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223e47cc LB |
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 | ||
223e47cc | 14 | #include "llvm/CodeGen/Passes.h" |
970d7e83 | 15 | #include "llvm/ADT/BitVector.h" |
970d7e83 LB |
16 | #include "llvm/ADT/SmallVector.h" |
17 | #include "llvm/ADT/Statistic.h" | |
223e47cc LB |
18 | #include "llvm/CodeGen/LiveIntervalAnalysis.h" |
19 | #include "llvm/CodeGen/LiveStackAnalysis.h" | |
1a4d82fc | 20 | #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" |
223e47cc LB |
21 | #include "llvm/CodeGen/MachineFrameInfo.h" |
22 | #include "llvm/CodeGen/MachineInstrBuilder.h" | |
223e47cc LB |
23 | #include "llvm/CodeGen/MachineMemOperand.h" |
24 | #include "llvm/CodeGen/MachineRegisterInfo.h" | |
25 | #include "llvm/CodeGen/PseudoSourceValue.h" | |
970d7e83 | 26 | #include "llvm/IR/Module.h" |
223e47cc LB |
27 | #include "llvm/Support/CommandLine.h" |
28 | #include "llvm/Support/Debug.h" | |
1a4d82fc | 29 | #include "llvm/Support/raw_ostream.h" |
223e47cc | 30 | #include "llvm/Target/TargetInstrInfo.h" |
1a4d82fc | 31 | #include "llvm/Target/TargetSubtargetInfo.h" |
223e47cc LB |
32 | #include <vector> |
33 | using namespace llvm; | |
34 | ||
1a4d82fc JJ |
35 | #define DEBUG_TYPE "stackslotcoloring" |
36 | ||
223e47cc LB |
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; | |
1a4d82fc | 52 | const MachineBlockFrequencyInfo *MBFI; |
223e47cc LB |
53 | |
54 | // SSIntervals - Spill slot intervals. | |
55 | std::vector<LiveInterval*> SSIntervals; | |
56 | ||
1a4d82fc JJ |
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; | |
223e47cc LB |
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 | |
86 | StackSlotColoring() : | |
87 | MachineFunctionPass(ID), NextColor(-1) { | |
88 | initializeStackSlotColoringPass(*PassRegistry::getPassRegistry()); | |
89 | } | |
90 | ||
1a4d82fc | 91 | void getAnalysisUsage(AnalysisUsage &AU) const override { |
223e47cc LB |
92 | AU.setPreservesCFG(); |
93 | AU.addRequired<SlotIndexes>(); | |
94 | AU.addPreserved<SlotIndexes>(); | |
95 | AU.addRequired<LiveStacks>(); | |
1a4d82fc JJ |
96 | AU.addRequired<MachineBlockFrequencyInfo>(); |
97 | AU.addPreserved<MachineBlockFrequencyInfo>(); | |
223e47cc LB |
98 | AU.addPreservedID(MachineDominatorsID); |
99 | MachineFunctionPass::getAnalysisUsage(AU); | |
100 | } | |
101 | ||
1a4d82fc | 102 | bool runOnMachineFunction(MachineFunction &MF) override; |
223e47cc LB |
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); | |
1a4d82fc | 110 | void RewriteInstruction(MachineInstr *MI, SmallVectorImpl<int> &SlotMapping, |
223e47cc LB |
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 { | |
131 | 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. | |
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; | |
223e47cc LB |
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()) | |
1a4d82fc JJ |
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 | } | |
223e47cc LB |
172 | } |
173 | } | |
174 | } | |
175 | } | |
176 | ||
177 | /// InitializeSlots - Process all spill stack slot liveintervals and add them | |
178 | /// to a sorted (by weight) list. | |
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 | |
212 | StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const { | |
1a4d82fc | 213 | const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color]; |
223e47cc LB |
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 | /// | |
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. | |
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 | ||
1a4d82fc | 307 | // Rewrite all MachineMemOperands. |
223e47cc LB |
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 | ||
1a4d82fc JJ |
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); | |
223e47cc LB |
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. | |
1a4d82fc JJ |
341 | void StackSlotColoring::RewriteInstruction(MachineInstr *MI, |
342 | SmallVectorImpl<int> &SlotMapping, | |
343 | MachineFunction &MF) { | |
223e47cc LB |
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; | |
1a4d82fc JJ |
349 | int OldFI = MO.getIndex(); |
350 | if (OldFI < 0) | |
351 | continue; | |
352 | int NewFI = SlotMapping[OldFI]; | |
353 | if (NewFI == -1 || NewFI == OldFI) | |
223e47cc LB |
354 | continue; |
355 | MO.setIndex(NewFI); | |
356 | } | |
357 | ||
1a4d82fc | 358 | // The MachineMemOperands have already been updated. |
223e47cc LB |
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. | |
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 | ||
1a4d82fc JJ |
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); | |
223e47cc LB |
390 | if (NextMI == MBB->end()) continue; |
391 | ||
223e47cc LB |
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 | ||
1a4d82fc | 401 | if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) { |
223e47cc LB |
402 | ++NumDead; |
403 | toErase.push_back(I); | |
404 | } | |
405 | ||
406 | toErase.push_back(NextMI); | |
407 | ++I; | |
408 | } | |
409 | ||
1a4d82fc | 410 | for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(), |
223e47cc LB |
411 | E = toErase.end(); I != E; ++I) |
412 | (*I)->eraseFromParent(); | |
413 | ||
414 | return changed; | |
415 | } | |
416 | ||
417 | ||
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(); | |
1a4d82fc | 425 | TII = MF.getSubtarget().getInstrInfo(); |
223e47cc | 426 | LS = &getAnalysis<LiveStacks>(); |
1a4d82fc | 427 | MBFI = &getAnalysis<MachineBlockFrequencyInfo>(); |
223e47cc LB |
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 | ||
223e47cc LB |
461 | return Changed; |
462 | } |