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//===-- 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "stackcoloring"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.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(NumDeadAccesses,
"Number of trivially dead stack accesses eliminated");
namespace {
class VISIBILITY_HIDDEN StackSlotColoring : public MachineFunctionPass {
LiveStacks* LS;
MachineFrameInfo *MFI;
const TargetInstrInfo *TII;
// SSIntervals - Spill slot intervals.
std::vector<LiveInterval*> SSIntervals;
// 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) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveStacks>();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char* getPassName() const {
return "Stack Slot Coloring";
}
private:
bool InitializeSlots();
bool OverlapWithAssignments(LiveInterval *li, int Color) const;
int ColorSlot(LiveInterval *li);
bool ColorSlots(MachineFunction &MF);
bool removeDeadStores(MachineBasicBlock* MBB);
};
} // end anonymous namespace
char StackSlotColoring::ID = 0;
static RegisterPass<StackSlotColoring>
X("stack-slot-coloring", "Stack Slot Coloring");
FunctionPass *llvm::createStackSlotColoringPass() {
return new StackSlotColoring();
}
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;
}
};
}
/// InitializeSlots - Process all spill stack slot liveintervals and add them
/// to a sorted (by weight) list.
bool StackSlotColoring::InitializeSlots() {
if (LS->getNumIntervals() < 2)
return false;
int LastFI = MFI->getObjectIndexEnd();
OrigAlignments.resize(LastFI);
OrigSizes.resize(LastFI);
AllColors.resize(LastFI);
UsedColors.resize(LastFI);
Assignments.resize(LastFI);
// Gather all spill slots into a list.
for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
LiveInterval &li = i->second;
int FI = li.getStackSlotIndex();
if (MFI->isDeadObjectIndex(FI))
continue;
SSIntervals.push_back(&li);
OrigAlignments[FI] = MFI->getObjectAlignment(FI);
OrigSizes[FI] = MFI->getObjectSize(FI);
AllColors.set(FI);
}
// Sort them by weight.
std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
// Get first "color".
NextColor = AllColors.find_first();
return true;
}
/// 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 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;
}
/// 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 = li->getStackSlotIndex();
DOUT << "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();
std::vector<int> SlotMapping(NumObjs, -1);
bool Changed = false;
for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
LiveInterval *li = SSIntervals[i];
int SS = li->getStackSlotIndex();
int NewSS = ColorSlot(li);
SlotMapping[SS] = NewSS;
Changed |= (SS != NewSS);
}
if (!Changed)
return false;
// Rewrite all MO_FrameIndex operands.
// FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
for (MachineFunction::iterator MBB = MF.begin(), E = MF.end();
MBB != E; ++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;
int NewFI = SlotMapping[FI];
if (NewFI == -1)
continue;
MO.setIndex(NewFI);
// Update the MachineMemOperand for the new memory location.
// FIXME: We need a better method of managing these too.
SmallVector<MachineMemOperand, 2> MMOs(MI.memoperands_begin(),
MI.memoperands_end());
MI.clearMemOperands(MF);
const Value *OldSV = PseudoSourceValue::getFixedStack(FI);
for (unsigned i = 0, e = MMOs.size(); i != e; ++i) {
if (MMOs[i].getValue() == OldSV) {
MachineMemOperand MMO(PseudoSourceValue::getFixedStack(NewFI),
MMOs[i].getFlags(), MMOs[i].getOffset(),
MMOs[i].getSize(), MMOs[i].getAlignment());
MI.addMemOperand(MF, MMO);
} else
MI.addMemOperand(MF, MMOs[i]);
}
}
}
}
// Delete unused stack slots.
while (NextColor != -1) {
DOUT << "Removing unused stack object fi#" << NextColor << "\n";
MFI->RemoveStackObject(NextColor);
NextColor = AllColors.find_next(NextColor);
}
return true;
}
/// 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)NumDeadAccesses >= DCELimit)
break;
MachineBasicBlock::iterator NextMI = 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;
++NumDeadAccesses;
changed = true;
if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
++NumDeadAccesses;
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) {
DOUT << "********** Stack Slot Coloring **********\n";
MFI = MF.getFrameInfo();
TII = MF.getTarget().getInstrInfo();
LS = &getAnalysis<LiveStacks>();
bool Changed = false;
if (InitializeSlots())
Changed = ColorSlots(MF);
NextColor = -1;
SSIntervals.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;
}
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