//===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the stack slot coloring pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.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/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "stackslotcoloring"
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 MachineBlockFrequencyInfo *MBFI;
// SSIntervals - Spill slot intervals.
std::vector<LiveInterval*> SSIntervals;
// SSRefs - Keep a list of MachineMemOperands for each spill slot.
// MachineMemOperands can be shared between instructions, so we need
// to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not
// become FI0 -> FI1 -> FI2.
SmallVector<SmallVector<MachineMemOperand *, 8>, 16> SSRefs;
// OrigAlignments - Alignments of stack objects before coloring.
SmallVector<unsigned, 16> OrigAlignments;
// OrigSizes - Sizess of stack objects before coloring.
SmallVector<unsigned, 16> OrigSizes;
// AllColors - If index is set, it's a spill slot, i.e. color.
// FIXME: This assumes PEI locate spill slot with smaller indices
// closest to stack pointer / frame pointer. Therefore, smaller
// index == better color.
BitVector AllColors;
// NextColor - Next "color" that's not yet used.
int NextColor;
// UsedColors - "Colors" that have been assigned.
BitVector UsedColors;
// Assignments - Color to intervals mapping.
SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
public:
static char ID; // Pass identification
StackSlotColoring() :
MachineFunctionPass(ID), NextColor(-1) {
initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<LiveStacks>();
AU.addRequired<MachineBlockFrequencyInfo>();
AU.addPreserved<MachineBlockFrequencyInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
bool runOnMachineFunction(MachineFunction &MF) override;
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, SmallVectorImpl<int> &SlotMapping,
MachineFunction &MF);
bool RemoveDeadStores(MachineBasicBlock* MBB);
};
} // end anonymous namespace
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 {
// IntervalSorter - Comparison predicate that sort live intervals by
// their weight.
struct IntervalSorter {
bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
return LHS->weight > RHS->weight;
}
};
}
/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
/// references and update spill slot weights.
void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
SSRefs.resize(MFI->getObjectIndexEnd());
// FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
MBBI != E; ++MBBI) {
MachineBasicBlock *MBB = &*MBBI;
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, MBFI, MI);
}
for (MachineInstr::mmo_iterator MMOI = MI->memoperands_begin(),
EE = MI->memoperands_end(); MMOI != EE; ++MMOI) {
MachineMemOperand *MMO = *MMOI;
if (const FixedStackPseudoSourceValue *FSV =
dyn_cast_or_null<FixedStackPseudoSourceValue>(
MMO->getPseudoValue())) {
int FI = FSV->getFrameIndex();
if (FI >= 0)
SSRefs[FI].push_back(MMO);
}
}
}
}
}
/// InitializeSlots - Process all spill stack slot liveintervals and add them
/// to a sorted (by weight) list.
void StackSlotColoring::InitializeSlots() {
int LastFI = MFI->getObjectIndexEnd();
OrigAlignments.resize(LastFI);
OrigSizes.resize(LastFI);
AllColors.resize(LastFI);
UsedColors.resize(LastFI);
Assignments.resize(LastFI);
typedef std::iterator_traits<LiveStacks::iterator>::value_type Pair;
SmallVector<Pair *, 16> Intervals;
Intervals.reserve(LS->getNumIntervals());
for (auto &I : *LS)
Intervals.push_back(&I);
std::sort(Intervals.begin(), Intervals.end(),
[](Pair *LHS, Pair *RHS) { return LHS->first < RHS->first; });
// Gather all spill slots into a list.
DEBUG(dbgs() << "Spill slot intervals:\n");
for (auto *I : Intervals) {
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');
// Sort them by weight.
std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
// Get first "color".
NextColor = AllColors.find_first();
}
/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
/// LiveIntervals that have already been assigned to the specified color.
bool
StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
const SmallVectorImpl<LiveInterval *> &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;
}
/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
///
int StackSlotColoring::ColorSlot(LiveInterval *li) {
int Color = -1;
bool Share = false;
if (!DisableSharing) {
// Check if it's possible to reuse any of the used colors.
Color = UsedColors.find_first();
while (Color != -1) {
if (!OverlapWithAssignments(li, Color)) {
Share = true;
++NumEliminated;
break;
}
Color = UsedColors.find_next(Color);
}
}
// Assign it to the first available color (assumed to be the best) if it's
// not possible to share a used color with other objects.
if (!Share) {
assert(NextColor != -1 && "No more spill slots?");
Color = NextColor;
UsedColors.set(Color);
NextColor = AllColors.find_next(NextColor);
}
// Record the assignment.
Assignments[Color].push_back(li);
int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
// Change size and alignment of the allocated slot. If there are multiple
// objects sharing the same slot, then make sure the size and alignment
// are large enough for all.
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;
}
/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
/// operands in the function.
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];
}
// Sort them by new weight.
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;
// Rewrite all MachineMemOperands.
for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
int NewFI = SlotMapping[SS];
if (NewFI == -1 || (NewFI == (int)SS))
continue;
const PseudoSourceValue *NewSV = PseudoSourceValue::getFixedStack(NewFI);
SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
RefMMOs[i]->setValue(NewSV);
}
// Rewrite all MO_FrameIndex operands. Look for dead stores.
for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
MBBI != E; ++MBBI) {
MachineBasicBlock *MBB = &*MBBI;
for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
MII != EE; ++MII)
RewriteInstruction(MII, SlotMapping, MF);
RemoveDeadStores(MBB);
}
// Delete unused stack slots.
while (NextColor != -1) {
DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
MFI->RemoveStackObject(NextColor);
NextColor = AllColors.find_next(NextColor);
}
return true;
}
/// RewriteInstruction - Rewrite specified instruction by replacing references
/// to old frame index with new one.
void StackSlotColoring::RewriteInstruction(MachineInstr *MI,
SmallVectorImpl<int> &SlotMapping,
MachineFunction &MF) {
// Update the operands.
for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isFI())
continue;
int OldFI = MO.getIndex();
if (OldFI < 0)
continue;
int NewFI = SlotMapping[OldFI];
if (NewFI == -1 || NewFI == OldFI)
continue;
MO.setIndex(NewFI);
}
// The MachineMemOperands have already been updated.
}
/// RemoveDeadStores - Scan through a basic block and look for loads followed
/// by stores. If they're both using the same stack slot, then the store is
/// definitely dead. This could obviously be much more aggressive (consider
/// pairs with instructions between them), but such extensions might have a
/// considerable compile time impact.
bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
// FIXME: This could be much more aggressive, but we need to investigate
// the compile time impact of doing so.
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;
int FirstSS, SecondSS;
if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
FirstSS == SecondSS &&
FirstSS != -1) {
++NumDead;
changed = true;
toErase.push_back(I);
continue;
}
MachineBasicBlock::iterator NextMI = std::next(I);
if (NextMI == MBB->end()) continue;
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, nullptr) != -1) {
++NumDead;
toErase.push_back(I);
}
toErase.push_back(NextMI);
++I;
}
for (SmallVectorImpl<MachineInstr *>::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.getSubtarget().getInstrInfo();
LS = &getAnalysis<LiveStacks>();
MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
bool Changed = false;
unsigned NumSlots = LS->getNumIntervals();
if (NumSlots == 0)
// Nothing to do!
return false;
// If there are calls to setjmp or sigsetjmp, don't perform stack slot
// coloring. The stack could be modified before the longjmp is executed,
// resulting in the wrong value being used afterwards. (See
// <rdar://problem/8007500>.)
if (MF.exposesReturnsTwice())
return false;
// Gather spill slot references
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();
return Changed;
}