI->isDeadObjectIndex(FI))
202 continue;
203 SSIntervals.push_back(&li);
204 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
205 OrigSizes[FI] = MFI->getObjectSize(FI);
206 AllColors.set(FI);
207 }
208 DEBUG(dbgs() << '\n');
209
210 // Sort them by weight.
211 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
212
213 // Get first "color".
214 NextColor = AllColors.find_first();
215 }
216
217 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
218 /// LiveIntervals that have already been assigned to the specified color.
219 bool
OverlapWithAssignments(LiveInterval * li,int Color) const220 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
221 const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color];
222 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
223 LiveInterval *OtherLI = OtherLIs[i];
224 if (OtherLI->overlaps(*li))
225 return true;
226 }
227 return false;
228 }
229
230 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
231 ///
ColorSlot(LiveInterval * li)232 int StackSlotColoring::ColorSlot(LiveInterval *li) {
233 int Color = -1;
234 bool Share = false;
235 if (!DisableSharing) {
236 // Check if it's possible to reuse any of the used colors.
237 Color = UsedColors.find_first();
238 while (Color != -1) {
239 if (!OverlapWithAssignments(li, Color)) {
240 Share = true;
241 ++NumEliminated;
242 break;
243 }
244 Color = UsedColors.find_next(Color);
245 }
246 }
247
248 // Assign it to the first available color (assumed to be the best) if it's
249 // not possible to share a used color with other objects.
250 if (!Share) {
251 assert(NextColor != -1 && "No more spill slots?");
252 Color = NextColor;
253 UsedColors.set(Color);
254 NextColor = AllColors.find_next(NextColor);
255 }
256
257 // Record the assignment.
258 Assignments[Color].push_back(li);
259 int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
260 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
261
262 // Change size and alignment of the allocated slot. If there are multiple
263 // objects sharing the same slot, then make sure the size and alignment
264 // are large enough for all.
265 unsigned Align = OrigAlignments[FI];
266 if (!Share || Align > MFI->getObjectAlignment(Color))
267 MFI->setObjectAlignment(Color, Align);
268 int64_t Size = OrigSizes[FI];
269 if (!Share || Size > MFI->getObjectSize(Color))
270 MFI->setObjectSize(Color, Size);
271 return Color;
272 }
273
274 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
275 /// operands in the function.
ColorSlots(MachineFunction & MF)276 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
277 unsigned NumObjs = MFI->getObjectIndexEnd();
278 SmallVector<int, 16> SlotMapping(NumObjs, -1);
279 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
280 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
281 BitVector UsedColors(NumObjs);
282
283 DEBUG(dbgs() << "Color spill slot intervals:\n");
284 bool Changed = false;
285 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
286 LiveInterval *li = SSIntervals[i];
287 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
288 int NewSS = ColorSlot(li);
289 assert(NewSS >= 0 && "Stack coloring failed?");
290 SlotMapping[SS] = NewSS;
291 RevMap[NewSS].push_back(SS);
292 SlotWeights[NewSS] += li->weight;
293 UsedColors.set(NewSS);
294 Changed |= (SS != NewSS);
295 }
296
297 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
298 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
299 LiveInterval *li = SSIntervals[i];
300 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
301 li->weight = SlotWeights[SS];
302 }
303 // Sort them by new weight.
304 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
305
306 #ifndef NDEBUG
307 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
308 DEBUG(SSIntervals[i]->dump());
309 DEBUG(dbgs() << '\n');
310 #endif
311
312 if (!Changed)
313 return false;
314
315 // Rewrite all MachineMemOperands.
316 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
317 int NewFI = SlotMapping[SS];
318 if (NewFI == -1 || (NewFI == (int)SS))
319 continue;
320
321 const PseudoSourceValue *NewSV = MF.getPSVManager().getFixedStack(NewFI);
322 SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
323 for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
324 RefMMOs[i]->setValue(NewSV);
325 }
326
327 // Rewrite all MO_FrameIndex operands. Look for dead stores.
328 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
329 MBBI != E; ++MBBI) {
330 MachineBasicBlock *MBB = &*MBBI;
331 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
332 MII != EE; ++MII)
333 RewriteInstruction(MII, SlotMapping, MF);
334 RemoveDeadStores(MBB);
335 }
336
337 // Delete unused stack slots.
338 while (NextColor != -1) {
339 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
340 MFI->RemoveStackObject(NextColor);
341 NextColor = AllColors.find_next(NextColor);
342 }
343
344 return true;
345 }
346
347 /// RewriteInstruction - Rewrite specified instruction by replacing references
348 /// to old frame index with new one.
RewriteInstruction(MachineInstr * MI,SmallVectorImpl<int> & SlotMapping,MachineFunction & MF)349 void StackSlotColoring::RewriteInstruction(MachineInstr *MI,
350 SmallVectorImpl<int> &SlotMapping,
351 MachineFunction &MF) {
352 // Update the operands.
353 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
354 MachineOperand &MO = MI->getOperand(i);
355 if (!MO.isFI())
356 continue;
357 int OldFI = MO.getIndex();
358 if (OldFI < 0)
359 continue;
360 int NewFI = SlotMapping[OldFI];
361 if (NewFI == -1 || NewFI == OldFI)
362 continue;
363 MO.setIndex(NewFI);
364 }
365
366 // The MachineMemOperands have already been updated.
367 }
368
369
370 /// RemoveDeadStores - Scan through a basic block and look for loads followed
371 /// by stores. If they're both using the same stack slot, then the store is
372 /// definitely dead. This could obviously be much more aggressive (consider
373 /// pairs with instructions between them), but such extensions might have a
374 /// considerable compile time impact.
RemoveDeadStores(MachineBasicBlock * MBB)375 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
376 // FIXME: This could be much more aggressive, but we need to investigate
377 // the compile time impact of doing so.
378 bool changed = false;
379
380 SmallVector<MachineInstr*, 4> toErase;
381
382 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
383 I != E; ++I) {
384 if (DCELimit != -1 && (int)NumDead >= DCELimit)
385 break;
386
387 int FirstSS, SecondSS;
388 if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
389 FirstSS == SecondSS &&
390 FirstSS != -1) {
391 ++NumDead;
392 changed = true;
393 toErase.push_back(I);
394 continue;
395 }
396
397 MachineBasicBlock::iterator NextMI = std::next(I);
398 if (NextMI == MBB->end()) continue;
399
400 unsigned LoadReg = 0;
401 unsigned StoreReg = 0;
402 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
403 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
404 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
405
406 ++NumDead;
407 changed = true;
408
409 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) {
410 ++NumDead;
411 toErase.push_back(I);
412 }
413
414 toErase.push_back(NextMI);
415 ++I;
416 }
417
418 for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(),
419 E = toErase.end(); I != E; ++I)
420 (*I)->eraseFromParent();
421
422 return changed;
423 }
424
425
runOnMachineFunction(MachineFunction & MF)426 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
427 DEBUG({
428 dbgs() << "********** Stack Slot Coloring **********\n"
429 << "********** Function: " << MF.getName() << '\n';
430 });
431
432 MFI = MF.getFrameInfo();
433 TII = MF.getSubtarget().getInstrInfo();
434 LS = &getAnalysis<LiveStacks>();
435 MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
436
437 bool Changed = false;
438
439 unsigned NumSlots = LS->getNumIntervals();
440 if (NumSlots == 0)
441 // Nothing to do!
442 return false;
443
444 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
445 // coloring. The stack could be modified before the longjmp is executed,
446 // resulting in the wrong value being used afterwards. (See
447 // <rdar://problem/8007500>.)
448 if (MF.exposesReturnsTwice())
449 return false;
450
451 // Gather spill slot references
452 ScanForSpillSlotRefs(MF);
453 InitializeSlots();
454 Changed = ColorSlots(MF);
455
456 NextColor = -1;
457 SSIntervals.clear();
458 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
459 SSRefs[i].clear();
460 SSRefs.clear();
461 OrigAlignments.clear();
462 OrigSizes.clear();
463 AllColors.clear();
464 UsedColors.clear();
465 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
466 Assignments[i].clear();
467 Assignments.clear();
468
469 return Changed;
470 }
471