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llvm-mirror/lib/CodeGen/PreAllocSplitting.cpp
Evan Cheng 28aa6c41d1 In some rare cases, the register allocator can spill registers but end up not utilizing registers at all. The fundamental problem is linearscan's backtracking can end up freeing more than one allocated registers. However, reloads and restores might be folded into uses / defs and freed registers might not be used at all. 
VirtRegMap keeps track of allocations so it knows what's not used. As a horrible hack, the stack coloring can color spill slots with *free* registers. That is, it replace reload and spills with copies from and to the free register. It unfold instructions that load and store the spill slot and replace them with register using variants.

Not yet enabled. This is part 1. More coming.

llvm-svn: 70787
2009-05-03 18:32:42 +00:00

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//===-- PreAllocSplitting.cpp - Pre-allocation Interval Spltting 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 machine instruction level pre-register allocation
// live interval splitting pass. It finds live interval barriers, i.e.
// instructions which will kill all physical registers in certain register
// classes, and split all live intervals which cross the barrier.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "pre-alloc-split"
#include "VirtRegMap.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterCoalescer.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
static cl::opt<int> PreSplitLimit("pre-split-limit", cl::init(-1), cl::Hidden);
static cl::opt<int> DeadSplitLimit("dead-split-limit", cl::init(-1), cl::Hidden);
static cl::opt<int> RestoreFoldLimit("restore-fold-limit", cl::init(-1), cl::Hidden);
STATISTIC(NumSplits, "Number of intervals split");
STATISTIC(NumRemats, "Number of intervals split by rematerialization");
STATISTIC(NumFolds, "Number of intervals split with spill folding");
STATISTIC(NumRestoreFolds, "Number of intervals split with restore folding");
STATISTIC(NumRenumbers, "Number of intervals renumbered into new registers");
STATISTIC(NumDeadSpills, "Number of dead spills removed");
namespace {
class VISIBILITY_HIDDEN PreAllocSplitting : public MachineFunctionPass {
MachineFunction *CurrMF;
const TargetMachine *TM;
const TargetInstrInfo *TII;
const TargetRegisterInfo* TRI;
MachineFrameInfo *MFI;
MachineRegisterInfo *MRI;
LiveIntervals *LIs;
LiveStacks *LSs;
VirtRegMap *VRM;
// Barrier - Current barrier being processed.
MachineInstr *Barrier;
// BarrierMBB - Basic block where the barrier resides in.
MachineBasicBlock *BarrierMBB;
// Barrier - Current barrier index.
unsigned BarrierIdx;
// CurrLI - Current live interval being split.
LiveInterval *CurrLI;
// CurrSLI - Current stack slot live interval.
LiveInterval *CurrSLI;
// CurrSValNo - Current val# for the stack slot live interval.
VNInfo *CurrSValNo;
// IntervalSSMap - A map from live interval to spill slots.
DenseMap<unsigned, int> IntervalSSMap;
// Def2SpillMap - A map from a def instruction index to spill index.
DenseMap<unsigned, unsigned> Def2SpillMap;
public:
static char ID;
PreAllocSplitting() : MachineFunctionPass(&ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveIntervals>();
AU.addPreserved<LiveIntervals>();
AU.addRequired<LiveStacks>();
AU.addPreserved<LiveStacks>();
AU.addPreserved<RegisterCoalescer>();
if (StrongPHIElim)
AU.addPreservedID(StrongPHIEliminationID);
else
AU.addPreservedID(PHIEliminationID);
AU.addRequired<MachineDominatorTree>();
AU.addRequired<MachineLoopInfo>();
AU.addRequired<VirtRegMap>();
AU.addPreserved<MachineDominatorTree>();
AU.addPreserved<MachineLoopInfo>();
AU.addPreserved<VirtRegMap>();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual void releaseMemory() {
IntervalSSMap.clear();
Def2SpillMap.clear();
}
virtual const char *getPassName() const {
return "Pre-Register Allocaton Live Interval Splitting";
}
/// print - Implement the dump method.
virtual void print(std::ostream &O, const Module* M = 0) const {
LIs->print(O, M);
}
void print(std::ostream *O, const Module* M = 0) const {
if (O) print(*O, M);
}
private:
MachineBasicBlock::iterator
findNextEmptySlot(MachineBasicBlock*, MachineInstr*,
unsigned&);
MachineBasicBlock::iterator
findSpillPoint(MachineBasicBlock*, MachineInstr*, MachineInstr*,
SmallPtrSet<MachineInstr*, 4>&, unsigned&);
MachineBasicBlock::iterator
findRestorePoint(MachineBasicBlock*, MachineInstr*, unsigned,
SmallPtrSet<MachineInstr*, 4>&, unsigned&);
int CreateSpillStackSlot(unsigned, const TargetRegisterClass *);
bool IsAvailableInStack(MachineBasicBlock*, unsigned, unsigned, unsigned,
unsigned&, int&) const;
void UpdateSpillSlotInterval(VNInfo*, unsigned, unsigned);
bool SplitRegLiveInterval(LiveInterval*);
bool SplitRegLiveIntervals(const TargetRegisterClass **,
SmallPtrSet<LiveInterval*, 8>&);
bool createsNewJoin(LiveRange* LR, MachineBasicBlock* DefMBB,
MachineBasicBlock* BarrierMBB);
bool Rematerialize(unsigned vreg, VNInfo* ValNo,
MachineInstr* DefMI,
MachineBasicBlock::iterator RestorePt,
unsigned RestoreIdx,
SmallPtrSet<MachineInstr*, 4>& RefsInMBB);
MachineInstr* FoldSpill(unsigned vreg, const TargetRegisterClass* RC,
MachineInstr* DefMI,
MachineInstr* Barrier,
MachineBasicBlock* MBB,
int& SS,
SmallPtrSet<MachineInstr*, 4>& RefsInMBB);
MachineInstr* FoldRestore(unsigned vreg,
const TargetRegisterClass* RC,
MachineInstr* Barrier,
MachineBasicBlock* MBB,
int SS,
SmallPtrSet<MachineInstr*, 4>& RefsInMBB);
void RenumberValno(VNInfo* VN);
void ReconstructLiveInterval(LiveInterval* LI);
bool removeDeadSpills(SmallPtrSet<LiveInterval*, 8>& split);
unsigned getNumberOfNonSpills(SmallPtrSet<MachineInstr*, 4>& MIs,
unsigned Reg, int FrameIndex, bool& TwoAddr);
VNInfo* PerformPHIConstruction(MachineBasicBlock::iterator Use,
MachineBasicBlock* MBB, LiveInterval* LI,
SmallPtrSet<MachineInstr*, 4>& Visited,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Defs,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Uses,
DenseMap<MachineInstr*, VNInfo*>& NewVNs,
DenseMap<MachineBasicBlock*, VNInfo*>& LiveOut,
DenseMap<MachineBasicBlock*, VNInfo*>& Phis,
bool IsTopLevel, bool IsIntraBlock);
VNInfo* PerformPHIConstructionFallBack(MachineBasicBlock::iterator Use,
MachineBasicBlock* MBB, LiveInterval* LI,
SmallPtrSet<MachineInstr*, 4>& Visited,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Defs,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Uses,
DenseMap<MachineInstr*, VNInfo*>& NewVNs,
DenseMap<MachineBasicBlock*, VNInfo*>& LiveOut,
DenseMap<MachineBasicBlock*, VNInfo*>& Phis,
bool IsTopLevel, bool IsIntraBlock);
};
} // end anonymous namespace
char PreAllocSplitting::ID = 0;
static RegisterPass<PreAllocSplitting>
X("pre-alloc-splitting", "Pre-Register Allocation Live Interval Splitting");
const PassInfo *const llvm::PreAllocSplittingID = &X;
/// findNextEmptySlot - Find a gap after the given machine instruction in the
/// instruction index map. If there isn't one, return end().
MachineBasicBlock::iterator
PreAllocSplitting::findNextEmptySlot(MachineBasicBlock *MBB, MachineInstr *MI,
unsigned &SpotIndex) {
MachineBasicBlock::iterator MII = MI;
if (++MII != MBB->end()) {
unsigned Index = LIs->findGapBeforeInstr(LIs->getInstructionIndex(MII));
if (Index) {
SpotIndex = Index;
return MII;
}
}
return MBB->end();
}
/// findSpillPoint - Find a gap as far away from the given MI that's suitable
/// for spilling the current live interval. The index must be before any
/// defs and uses of the live interval register in the mbb. Return begin() if
/// none is found.
MachineBasicBlock::iterator
PreAllocSplitting::findSpillPoint(MachineBasicBlock *MBB, MachineInstr *MI,
MachineInstr *DefMI,
SmallPtrSet<MachineInstr*, 4> &RefsInMBB,
unsigned &SpillIndex) {
MachineBasicBlock::iterator Pt = MBB->begin();
MachineBasicBlock::iterator MII = MI;
MachineBasicBlock::iterator EndPt = DefMI
? MachineBasicBlock::iterator(DefMI) : MBB->begin();
while (MII != EndPt && !RefsInMBB.count(MII) &&
MII->getOpcode() != TRI->getCallFrameSetupOpcode())
--MII;
if (MII == EndPt || RefsInMBB.count(MII)) return Pt;
while (MII != EndPt && !RefsInMBB.count(MII)) {
unsigned Index = LIs->getInstructionIndex(MII);
// We can't insert the spill between the barrier (a call), and its
// corresponding call frame setup.
if (MII->getOpcode() == TRI->getCallFrameDestroyOpcode()) {
while (MII->getOpcode() != TRI->getCallFrameSetupOpcode()) {
--MII;
if (MII == EndPt) {
return Pt;
}
}
continue;
} else if (LIs->hasGapBeforeInstr(Index)) {
Pt = MII;
SpillIndex = LIs->findGapBeforeInstr(Index, true);
}
if (RefsInMBB.count(MII))
return Pt;
--MII;
}
return Pt;
}
/// findRestorePoint - Find a gap in the instruction index map that's suitable
/// for restoring the current live interval value. The index must be before any
/// uses of the live interval register in the mbb. Return end() if none is
/// found.
MachineBasicBlock::iterator
PreAllocSplitting::findRestorePoint(MachineBasicBlock *MBB, MachineInstr *MI,
unsigned LastIdx,
SmallPtrSet<MachineInstr*, 4> &RefsInMBB,
unsigned &RestoreIndex) {
// FIXME: Allow spill to be inserted to the beginning of the mbb. Update mbb
// begin index accordingly.
MachineBasicBlock::iterator Pt = MBB->end();
MachineBasicBlock::iterator EndPt = MBB->getFirstTerminator();
// We start at the call, so walk forward until we find the call frame teardown
// since we can't insert restores before that. Bail if we encounter a use
// during this time.
MachineBasicBlock::iterator MII = MI;
if (MII == EndPt) return Pt;
while (MII != EndPt && !RefsInMBB.count(MII) &&
MII->getOpcode() != TRI->getCallFrameDestroyOpcode())
++MII;
if (MII == EndPt || RefsInMBB.count(MII)) return Pt;
++MII;
// FIXME: Limit the number of instructions to examine to reduce
// compile time?
while (MII != EndPt) {
unsigned Index = LIs->getInstructionIndex(MII);
if (Index > LastIdx)
break;
unsigned Gap = LIs->findGapBeforeInstr(Index);
// We can't insert a restore between the barrier (a call) and its
// corresponding call frame teardown.
if (MII->getOpcode() == TRI->getCallFrameSetupOpcode()) {
do {
if (MII == EndPt || RefsInMBB.count(MII)) return Pt;
++MII;
} while (MII->getOpcode() != TRI->getCallFrameDestroyOpcode());
} else if (Gap) {
Pt = MII;
RestoreIndex = Gap;
}
if (RefsInMBB.count(MII))
return Pt;
++MII;
}
return Pt;
}
/// CreateSpillStackSlot - Create a stack slot for the live interval being
/// split. If the live interval was previously split, just reuse the same
/// slot.
int PreAllocSplitting::CreateSpillStackSlot(unsigned Reg,
const TargetRegisterClass *RC) {
int SS;
DenseMap<unsigned, int>::iterator I = IntervalSSMap.find(Reg);
if (I != IntervalSSMap.end()) {
SS = I->second;
} else {
SS = MFI->CreateStackObject(RC->getSize(), RC->getAlignment());
IntervalSSMap[Reg] = SS;
}
// Create live interval for stack slot.
CurrSLI = &LSs->getOrCreateInterval(SS, RC);
if (CurrSLI->hasAtLeastOneValue())
CurrSValNo = CurrSLI->getValNumInfo(0);
else
CurrSValNo = CurrSLI->getNextValue(~0U, 0, LSs->getVNInfoAllocator());
return SS;
}
/// IsAvailableInStack - Return true if register is available in a split stack
/// slot at the specified index.
bool
PreAllocSplitting::IsAvailableInStack(MachineBasicBlock *DefMBB,
unsigned Reg, unsigned DefIndex,
unsigned RestoreIndex, unsigned &SpillIndex,
int& SS) const {
if (!DefMBB)
return false;
DenseMap<unsigned, int>::iterator I = IntervalSSMap.find(Reg);
if (I == IntervalSSMap.end())
return false;
DenseMap<unsigned, unsigned>::iterator II = Def2SpillMap.find(DefIndex);
if (II == Def2SpillMap.end())
return false;
// If last spill of def is in the same mbb as barrier mbb (where restore will
// be), make sure it's not below the intended restore index.
// FIXME: Undo the previous spill?
assert(LIs->getMBBFromIndex(II->second) == DefMBB);
if (DefMBB == BarrierMBB && II->second >= RestoreIndex)
return false;
SS = I->second;
SpillIndex = II->second;
return true;
}
/// UpdateSpillSlotInterval - Given the specified val# of the register live
/// interval being split, and the spill and restore indicies, update the live
/// interval of the spill stack slot.
void
PreAllocSplitting::UpdateSpillSlotInterval(VNInfo *ValNo, unsigned SpillIndex,
unsigned RestoreIndex) {
assert(LIs->getMBBFromIndex(RestoreIndex) == BarrierMBB &&
"Expect restore in the barrier mbb");
MachineBasicBlock *MBB = LIs->getMBBFromIndex(SpillIndex);
if (MBB == BarrierMBB) {
// Intra-block spill + restore. We are done.
LiveRange SLR(SpillIndex, RestoreIndex, CurrSValNo);
CurrSLI->addRange(SLR);
return;
}
SmallPtrSet<MachineBasicBlock*, 4> Processed;
unsigned EndIdx = LIs->getMBBEndIdx(MBB);
LiveRange SLR(SpillIndex, EndIdx+1, CurrSValNo);
CurrSLI->addRange(SLR);
Processed.insert(MBB);
// Start from the spill mbb, figure out the extend of the spill slot's
// live interval.
SmallVector<MachineBasicBlock*, 4> WorkList;
const LiveRange *LR = CurrLI->getLiveRangeContaining(SpillIndex);
if (LR->end > EndIdx)
// If live range extend beyond end of mbb, add successors to work list.
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI)
WorkList.push_back(*SI);
while (!WorkList.empty()) {
MachineBasicBlock *MBB = WorkList.back();
WorkList.pop_back();
if (Processed.count(MBB))
continue;
unsigned Idx = LIs->getMBBStartIdx(MBB);
LR = CurrLI->getLiveRangeContaining(Idx);
if (LR && LR->valno == ValNo) {
EndIdx = LIs->getMBBEndIdx(MBB);
if (Idx <= RestoreIndex && RestoreIndex < EndIdx) {
// Spill slot live interval stops at the restore.
LiveRange SLR(Idx, RestoreIndex, CurrSValNo);
CurrSLI->addRange(SLR);
} else if (LR->end > EndIdx) {
// Live range extends beyond end of mbb, process successors.
LiveRange SLR(Idx, EndIdx+1, CurrSValNo);
CurrSLI->addRange(SLR);
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
SE = MBB->succ_end(); SI != SE; ++SI)
WorkList.push_back(*SI);
} else {
LiveRange SLR(Idx, LR->end, CurrSValNo);
CurrSLI->addRange(SLR);
}
Processed.insert(MBB);
}
}
}
/// PerformPHIConstruction - From properly set up use and def lists, use a PHI
/// construction algorithm to compute the ranges and valnos for an interval.
VNInfo*
PreAllocSplitting::PerformPHIConstruction(MachineBasicBlock::iterator UseI,
MachineBasicBlock* MBB, LiveInterval* LI,
SmallPtrSet<MachineInstr*, 4>& Visited,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Defs,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Uses,
DenseMap<MachineInstr*, VNInfo*>& NewVNs,
DenseMap<MachineBasicBlock*, VNInfo*>& LiveOut,
DenseMap<MachineBasicBlock*, VNInfo*>& Phis,
bool IsTopLevel, bool IsIntraBlock) {
// Return memoized result if it's available.
if (IsTopLevel && Visited.count(UseI) && NewVNs.count(UseI))
return NewVNs[UseI];
else if (!IsTopLevel && IsIntraBlock && NewVNs.count(UseI))
return NewVNs[UseI];
else if (!IsIntraBlock && LiveOut.count(MBB))
return LiveOut[MBB];
// Check if our block contains any uses or defs.
bool ContainsDefs = Defs.count(MBB);
bool ContainsUses = Uses.count(MBB);
VNInfo* RetVNI = 0;
// Enumerate the cases of use/def contaning blocks.
if (!ContainsDefs && !ContainsUses) {
return PerformPHIConstructionFallBack(UseI, MBB, LI, Visited, Defs, Uses,
NewVNs, LiveOut, Phis,
IsTopLevel, IsIntraBlock);
} else if (ContainsDefs && !ContainsUses) {
SmallPtrSet<MachineInstr*, 2>& BlockDefs = Defs[MBB];
// Search for the def in this block. If we don't find it before the
// instruction we care about, go to the fallback case. Note that that
// should never happen: this cannot be intrablock, so use should
// always be an end() iterator.
assert(UseI == MBB->end() && "No use marked in intrablock");
MachineBasicBlock::iterator Walker = UseI;
--Walker;
while (Walker != MBB->begin()) {
if (BlockDefs.count(Walker))
break;
--Walker;
}
// Once we've found it, extend its VNInfo to our instruction.
unsigned DefIndex = LIs->getInstructionIndex(Walker);
DefIndex = LiveIntervals::getDefIndex(DefIndex);
unsigned EndIndex = LIs->getMBBEndIdx(MBB);
RetVNI = NewVNs[Walker];
LI->addRange(LiveRange(DefIndex, EndIndex+1, RetVNI));
} else if (!ContainsDefs && ContainsUses) {
SmallPtrSet<MachineInstr*, 2>& BlockUses = Uses[MBB];
// Search for the use in this block that precedes the instruction we care
// about, going to the fallback case if we don't find it.
if (UseI == MBB->begin())
return PerformPHIConstructionFallBack(UseI, MBB, LI, Visited, Defs,
Uses, NewVNs, LiveOut, Phis,
IsTopLevel, IsIntraBlock);
MachineBasicBlock::iterator Walker = UseI;
--Walker;
bool found = false;
while (Walker != MBB->begin()) {
if (BlockUses.count(Walker)) {
found = true;
break;
}
--Walker;
}
// Must check begin() too.
if (!found) {
if (BlockUses.count(Walker))
found = true;
else
return PerformPHIConstructionFallBack(UseI, MBB, LI, Visited, Defs,
Uses, NewVNs, LiveOut, Phis,
IsTopLevel, IsIntraBlock);
}
unsigned UseIndex = LIs->getInstructionIndex(Walker);
UseIndex = LiveIntervals::getUseIndex(UseIndex);
unsigned EndIndex = 0;
if (IsIntraBlock) {
EndIndex = LIs->getInstructionIndex(UseI);
EndIndex = LiveIntervals::getUseIndex(EndIndex);
} else
EndIndex = LIs->getMBBEndIdx(MBB);
// Now, recursively phi construct the VNInfo for the use we found,
// and then extend it to include the instruction we care about
RetVNI = PerformPHIConstruction(Walker, MBB, LI, Visited, Defs, Uses,
NewVNs, LiveOut, Phis, false, true);
LI->addRange(LiveRange(UseIndex, EndIndex+1, RetVNI));
// FIXME: Need to set kills properly for inter-block stuff.
if (LI->isKill(RetVNI, UseIndex)) LI->removeKill(RetVNI, UseIndex);
if (IsIntraBlock)
LI->addKill(RetVNI, EndIndex);
} else if (ContainsDefs && ContainsUses) {
SmallPtrSet<MachineInstr*, 2>& BlockDefs = Defs[MBB];
SmallPtrSet<MachineInstr*, 2>& BlockUses = Uses[MBB];
// This case is basically a merging of the two preceding case, with the
// special note that checking for defs must take precedence over checking
// for uses, because of two-address instructions.
if (UseI == MBB->begin())
return PerformPHIConstructionFallBack(UseI, MBB, LI, Visited, Defs, Uses,
NewVNs, LiveOut, Phis,
IsTopLevel, IsIntraBlock);
MachineBasicBlock::iterator Walker = UseI;
--Walker;
bool foundDef = false;
bool foundUse = false;
while (Walker != MBB->begin()) {
if (BlockDefs.count(Walker)) {
foundDef = true;
break;
} else if (BlockUses.count(Walker)) {
foundUse = true;
break;
}
--Walker;
}
// Must check begin() too.
if (!foundDef && !foundUse) {
if (BlockDefs.count(Walker))
foundDef = true;
else if (BlockUses.count(Walker))
foundUse = true;
else
return PerformPHIConstructionFallBack(UseI, MBB, LI, Visited, Defs,
Uses, NewVNs, LiveOut, Phis,
IsTopLevel, IsIntraBlock);
}
unsigned StartIndex = LIs->getInstructionIndex(Walker);
StartIndex = foundDef ? LiveIntervals::getDefIndex(StartIndex) :
LiveIntervals::getUseIndex(StartIndex);
unsigned EndIndex = 0;
if (IsIntraBlock) {
EndIndex = LIs->getInstructionIndex(UseI);
EndIndex = LiveIntervals::getUseIndex(EndIndex);
} else
EndIndex = LIs->getMBBEndIdx(MBB);
if (foundDef)
RetVNI = NewVNs[Walker];
else
RetVNI = PerformPHIConstruction(Walker, MBB, LI, Visited, Defs, Uses,
NewVNs, LiveOut, Phis, false, true);
LI->addRange(LiveRange(StartIndex, EndIndex+1, RetVNI));
if (foundUse && LI->isKill(RetVNI, StartIndex))
LI->removeKill(RetVNI, StartIndex);
if (IsIntraBlock) {
LI->addKill(RetVNI, EndIndex);
}
}
// Memoize results so we don't have to recompute them.
if (!IsIntraBlock) LiveOut[MBB] = RetVNI;
else {
if (!NewVNs.count(UseI))
NewVNs[UseI] = RetVNI;
Visited.insert(UseI);
}
return RetVNI;
}
/// PerformPHIConstructionFallBack - PerformPHIConstruction fall back path.
///
VNInfo*
PreAllocSplitting::PerformPHIConstructionFallBack(MachineBasicBlock::iterator UseI,
MachineBasicBlock* MBB, LiveInterval* LI,
SmallPtrSet<MachineInstr*, 4>& Visited,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Defs,
DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> >& Uses,
DenseMap<MachineInstr*, VNInfo*>& NewVNs,
DenseMap<MachineBasicBlock*, VNInfo*>& LiveOut,
DenseMap<MachineBasicBlock*, VNInfo*>& Phis,
bool IsTopLevel, bool IsIntraBlock) {
// NOTE: Because this is the fallback case from other cases, we do NOT
// assume that we are not intrablock here.
if (Phis.count(MBB)) return Phis[MBB];
unsigned StartIndex = LIs->getMBBStartIdx(MBB);
VNInfo *RetVNI = Phis[MBB] = LI->getNextValue(~0U, /*FIXME*/ 0,
LIs->getVNInfoAllocator());
if (!IsIntraBlock) LiveOut[MBB] = RetVNI;
// If there are no uses or defs between our starting point and the
// beginning of the block, then recursive perform phi construction
// on our predecessors.
DenseMap<MachineBasicBlock*, VNInfo*> IncomingVNs;
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
VNInfo* Incoming = PerformPHIConstruction((*PI)->end(), *PI, LI,
Visited, Defs, Uses, NewVNs,
LiveOut, Phis, false, false);
if (Incoming != 0)
IncomingVNs[*PI] = Incoming;
}
if (MBB->pred_size() == 1 && !RetVNI->hasPHIKill) {
VNInfo* OldVN = RetVNI;
VNInfo* NewVN = IncomingVNs.begin()->second;
VNInfo* MergedVN = LI->MergeValueNumberInto(OldVN, NewVN);
if (MergedVN == OldVN) std::swap(OldVN, NewVN);
for (DenseMap<MachineBasicBlock*, VNInfo*>::iterator LOI = LiveOut.begin(),
LOE = LiveOut.end(); LOI != LOE; ++LOI)
if (LOI->second == OldVN)
LOI->second = MergedVN;
for (DenseMap<MachineInstr*, VNInfo*>::iterator NVI = NewVNs.begin(),
NVE = NewVNs.end(); NVI != NVE; ++NVI)
if (NVI->second == OldVN)
NVI->second = MergedVN;
for (DenseMap<MachineBasicBlock*, VNInfo*>::iterator PI = Phis.begin(),
PE = Phis.end(); PI != PE; ++PI)
if (PI->second == OldVN)
PI->second = MergedVN;
RetVNI = MergedVN;
} else {
// Otherwise, merge the incoming VNInfos with a phi join. Create a new
// VNInfo to represent the joined value.
for (DenseMap<MachineBasicBlock*, VNInfo*>::iterator I =
IncomingVNs.begin(), E = IncomingVNs.end(); I != E; ++I) {
I->second->hasPHIKill = true;
unsigned KillIndex = LIs->getMBBEndIdx(I->first);
if (!LiveInterval::isKill(I->second, KillIndex))
LI->addKill(I->second, KillIndex);
}
}
unsigned EndIndex = 0;
if (IsIntraBlock) {
EndIndex = LIs->getInstructionIndex(UseI);
EndIndex = LiveIntervals::getUseIndex(EndIndex);
} else
EndIndex = LIs->getMBBEndIdx(MBB);
LI->addRange(LiveRange(StartIndex, EndIndex+1, RetVNI));
if (IsIntraBlock)
LI->addKill(RetVNI, EndIndex);
// Memoize results so we don't have to recompute them.
if (!IsIntraBlock)
LiveOut[MBB] = RetVNI;
else {
if (!NewVNs.count(UseI))
NewVNs[UseI] = RetVNI;
Visited.insert(UseI);
}
return RetVNI;
}
/// ReconstructLiveInterval - Recompute a live interval from scratch.
void PreAllocSplitting::ReconstructLiveInterval(LiveInterval* LI) {
BumpPtrAllocator& Alloc = LIs->getVNInfoAllocator();
// Clear the old ranges and valnos;
LI->clear();
// Cache the uses and defs of the register
typedef DenseMap<MachineBasicBlock*, SmallPtrSet<MachineInstr*, 2> > RegMap;
RegMap Defs, Uses;
// Keep track of the new VNs we're creating.
DenseMap<MachineInstr*, VNInfo*> NewVNs;
SmallPtrSet<VNInfo*, 2> PhiVNs;
// Cache defs, and create a new VNInfo for each def.
for (MachineRegisterInfo::def_iterator DI = MRI->def_begin(LI->reg),
DE = MRI->def_end(); DI != DE; ++DI) {
Defs[(*DI).getParent()].insert(&*DI);
unsigned DefIdx = LIs->getInstructionIndex(&*DI);
DefIdx = LiveIntervals::getDefIndex(DefIdx);
VNInfo* NewVN = LI->getNextValue(DefIdx, 0, Alloc);
// If the def is a move, set the copy field.
unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
if (TII->isMoveInstr(*DI, SrcReg, DstReg, SrcSubIdx, DstSubIdx))
if (DstReg == LI->reg)
NewVN->copy = &*DI;
NewVNs[&*DI] = NewVN;
}
// Cache uses as a separate pass from actually processing them.
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(LI->reg),
UE = MRI->use_end(); UI != UE; ++UI)
Uses[(*UI).getParent()].insert(&*UI);
// Now, actually process every use and use a phi construction algorithm
// to walk from it to its reaching definitions, building VNInfos along
// the way.
DenseMap<MachineBasicBlock*, VNInfo*> LiveOut;
DenseMap<MachineBasicBlock*, VNInfo*> Phis;
SmallPtrSet<MachineInstr*, 4> Visited;
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(LI->reg),
UE = MRI->use_end(); UI != UE; ++UI) {
PerformPHIConstruction(&*UI, UI->getParent(), LI, Visited, Defs,
Uses, NewVNs, LiveOut, Phis, true, true);
}
// Add ranges for dead defs
for (MachineRegisterInfo::def_iterator DI = MRI->def_begin(LI->reg),
DE = MRI->def_end(); DI != DE; ++DI) {
unsigned DefIdx = LIs->getInstructionIndex(&*DI);
DefIdx = LiveIntervals::getDefIndex(DefIdx);
if (LI->liveAt(DefIdx)) continue;
VNInfo* DeadVN = NewVNs[&*DI];
LI->addRange(LiveRange(DefIdx, DefIdx+1, DeadVN));
LI->addKill(DeadVN, DefIdx);
}
}
/// RenumberValno - Split the given valno out into a new vreg, allowing it to
/// be allocated to a different register. This function creates a new vreg,
/// copies the valno and its live ranges over to the new vreg's interval,
/// removes them from the old interval, and rewrites all uses and defs of
/// the original reg to the new vreg within those ranges.
void PreAllocSplitting::RenumberValno(VNInfo* VN) {
SmallVector<VNInfo*, 4> Stack;
SmallVector<VNInfo*, 4> VNsToCopy;
Stack.push_back(VN);
// Walk through and copy the valno we care about, and any other valnos
// that are two-address redefinitions of the one we care about. These
// will need to be rewritten as well. We also check for safety of the
// renumbering here, by making sure that none of the valno involved has
// phi kills.
while (!Stack.empty()) {
VNInfo* OldVN = Stack.back();
Stack.pop_back();
// Bail out if we ever encounter a valno that has a PHI kill. We can't
// renumber these.
if (OldVN->hasPHIKill) return;
VNsToCopy.push_back(OldVN);
// Locate two-address redefinitions
for (SmallVector<unsigned, 4>::iterator KI = OldVN->kills.begin(),
KE = OldVN->kills.end(); KI != KE; ++KI) {
MachineInstr* MI = LIs->getInstructionFromIndex(*KI);
unsigned DefIdx = MI->findRegisterDefOperandIdx(CurrLI->reg);
if (DefIdx == ~0U) continue;
if (MI->isRegTiedToUseOperand(DefIdx)) {
VNInfo* NextVN =
CurrLI->findDefinedVNInfo(LiveIntervals::getDefIndex(*KI));
if (NextVN == OldVN) continue;
Stack.push_back(NextVN);
}
}
}
// Create the new vreg
unsigned NewVReg = MRI->createVirtualRegister(MRI->getRegClass(CurrLI->reg));
// Create the new live interval
LiveInterval& NewLI = LIs->getOrCreateInterval(NewVReg);
for (SmallVector<VNInfo*, 4>::iterator OI = VNsToCopy.begin(), OE =
VNsToCopy.end(); OI != OE; ++OI) {
VNInfo* OldVN = *OI;
// Copy the valno over
VNInfo* NewVN = NewLI.getNextValue(OldVN->def, OldVN->copy,
LIs->getVNInfoAllocator());
NewLI.copyValNumInfo(NewVN, OldVN);
NewLI.MergeValueInAsValue(*CurrLI, OldVN, NewVN);
// Remove the valno from the old interval
CurrLI->removeValNo(OldVN);
}
// Rewrite defs and uses. This is done in two stages to avoid invalidating
// the reg_iterator.
SmallVector<std::pair<MachineInstr*, unsigned>, 8> OpsToChange;
for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(CurrLI->reg),
E = MRI->reg_end(); I != E; ++I) {
MachineOperand& MO = I.getOperand();
unsigned InstrIdx = LIs->getInstructionIndex(&*I);
if ((MO.isUse() && NewLI.liveAt(LiveIntervals::getUseIndex(InstrIdx))) ||
(MO.isDef() && NewLI.liveAt(LiveIntervals::getDefIndex(InstrIdx))))
OpsToChange.push_back(std::make_pair(&*I, I.getOperandNo()));
}
for (SmallVector<std::pair<MachineInstr*, unsigned>, 8>::iterator I =
OpsToChange.begin(), E = OpsToChange.end(); I != E; ++I) {
MachineInstr* Inst = I->first;
unsigned OpIdx = I->second;
MachineOperand& MO = Inst->getOperand(OpIdx);
MO.setReg(NewVReg);
}
// Grow the VirtRegMap, since we've created a new vreg.
VRM->grow();
// The renumbered vreg shares a stack slot with the old register.
if (IntervalSSMap.count(CurrLI->reg))
IntervalSSMap[NewVReg] = IntervalSSMap[CurrLI->reg];
NumRenumbers++;
}
bool PreAllocSplitting::Rematerialize(unsigned vreg, VNInfo* ValNo,
MachineInstr* DefMI,
MachineBasicBlock::iterator RestorePt,
unsigned RestoreIdx,
SmallPtrSet<MachineInstr*, 4>& RefsInMBB) {
MachineBasicBlock& MBB = *RestorePt->getParent();
MachineBasicBlock::iterator KillPt = BarrierMBB->end();
unsigned KillIdx = 0;
if (ValNo->def == ~0U || DefMI->getParent() == BarrierMBB)
KillPt = findSpillPoint(BarrierMBB, Barrier, NULL, RefsInMBB, KillIdx);
else
KillPt = findNextEmptySlot(DefMI->getParent(), DefMI, KillIdx);
if (KillPt == DefMI->getParent()->end())
return false;
TII->reMaterialize(MBB, RestorePt, vreg, DefMI);
LIs->InsertMachineInstrInMaps(prior(RestorePt), RestoreIdx);
ReconstructLiveInterval(CurrLI);
unsigned RematIdx = LIs->getInstructionIndex(prior(RestorePt));
RematIdx = LiveIntervals::getDefIndex(RematIdx);
RenumberValno(CurrLI->findDefinedVNInfo(RematIdx));
++NumSplits;
++NumRemats;
return true;
}
MachineInstr* PreAllocSplitting::FoldSpill(unsigned vreg,
const TargetRegisterClass* RC,
MachineInstr* DefMI,
MachineInstr* Barrier,
MachineBasicBlock* MBB,
int& SS,
SmallPtrSet<MachineInstr*, 4>& RefsInMBB) {
MachineBasicBlock::iterator Pt = MBB->begin();
// Go top down if RefsInMBB is empty.
if (RefsInMBB.empty())
return 0;
MachineBasicBlock::iterator FoldPt = Barrier;
while (&*FoldPt != DefMI && FoldPt != MBB->begin() &&
!RefsInMBB.count(FoldPt))
--FoldPt;
int OpIdx = FoldPt->findRegisterDefOperandIdx(vreg, false);
if (OpIdx == -1)
return 0;
SmallVector<unsigned, 1> Ops;
Ops.push_back(OpIdx);
if (!TII->canFoldMemoryOperand(FoldPt, Ops))
return 0;
DenseMap<unsigned, int>::iterator I = IntervalSSMap.find(vreg);
if (I != IntervalSSMap.end()) {
SS = I->second;
} else {
SS = MFI->CreateStackObject(RC->getSize(), RC->getAlignment());
}
MachineInstr* FMI = TII->foldMemoryOperand(*MBB->getParent(),
FoldPt, Ops, SS);
if (FMI) {
LIs->ReplaceMachineInstrInMaps(FoldPt, FMI);
FMI = MBB->insert(MBB->erase(FoldPt), FMI);
++NumFolds;
IntervalSSMap[vreg] = SS;
CurrSLI = &LSs->getOrCreateInterval(SS, RC);
if (CurrSLI->hasAtLeastOneValue())
CurrSValNo = CurrSLI->getValNumInfo(0);
else
CurrSValNo = CurrSLI->getNextValue(~0U, 0, LSs->getVNInfoAllocator());
}
return FMI;
}
MachineInstr* PreAllocSplitting::FoldRestore(unsigned vreg,
const TargetRegisterClass* RC,
MachineInstr* Barrier,
MachineBasicBlock* MBB,
int SS,
SmallPtrSet<MachineInstr*, 4>& RefsInMBB) {
if ((int)RestoreFoldLimit != -1 && RestoreFoldLimit == (int)NumRestoreFolds)
return 0;
// Go top down if RefsInMBB is empty.
if (RefsInMBB.empty())
return 0;
// Can't fold a restore between a call stack setup and teardown.
MachineBasicBlock::iterator FoldPt = Barrier;
// Advance from barrier to call frame teardown.
while (FoldPt != MBB->getFirstTerminator() &&
FoldPt->getOpcode() != TRI->getCallFrameDestroyOpcode()) {
if (RefsInMBB.count(FoldPt))
return 0;
++FoldPt;
}
if (FoldPt == MBB->getFirstTerminator())
return 0;
else
++FoldPt;
// Now find the restore point.
while (FoldPt != MBB->getFirstTerminator() && !RefsInMBB.count(FoldPt)) {
if (FoldPt->getOpcode() == TRI->getCallFrameSetupOpcode()) {
while (FoldPt != MBB->getFirstTerminator() &&
FoldPt->getOpcode() != TRI->getCallFrameDestroyOpcode()) {
if (RefsInMBB.count(FoldPt))
return 0;
++FoldPt;
}
if (FoldPt == MBB->getFirstTerminator())
return 0;
}
++FoldPt;
}
if (FoldPt == MBB->getFirstTerminator())
return 0;
int OpIdx = FoldPt->findRegisterUseOperandIdx(vreg, true);
if (OpIdx == -1)
return 0;
SmallVector<unsigned, 1> Ops;
Ops.push_back(OpIdx);
if (!TII->canFoldMemoryOperand(FoldPt, Ops))
return 0;
MachineInstr* FMI = TII->foldMemoryOperand(*MBB->getParent(),
FoldPt, Ops, SS);
if (FMI) {
LIs->ReplaceMachineInstrInMaps(FoldPt, FMI);
FMI = MBB->insert(MBB->erase(FoldPt), FMI);
++NumRestoreFolds;
}
return FMI;
}
/// SplitRegLiveInterval - Split (spill and restore) the given live interval
/// so it would not cross the barrier that's being processed. Shrink wrap
/// (minimize) the live interval to the last uses.
bool PreAllocSplitting::SplitRegLiveInterval(LiveInterval *LI) {
CurrLI = LI;
// Find live range where current interval cross the barrier.
LiveInterval::iterator LR =
CurrLI->FindLiveRangeContaining(LIs->getUseIndex(BarrierIdx));
VNInfo *ValNo = LR->valno;
if (ValNo->def == ~1U) {
// Defined by a dead def? How can this be?
assert(0 && "Val# is defined by a dead def?");
abort();
}
MachineInstr *DefMI = (ValNo->def != ~0U)
? LIs->getInstructionFromIndex(ValNo->def) : NULL;
// If this would create a new join point, do not split.
if (DefMI && createsNewJoin(LR, DefMI->getParent(), Barrier->getParent()))
return false;
// Find all references in the barrier mbb.
SmallPtrSet<MachineInstr*, 4> RefsInMBB;
for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(CurrLI->reg),
E = MRI->reg_end(); I != E; ++I) {
MachineInstr *RefMI = &*I;
if (RefMI->getParent() == BarrierMBB)
RefsInMBB.insert(RefMI);
}
// Find a point to restore the value after the barrier.
unsigned RestoreIndex = 0;
MachineBasicBlock::iterator RestorePt =
findRestorePoint(BarrierMBB, Barrier, LR->end, RefsInMBB, RestoreIndex);
if (RestorePt == BarrierMBB->end())
return false;
if (DefMI && LIs->isReMaterializable(*LI, ValNo, DefMI))
if (Rematerialize(LI->reg, ValNo, DefMI, RestorePt,
RestoreIndex, RefsInMBB))
return true;
// Add a spill either before the barrier or after the definition.
MachineBasicBlock *DefMBB = DefMI ? DefMI->getParent() : NULL;
const TargetRegisterClass *RC = MRI->getRegClass(CurrLI->reg);
unsigned SpillIndex = 0;
MachineInstr *SpillMI = NULL;
int SS = -1;
if (ValNo->def == ~0U) {
// If it's defined by a phi, we must split just before the barrier.
if ((SpillMI = FoldSpill(LI->reg, RC, 0, Barrier,
BarrierMBB, SS, RefsInMBB))) {
SpillIndex = LIs->getInstructionIndex(SpillMI);
} else {
MachineBasicBlock::iterator SpillPt =
findSpillPoint(BarrierMBB, Barrier, NULL, RefsInMBB, SpillIndex);
if (SpillPt == BarrierMBB->begin())
return false; // No gap to insert spill.
// Add spill.
SS = CreateSpillStackSlot(CurrLI->reg, RC);
TII->storeRegToStackSlot(*BarrierMBB, SpillPt, CurrLI->reg, true, SS, RC);
SpillMI = prior(SpillPt);
LIs->InsertMachineInstrInMaps(SpillMI, SpillIndex);
}
} else if (!IsAvailableInStack(DefMBB, CurrLI->reg, ValNo->def,
RestoreIndex, SpillIndex, SS)) {
// If it's already split, just restore the value. There is no need to spill
// the def again.
if (!DefMI)
return false; // Def is dead. Do nothing.
if ((SpillMI = FoldSpill(LI->reg, RC, DefMI, Barrier,
BarrierMBB, SS, RefsInMBB))) {
SpillIndex = LIs->getInstructionIndex(SpillMI);
} else {
// Check if it's possible to insert a spill after the def MI.
MachineBasicBlock::iterator SpillPt;
if (DefMBB == BarrierMBB) {
// Add spill after the def and the last use before the barrier.
SpillPt = findSpillPoint(BarrierMBB, Barrier, DefMI,
RefsInMBB, SpillIndex);
if (SpillPt == DefMBB->begin())
return false; // No gap to insert spill.
} else {
SpillPt = findNextEmptySlot(DefMBB, DefMI, SpillIndex);
if (SpillPt == DefMBB->end())
return false; // No gap to insert spill.
}
// Add spill. The store instruction kills the register if def is before
// the barrier in the barrier block.
SS = CreateSpillStackSlot(CurrLI->reg, RC);
TII->storeRegToStackSlot(*DefMBB, SpillPt, CurrLI->reg,
DefMBB == BarrierMBB, SS, RC);
SpillMI = prior(SpillPt);
LIs->InsertMachineInstrInMaps(SpillMI, SpillIndex);
}
}
// Remember def instruction index to spill index mapping.
if (DefMI && SpillMI)
Def2SpillMap[ValNo->def] = SpillIndex;
// Add restore.
bool FoldedRestore = false;
if (MachineInstr* LMI = FoldRestore(CurrLI->reg, RC, Barrier,
BarrierMBB, SS, RefsInMBB)) {
RestorePt = LMI;
RestoreIndex = LIs->getInstructionIndex(RestorePt);
FoldedRestore = true;
} else {
TII->loadRegFromStackSlot(*BarrierMBB, RestorePt, CurrLI->reg, SS, RC);
MachineInstr *LoadMI = prior(RestorePt);
LIs->InsertMachineInstrInMaps(LoadMI, RestoreIndex);
}
// Update spill stack slot live interval.
UpdateSpillSlotInterval(ValNo, LIs->getUseIndex(SpillIndex)+1,
LIs->getDefIndex(RestoreIndex));
ReconstructLiveInterval(CurrLI);
if (!FoldedRestore) {
unsigned RestoreIdx = LIs->getInstructionIndex(prior(RestorePt));
RestoreIdx = LiveIntervals::getDefIndex(RestoreIdx);
RenumberValno(CurrLI->findDefinedVNInfo(RestoreIdx));
}
++NumSplits;
return true;
}
/// SplitRegLiveIntervals - Split all register live intervals that cross the
/// barrier that's being processed.
bool
PreAllocSplitting::SplitRegLiveIntervals(const TargetRegisterClass **RCs,
SmallPtrSet<LiveInterval*, 8>& Split) {
// First find all the virtual registers whose live intervals are intercepted
// by the current barrier.
SmallVector<LiveInterval*, 8> Intervals;
for (const TargetRegisterClass **RC = RCs; *RC; ++RC) {
// FIXME: If it's not safe to move any instruction that defines the barrier
// register class, then it means there are some special dependencies which
// codegen is not modelling. Ignore these barriers for now.
if (!TII->isSafeToMoveRegClassDefs(*RC))
continue;
std::vector<unsigned> &VRs = MRI->getRegClassVirtRegs(*RC);
for (unsigned i = 0, e = VRs.size(); i != e; ++i) {
unsigned Reg = VRs[i];
if (!LIs->hasInterval(Reg))
continue;
LiveInterval *LI = &LIs->getInterval(Reg);
if (LI->liveAt(BarrierIdx) && !Barrier->readsRegister(Reg))
// Virtual register live interval is intercepted by the barrier. We
// should split and shrink wrap its interval if possible.
Intervals.push_back(LI);
}
}
// Process the affected live intervals.
bool Change = false;
while (!Intervals.empty()) {
if (PreSplitLimit != -1 && (int)NumSplits == PreSplitLimit)
break;
else if (NumSplits == 4)
Change |= Change;
LiveInterval *LI = Intervals.back();
Intervals.pop_back();
bool result = SplitRegLiveInterval(LI);
if (result) Split.insert(LI);
Change |= result;
}
return Change;
}
unsigned PreAllocSplitting::getNumberOfNonSpills(
SmallPtrSet<MachineInstr*, 4>& MIs,
unsigned Reg, int FrameIndex,
bool& FeedsTwoAddr) {
unsigned NonSpills = 0;
for (SmallPtrSet<MachineInstr*, 4>::iterator UI = MIs.begin(), UE = MIs.end();
UI != UE; ++UI) {
int StoreFrameIndex;
unsigned StoreVReg = TII->isStoreToStackSlot(*UI, StoreFrameIndex);
if (StoreVReg != Reg || StoreFrameIndex != FrameIndex)
NonSpills++;
int DefIdx = (*UI)->findRegisterDefOperandIdx(Reg);
if (DefIdx != -1 && (*UI)->isRegTiedToUseOperand(DefIdx))
FeedsTwoAddr = true;
}
return NonSpills;
}
/// removeDeadSpills - After doing splitting, filter through all intervals we've
/// split, and see if any of the spills are unnecessary. If so, remove them.
bool PreAllocSplitting::removeDeadSpills(SmallPtrSet<LiveInterval*, 8>& split) {
bool changed = false;
// Walk over all of the live intervals that were touched by the splitter,
// and see if we can do any DCE and/or folding.
for (SmallPtrSet<LiveInterval*, 8>::iterator LI = split.begin(),
LE = split.end(); LI != LE; ++LI) {
DenseMap<VNInfo*, SmallPtrSet<MachineInstr*, 4> > VNUseCount;
// First, collect all the uses of the vreg, and sort them by their
// reaching definition (VNInfo).
for (MachineRegisterInfo::use_iterator UI = MRI->use_begin((*LI)->reg),
UE = MRI->use_end(); UI != UE; ++UI) {
unsigned index = LIs->getInstructionIndex(&*UI);
index = LiveIntervals::getUseIndex(index);
const LiveRange* LR = (*LI)->getLiveRangeContaining(index);
VNUseCount[LR->valno].insert(&*UI);
}
// Now, take the definitions (VNInfo's) one at a time and try to DCE
// and/or fold them away.
for (LiveInterval::vni_iterator VI = (*LI)->vni_begin(),
VE = (*LI)->vni_end(); VI != VE; ++VI) {
if (DeadSplitLimit != -1 && (int)NumDeadSpills == DeadSplitLimit)
return changed;
VNInfo* CurrVN = *VI;
// We don't currently try to handle definitions with PHI kills, because
// it would involve processing more than one VNInfo at once.
if (CurrVN->hasPHIKill) continue;
// We also don't try to handle the results of PHI joins, since there's
// no defining instruction to analyze.
unsigned DefIdx = CurrVN->def;
if (DefIdx == ~0U || DefIdx == ~1U) continue;
// We're only interested in eliminating cruft introduced by the splitter,
// is of the form load-use or load-use-store. First, check that the
// definition is a load, and remember what stack slot we loaded it from.
MachineInstr* DefMI = LIs->getInstructionFromIndex(DefIdx);
int FrameIndex;
if (!TII->isLoadFromStackSlot(DefMI, FrameIndex)) continue;
// If the definition has no uses at all, just DCE it.
if (VNUseCount[CurrVN].size() == 0) {
LIs->RemoveMachineInstrFromMaps(DefMI);
(*LI)->removeValNo(CurrVN);
DefMI->eraseFromParent();
VNUseCount.erase(CurrVN);
NumDeadSpills++;
changed = true;
continue;
}
// Second, get the number of non-store uses of the definition, as well as
// a flag indicating whether it feeds into a later two-address definition.
bool FeedsTwoAddr = false;
unsigned NonSpillCount = getNumberOfNonSpills(VNUseCount[CurrVN],
(*LI)->reg, FrameIndex,
FeedsTwoAddr);
// If there's one non-store use and it doesn't feed a two-addr, then
// this is a load-use-store case that we can try to fold.
if (NonSpillCount == 1 && !FeedsTwoAddr) {
// Start by finding the non-store use MachineInstr.
SmallPtrSet<MachineInstr*, 4>::iterator UI = VNUseCount[CurrVN].begin();
int StoreFrameIndex;
unsigned StoreVReg = TII->isStoreToStackSlot(*UI, StoreFrameIndex);
while (UI != VNUseCount[CurrVN].end() &&
(StoreVReg == (*LI)->reg && StoreFrameIndex == FrameIndex)) {
++UI;
if (UI != VNUseCount[CurrVN].end())
StoreVReg = TII->isStoreToStackSlot(*UI, StoreFrameIndex);
}
if (UI == VNUseCount[CurrVN].end()) continue;
MachineInstr* use = *UI;
// Attempt to fold it away!
int OpIdx = use->findRegisterUseOperandIdx((*LI)->reg, false);
if (OpIdx == -1) continue;
SmallVector<unsigned, 1> Ops;
Ops.push_back(OpIdx);
if (!TII->canFoldMemoryOperand(use, Ops)) continue;
MachineInstr* NewMI =
TII->foldMemoryOperand(*use->getParent()->getParent(),
use, Ops, FrameIndex);
if (!NewMI) continue;
// Update relevant analyses.
LIs->RemoveMachineInstrFromMaps(DefMI);
LIs->ReplaceMachineInstrInMaps(use, NewMI);
(*LI)->removeValNo(CurrVN);
DefMI->eraseFromParent();
MachineBasicBlock* MBB = use->getParent();
NewMI = MBB->insert(MBB->erase(use), NewMI);
VNUseCount[CurrVN].erase(use);
// Remove deleted instructions. Note that we need to remove them from
// the VNInfo->use map as well, just to be safe.
for (SmallPtrSet<MachineInstr*, 4>::iterator II =
VNUseCount[CurrVN].begin(), IE = VNUseCount[CurrVN].end();
II != IE; ++II) {
for (DenseMap<VNInfo*, SmallPtrSet<MachineInstr*, 4> >::iterator
VNI = VNUseCount.begin(), VNE = VNUseCount.end(); VNI != VNE;
++VNI)
if (VNI->first != CurrVN)
VNI->second.erase(*II);
LIs->RemoveMachineInstrFromMaps(*II);
(*II)->eraseFromParent();
}
VNUseCount.erase(CurrVN);
for (DenseMap<VNInfo*, SmallPtrSet<MachineInstr*, 4> >::iterator
VI = VNUseCount.begin(), VE = VNUseCount.end(); VI != VE; ++VI)
if (VI->second.erase(use))
VI->second.insert(NewMI);
NumDeadSpills++;
changed = true;
continue;
}
// If there's more than one non-store instruction, we can't profitably
// fold it, so bail.
if (NonSpillCount) continue;
// Otherwise, this is a load-store case, so DCE them.
for (SmallPtrSet<MachineInstr*, 4>::iterator UI =
VNUseCount[CurrVN].begin(), UE = VNUseCount[CurrVN].end();
UI != UI; ++UI) {
LIs->RemoveMachineInstrFromMaps(*UI);
(*UI)->eraseFromParent();
}
VNUseCount.erase(CurrVN);
LIs->RemoveMachineInstrFromMaps(DefMI);
(*LI)->removeValNo(CurrVN);
DefMI->eraseFromParent();
NumDeadSpills++;
changed = true;
}
}
return changed;
}
bool PreAllocSplitting::createsNewJoin(LiveRange* LR,
MachineBasicBlock* DefMBB,
MachineBasicBlock* BarrierMBB) {
if (DefMBB == BarrierMBB)
return false;
if (LR->valno->hasPHIKill)
return false;
unsigned MBBEnd = LIs->getMBBEndIdx(BarrierMBB);
if (LR->end < MBBEnd)
return false;
MachineLoopInfo& MLI = getAnalysis<MachineLoopInfo>();
if (MLI.getLoopFor(DefMBB) != MLI.getLoopFor(BarrierMBB))
return true;
MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
SmallPtrSet<MachineBasicBlock*, 4> Visited;
typedef std::pair<MachineBasicBlock*,
MachineBasicBlock::succ_iterator> ItPair;
SmallVector<ItPair, 4> Stack;
Stack.push_back(std::make_pair(BarrierMBB, BarrierMBB->succ_begin()));
while (!Stack.empty()) {
ItPair P = Stack.back();
Stack.pop_back();
MachineBasicBlock* PredMBB = P.first;
MachineBasicBlock::succ_iterator S = P.second;
if (S == PredMBB->succ_end())
continue;
else if (Visited.count(*S)) {
Stack.push_back(std::make_pair(PredMBB, ++S));
continue;
} else
Stack.push_back(std::make_pair(PredMBB, S+1));
MachineBasicBlock* MBB = *S;
Visited.insert(MBB);
if (MBB == BarrierMBB)
return true;
MachineDomTreeNode* DefMDTN = MDT.getNode(DefMBB);
MachineDomTreeNode* BarrierMDTN = MDT.getNode(BarrierMBB);
MachineDomTreeNode* MDTN = MDT.getNode(MBB)->getIDom();
while (MDTN) {
if (MDTN == DefMDTN)
return true;
else if (MDTN == BarrierMDTN)
break;
MDTN = MDTN->getIDom();
}
MBBEnd = LIs->getMBBEndIdx(MBB);
if (LR->end > MBBEnd)
Stack.push_back(std::make_pair(MBB, MBB->succ_begin()));
}
return false;
}
bool PreAllocSplitting::runOnMachineFunction(MachineFunction &MF) {
CurrMF = &MF;
TM = &MF.getTarget();
TRI = TM->getRegisterInfo();
TII = TM->getInstrInfo();
MFI = MF.getFrameInfo();
MRI = &MF.getRegInfo();
LIs = &getAnalysis<LiveIntervals>();
LSs = &getAnalysis<LiveStacks>();
VRM = &getAnalysis<VirtRegMap>();
bool MadeChange = false;
// Make sure blocks are numbered in order.
MF.RenumberBlocks();
MachineBasicBlock *Entry = MF.begin();
SmallPtrSet<MachineBasicBlock*,16> Visited;
SmallPtrSet<LiveInterval*, 8> Split;
for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*,16> >
DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
DFI != E; ++DFI) {
BarrierMBB = *DFI;
for (MachineBasicBlock::iterator I = BarrierMBB->begin(),
E = BarrierMBB->end(); I != E; ++I) {
Barrier = &*I;
const TargetRegisterClass **BarrierRCs =
Barrier->getDesc().getRegClassBarriers();
if (!BarrierRCs)
continue;
BarrierIdx = LIs->getInstructionIndex(Barrier);
MadeChange |= SplitRegLiveIntervals(BarrierRCs, Split);
}
}
MadeChange |= removeDeadSpills(Split);
return MadeChange;
}
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