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/TargetMachine.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 ()__anone605ea8f0211::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 // Gather all spill slots into a list.
188 DEBUG(dbgs() << "Spill slot intervals:\n");
189 for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
190 LiveInterval &li = i->second;
191 DEBUG(li.dump());
192 int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
193 if (MFI->isDeadObjectIndex(FI))
194 continue;
195 SSIntervals.push_back(&li);
196 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
197 OrigSizes[FI] = MFI->getObjectSize(FI);
198 AllColors.set(FI);
199 }
200 DEBUG(dbgs() << '\n');
201
202 // Sort them by weight.
203 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
204
205 // Get first "color".
206 NextColor = AllColors.find_first();
207 }
208
209 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
210 /// LiveIntervals that have already been assigned to the specified color.
211 bool
OverlapWithAssignments(LiveInterval * li,int Color) const212 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
213 const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color];
214 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
215 LiveInterval *OtherLI = OtherLIs[i];
216 if (OtherLI->overlaps(*li))
217 return true;
218 }
219 return false;
220 }
221
222 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
223 ///
ColorSlot(LiveInterval * li)224 int StackSlotColoring::ColorSlot(LiveInterval *li) {
225 int Color = -1;
226 bool Share = false;
227 if (!DisableSharing) {
228 // Check if it's possible to reuse any of the used colors.
229 Color = UsedColors.find_first();
230 while (Color != -1) {
231 if (!OverlapWithAssignments(li, Color)) {
232 Share = true;
233 ++NumEliminated;
234 break;
235 }
236 Color = UsedColors.find_next(Color);
237 }
238 }
239
240 // Assign it to the first available color (assumed to be the best) if it's
241 // not possible to share a used color with other objects.
242 if (!Share) {
243 assert(NextColor != -1 && "No more spill slots?");
244 Color = NextColor;
245 UsedColors.set(Color);
246 NextColor = AllColors.find_next(NextColor);
247 }
248
249 // Record the assignment.
250 Assignments[Color].push_back(li);
251 int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
252 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
253
254 // Change size and alignment of the allocated slot. If there are multiple
255 // objects sharing the same slot, then make sure the size and alignment
256 // are large enough for all.
257 unsigned Align = OrigAlignments[FI];
258 if (!Share || Align > MFI->getObjectAlignment(Color))
259 MFI->setObjectAlignment(Color, Align);
260 int64_t Size = OrigSizes[FI];
261 if (!Share || Size > MFI->getObjectSize(Color))
262 MFI->setObjectSize(Color, Size);
263 return Color;
264 }
265
266 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
267 /// operands in the function.
ColorSlots(MachineFunction & MF)268 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
269 unsigned NumObjs = MFI->getObjectIndexEnd();
270 SmallVector<int, 16> SlotMapping(NumObjs, -1);
271 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
272 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
273 BitVector UsedColors(NumObjs);
274
275 DEBUG(dbgs() << "Color spill slot intervals:\n");
276 bool Changed = false;
277 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
278 LiveInterval *li = SSIntervals[i];
279 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
280 int NewSS = ColorSlot(li);
281 assert(NewSS >= 0 && "Stack coloring failed?");
282 SlotMapping[SS] = NewSS;
283 RevMap[NewSS].push_back(SS);
284 SlotWeights[NewSS] += li->weight;
285 UsedColors.set(NewSS);
286 Changed |= (SS != NewSS);
287 }
288
289 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
290 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
291 LiveInterval *li = SSIntervals[i];
292 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
293 li->weight = SlotWeights[SS];
294 }
295 // Sort them by new weight.
296 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
297
298 #ifndef NDEBUG
299 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
300 DEBUG(SSIntervals[i]->dump());
301 DEBUG(dbgs() << '\n');
302 #endif
303
304 if (!Changed)
305 return false;
306
307 // Rewrite all MachineMemOperands.
308 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
309 int NewFI = SlotMapping[SS];
310 if (NewFI == -1 || (NewFI == (int)SS))
311 continue;
312
313 const PseudoSourceValue *NewSV = PseudoSourceValue::getFixedStack(NewFI);
314 SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
315 for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
316 RefMMOs[i]->setValue(NewSV);
317 }
318
319 // Rewrite all MO_FrameIndex operands. Look for dead stores.
320 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
321 MBBI != E; ++MBBI) {
322 MachineBasicBlock *MBB = &*MBBI;
323 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
324 MII != EE; ++MII)
325 RewriteInstruction(MII, SlotMapping, MF);
326 RemoveDeadStores(MBB);
327 }
328
329 // Delete unused stack slots.
330 while (NextColor != -1) {
331 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
332 MFI->RemoveStackObject(NextColor);
333 NextColor = AllColors.find_next(NextColor);
334 }
335
336 return true;
337 }
338
339 /// RewriteInstruction - Rewrite specified instruction by replacing references
340 /// to old frame index with new one.
RewriteInstruction(MachineInstr * MI,SmallVectorImpl<int> & SlotMapping,MachineFunction & MF)341 void StackSlotColoring::RewriteInstruction(MachineInstr *MI,
342 SmallVectorImpl<int> &SlotMapping,
343 MachineFunction &MF) {
344 // Update the operands.
345 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
346 MachineOperand &MO = MI->getOperand(i);
347 if (!MO.isFI())
348 continue;
349 int OldFI = MO.getIndex();
350 if (OldFI < 0)
351 continue;
352 int NewFI = SlotMapping[OldFI];
353 if (NewFI == -1 || NewFI == OldFI)
354 continue;
355 MO.setIndex(NewFI);
356 }
357
358 // The MachineMemOperands have already been updated.
359 }
360
361
362 /// RemoveDeadStores - Scan through a basic block and look for loads followed
363 /// by stores. If they're both using the same stack slot, then the store is
364 /// definitely dead. This could obviously be much more aggressive (consider
365 /// pairs with instructions between them), but such extensions might have a
366 /// considerable compile time impact.
RemoveDeadStores(MachineBasicBlock * MBB)367 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
368 // FIXME: This could be much more aggressive, but we need to investigate
369 // the compile time impact of doing so.
370 bool changed = false;
371
372 SmallVector<MachineInstr*, 4> toErase;
373
374 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
375 I != E; ++I) {
376 if (DCELimit != -1 && (int)NumDead >= DCELimit)
377 break;
378
379 int FirstSS, SecondSS;
380 if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
381 FirstSS == SecondSS &&
382 FirstSS != -1) {
383 ++NumDead;
384 changed = true;
385 toErase.push_back(I);
386 continue;
387 }
388
389 MachineBasicBlock::iterator NextMI = std::next(I);
390 if (NextMI == MBB->end()) continue;
391
392 unsigned LoadReg = 0;
393 unsigned StoreReg = 0;
394 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
395 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
396 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
397
398 ++NumDead;
399 changed = true;
400
401 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) {
402 ++NumDead;
403 toErase.push_back(I);
404 }
405
406 toErase.push_back(NextMI);
407 ++I;
408 }
409
410 for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(),
411 E = toErase.end(); I != E; ++I)
412 (*I)->eraseFromParent();
413
414 return changed;
415 }
416
417
runOnMachineFunction(MachineFunction & MF)418 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
419 DEBUG({
420 dbgs() << "********** Stack Slot Coloring **********\n"
421 << "********** Function: " << MF.getName() << '\n';
422 });
423
424 MFI = MF.getFrameInfo();
425 TII = MF.getTarget().getInstrInfo();
426 LS = &getAnalysis<LiveStacks>();
427 MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
428
429 bool Changed = false;
430
431 unsigned NumSlots = LS->getNumIntervals();
432 if (NumSlots == 0)
433 // Nothing to do!
434 return false;
435
436 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
437 // coloring. The stack could be modified before the longjmp is executed,
438 // resulting in the wrong value being used afterwards. (See
439 // <rdar://problem/8007500>.)
440 if (MF.exposesReturnsTwice())
441 return false;
442
443 // Gather spill slot references
444 ScanForSpillSlotRefs(MF);
445 InitializeSlots();
446 Changed = ColorSlots(MF);
447
448 NextColor = -1;
449 SSIntervals.clear();
450 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
451 SSRefs[i].clear();
452 SSRefs.clear();
453 OrigAlignments.clear();
454 OrigSizes.clear();
455 AllColors.clear();
456 UsedColors.clear();
457 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
458 Assignments[i].clear();
459 Assignments.clear();
460
461 return Changed;
462 }
463