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llvm/lib/CodeGen/StackSlotColoring.cpp
Mike Stump fe095f39e7 Restore minor deletion. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70892 91177308-0d34-0410-b5e6-96231b3b80d8
2009-05-04 18:40:41 +00:00

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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 "VirtRegMap.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.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<bool>
ColorWithRegs("color-ss-with-regs",
cl::init(false), cl::Hidden,
cl::desc("Color stack slots with free registers"));
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");
STATISTIC(NumRegRepl, "Number of stack slot refs replaced with reg refs");
namespace {
class VISIBILITY_HIDDEN StackSlotColoring : public MachineFunctionPass {
LiveStacks* LS;
VirtRegMap* VRM;
MachineFrameInfo *MFI;
MachineRegisterInfo *MRI;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const MachineLoopInfo *loopInfo;
// SSIntervals - Spill slot intervals.
std::vector<LiveInterval*> SSIntervals;
// SSRefs - Keep a list of frame index references for each spill slot.
SmallVector<SmallVector<MachineInstr*, 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) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveStacks>();
AU.addRequired<VirtRegMap>();
AU.addPreserved<VirtRegMap>();
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char* getPassName() const {
return "Stack Slot Coloring";
}
private:
void InitializeSlots();
void ScanForSpillSlotRefs(MachineFunction &MF);
bool OverlapWithAssignments(LiveInterval *li, int Color) const;
int ColorSlot(LiveInterval *li);
bool ColorSlots(MachineFunction &MF);
bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
SmallVector<SmallVector<int, 4>, 16> &RevMap,
BitVector &SlotIsReg);
void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
MachineFunction &MF);
void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
unsigned Reg, MachineFunction &MF);
bool AllMemRefsCanBeUnfolded(int SS);
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;
}
};
}
/// 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;
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);
li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
SSRefs[FI].push_back(MI);
}
}
}
}
/// 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);
// Gather all spill slots into a list.
DOUT << "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 = li.getStackSlotIndex();
if (MFI->isDeadObjectIndex(FI))
continue;
SSIntervals.push_back(&li);
OrigAlignments[FI] = MFI->getObjectAlignment(FI);
OrigSizes[FI] = MFI->getObjectSize(FI);
AllColors.set(FI);
}
DOUT << '\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 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;
}
/// ColorSlotsWithFreeRegs - If there are any free registers available, try
/// replacing spill slots references with registers instead.
bool
StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
SmallVector<SmallVector<int, 4>, 16> &RevMap,
BitVector &SlotIsReg) {
if (!ColorWithRegs || !VRM->HasUnusedRegisters())
return false;
bool Changed = false;
DOUT << "Assigning unused registers to spill slots:\n";
for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
LiveInterval *li = SSIntervals[i];
int SS = li->getStackSlotIndex();
if (!UsedColors[SS])
continue;
// These slots allow to share the same registers.
bool AllColored = true;
SmallVector<unsigned, 4> ColoredRegs;
for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
int RSS = RevMap[SS][j];
const TargetRegisterClass *RC = LS->getIntervalRegClass(RSS);
// If it's not colored to another stack slot, try coloring it
// to a "free" register.
if (!RC) {
AllColored = false;
continue;
}
unsigned Reg = VRM->getFirstUnusedRegister(RC);
if (!Reg) {
AllColored = false;
continue;
}
if (!AllMemRefsCanBeUnfolded(RSS)) {
AllColored = false;
continue;
} else {
DOUT << "Assigning fi#" << RSS << " to " << TRI->getName(Reg) << '\n';
ColoredRegs.push_back(Reg);
SlotMapping[RSS] = Reg;
SlotIsReg.set(RSS);
Changed = true;
}
}
// Register and its sub-registers are no longer free.
while (!ColoredRegs.empty()) {
unsigned Reg = ColoredRegs.back();
ColoredRegs.pop_back();
VRM->setRegisterUsed(Reg);
// If reg is a callee-saved register, it will have to be spilled in
// the prologue.
MRI->setPhysRegUsed(Reg);
for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
VRM->setRegisterUsed(*AS);
MRI->setPhysRegUsed(*AS);
}
}
// This spill slot is dead after the rewrites
if (AllColored) {
MFI->RemoveStackObject(SS);
++NumEliminated;
}
}
DOUT << '\n';
return Changed;
}
/// 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();
SmallVector<int, 16> SlotMapping(NumObjs, -1);
SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
BitVector SlotIsReg(NumObjs);
BitVector UsedColors(NumObjs);
DOUT << "Color spill slot intervals:\n";
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);
assert(NewSS >= 0 && "Stack coloring failed?");
SlotMapping[SS] = NewSS;
RevMap[NewSS].push_back(SS);
SlotWeights[NewSS] += li->weight;
UsedColors.set(NewSS);
Changed |= (SS != NewSS);
}
DOUT << "\nSpill slots after coloring:\n";
for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
LiveInterval *li = SSIntervals[i];
int SS = li->getStackSlotIndex();
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());
DOUT << '\n';
#endif
// Can we "color" a stack slot with a unused register?
Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
if (!Changed)
return false;
// Rewrite all MO_FrameIndex operands.
for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
bool isReg = SlotIsReg[SS];
int NewFI = SlotMapping[SS];
if (NewFI == -1 || (NewFI == (int)SS && !isReg))
continue;
SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
if (isReg)
// Rewrite to use a register instead.
UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, MF);
else
RewriteInstruction(RefMIs[i], SS, NewFI, MF);
}
// 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;
}
/// AllMemRefsCanBeUnfolded - Return true if all references of the specified
/// spill slot index can be unfolded.
bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
MachineInstr *MI = RefMIs[i];
if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
return false;
for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
MachineOperand &MO = MI->getOperand(j);
if (MO.isFI() && MO.getIndex() != SS)
// If it uses another frameindex, we can, currently* unfold it.
return false;
}
}
return true;
}
/// RewriteInstruction - Rewrite specified instruction by replacing references
/// to old frame index with new one.
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);
}
// 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(OldFI);
for (unsigned i = 0, ee = MMOs.size(); i != ee; ++i) {
if (MMOs[i].getValue() != OldSV)
MI->addMemOperand(MF, MMOs[i]);
else {
MachineMemOperand MMO(PseudoSourceValue::getFixedStack(NewFI),
MMOs[i].getFlags(), MMOs[i].getOffset(),
MMOs[i].getSize(), MMOs[i].getAlignment());
MI->addMemOperand(MF, MMO);
}
}
}
/// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
/// folded memory references and replacing those references with register
/// references instead.
void StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
unsigned Reg,
MachineFunction &MF) {
MachineBasicBlock *MBB = MI->getParent();
SmallVector<MachineInstr*, 4> NewMIs;
bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
assert(Success && "Failed to unfold!");
MBB->insert(MI, NewMIs[0]);
MBB->erase(MI);
++NumRegRepl;
}
/// 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;
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;
++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) {
DOUT << "********** Stack Slot Coloring **********\n";
MFI = MF.getFrameInfo();
MRI = &MF.getRegInfo();
TII = MF.getTarget().getInstrInfo();
TRI = MF.getTarget().getRegisterInfo();
LS = &getAnalysis<LiveStacks>();
VRM = &getAnalysis<VirtRegMap>();
loopInfo = &getAnalysis<MachineLoopInfo>();
bool Changed = false;
unsigned NumSlots = LS->getNumIntervals();
if (NumSlots < 2) {
if (NumSlots == 0 || !VRM->HasUnusedRegisters())
// Nothing to do!
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();
if (Changed) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
Changed |= RemoveDeadStores(I);
}
return Changed;
}
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