StackSlotColoring.cpp [plain text]
#define DEBUG_TYPE "stackslotcoloring"
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include <vector>
using namespace llvm;
static cl::opt<bool>
DisableSharing("no-stack-slot-sharing",
cl::init(false), cl::Hidden,
cl::desc("Suppress slot sharing during stack coloring"));
static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
namespace {
class StackSlotColoring : public MachineFunctionPass {
LiveStacks* LS;
MachineFrameInfo *MFI;
const TargetInstrInfo *TII;
const MachineLoopInfo *loopInfo;
std::vector<LiveInterval*> SSIntervals;
SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
SmallVector<unsigned, 16> OrigAlignments;
SmallVector<unsigned, 16> OrigSizes;
BitVector AllColors;
int NextColor;
BitVector UsedColors;
SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
public:
static char ID; StackSlotColoring() :
MachineFunctionPass(ID), NextColor(-1) {
initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<LiveStacks>();
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
private:
void InitializeSlots();
void ScanForSpillSlotRefs(MachineFunction &MF);
bool OverlapWithAssignments(LiveInterval *li, int Color) const;
int ColorSlot(LiveInterval *li);
bool ColorSlots(MachineFunction &MF);
void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
MachineFunction &MF);
bool RemoveDeadStores(MachineBasicBlock* MBB);
};
}
char StackSlotColoring::ID = 0;
char &llvm::StackSlotColoringID = StackSlotColoring::ID;
INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
"Stack Slot Coloring", false, false)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(LiveStacks)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
"Stack Slot Coloring", false, false)
namespace {
struct IntervalSorter {
bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
return LHS->weight > RHS->weight;
}
};
}
void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
SSRefs.resize(MFI->getObjectIndexEnd());
for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
MBBI != E; ++MBBI) {
MachineBasicBlock *MBB = &*MBBI;
unsigned loopDepth = loopInfo->getLoopDepth(MBB);
for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
MII != EE; ++MII) {
MachineInstr *MI = &*MII;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isFI())
continue;
int FI = MO.getIndex();
if (FI < 0)
continue;
if (!LS->hasInterval(FI))
continue;
LiveInterval &li = LS->getInterval(FI);
if (!MI->isDebugValue())
li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
SSRefs[FI].push_back(MI);
}
}
}
}
void StackSlotColoring::InitializeSlots() {
int LastFI = MFI->getObjectIndexEnd();
OrigAlignments.resize(LastFI);
OrigSizes.resize(LastFI);
AllColors.resize(LastFI);
UsedColors.resize(LastFI);
Assignments.resize(LastFI);
DEBUG(dbgs() << "Spill slot intervals:\n");
for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
LiveInterval &li = i->second;
DEBUG(li.dump());
int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
if (MFI->isDeadObjectIndex(FI))
continue;
SSIntervals.push_back(&li);
OrigAlignments[FI] = MFI->getObjectAlignment(FI);
OrigSizes[FI] = MFI->getObjectSize(FI);
AllColors.set(FI);
}
DEBUG(dbgs() << '\n');
std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
NextColor = AllColors.find_first();
}
bool
StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
LiveInterval *OtherLI = OtherLIs[i];
if (OtherLI->overlaps(*li))
return true;
}
return false;
}
int StackSlotColoring::ColorSlot(LiveInterval *li) {
int Color = -1;
bool Share = false;
if (!DisableSharing) {
Color = UsedColors.find_first();
while (Color != -1) {
if (!OverlapWithAssignments(li, Color)) {
Share = true;
++NumEliminated;
break;
}
Color = UsedColors.find_next(Color);
}
}
if (!Share) {
assert(NextColor != -1 && "No more spill slots?");
Color = NextColor;
UsedColors.set(Color);
NextColor = AllColors.find_next(NextColor);
}
Assignments[Color].push_back(li);
int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
unsigned Align = OrigAlignments[FI];
if (!Share || Align > MFI->getObjectAlignment(Color))
MFI->setObjectAlignment(Color, Align);
int64_t Size = OrigSizes[FI];
if (!Share || Size > MFI->getObjectSize(Color))
MFI->setObjectSize(Color, Size);
return Color;
}
bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
unsigned NumObjs = MFI->getObjectIndexEnd();
SmallVector<int, 16> SlotMapping(NumObjs, -1);
SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
BitVector UsedColors(NumObjs);
DEBUG(dbgs() << "Color spill slot intervals:\n");
bool Changed = false;
for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
LiveInterval *li = SSIntervals[i];
int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
int NewSS = ColorSlot(li);
assert(NewSS >= 0 && "Stack coloring failed?");
SlotMapping[SS] = NewSS;
RevMap[NewSS].push_back(SS);
SlotWeights[NewSS] += li->weight;
UsedColors.set(NewSS);
Changed |= (SS != NewSS);
}
DEBUG(dbgs() << "\nSpill slots after coloring:\n");
for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
LiveInterval *li = SSIntervals[i];
int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
li->weight = SlotWeights[SS];
}
std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
#ifndef NDEBUG
for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
DEBUG(SSIntervals[i]->dump());
DEBUG(dbgs() << '\n');
#endif
if (!Changed)
return false;
SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
int NewFI = SlotMapping[SS];
if (NewFI == -1 || (NewFI == (int)SS))
continue;
SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
RewriteInstruction(RefMIs[i], SS, NewFI, MF);
}
while (NextColor != -1) {
DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
MFI->RemoveStackObject(NextColor);
NextColor = AllColors.find_next(NextColor);
}
return true;
}
void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
int NewFI, MachineFunction &MF) {
for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isFI())
continue;
int FI = MO.getIndex();
if (FI != OldFI)
continue;
MO.setIndex(NewFI);
}
const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
E = MI->memoperands_end(); I != E; ++I)
if ((*I)->getValue() == OldSV)
(*I)->setValue(NewSV);
}
bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
bool changed = false;
SmallVector<MachineInstr*, 4> toErase;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
if (DCELimit != -1 && (int)NumDead >= DCELimit)
break;
MachineBasicBlock::iterator NextMI = llvm::next(I);
if (NextMI == MBB->end()) continue;
int FirstSS, SecondSS;
unsigned LoadReg = 0;
unsigned StoreReg = 0;
if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
++NumDead;
changed = true;
if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
++NumDead;
toErase.push_back(I);
}
toErase.push_back(NextMI);
++I;
}
for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
E = toErase.end(); I != E; ++I)
(*I)->eraseFromParent();
return changed;
}
bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
DEBUG({
dbgs() << "********** Stack Slot Coloring **********\n"
<< "********** Function: " << MF.getName() << '\n';
});
MFI = MF.getFrameInfo();
TII = MF.getTarget().getInstrInfo();
LS = &getAnalysis<LiveStacks>();
loopInfo = &getAnalysis<MachineLoopInfo>();
bool Changed = false;
unsigned NumSlots = LS->getNumIntervals();
if (NumSlots == 0)
return false;
if (MF.exposesReturnsTwice())
return false;
ScanForSpillSlotRefs(MF);
InitializeSlots();
Changed = ColorSlots(MF);
NextColor = -1;
SSIntervals.clear();
for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
SSRefs[i].clear();
SSRefs.clear();
OrigAlignments.clear();
OrigSizes.clear();
AllColors.clear();
UsedColors.clear();
for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
Assignments[i].clear();
Assignments.clear();
if (Changed) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
Changed |= RemoveDeadStores(I);
}
return Changed;
}