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/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"
38 DisableSharing("no-stack-slot-sharing",
39 cl::init(false), cl::Hidden,
40 cl::desc("Suppress slot sharing during stack coloring"));
43 ColorWithRegsOpt("color-ss-with-regs",
44 cl::init(false), cl::Hidden,
45 cl::desc("Color stack slots with free registers"));
48 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
50 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
51 STATISTIC(NumRegRepl, "Number of stack slot refs replaced with reg refs");
52 STATISTIC(NumLoadElim, "Number of loads eliminated");
53 STATISTIC(NumStoreElim, "Number of stores eliminated");
54 STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
57 class StackSlotColoring : public MachineFunctionPass {
61 MachineFrameInfo *MFI;
62 MachineRegisterInfo *MRI;
63 const TargetInstrInfo *TII;
64 const TargetRegisterInfo *TRI;
65 const MachineLoopInfo *loopInfo;
67 // SSIntervals - Spill slot intervals.
68 std::vector<LiveInterval*> SSIntervals;
70 // SSRefs - Keep a list of frame index references for each spill slot.
71 SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
73 // OrigAlignments - Alignments of stack objects before coloring.
74 SmallVector<unsigned, 16> OrigAlignments;
76 // OrigSizes - Sizess of stack objects before coloring.
77 SmallVector<unsigned, 16> OrigSizes;
79 // AllColors - If index is set, it's a spill slot, i.e. color.
80 // FIXME: This assumes PEI locate spill slot with smaller indices
81 // closest to stack pointer / frame pointer. Therefore, smaller
82 // index == better color.
85 // NextColor - Next "color" that's not yet used.
88 // UsedColors - "Colors" that have been assigned.
91 // Assignments - Color to intervals mapping.
92 SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
95 static char ID; // Pass identification
97 MachineFunctionPass(&ID), ColorWithRegs(false), NextColor(-1) {}
98 StackSlotColoring(bool RegColor) :
99 MachineFunctionPass(&ID), ColorWithRegs(RegColor), NextColor(-1) {}
101 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
102 AU.setPreservesCFG();
103 AU.addRequired<SlotIndexes>();
104 AU.addPreserved<SlotIndexes>();
105 AU.addRequired<LiveStacks>();
106 AU.addRequired<VirtRegMap>();
107 AU.addPreserved<VirtRegMap>();
108 AU.addRequired<MachineLoopInfo>();
109 AU.addPreserved<MachineLoopInfo>();
110 AU.addPreservedID(MachineDominatorsID);
111 MachineFunctionPass::getAnalysisUsage(AU);
114 virtual bool runOnMachineFunction(MachineFunction &MF);
115 virtual const char* getPassName() const {
116 return "Stack Slot Coloring";
120 void InitializeSlots();
121 bool CheckForSetJmpCall(const MachineFunction &MF);
122 void ScanForSpillSlotRefs(MachineFunction &MF);
123 bool OverlapWithAssignments(LiveInterval *li, int Color) const;
124 int ColorSlot(LiveInterval *li);
125 bool ColorSlots(MachineFunction &MF);
126 bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
127 SmallVector<SmallVector<int, 4>, 16> &RevMap,
128 BitVector &SlotIsReg);
129 void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
130 MachineFunction &MF);
131 bool PropagateBackward(MachineBasicBlock::iterator MII,
132 MachineBasicBlock *MBB,
133 unsigned OldReg, unsigned NewReg);
134 bool PropagateForward(MachineBasicBlock::iterator MII,
135 MachineBasicBlock *MBB,
136 unsigned OldReg, unsigned NewReg);
137 void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
138 unsigned Reg, const TargetRegisterClass *RC,
139 SmallSet<unsigned, 4> &Defs,
140 MachineFunction &MF);
141 bool AllMemRefsCanBeUnfolded(int SS);
142 bool RemoveDeadStores(MachineBasicBlock* MBB);
144 } // end anonymous namespace
146 char StackSlotColoring::ID = 0;
148 static RegisterPass<StackSlotColoring>
149 X("stack-slot-coloring", "Stack Slot Coloring");
151 FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
152 return new StackSlotColoring(RegColor);
156 // IntervalSorter - Comparison predicate that sort live intervals by
158 struct IntervalSorter {
159 bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
160 return LHS->weight > RHS->weight;
165 /// CheckForSetJmpCall - Return true if there's a call to setjmp/sigsetjmp in
167 bool StackSlotColoring::CheckForSetJmpCall(const MachineFunction &MF) {
168 const Function *F = MF.getFunction();
169 const Module *M = F->getParent();
170 const Function *SetJmp = M->getFunction("setjmp");
171 const Function *SigSetJmp = M->getFunction("sigsetjmp");
173 if (!SetJmp && !SigSetJmp)
176 if (SetJmp && !SetJmp->use_empty())
177 for (Value::const_use_iterator
178 I = SetJmp->use_begin(), E = SetJmp->use_end(); I != E; ++I)
179 if (const CallInst *CI = dyn_cast<CallInst>(I))
180 if (CI->getParent()->getParent() == F)
183 if (SigSetJmp && !SigSetJmp->use_empty())
184 for (Value::const_use_iterator
185 I = SigSetJmp->use_begin(), E = SigSetJmp->use_end(); I != E; ++I)
186 if (const CallInst *CI = dyn_cast<CallInst>(I))
187 if (CI->getParent()->getParent() == F)
193 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
194 /// references and update spill slot weights.
195 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
196 SSRefs.resize(MFI->getObjectIndexEnd());
198 // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
199 for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
201 MachineBasicBlock *MBB = &*MBBI;
202 unsigned loopDepth = loopInfo->getLoopDepth(MBB);
203 for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
205 MachineInstr *MI = &*MII;
206 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
207 MachineOperand &MO = MI->getOperand(i);
210 int FI = MO.getIndex();
213 if (!LS->hasInterval(FI))
215 LiveInterval &li = LS->getInterval(FI);
216 if (!MI->isDebugValue())
217 li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
218 SSRefs[FI].push_back(MI);
224 /// InitializeSlots - Process all spill stack slot liveintervals and add them
225 /// to a sorted (by weight) list.
226 void StackSlotColoring::InitializeSlots() {
227 int LastFI = MFI->getObjectIndexEnd();
228 OrigAlignments.resize(LastFI);
229 OrigSizes.resize(LastFI);
230 AllColors.resize(LastFI);
231 UsedColors.resize(LastFI);
232 Assignments.resize(LastFI);
234 // Gather all spill slots into a list.
235 DEBUG(dbgs() << "Spill slot intervals:\n");
236 for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
237 LiveInterval &li = i->second;
239 int FI = li.getStackSlotIndex();
240 if (MFI->isDeadObjectIndex(FI))
242 SSIntervals.push_back(&li);
243 OrigAlignments[FI] = MFI->getObjectAlignment(FI);
244 OrigSizes[FI] = MFI->getObjectSize(FI);
247 DEBUG(dbgs() << '\n');
249 // Sort them by weight.
250 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
252 // Get first "color".
253 NextColor = AllColors.find_first();
256 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
257 /// LiveIntervals that have already been assigned to the specified color.
259 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
260 const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
261 for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
262 LiveInterval *OtherLI = OtherLIs[i];
263 if (OtherLI->overlaps(*li))
269 /// ColorSlotsWithFreeRegs - If there are any free registers available, try
270 /// replacing spill slots references with registers instead.
272 StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
273 SmallVector<SmallVector<int, 4>, 16> &RevMap,
274 BitVector &SlotIsReg) {
275 if (!(ColorWithRegs || ColorWithRegsOpt) || !VRM->HasUnusedRegisters())
278 bool Changed = false;
279 DEBUG(dbgs() << "Assigning unused registers to spill slots:\n");
280 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
281 LiveInterval *li = SSIntervals[i];
282 int SS = li->getStackSlotIndex();
283 if (!UsedColors[SS] || li->weight < 20)
284 // If the weight is < 20, i.e. two references in a loop with depth 1,
285 // don't bother with it.
288 // These slots allow to share the same registers.
289 bool AllColored = true;
290 SmallVector<unsigned, 4> ColoredRegs;
291 for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
292 int RSS = RevMap[SS][j];
293 const TargetRegisterClass *RC = LS->getIntervalRegClass(RSS);
294 // If it's not colored to another stack slot, try coloring it
295 // to a "free" register.
300 unsigned Reg = VRM->getFirstUnusedRegister(RC);
305 if (!AllMemRefsCanBeUnfolded(RSS)) {
309 DEBUG(dbgs() << "Assigning fi#" << RSS << " to "
310 << TRI->getName(Reg) << '\n');
311 ColoredRegs.push_back(Reg);
312 SlotMapping[RSS] = Reg;
318 // Register and its sub-registers are no longer free.
319 while (!ColoredRegs.empty()) {
320 unsigned Reg = ColoredRegs.back();
321 ColoredRegs.pop_back();
322 VRM->setRegisterUsed(Reg);
323 // If reg is a callee-saved register, it will have to be spilled in
325 MRI->setPhysRegUsed(Reg);
326 for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
327 VRM->setRegisterUsed(*AS);
328 MRI->setPhysRegUsed(*AS);
331 // This spill slot is dead after the rewrites
333 MFI->RemoveStackObject(SS);
337 DEBUG(dbgs() << '\n');
342 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
344 int StackSlotColoring::ColorSlot(LiveInterval *li) {
347 if (!DisableSharing) {
348 // Check if it's possible to reuse any of the used colors.
349 Color = UsedColors.find_first();
350 while (Color != -1) {
351 if (!OverlapWithAssignments(li, Color)) {
356 Color = UsedColors.find_next(Color);
360 // Assign it to the first available color (assumed to be the best) if it's
361 // not possible to share a used color with other objects.
363 assert(NextColor != -1 && "No more spill slots?");
365 UsedColors.set(Color);
366 NextColor = AllColors.find_next(NextColor);
369 // Record the assignment.
370 Assignments[Color].push_back(li);
371 int FI = li->getStackSlotIndex();
372 DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
374 // Change size and alignment of the allocated slot. If there are multiple
375 // objects sharing the same slot, then make sure the size and alignment
376 // are large enough for all.
377 unsigned Align = OrigAlignments[FI];
378 if (!Share || Align > MFI->getObjectAlignment(Color))
379 MFI->setObjectAlignment(Color, Align);
380 int64_t Size = OrigSizes[FI];
381 if (!Share || Size > MFI->getObjectSize(Color))
382 MFI->setObjectSize(Color, Size);
386 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
387 /// operands in the function.
388 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
389 unsigned NumObjs = MFI->getObjectIndexEnd();
390 SmallVector<int, 16> SlotMapping(NumObjs, -1);
391 SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
392 SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
393 BitVector SlotIsReg(NumObjs);
394 BitVector UsedColors(NumObjs);
396 DEBUG(dbgs() << "Color spill slot intervals:\n");
397 bool Changed = false;
398 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
399 LiveInterval *li = SSIntervals[i];
400 int SS = li->getStackSlotIndex();
401 int NewSS = ColorSlot(li);
402 assert(NewSS >= 0 && "Stack coloring failed?");
403 SlotMapping[SS] = NewSS;
404 RevMap[NewSS].push_back(SS);
405 SlotWeights[NewSS] += li->weight;
406 UsedColors.set(NewSS);
407 Changed |= (SS != NewSS);
410 DEBUG(dbgs() << "\nSpill slots after coloring:\n");
411 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
412 LiveInterval *li = SSIntervals[i];
413 int SS = li->getStackSlotIndex();
414 li->weight = SlotWeights[SS];
416 // Sort them by new weight.
417 std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
420 for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
421 DEBUG(SSIntervals[i]->dump());
422 DEBUG(dbgs() << '\n');
425 // Can we "color" a stack slot with a unused register?
426 Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
431 // Rewrite all MO_FrameIndex operands.
432 SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
433 for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
434 bool isReg = SlotIsReg[SS];
435 int NewFI = SlotMapping[SS];
436 if (NewFI == -1 || (NewFI == (int)SS && !isReg))
439 const TargetRegisterClass *RC = LS->getIntervalRegClass(SS);
440 SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
441 for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
443 RewriteInstruction(RefMIs[i], SS, NewFI, MF);
445 // Rewrite to use a register instead.
446 unsigned MBBId = RefMIs[i]->getParent()->getNumber();
447 SmallSet<unsigned, 4> &Defs = NewDefs[MBBId];
448 UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, RC, Defs, MF);
452 // Delete unused stack slots.
453 while (NextColor != -1) {
454 DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
455 MFI->RemoveStackObject(NextColor);
456 NextColor = AllColors.find_next(NextColor);
462 /// AllMemRefsCanBeUnfolded - Return true if all references of the specified
463 /// spill slot index can be unfolded.
464 bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
465 SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
466 for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
467 MachineInstr *MI = RefMIs[i];
468 if (TII->isLoadFromStackSlot(MI, SS) ||
469 TII->isStoreToStackSlot(MI, SS))
470 // Restore and spill will become copies.
472 if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
474 for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
475 MachineOperand &MO = MI->getOperand(j);
476 if (MO.isFI() && MO.getIndex() != SS)
477 // If it uses another frameindex, we can, currently* unfold it.
484 /// RewriteInstruction - Rewrite specified instruction by replacing references
485 /// to old frame index with new one.
486 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
487 int NewFI, MachineFunction &MF) {
488 // Update the operands.
489 for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
490 MachineOperand &MO = MI->getOperand(i);
493 int FI = MO.getIndex();
499 // Update the memory references. This changes the MachineMemOperands
500 // directly. They may be in use by multiple instructions, however all
501 // instructions using OldFI are being rewritten to use NewFI.
502 const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
503 const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
504 for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
505 E = MI->memoperands_end(); I != E; ++I)
506 if ((*I)->getValue() == OldSV)
507 (*I)->setValue(NewSV);
510 /// PropagateBackward - Traverse backward and look for the definition of
511 /// OldReg. If it can successfully update all of the references with NewReg,
512 /// do so and return true.
513 bool StackSlotColoring::PropagateBackward(MachineBasicBlock::iterator MII,
514 MachineBasicBlock *MBB,
515 unsigned OldReg, unsigned NewReg) {
516 if (MII == MBB->begin())
519 SmallVector<MachineOperand*, 4> Uses;
520 SmallVector<MachineOperand*, 4> Refs;
521 while (--MII != MBB->begin()) {
522 bool FoundDef = false; // Not counting 2address def.
525 const TargetInstrDesc &TID = MII->getDesc();
526 for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
527 MachineOperand &MO = MII->getOperand(i);
530 unsigned Reg = MO.getReg();
537 // Abort the use is actually a sub-register def. We don't have enough
538 // information to figure out if it is really legal.
539 if (MO.getSubReg() || MII->isExtractSubreg() ||
540 MII->isInsertSubreg() || MII->isSubregToReg())
543 const TargetRegisterClass *RC = TID.OpInfo[i].getRegClass(TRI);
544 if (RC && !RC->contains(NewReg))
551 if (!MII->isRegTiedToUseOperand(i))
554 } else if (TRI->regsOverlap(Reg, NewReg)) {
556 } else if (TRI->regsOverlap(Reg, OldReg)) {
557 if (!MO.isUse() || !MO.isKill())
563 // Found non-two-address def. Stop here.
564 for (unsigned i = 0, e = Refs.size(); i != e; ++i)
565 Refs[i]->setReg(NewReg);
569 // Two-address uses must be updated as well.
570 for (unsigned i = 0, e = Uses.size(); i != e; ++i)
571 Refs.push_back(Uses[i]);
576 /// PropagateForward - Traverse forward and look for the kill of OldReg. If
577 /// it can successfully update all of the uses with NewReg, do so and
579 bool StackSlotColoring::PropagateForward(MachineBasicBlock::iterator MII,
580 MachineBasicBlock *MBB,
581 unsigned OldReg, unsigned NewReg) {
582 if (MII == MBB->end())
585 SmallVector<MachineOperand*, 4> Uses;
586 while (++MII != MBB->end()) {
587 bool FoundKill = false;
588 const TargetInstrDesc &TID = MII->getDesc();
589 for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
590 MachineOperand &MO = MII->getOperand(i);
593 unsigned Reg = MO.getReg();
597 if (MO.isDef() || MO.isImplicit())
600 // Abort the use is actually a sub-register use. We don't have enough
601 // information to figure out if it is really legal.
602 if (MO.getSubReg() || MII->isExtractSubreg())
605 const TargetRegisterClass *RC = TID.OpInfo[i].getRegClass(TRI);
606 if (RC && !RC->contains(NewReg))
612 } else if (TRI->regsOverlap(Reg, NewReg) ||
613 TRI->regsOverlap(Reg, OldReg))
617 for (unsigned i = 0, e = Uses.size(); i != e; ++i)
618 Uses[i]->setReg(NewReg);
625 /// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
626 /// folded memory references and replacing those references with register
627 /// references instead.
629 StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
631 const TargetRegisterClass *RC,
632 SmallSet<unsigned, 4> &Defs,
633 MachineFunction &MF) {
634 MachineBasicBlock *MBB = MI->getParent();
635 if (unsigned DstReg = TII->isLoadFromStackSlot(MI, OldFI)) {
636 if (PropagateForward(MI, MBB, DstReg, Reg)) {
637 DEBUG(dbgs() << "Eliminated load: ");
641 TII->copyRegToReg(*MBB, MI, DstReg, Reg, RC, RC,
646 if (!Defs.count(Reg)) {
647 // If this is the first use of Reg in this MBB and it wasn't previously
648 // defined in MBB, add it to livein.
652 } else if (unsigned SrcReg = TII->isStoreToStackSlot(MI, OldFI)) {
653 if (MI->killsRegister(SrcReg) && PropagateBackward(MI, MBB, SrcReg, Reg)) {
654 DEBUG(dbgs() << "Eliminated store: ");
658 TII->copyRegToReg(*MBB, MI, Reg, SrcReg, RC, RC,
663 // Remember reg has been defined in MBB.
666 SmallVector<MachineInstr*, 4> NewMIs;
667 bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
668 Success = Success; // Silence compiler warning.
669 assert(Success && "Failed to unfold!");
670 MachineInstr *NewMI = NewMIs[0];
671 MBB->insert(MI, NewMI);
674 if (NewMI->readsRegister(Reg)) {
675 if (!Defs.count(Reg))
676 // If this is the first use of Reg in this MBB and it wasn't previously
677 // defined in MBB, add it to livein.
685 /// RemoveDeadStores - Scan through a basic block and look for loads followed
686 /// by stores. If they're both using the same stack slot, then the store is
687 /// definitely dead. This could obviously be much more aggressive (consider
688 /// pairs with instructions between them), but such extensions might have a
689 /// considerable compile time impact.
690 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
691 // FIXME: This could be much more aggressive, but we need to investigate
692 // the compile time impact of doing so.
693 bool changed = false;
695 SmallVector<MachineInstr*, 4> toErase;
697 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
699 if (DCELimit != -1 && (int)NumDead >= DCELimit)
702 MachineBasicBlock::iterator NextMI = llvm::next(I);
703 if (NextMI == MBB->end()) continue;
705 int FirstSS, SecondSS;
706 unsigned LoadReg = 0;
707 unsigned StoreReg = 0;
708 if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
709 if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
710 if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
715 if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
717 toErase.push_back(I);
720 toErase.push_back(NextMI);
724 for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
725 E = toErase.end(); I != E; ++I)
726 (*I)->eraseFromParent();
732 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
734 dbgs() << "********** Stack Slot Coloring **********\n"
735 << "********** Function: "
736 << MF.getFunction()->getName() << '\n';
739 MFI = MF.getFrameInfo();
740 MRI = &MF.getRegInfo();
741 TII = MF.getTarget().getInstrInfo();
742 TRI = MF.getTarget().getRegisterInfo();
743 LS = &getAnalysis<LiveStacks>();
744 VRM = &getAnalysis<VirtRegMap>();
745 loopInfo = &getAnalysis<MachineLoopInfo>();
747 bool Changed = false;
749 unsigned NumSlots = LS->getNumIntervals();
751 if (NumSlots == 0 || !VRM->HasUnusedRegisters())
756 // If there are calls to setjmp or sigsetjmp, don't perform stack slot
757 // coloring. The stack could be modified before the longjmp is executed,
758 // resulting in the wrong value being used afterwards. (See
759 // <rdar://problem/8007500>.)
761 // FIXME: This goes beyond the setjmp/sigsetjmp functions. Ideally, we should
762 // check for the GCC "returns twice" attribute.
763 if (CheckForSetJmpCall(MF))
766 // Gather spill slot references
767 ScanForSpillSlotRefs(MF);
769 Changed = ColorSlots(MF);
773 for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
776 OrigAlignments.clear();
780 for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
781 Assignments[i].clear();
785 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
786 Changed |= RemoveDeadStores(I);