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 "stackcoloring"
15 #include "VirtRegMap.h"
16 #include "llvm/Function.h"
17 #include "llvm/Module.h"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
20 #include "llvm/CodeGen/LiveStackAnalysis.h"
21 #include "llvm/CodeGen/MachineFrameInfo.h"
22 #include "llvm/CodeGen/MachineInstrBuilder.h"
23 #include "llvm/CodeGen/MachineLoopInfo.h"
24 #include "llvm/CodeGen/MachineMemOperand.h"
25 #include "llvm/CodeGen/MachineRegisterInfo.h"
26 #include "llvm/CodeGen/PseudoSourceValue.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Target/TargetInstrInfo.h"
30 #include "llvm/Target/TargetMachine.h"
31 #include "llvm/ADT/BitVector.h"
32 #include "llvm/ADT/SmallSet.h"
33 #include "llvm/ADT/SmallVector.h"
34 #include "llvm/ADT/Statistic.h"
39 DisableSharing("no-stack-slot-sharing",
40 cl::init(false), cl::Hidden,
41 cl::desc("Suppress slot sharing during stack coloring"));
43 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
45 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
46 STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
49 class StackSlotColoring : public MachineFunctionPass {
53 MachineFrameInfo *MFI;
54 MachineRegisterInfo *MRI;
55 const TargetInstrInfo *TII;
56 const TargetRegisterInfo *TRI;
57 const MachineLoopInfo *loopInfo;
59 // SSIntervals - Spill slot intervals.
60 std::vector<LiveInterval*> SSIntervals;
62 // SSRefs - Keep a list of frame index references for each spill slot.
63 SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
65 // OrigAlignments - Alignments of stack objects before coloring.
66 SmallVector<unsigned, 16> OrigAlignments;
68 // OrigSizes - Sizess of stack objects before coloring.
69 SmallVector<unsigned, 16> OrigSizes;
71 // AllColors - If index is set, it's a spill slot, i.e. color.
72 // FIXME: This assumes PEI locate spill slot with smaller indices
73 // closest to stack pointer / frame pointer. Therefore, smaller
74 // index == better color.
77 // NextColor - Next "color" that's not yet used.
80 // UsedColors - "Colors" that have been assigned.
83 // Assignments - Color to intervals mapping.
84 SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
87 static char ID; // Pass identification
89 MachineFunctionPass(ID), ColorWithRegs(false), NextColor(-1) {
90 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
92 StackSlotColoring(bool RegColor) :
93 MachineFunctionPass(ID), ColorWithRegs(RegColor), NextColor(-1) {
94 initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
97 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
99 AU.addRequired<SlotIndexes>();
100 AU.addPreserved<SlotIndexes>();
101 AU.addRequired<LiveStacks>();
102 AU.addRequired<VirtRegMap>();
103 AU.addPreserved<VirtRegMap>();
104 AU.addRequired<MachineLoopInfo>();
105 AU.addPreserved<MachineLoopInfo>();
106 AU.addPreservedID(MachineDominatorsID);
107 MachineFunctionPass::getAnalysisUsage(AU);
110 virtual bool runOnMachineFunction(MachineFunction &MF);
111 virtual const char* getPassName() const {
112 return "Stack Slot Coloring";
116 void InitializeSlots();
117 void ScanForSpillSlotRefs(MachineFunction &MF);
118 bool OverlapWithAssignments(LiveInterval *li, int Color) const;
119 int ColorSlot(LiveInterval *li);
120 bool ColorSlots(MachineFunction &MF);
121 void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
122 MachineFunction &MF);
123 bool RemoveDeadStores(MachineBasicBlock* MBB);
125 } // end anonymous namespace
127 char StackSlotColoring::ID = 0;
129 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
130 "Stack Slot Coloring", false, false)
131 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
132 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
133 INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
134 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
135 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
136 "Stack Slot Coloring", false, false)
138 FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
139 return new StackSlotColoring(RegColor);
143 // IntervalSorter - Comparison predicate that sort live intervals by
145 struct IntervalSorter {
146 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
147 return LHS->weight > RHS->weight;
152 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
153 /// references and update spill slot weights.
154 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
155 SSRefs.resize(MFI->getObjectIndexEnd());
157 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
158 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
160 MachineBasicBlock *MBB = &*MBBI;
161 unsigned loopDepth = loopInfo->getLoopDepth(MBB);
162 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
164 MachineInstr *MI = &*MII;
165 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
166 MachineOperand &MO = MI->getOperand(i);
169 int FI = MO.getIndex();
172 if (!LS->hasInterval(FI))
174 LiveInterval &li = LS->getInterval(FI);
175 if (!MI->isDebugValue())
176 li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
177 SSRefs[FI].push_back(MI);
183 /// InitializeSlots - Process all spill stack slot liveintervals and add them
184 /// to a sorted (by weight) list.
185 void StackSlotColoring::InitializeSlots() {
186 int LastFI = MFI->getObjectIndexEnd();
187 OrigAlignments.resize(LastFI);
188 OrigSizes.resize(LastFI);
189 AllColors.resize(LastFI);
190 UsedColors.resize(LastFI);
191 Assignments.resize(LastFI);
193 // Gather all spill slots into a list.
194 DEBUG(dbgs() << "Spill slot intervals:\n");
195 for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
196 LiveInterval &li = i->second;
198 int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
199 if (MFI->isDeadObjectIndex(FI))
201 SSIntervals.push_back(&li);
202 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
203 OrigSizes[FI] = MFI->getObjectSize(FI);
206 DEBUG(dbgs() << '\n');
208 // Sort them by weight.
209 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
211 // Get first "color".
212 NextColor = AllColors.find_first();
215 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
216 /// LiveIntervals that have already been assigned to the specified color.
218 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
219 const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
220 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
221 LiveInterval *OtherLI = OtherLIs[i];
222 if (OtherLI->overlaps(*li))
228 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
230 int StackSlotColoring::ColorSlot(LiveInterval *li) {
233 if (!DisableSharing) {
234 // Check if it's possible to reuse any of the used colors.
235 Color = UsedColors.find_first();
236 while (Color != -1) {
237 if (!OverlapWithAssignments(li, Color)) {
242 Color = UsedColors.find_next(Color);
246 // Assign it to the first available color (assumed to be the best) if it's
247 // not possible to share a used color with other objects.
249 assert(NextColor != -1 && "No more spill slots?");
251 UsedColors.set(Color);
252 NextColor = AllColors.find_next(NextColor);
255 // Record the assignment.
256 Assignments[Color].push_back(li);
257 int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
258 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
260 // Change size and alignment of the allocated slot. If there are multiple
261 // objects sharing the same slot, then make sure the size and alignment
262 // are large enough for all.
263 unsigned Align = OrigAlignments[FI];
264 if (!Share || Align > MFI->getObjectAlignment(Color))
265 MFI->setObjectAlignment(Color, Align);
266 int64_t Size = OrigSizes[FI];
267 if (!Share || Size > MFI->getObjectSize(Color))
268 MFI->setObjectSize(Color, Size);
272 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
273 /// operands in the function.
274 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
275 unsigned NumObjs = MFI->getObjectIndexEnd();
276 SmallVector<int, 16> SlotMapping(NumObjs, -1);
277 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
278 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
279 BitVector UsedColors(NumObjs);
281 DEBUG(dbgs() << "Color spill slot intervals:\n");
282 bool Changed = false;
283 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
284 LiveInterval *li = SSIntervals[i];
285 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
286 int NewSS = ColorSlot(li);
287 assert(NewSS >= 0 && "Stack coloring failed?");
288 SlotMapping[SS] = NewSS;
289 RevMap[NewSS].push_back(SS);
290 SlotWeights[NewSS] += li->weight;
291 UsedColors.set(NewSS);
292 Changed |= (SS != NewSS);
295 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
296 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
297 LiveInterval *li = SSIntervals[i];
298 int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
299 li->weight = SlotWeights[SS];
301 // Sort them by new weight.
302 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
305 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
306 DEBUG(SSIntervals[i]->dump());
307 DEBUG(dbgs() << '\n');
313 // Rewrite all MO_FrameIndex operands.
314 SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
315 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
316 int NewFI = SlotMapping[SS];
317 if (NewFI == -1 || (NewFI == (int)SS))
320 SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
321 for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
322 RewriteInstruction(RefMIs[i], SS, NewFI, MF);
325 // Delete unused stack slots.
326 while (NextColor != -1) {
327 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
328 MFI->RemoveStackObject(NextColor);
329 NextColor = AllColors.find_next(NextColor);
335 /// RewriteInstruction - Rewrite specified instruction by replacing references
336 /// to old frame index with new one.
337 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
338 int NewFI, MachineFunction &MF) {
339 // Update the operands.
340 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
341 MachineOperand &MO = MI->getOperand(i);
344 int FI = MO.getIndex();
350 // Update the memory references. This changes the MachineMemOperands
351 // directly. They may be in use by multiple instructions, however all
352 // instructions using OldFI are being rewritten to use NewFI.
353 const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
354 const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
355 for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
356 E = MI->memoperands_end(); I != E; ++I)
357 if ((*I)->getValue() == OldSV)
358 (*I)->setValue(NewSV);
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;
372 SmallVector<MachineInstr*, 4> toErase;
374 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
376 if (DCELimit != -1 && (int)NumDead >= DCELimit)
379 MachineBasicBlock::iterator NextMI = llvm::next(I);
380 if (NextMI == MBB->end()) continue;
382 int FirstSS, SecondSS;
383 unsigned LoadReg = 0;
384 unsigned StoreReg = 0;
385 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
386 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
387 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
392 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
394 toErase.push_back(I);
397 toErase.push_back(NextMI);
401 for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
402 E = toErase.end(); I != E; ++I)
403 (*I)->eraseFromParent();
409 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
411 dbgs() << "********** Stack Slot Coloring **********\n"
412 << "********** Function: "
413 << MF.getFunction()->getName() << '\n';
416 MFI = MF.getFrameInfo();
417 MRI = &MF.getRegInfo();
418 TII = MF.getTarget().getInstrInfo();
419 TRI = MF.getTarget().getRegisterInfo();
420 LS = &getAnalysis<LiveStacks>();
421 VRM = &getAnalysis<VirtRegMap>();
422 loopInfo = &getAnalysis<MachineLoopInfo>();
424 bool Changed = false;
426 unsigned NumSlots = LS->getNumIntervals();
428 if (NumSlots == 0 || !VRM->HasUnusedRegisters())
433 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
434 // coloring. The stack could be modified before the longjmp is executed,
435 // resulting in the wrong value being used afterwards. (See
436 // <rdar://problem/8007500>.)
437 if (MF.callsSetJmp())
440 // Gather spill slot references
441 ScanForSpillSlotRefs(MF);
443 Changed = ColorSlots(MF);
447 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
450 OrigAlignments.clear();
454 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
455 Assignments[i].clear();
459 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
460 Changed |= RemoveDeadStores(I);