X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FRegisterScavenging.cpp;h=d673794e1b9392ab3e660d175ebe6063807e8424;hb=3574eca1b02600bac4e625297f4ecf745f4c4f32;hp=add639a967129da54de59d94aec1934d68fa8abd;hpb=1385758215bb31ba042a3d42e40d28e521616a0c;p=oota-llvm.git diff --git a/lib/CodeGen/RegisterScavenging.cpp b/lib/CodeGen/RegisterScavenging.cpp index add639a9671..d673794e1b9 100644 --- a/lib/CodeGen/RegisterScavenging.cpp +++ b/lib/CodeGen/RegisterScavenging.cpp @@ -16,68 +16,58 @@ #define DEBUG_TYPE "reg-scavenging" #include "llvm/CodeGen/RegisterScavenging.h" +#include "llvm/CodeGen/MachineFrameInfo.h" #include "llvm/CodeGen/MachineFunction.h" #include "llvm/CodeGen/MachineBasicBlock.h" #include "llvm/CodeGen/MachineInstr.h" #include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" #include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" +#include "llvm/ADT/DenseMap.h" #include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" #include "llvm/ADT/STLExtras.h" using namespace llvm; -/// RedefinesSuperRegPart - Return true if the specified register is redefining -/// part of a super-register. -static bool RedefinesSuperRegPart(const MachineInstr *MI, unsigned SubReg, - const TargetRegisterInfo *TRI) { - bool SeenSuperUse = false; - bool SeenSuperDef = false; - for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { - const MachineOperand &MO = MI->getOperand(i); - if (!MO.isReg()) - continue; - if (TRI->isSuperRegister(SubReg, MO.getReg())) { - if (MO.isUse()) - SeenSuperUse = true; - else if (MO.isImplicit()) - SeenSuperDef = true; - } - } +/// setUsed - Set the register and its sub-registers as being used. +void RegScavenger::setUsed(unsigned Reg) { + RegsAvailable.reset(Reg); - return SeenSuperDef && SeenSuperUse; + for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) + RegsAvailable.reset(*SubRegs); } -static bool RedefinesSuperRegPart(const MachineInstr *MI, - const MachineOperand &MO, - const TargetRegisterInfo *TRI) { - assert(MO.isReg() && MO.isDef() && "Not a register def!"); - return RedefinesSuperRegPart(MI, MO.getReg(), TRI); +bool RegScavenger::isAliasUsed(unsigned Reg) const { + for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) + if (isUsed(*AI)) + return true; + return false; } -/// setUsed - Set the register and its sub-registers as being used. -void RegScavenger::setUsed(unsigned Reg, bool ImpDef) { - RegsAvailable.reset(Reg); - ImplicitDefed[Reg] = ImpDef; +void RegScavenger::initRegState() { + ScavengedReg = 0; + ScavengedRC = NULL; + ScavengeRestore = NULL; - for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); - unsigned SubReg = *SubRegs; ++SubRegs) { - RegsAvailable.reset(SubReg); - ImplicitDefed[SubReg] = ImpDef; - } -} + // All registers started out unused. + RegsAvailable.set(); -/// setUnused - Set the register and its sub-registers as being unused. -void RegScavenger::setUnused(unsigned Reg, const MachineInstr *MI) { - RegsAvailable.set(Reg); - ImplicitDefed.reset(Reg); + if (!MBB) + return; - for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); - unsigned SubReg = *SubRegs; ++SubRegs) - if (!RedefinesSuperRegPart(MI, Reg, TRI)) { - RegsAvailable.set(SubReg); - ImplicitDefed.reset(SubReg); - } + // Live-in registers are in use. + for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(), + E = MBB->livein_end(); I != E; ++I) + setUsed(*I); + + // Pristine CSRs are also unavailable. + BitVector PR = MBB->getParent()->getFrameInfo()->getPristineRegs(MBB); + for (int I = PR.find_first(); I>0; I = PR.find_next(I)) + setUsed(I); } void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) { @@ -90,87 +80,39 @@ void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) { assert((NumPhysRegs == 0 || NumPhysRegs == TRI->getNumRegs()) && "Target changed?"); + // It is not possible to use the register scavenger after late optimization + // passes that don't preserve accurate liveness information. + assert(MRI->tracksLiveness() && + "Cannot use register scavenger with inaccurate liveness"); + + // Self-initialize. if (!MBB) { NumPhysRegs = TRI->getNumRegs(); RegsAvailable.resize(NumPhysRegs); - ImplicitDefed.resize(NumPhysRegs); + KillRegs.resize(NumPhysRegs); + DefRegs.resize(NumPhysRegs); // Create reserved registers bitvector. ReservedRegs = TRI->getReservedRegs(MF); // Create callee-saved registers bitvector. CalleeSavedRegs.resize(NumPhysRegs); - const unsigned *CSRegs = TRI->getCalleeSavedRegs(); + const uint16_t *CSRegs = TRI->getCalleeSavedRegs(&MF); if (CSRegs != NULL) for (unsigned i = 0; CSRegs[i]; ++i) CalleeSavedRegs.set(CSRegs[i]); } MBB = mbb; - ScavengedReg = 0; - ScavengedRC = NULL; - ScavengeRestore = NULL; - CurrDist = 0; - DistanceMap.clear(); - ImplicitDefed.reset(); - - // All registers started out unused. - RegsAvailable.set(); - - // Reserved registers are always used. - RegsAvailable ^= ReservedRegs; - - // Live-in registers are in use. - if (!MBB->livein_empty()) - for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(), - E = MBB->livein_end(); I != E; ++I) - setUsed(*I); + initRegState(); Tracking = false; } -void RegScavenger::restoreScavengedReg() { - TII->loadRegFromStackSlot(*MBB, MBBI, ScavengedReg, - ScavengingFrameIndex, ScavengedRC); - MachineBasicBlock::iterator II = prior(MBBI); - TRI->eliminateFrameIndex(II, 0, this); - setUsed(ScavengedReg); - ScavengedReg = 0; - ScavengedRC = NULL; -} - -/// isLiveInButUnusedBefore - Return true if register is livein the MBB not -/// not used before it reaches the MI that defines register. -static bool isLiveInButUnusedBefore(unsigned Reg, MachineInstr *MI, - MachineBasicBlock *MBB, - const TargetRegisterInfo *TRI, - MachineRegisterInfo* MRI) { - // First check if register is livein. - bool isLiveIn = false; - for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(), - E = MBB->livein_end(); I != E; ++I) - if (Reg == *I || TRI->isSuperRegister(Reg, *I)) { - isLiveIn = true; - break; - } - if (!isLiveIn) - return false; - - // Is there any use of it before the specified MI? - SmallPtrSet UsesInMBB; - for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg), - UE = MRI->use_end(); UI != UE; ++UI) { - MachineInstr *UseMI = &*UI; - if (UseMI->getParent() == MBB) - UsesInMBB.insert(UseMI); - } - if (UsesInMBB.empty()) - return true; - - for (MachineBasicBlock::iterator I = MBB->begin(), E = MI; I != E; ++I) - if (UsesInMBB.count(&*I)) - return false; - return true; +void RegScavenger::addRegWithSubRegs(BitVector &BV, unsigned Reg) { + BV.set(Reg); + for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) + BV.set(*SubRegs); } void RegScavenger::forward() { @@ -179,13 +121,12 @@ void RegScavenger::forward() { MBBI = MBB->begin(); Tracking = true; } else { - assert(MBBI != MBB->end() && "Already at the end of the basic block!"); - MBBI = next(MBBI); + assert(MBBI != MBB->end() && "Already past the end of the basic block!"); + MBBI = llvm::next(MBBI); } + assert(MBBI != MBB->end() && "Already at the end of the basic block!"); MachineInstr *MI = MBBI; - DistanceMap.insert(std::make_pair(MI, CurrDist++)); - const TargetInstrDesc &TID = MI->getDesc(); if (MI == ScavengeRestore) { ScavengedReg = 0; @@ -193,287 +134,259 @@ void RegScavenger::forward() { ScavengeRestore = NULL; } - bool IsImpDef = MI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF; - - // Separate register operands into 3 classes: uses, defs, earlyclobbers. - SmallVector, 4> UseMOs; - SmallVector, 4> DefMOs; - SmallVector, 4> EarlyClobberMOs; + if (MI->isDebugValue()) + return; + + // Find out which registers are early clobbered, killed, defined, and marked + // def-dead in this instruction. + // FIXME: The scavenger is not predication aware. If the instruction is + // predicated, conservatively assume "kill" markers do not actually kill the + // register. Similarly ignores "dead" markers. + bool isPred = TII->isPredicated(MI); + KillRegs.reset(); + DefRegs.reset(); for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &MO = MI->getOperand(i); - if (!MO.isReg() || MO.getReg() == 0) + if (MO.isRegMask()) + (isPred ? DefRegs : KillRegs).setBitsNotInMask(MO.getRegMask()); + if (!MO.isReg()) continue; - if (MO.isUse()) - UseMOs.push_back(std::make_pair(&MO,i)); - else if (MO.isEarlyClobber()) - EarlyClobberMOs.push_back(std::make_pair(&MO,i)); - else - DefMOs.push_back(std::make_pair(&MO,i)); - } - - // Process uses first. - BitVector UseRegs(NumPhysRegs); - for (unsigned i = 0, e = UseMOs.size(); i != e; ++i) { - const MachineOperand MO = *UseMOs[i].first; unsigned Reg = MO.getReg(); - - assert(isUsed(Reg) && "Using an undefined register!"); - - if (MO.isKill() && !isReserved(Reg)) { - UseRegs.set(Reg); - - // Mark sub-registers as used. - for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); - unsigned SubReg = *SubRegs; ++SubRegs) - UseRegs.set(SubReg); - } - } - - // Change states of all registers after all the uses are processed to guard - // against multiple uses. - setUnused(UseRegs); - - // Process early clobber defs then process defs. We can have a early clobber - // that is dead, it should not conflict with a def that happens one "slot" - // (see InstrSlots in LiveIntervalAnalysis.h) later. - unsigned NumECs = EarlyClobberMOs.size(); - unsigned NumDefs = DefMOs.size(); - - for (unsigned i = 0, e = NumECs + NumDefs; i != e; ++i) { - const MachineOperand &MO = (i < NumECs) - ? *EarlyClobberMOs[i].first : *DefMOs[i-NumECs].first; - unsigned Idx = (i < NumECs) - ? EarlyClobberMOs[i].second : DefMOs[i-NumECs].second; - unsigned Reg = MO.getReg(); - - // If it's dead upon def, then it is now free. - if (MO.isDead()) { - setUnused(Reg, MI); + if (!Reg || isReserved(Reg)) continue; - } - // Skip two-address destination operand. - if (TID.findTiedToSrcOperand(Idx) != -1) { - assert(isUsed(Reg) && "Using an undefined register!"); - continue; + if (MO.isUse()) { + // Ignore undef uses. + if (MO.isUndef()) + continue; + if (!isPred && MO.isKill()) + addRegWithSubRegs(KillRegs, Reg); + } else { + assert(MO.isDef()); + if (!isPred && MO.isDead()) + addRegWithSubRegs(KillRegs, Reg); + else + addRegWithSubRegs(DefRegs, Reg); } - - // Skip if this is merely redefining part of a super-register. - if (RedefinesSuperRegPart(MI, MO, TRI)) - continue; - - // Implicit def is allowed to "re-define" any register. Similarly, - // implicitly defined registers can be clobbered. - assert((isReserved(Reg) || isUnused(Reg) || - IsImpDef || isImplicitlyDefined(Reg) || - isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) && - "Re-defining a live register!"); - setUsed(Reg, IsImpDef); } -} -void RegScavenger::backward() { - assert(Tracking && "Not tracking states!"); - assert(MBBI != MBB->begin() && "Already at start of basic block!"); - // Move ptr backward. - MBBI = prior(MBBI); - - MachineInstr *MI = MBBI; - DistanceMap.erase(MI); - --CurrDist; - const TargetInstrDesc &TID = MI->getDesc(); - - // Separate register operands into 3 classes: uses, defs, earlyclobbers. - SmallVector, 4> UseMOs; - SmallVector, 4> DefMOs; - SmallVector, 4> EarlyClobberMOs; + // Verify uses and defs. +#ifndef NDEBUG for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &MO = MI->getOperand(i); - if (!MO.isReg() || MO.getReg() == 0) - continue; - if (MO.isUse()) - UseMOs.push_back(std::make_pair(&MO,i)); - else if (MO.isEarlyClobber()) - EarlyClobberMOs.push_back(std::make_pair(&MO,i)); - else - DefMOs.push_back(std::make_pair(&MO,i)); - } - - - // Process defs first. - unsigned NumECs = EarlyClobberMOs.size(); - unsigned NumDefs = DefMOs.size(); - for (unsigned i = 0, e = NumECs + NumDefs; i != e; ++i) { - const MachineOperand &MO = (i < NumDefs) - ? *DefMOs[i].first : *EarlyClobberMOs[i-NumDefs].first; - unsigned Idx = (i < NumECs) - ? DefMOs[i].second : EarlyClobberMOs[i-NumDefs].second; - - // Skip two-address destination operand. - if (TID.findTiedToSrcOperand(Idx) != -1) + if (!MO.isReg()) continue; - unsigned Reg = MO.getReg(); - assert(isUsed(Reg)); - if (!isReserved(Reg)) - setUnused(Reg, MI); + if (!Reg || isReserved(Reg)) + continue; + if (MO.isUse()) { + if (MO.isUndef()) + continue; + if (!isUsed(Reg)) { + // Check if it's partial live: e.g. + // D0 = insert_subreg D0, S0 + // ... D0 + // The problem is the insert_subreg could be eliminated. The use of + // D0 is using a partially undef value. This is not *incorrect* since + // S1 is can be freely clobbered. + // Ideally we would like a way to model this, but leaving the + // insert_subreg around causes both correctness and performance issues. + bool SubUsed = false; + for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) + if (isUsed(*SubRegs)) { + SubUsed = true; + break; + } + if (!SubUsed) { + MBB->getParent()->verify(NULL, "In Register Scavenger"); + llvm_unreachable("Using an undefined register!"); + } + (void)SubUsed; + } + } else { + assert(MO.isDef()); +#if 0 + // FIXME: Enable this once we've figured out how to correctly transfer + // implicit kills during codegen passes like the coalescer. + assert((KillRegs.test(Reg) || isUnused(Reg) || + isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) && + "Re-defining a live register!"); +#endif + } } +#endif // NDEBUG - // Process uses. - BitVector UseRegs(NumPhysRegs); - for (unsigned i = 0, e = UseMOs.size(); i != e; ++i) { - const MachineOperand MO = *UseMOs[i].first; - unsigned Reg = MO.getReg(); - assert(isUnused(Reg) || isReserved(Reg)); - UseRegs.set(Reg); - - // Set the sub-registers as "used". - for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); - unsigned SubReg = *SubRegs; ++SubRegs) - UseRegs.set(SubReg); - } - setUsed(UseRegs); + // Commit the changes. + setUnused(KillRegs); + setUsed(DefRegs); } void RegScavenger::getRegsUsed(BitVector &used, bool includeReserved) { + used = RegsAvailable; + used.flip(); if (includeReserved) - used = ~RegsAvailable; + used |= ReservedRegs; else - used = ~RegsAvailable & ~ReservedRegs; + used.reset(ReservedRegs); } -/// CreateRegClassMask - Set the bits that represent the registers in the -/// TargetRegisterClass. -static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) { - for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E; - ++I) - Mask.set(*I); -} - -unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass, - const BitVector &Candidates) const { - // Mask off the registers which are not in the TargetRegisterClass. - BitVector RegsAvailableCopy(NumPhysRegs, false); - CreateRegClassMask(RegClass, RegsAvailableCopy); - RegsAvailableCopy &= RegsAvailable; - - // Restrict the search to candidates. - RegsAvailableCopy &= Candidates; - - // Returns the first unused (bit is set) register, or 0 is none is found. - int Reg = RegsAvailableCopy.find_first(); - return (Reg == -1) ? 0 : Reg; +unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const { + for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); + I != E; ++I) + if (!isAliasUsed(*I)) { + DEBUG(dbgs() << "Scavenger found unused reg: " << TRI->getName(*I) << + "\n"); + return *I; + } + return 0; } -unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass, - bool ExCalleeSaved) const { - // Mask off the registers which are not in the TargetRegisterClass. - BitVector RegsAvailableCopy(NumPhysRegs, false); - CreateRegClassMask(RegClass, RegsAvailableCopy); - RegsAvailableCopy &= RegsAvailable; - - // If looking for a non-callee-saved register, mask off all the callee-saved - // registers. - if (ExCalleeSaved) - RegsAvailableCopy &= ~CalleeSavedRegs; - - // Returns the first unused (bit is set) register, or 0 is none is found. - int Reg = RegsAvailableCopy.find_first(); - return (Reg == -1) ? 0 : Reg; +/// getRegsAvailable - Return all available registers in the register class +/// in Mask. +BitVector RegScavenger::getRegsAvailable(const TargetRegisterClass *RC) { + BitVector Mask(TRI->getNumRegs()); + for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); + I != E; ++I) + if (!isAliasUsed(*I)) + Mask.set(*I); + return Mask; } -/// findFirstUse - Calculate the distance to the first use of the -/// specified register. -MachineInstr* -RegScavenger::findFirstUse(MachineBasicBlock *MBB, - MachineBasicBlock::iterator I, unsigned Reg, - unsigned &Dist) { - MachineInstr *UseMI = 0; - Dist = ~0U; - for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(Reg), - RE = MRI->reg_end(); RI != RE; ++RI) { - MachineInstr *UDMI = &*RI; - if (UDMI->getParent() != MBB) +/// findSurvivorReg - Return the candidate register that is unused for the +/// longest after StargMII. UseMI is set to the instruction where the search +/// stopped. +/// +/// No more than InstrLimit instructions are inspected. +/// +unsigned RegScavenger::findSurvivorReg(MachineBasicBlock::iterator StartMI, + BitVector &Candidates, + unsigned InstrLimit, + MachineBasicBlock::iterator &UseMI) { + int Survivor = Candidates.find_first(); + assert(Survivor > 0 && "No candidates for scavenging"); + + MachineBasicBlock::iterator ME = MBB->getFirstTerminator(); + assert(StartMI != ME && "MI already at terminator"); + MachineBasicBlock::iterator RestorePointMI = StartMI; + MachineBasicBlock::iterator MI = StartMI; + + bool inVirtLiveRange = false; + for (++MI; InstrLimit > 0 && MI != ME; ++MI, --InstrLimit) { + if (MI->isDebugValue()) { + ++InstrLimit; // Don't count debug instructions continue; - DenseMap::iterator DI = DistanceMap.find(UDMI); - if (DI == DistanceMap.end()) { - // If it's not in map, it's below current MI, let's initialize the - // map. - I = next(I); - unsigned Dist = CurrDist + 1; - while (I != MBB->end()) { - DistanceMap.insert(std::make_pair(I, Dist++)); - I = next(I); - } } - DI = DistanceMap.find(UDMI); - if (DI->second > CurrDist && DI->second < Dist) { - Dist = DI->second; - UseMI = UDMI; + bool isVirtKillInsn = false; + bool isVirtDefInsn = false; + // Remove any candidates touched by instruction. + for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { + const MachineOperand &MO = MI->getOperand(i); + if (MO.isRegMask()) + Candidates.clearBitsNotInMask(MO.getRegMask()); + if (!MO.isReg() || MO.isUndef() || !MO.getReg()) + continue; + if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) { + if (MO.isDef()) + isVirtDefInsn = true; + else if (MO.isKill()) + isVirtKillInsn = true; + continue; + } + for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI) + Candidates.reset(*AI); } + // If we're not in a virtual reg's live range, this is a valid + // restore point. + if (!inVirtLiveRange) RestorePointMI = MI; + + // Update whether we're in the live range of a virtual register + if (isVirtKillInsn) inVirtLiveRange = false; + if (isVirtDefInsn) inVirtLiveRange = true; + + // Was our survivor untouched by this instruction? + if (Candidates.test(Survivor)) + continue; + + // All candidates gone? + if (Candidates.none()) + break; + + Survivor = Candidates.find_first(); } - return UseMI; + // If we ran off the end, that's where we want to restore. + if (MI == ME) RestorePointMI = ME; + assert (RestorePointMI != StartMI && + "No available scavenger restore location!"); + + // We ran out of candidates, so stop the search. + UseMI = RestorePointMI; + return Survivor; } unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC, MachineBasicBlock::iterator I, int SPAdj) { - assert(ScavengingFrameIndex >= 0 && - "Cannot scavenge a register without an emergency spill slot!"); - - // Mask off the registers which are not in the TargetRegisterClass. - BitVector Candidates(NumPhysRegs, false); - CreateRegClassMask(RC, Candidates); - Candidates ^= ReservedRegs; // Do not include reserved registers. + // Consider all allocatable registers in the register class initially + BitVector Candidates = + TRI->getAllocatableSet(*I->getParent()->getParent(), RC); // Exclude all the registers being used by the instruction. for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { MachineOperand &MO = I->getOperand(i); - if (MO.isReg()) + if (MO.isReg() && MO.getReg() != 0 && + !TargetRegisterInfo::isVirtualRegister(MO.getReg())) Candidates.reset(MO.getReg()); } + // Try to find a register that's unused if there is one, as then we won't + // have to spill. Search explicitly rather than masking out based on + // RegsAvailable, as RegsAvailable does not take aliases into account. + // That's what getRegsAvailable() is for. + BitVector Available = getRegsAvailable(RC); + Available &= Candidates; + if (Available.any()) + Candidates = Available; + // Find the register whose use is furthest away. - unsigned SReg = 0; - unsigned MaxDist = 0; - MachineInstr *MaxUseMI = 0; - int Reg = Candidates.find_first(); - while (Reg != -1) { - unsigned Dist; - MachineInstr *UseMI = findFirstUse(MBB, I, Reg, Dist); - for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) { - unsigned AsDist; - MachineInstr *AsUseMI = findFirstUse(MBB, I, *AS, AsDist); - if (AsDist < Dist) { - Dist = AsDist; - UseMI = AsUseMI; - } - } - if (Dist >= MaxDist) { - MaxDist = Dist; - MaxUseMI = UseMI; - SReg = Reg; - } - Reg = Candidates.find_next(Reg); - } + MachineBasicBlock::iterator UseMI; + unsigned SReg = findSurvivorReg(I, Candidates, 25, UseMI); - if (ScavengedReg != 0) { - assert(0 && "Scavenger slot is live, unable to scavenge another register!"); - abort(); + // If we found an unused register there is no reason to spill it. + if (!isAliasUsed(SReg)) { + DEBUG(dbgs() << "Scavenged register: " << TRI->getName(SReg) << "\n"); + return SReg; } - // Spill the scavenged register before I. - TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC); - MachineBasicBlock::iterator II = prior(I); - TRI->eliminateFrameIndex(II, SPAdj, this); + assert(ScavengedReg == 0 && + "Scavenger slot is live, unable to scavenge another register!"); - // Restore the scavenged register before its use (or first terminator). - II = MaxUseMI - ? MachineBasicBlock::iterator(MaxUseMI) : MBB->getFirstTerminator(); - TII->loadRegFromStackSlot(*MBB, II, SReg, ScavengingFrameIndex, RC); - ScavengeRestore = prior(II); + // Avoid infinite regress ScavengedReg = SReg; + + // If the target knows how to save/restore the register, let it do so; + // otherwise, use the emergency stack spill slot. + if (!TRI->saveScavengerRegister(*MBB, I, UseMI, RC, SReg)) { + // Spill the scavenged register before I. + assert(ScavengingFrameIndex >= 0 && + "Cannot scavenge register without an emergency spill slot!"); + TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC,TRI); + MachineBasicBlock::iterator II = prior(I); + TRI->eliminateFrameIndex(II, SPAdj, this); + + // Restore the scavenged register before its use (or first terminator). + TII->loadRegFromStackSlot(*MBB, UseMI, SReg, ScavengingFrameIndex, RC, TRI); + II = prior(UseMI); + TRI->eliminateFrameIndex(II, SPAdj, this); + } + + ScavengeRestore = prior(UseMI); + + // Doing this here leads to infinite regress. + // ScavengedReg = SReg; ScavengedRC = RC; + DEBUG(dbgs() << "Scavenged register (with spill): " << TRI->getName(SReg) << + "\n"); + return SReg; }