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 #define DEBUG_TYPE "stackcoloring"
15 #include "llvm/Function.h"
16 #include "llvm/Module.h"
17 #include "llvm/CodeGen/Passes.h"
18 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
19 #include "llvm/CodeGen/LiveStackAnalysis.h"
20 #include "llvm/CodeGen/MachineFrameInfo.h"
21 #include "llvm/CodeGen/MachineInstrBuilder.h"
22 #include "llvm/CodeGen/MachineLoopInfo.h"
23 #include "llvm/CodeGen/MachineMemOperand.h"
24 #include "llvm/CodeGen/MachineRegisterInfo.h"
25 #include "llvm/CodeGen/PseudoSourceValue.h"
26 #include "llvm/Support/CommandLine.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Target/TargetInstrInfo.h"
29 #include "llvm/Target/TargetMachine.h"
30 #include "llvm/ADT/BitVector.h"
31 #include "llvm/ADT/SmallSet.h"
32 #include "llvm/ADT/SmallVector.h"
33 #include "llvm/ADT/Statistic.h"
34 #include <vector>
35 using namespace llvm;
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 bool ColorWithRegs;
50 LiveStacks* LS;
51 MachineFrameInfo *MFI;
52 const TargetInstrInfo *TII;
53 const MachineLoopInfo *loopInfo;
54
55 // SSIntervals - Spill slot intervals.
56 std::vector<LiveInterval*> SSIntervals;
57
58 // SSRefs - Keep a list of frame index references for each spill slot.
59 SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
60
61 // OrigAlignments - Alignments of stack objects before coloring.
62 SmallVector<unsigned, 16> OrigAlignments;
63
64 // OrigSizes - Sizess of stack objects before coloring.
65 SmallVector<unsigned, 16> OrigSizes;
66
67 // AllColors - If index is set, it's a spill slot, i.e. color.
68 // FIXME: This assumes PEI locate spill slot with smaller indices
69 // closest to stack pointer / frame pointer. Therefore, smaller
70 // index == better color.
71 BitVector AllColors;
72
73 // NextColor - Next "color" that's not yet used.
74 int NextColor;
75
76 // UsedColors - "Colors" that have been assigned.
77 BitVector UsedColors;
78
79 // Assignments - Color to intervals mapping.
80 SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
81
82 public:
83 static char ID; // Pass identification
StackSlotColoring()84 StackSlotColoring() :
85 MachineFunctionPass(ID), ColorWithRegs(false), NextColor(-1) {
86 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
87 }
88
getAnalysisUsage(AnalysisUsage & AU) const89 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
90 AU.setPreservesCFG();
91 AU.addRequired<SlotIndexes>();
92 AU.addPreserved<SlotIndexes>();
93 AU.addRequired<LiveStacks>();
94 AU.addRequired<MachineLoopInfo>();
95 AU.addPreserved<MachineLoopInfo>();
96 AU.addPreservedID(MachineDominatorsID);
97 MachineFunctionPass::getAnalysisUsage(AU);
98 }
99
100 virtual bool runOnMachineFunction(MachineFunction &MF);
101
102 private:
103 void InitializeSlots();
104 void ScanForSpillSlotRefs(MachineFunction &MF);
105 bool OverlapWithAssignments(LiveInterval *li, int Color) const;
106 int ColorSlot(LiveInterval *li);
107 bool ColorSlots(MachineFunction &MF);
108 void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
109 MachineFunction &MF);
110 bool RemoveDeadStores(MachineBasicBlock* MBB);
111 };
112 } // end anonymous namespace
113
114 char StackSlotColoring::ID = 0;
115 char &llvm::StackSlotColoringID = StackSlotColoring::ID;
116
117 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
118 "Stack Slot Coloring", false, false)
119 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
120 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
121 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
122 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
123 "Stack Slot Coloring", false, false)
124
125 namespace {
126 // IntervalSorter - Comparison predicate that sort live intervals by
127 // their weight.
128 struct IntervalSorter {
operator ()__anonf227be4f0211::IntervalSorter129 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
130 return LHS->weight > RHS->weight;
131 }
132 };
133 }
134
135 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
136 /// references and update spill slot weights.
ScanForSpillSlotRefs(MachineFunction & MF)137 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
138 SSRefs.resize(MFI->getObjectIndexEnd());
139
140 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
141 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
142 MBBI != E; ++MBBI) {
143 MachineBasicBlock *MBB = &*MBBI;
144 unsigned loopDepth = loopInfo->getLoopDepth(MBB);
145 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
146 MII != EE; ++MII) {
147 MachineInstr *MI = &*MII;
148 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
149 MachineOperand &MO = MI->getOperand(i);
150 if (!MO.isFI())
151 continue;
152 int FI = MO.getIndex();
153 if (FI < 0)
154 continue;
155 if (!LS->hasInterval(FI))
156 continue;
157 LiveInterval &li = LS->getInterval(FI);
158 if (!MI->isDebugValue())
159 li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
160 SSRefs[FI].push_back(MI);
161 }
162 }
163 }
164 }
165
166 /// InitializeSlots - Process all spill stack slot liveintervals and add them
167 /// to a sorted (by weight) list.
InitializeSlots()168 void StackSlotColoring::InitializeSlots() {
169 int LastFI = MFI->getObjectIndexEnd();
170 OrigAlignments.resize(LastFI);
171 OrigSizes.resize(LastFI);
172 AllColors.resize(LastFI);
173 UsedColors.resize(LastFI);
174 Assignments.resize(LastFI);
175
176 // Gather all spill slots into a list.
177 DEBUG(dbgs() << "Spill slot intervals:\n");
178 for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
179 LiveInterval &li = i->second;
180 DEBUG(li.dump());
181 int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
182 if (MFI->isDeadObjectIndex(FI))
183 continue;
184 SSIntervals.push_back(&li);
185 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
186 OrigSizes[FI] = MFI->getObjectSize(FI);
187 AllColors.set(FI);
188 }
189 DEBUG(dbgs() << '\n');
190
191 // Sort them by weight.
192 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
193
194 // Get first "color".
195 NextColor = AllColors.find_first();
196 }
197
198 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
199 /// LiveIntervals that have already been assigned to the specified color.
200 bool
OverlapWithAssignments(LiveInterval * li,int Color) const201 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
202 const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
203 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
204 LiveInterval *OtherLI = OtherLIs[i];
205 if (OtherLI->overlaps(*li))
206 return true;
207 }
208 return false;
209 }
210
211 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
212 ///
ColorSlot(LiveInterval * li)213 int StackSlotColoring::ColorSlot(LiveInterval *li) {
214 int Color = -1;
215 bool Share = false;
216 if (!DisableSharing) {
217 // Check if it's possible to reuse any of the used colors.
218 Color = UsedColors.find_first();
219 while (Color != -1) {
220 if (!OverlapWithAssignments(li, Color)) {
221 Share = true;
222 ++NumEliminated;
223 break;
224 }
225 Color = UsedColors.find_next(Color);
226 }
227 }
228
229 // Assign it to the first available color (assumed to be the best) if it's
230 // not possible to share a used color with other objects.
231 if (!Share) {
232 assert(NextColor != -1 && "No more spill slots?");
233 Color = NextColor;
234 UsedColors.set(Color);
235 NextColor = AllColors.find_next(NextColor);
236 }
237
238 // Record the assignment.
239 Assignments[Color].push_back(li);
240 int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
241 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
242
243 // Change size and alignment of the allocated slot. If there are multiple
244 // objects sharing the same slot, then make sure the size and alignment
245 // are large enough for all.
246 unsigned Align = OrigAlignments[FI];
247 if (!Share || Align > MFI->getObjectAlignment(Color))
248 MFI->setObjectAlignment(Color, Align);
249 int64_t Size = OrigSizes[FI];
250 if (!Share || Size > MFI->getObjectSize(Color))
251 MFI->setObjectSize(Color, Size);
252 return Color;
253 }
254
255 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
256 /// operands in the function.
ColorSlots(MachineFunction & MF)257 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
258 unsigned NumObjs = MFI->getObjectIndexEnd();
259 SmallVector<int, 16> SlotMapping(NumObjs, -1);
260 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
261 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
262 BitVector UsedColors(NumObjs);
263
264 DEBUG(dbgs() << "Color spill slot intervals:\n");
265 bool Changed = false;
266 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
267 LiveInterval *li = SSIntervals[i];
268 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
269 int NewSS = ColorSlot(li);
270 assert(NewSS >= 0 && "Stack coloring failed?");
271 SlotMapping[SS] = NewSS;
272 RevMap[NewSS].push_back(SS);
273 SlotWeights[NewSS] += li->weight;
274 UsedColors.set(NewSS);
275 Changed |= (SS != NewSS);
276 }
277
278 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
279 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
280 LiveInterval *li = SSIntervals[i];
281 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
282 li->weight = SlotWeights[SS];
283 }
284 // Sort them by new weight.
285 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
286
287 #ifndef NDEBUG
288 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
289 DEBUG(SSIntervals[i]->dump());
290 DEBUG(dbgs() << '\n');
291 #endif
292
293 if (!Changed)
294 return false;
295
296 // Rewrite all MO_FrameIndex operands.
297 SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
298 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
299 int NewFI = SlotMapping[SS];
300 if (NewFI == -1 || (NewFI == (int)SS))
301 continue;
302
303 SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
304 for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
305 RewriteInstruction(RefMIs[i], SS, NewFI, MF);
306 }
307
308 // Delete unused stack slots.
309 while (NextColor != -1) {
310 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
311 MFI->RemoveStackObject(NextColor);
312 NextColor = AllColors.find_next(NextColor);
313 }
314
315 return true;
316 }
317
318 /// RewriteInstruction - Rewrite specified instruction by replacing references
319 /// to old frame index with new one.
RewriteInstruction(MachineInstr * MI,int OldFI,int NewFI,MachineFunction & MF)320 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
321 int NewFI, MachineFunction &MF) {
322 // Update the operands.
323 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
324 MachineOperand &MO = MI->getOperand(i);
325 if (!MO.isFI())
326 continue;
327 int FI = MO.getIndex();
328 if (FI != OldFI)
329 continue;
330 MO.setIndex(NewFI);
331 }
332
333 // Update the memory references. This changes the MachineMemOperands
334 // directly. They may be in use by multiple instructions, however all
335 // instructions using OldFI are being rewritten to use NewFI.
336 const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
337 const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
338 for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
339 E = MI->memoperands_end(); I != E; ++I)
340 if ((*I)->getValue() == OldSV)
341 (*I)->setValue(NewSV);
342 }
343
344
345 /// RemoveDeadStores - Scan through a basic block and look for loads followed
346 /// by stores. If they're both using the same stack slot, then the store is
347 /// definitely dead. This could obviously be much more aggressive (consider
348 /// pairs with instructions between them), but such extensions might have a
349 /// considerable compile time impact.
RemoveDeadStores(MachineBasicBlock * MBB)350 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
351 // FIXME: This could be much more aggressive, but we need to investigate
352 // the compile time impact of doing so.
353 bool changed = false;
354
355 SmallVector<MachineInstr*, 4> toErase;
356
357 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
358 I != E; ++I) {
359 if (DCELimit != -1 && (int)NumDead >= DCELimit)
360 break;
361
362 MachineBasicBlock::iterator NextMI = llvm::next(I);
363 if (NextMI == MBB->end()) continue;
364
365 int FirstSS, SecondSS;
366 unsigned LoadReg = 0;
367 unsigned StoreReg = 0;
368 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
369 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
370 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
371
372 ++NumDead;
373 changed = true;
374
375 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
376 ++NumDead;
377 toErase.push_back(I);
378 }
379
380 toErase.push_back(NextMI);
381 ++I;
382 }
383
384 for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
385 E = toErase.end(); I != E; ++I)
386 (*I)->eraseFromParent();
387
388 return changed;
389 }
390
391
runOnMachineFunction(MachineFunction & MF)392 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
393 DEBUG({
394 dbgs() << "********** Stack Slot Coloring **********\n"
395 << "********** Function: "
396 << MF.getFunction()->getName() << '\n';
397 });
398
399 MFI = MF.getFrameInfo();
400 TII = MF.getTarget().getInstrInfo();
401 LS = &getAnalysis<LiveStacks>();
402 loopInfo = &getAnalysis<MachineLoopInfo>();
403
404 bool Changed = false;
405
406 unsigned NumSlots = LS->getNumIntervals();
407 if (NumSlots == 0)
408 // Nothing to do!
409 return false;
410
411 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
412 // coloring. The stack could be modified before the longjmp is executed,
413 // resulting in the wrong value being used afterwards. (See
414 // <rdar://problem/8007500>.)
415 if (MF.exposesReturnsTwice())
416 return false;
417
418 // Gather spill slot references
419 ScanForSpillSlotRefs(MF);
420 InitializeSlots();
421 Changed = ColorSlots(MF);
422
423 NextColor = -1;
424 SSIntervals.clear();
425 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
426 SSRefs[i].clear();
427 SSRefs.clear();
428 OrigAlignments.clear();
429 OrigSizes.clear();
430 AllColors.clear();
431 UsedColors.clear();
432 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
433 Assignments[i].clear();
434 Assignments.clear();
435
436 if (Changed) {
437 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
438 Changed |= RemoveDeadStores(I);
439 }
440
441 return Changed;
442 }
443