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Diffstat (limited to 'lib/CodeGen/VirtRegMap.cpp')
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diff --git a/lib/CodeGen/VirtRegMap.cpp b/lib/CodeGen/VirtRegMap.cpp new file mode 100644 index 0000000..196e849 --- /dev/null +++ b/lib/CodeGen/VirtRegMap.cpp @@ -0,0 +1,1118 @@ +//===-- llvm/CodeGen/VirtRegMap.cpp - Virtual Register Map ----------------===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and is distributed under +// the University of Illinois Open Source License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements the VirtRegMap class. +// +// It also contains implementations of the the Spiller interface, which, given a +// virtual register map and a machine function, eliminates all virtual +// references by replacing them with physical register references - adding spill +// code as necessary. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "spiller" +#include "VirtRegMap.h" +#include "llvm/Function.h" +#include "llvm/CodeGen/MachineFrameInfo.h" +#include "llvm/CodeGen/MachineFunction.h" +#include "llvm/CodeGen/SSARegMap.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/Compiler.h" +#include "llvm/ADT/BitVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallSet.h" +#include <algorithm> +using namespace llvm; + +STATISTIC(NumSpills, "Number of register spills"); +STATISTIC(NumReMats, "Number of re-materialization"); +STATISTIC(NumStores, "Number of stores added"); +STATISTIC(NumLoads , "Number of loads added"); +STATISTIC(NumReused, "Number of values reused"); +STATISTIC(NumDSE , "Number of dead stores elided"); +STATISTIC(NumDCE , "Number of copies elided"); + +namespace { + enum SpillerName { simple, local }; + + static cl::opt<SpillerName> + SpillerOpt("spiller", + cl::desc("Spiller to use: (default: local)"), + cl::Prefix, + cl::values(clEnumVal(simple, " simple spiller"), + clEnumVal(local, " local spiller"), + clEnumValEnd), + cl::init(local)); +} + +//===----------------------------------------------------------------------===// +// VirtRegMap implementation +//===----------------------------------------------------------------------===// + +VirtRegMap::VirtRegMap(MachineFunction &mf) + : TII(*mf.getTarget().getInstrInfo()), MF(mf), + Virt2PhysMap(NO_PHYS_REG), Virt2StackSlotMap(NO_STACK_SLOT), + ReMatId(MAX_STACK_SLOT+1) { + grow(); +} + +void VirtRegMap::grow() { + Virt2PhysMap.grow(MF.getSSARegMap()->getLastVirtReg()); + Virt2StackSlotMap.grow(MF.getSSARegMap()->getLastVirtReg()); +} + +int VirtRegMap::assignVirt2StackSlot(unsigned virtReg) { + assert(MRegisterInfo::isVirtualRegister(virtReg)); + assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && + "attempt to assign stack slot to already spilled register"); + const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(virtReg); + int frameIndex = MF.getFrameInfo()->CreateStackObject(RC->getSize(), + RC->getAlignment()); + Virt2StackSlotMap[virtReg] = frameIndex; + ++NumSpills; + return frameIndex; +} + +void VirtRegMap::assignVirt2StackSlot(unsigned virtReg, int frameIndex) { + assert(MRegisterInfo::isVirtualRegister(virtReg)); + assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && + "attempt to assign stack slot to already spilled register"); + assert((frameIndex >= 0 || + (frameIndex >= MF.getFrameInfo()->getObjectIndexBegin())) && + "illegal fixed frame index"); + Virt2StackSlotMap[virtReg] = frameIndex; +} + +int VirtRegMap::assignVirtReMatId(unsigned virtReg) { + assert(MRegisterInfo::isVirtualRegister(virtReg)); + assert(Virt2StackSlotMap[virtReg] == NO_STACK_SLOT && + "attempt to assign re-mat id to already spilled register"); + const MachineInstr *DefMI = getReMaterializedMI(virtReg); + int FrameIdx; + if (TII.isLoadFromStackSlot((MachineInstr*)DefMI, FrameIdx)) { + // Load from stack slot is re-materialize as reload from the stack slot! + Virt2StackSlotMap[virtReg] = FrameIdx; + return FrameIdx; + } + Virt2StackSlotMap[virtReg] = ReMatId; + return ReMatId++; +} + +void VirtRegMap::virtFolded(unsigned VirtReg, MachineInstr *OldMI, + unsigned OpNo, MachineInstr *NewMI) { + // Move previous memory references folded to new instruction. + MI2VirtMapTy::iterator IP = MI2VirtMap.lower_bound(NewMI); + for (MI2VirtMapTy::iterator I = MI2VirtMap.lower_bound(OldMI), + E = MI2VirtMap.end(); I != E && I->first == OldMI; ) { + MI2VirtMap.insert(IP, std::make_pair(NewMI, I->second)); + MI2VirtMap.erase(I++); + } + + ModRef MRInfo; + const TargetInstrDescriptor *TID = OldMI->getInstrDescriptor(); + if (TID->getOperandConstraint(OpNo, TOI::TIED_TO) != -1 || + TID->findTiedToSrcOperand(OpNo) != -1) { + // Folded a two-address operand. + MRInfo = isModRef; + } else if (OldMI->getOperand(OpNo).isDef()) { + MRInfo = isMod; + } else { + MRInfo = isRef; + } + + // add new memory reference + MI2VirtMap.insert(IP, std::make_pair(NewMI, std::make_pair(VirtReg, MRInfo))); +} + +void VirtRegMap::print(std::ostream &OS) const { + const MRegisterInfo* MRI = MF.getTarget().getRegisterInfo(); + + OS << "********** REGISTER MAP **********\n"; + for (unsigned i = MRegisterInfo::FirstVirtualRegister, + e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) { + if (Virt2PhysMap[i] != (unsigned)VirtRegMap::NO_PHYS_REG) + OS << "[reg" << i << " -> " << MRI->getName(Virt2PhysMap[i]) << "]\n"; + + } + + for (unsigned i = MRegisterInfo::FirstVirtualRegister, + e = MF.getSSARegMap()->getLastVirtReg(); i <= e; ++i) + if (Virt2StackSlotMap[i] != VirtRegMap::NO_STACK_SLOT) + OS << "[reg" << i << " -> fi#" << Virt2StackSlotMap[i] << "]\n"; + OS << '\n'; +} + +void VirtRegMap::dump() const { + print(DOUT); +} + + +//===----------------------------------------------------------------------===// +// Simple Spiller Implementation +//===----------------------------------------------------------------------===// + +Spiller::~Spiller() {} + +namespace { + struct VISIBILITY_HIDDEN SimpleSpiller : public Spiller { + bool runOnMachineFunction(MachineFunction& mf, VirtRegMap &VRM); + }; +} + +bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { + DOUT << "********** REWRITE MACHINE CODE **********\n"; + DOUT << "********** Function: " << MF.getFunction()->getName() << '\n'; + const TargetMachine &TM = MF.getTarget(); + const MRegisterInfo &MRI = *TM.getRegisterInfo(); + + // LoadedRegs - Keep track of which vregs are loaded, so that we only load + // each vreg once (in the case where a spilled vreg is used by multiple + // operands). This is always smaller than the number of operands to the + // current machine instr, so it should be small. + std::vector<unsigned> LoadedRegs; + + for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end(); + MBBI != E; ++MBBI) { + DOUT << MBBI->getBasicBlock()->getName() << ":\n"; + MachineBasicBlock &MBB = *MBBI; + for (MachineBasicBlock::iterator MII = MBB.begin(), + E = MBB.end(); MII != E; ++MII) { + MachineInstr &MI = *MII; + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (MO.isRegister() && MO.getReg()) + if (MRegisterInfo::isVirtualRegister(MO.getReg())) { + unsigned VirtReg = MO.getReg(); + unsigned PhysReg = VRM.getPhys(VirtReg); + if (VRM.hasStackSlot(VirtReg)) { + int StackSlot = VRM.getStackSlot(VirtReg); + const TargetRegisterClass* RC = + MF.getSSARegMap()->getRegClass(VirtReg); + + if (MO.isUse() && + std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg) + == LoadedRegs.end()) { + MRI.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); + LoadedRegs.push_back(VirtReg); + ++NumLoads; + DOUT << '\t' << *prior(MII); + } + + if (MO.isDef()) { + MRI.storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); + ++NumStores; + } + } + MF.setPhysRegUsed(PhysReg); + MI.getOperand(i).setReg(PhysReg); + } else { + MF.setPhysRegUsed(MO.getReg()); + } + } + + DOUT << '\t' << MI; + LoadedRegs.clear(); + } + } + return true; +} + +//===----------------------------------------------------------------------===// +// Local Spiller Implementation +//===----------------------------------------------------------------------===// + +namespace { + /// LocalSpiller - This spiller does a simple pass over the machine basic + /// block to attempt to keep spills in registers as much as possible for + /// blocks that have low register pressure (the vreg may be spilled due to + /// register pressure in other blocks). + class VISIBILITY_HIDDEN LocalSpiller : public Spiller { + const MRegisterInfo *MRI; + const TargetInstrInfo *TII; + public: + bool runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) { + MRI = MF.getTarget().getRegisterInfo(); + TII = MF.getTarget().getInstrInfo(); + DOUT << "\n**** Local spiller rewriting function '" + << MF.getFunction()->getName() << "':\n"; + + std::vector<MachineInstr *> ReMatedMIs; + for (MachineFunction::iterator MBB = MF.begin(), E = MF.end(); + MBB != E; ++MBB) + RewriteMBB(*MBB, VRM, ReMatedMIs); + for (unsigned i = 0, e = ReMatedMIs.size(); i != e; ++i) + delete ReMatedMIs[i]; + return true; + } + private: + void RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM, + std::vector<MachineInstr*> &ReMatedMIs); + }; +} + +/// AvailableSpills - As the local spiller is scanning and rewriting an MBB from +/// top down, keep track of which spills slots are available in each register. +/// +/// Note that not all physregs are created equal here. In particular, some +/// physregs are reloads that we are allowed to clobber or ignore at any time. +/// Other physregs are values that the register allocated program is using that +/// we cannot CHANGE, but we can read if we like. We keep track of this on a +/// per-stack-slot basis as the low bit in the value of the SpillSlotsAvailable +/// entries. The predicate 'canClobberPhysReg()' checks this bit and +/// addAvailable sets it if. +namespace { +class VISIBILITY_HIDDEN AvailableSpills { + const MRegisterInfo *MRI; + const TargetInstrInfo *TII; + + // SpillSlotsAvailable - This map keeps track of all of the spilled virtual + // register values that are still available, due to being loaded or stored to, + // but not invalidated yet. + std::map<int, unsigned> SpillSlotsAvailable; + + // PhysRegsAvailable - This is the inverse of SpillSlotsAvailable, indicating + // which stack slot values are currently held by a physreg. This is used to + // invalidate entries in SpillSlotsAvailable when a physreg is modified. + std::multimap<unsigned, int> PhysRegsAvailable; + + void disallowClobberPhysRegOnly(unsigned PhysReg); + + void ClobberPhysRegOnly(unsigned PhysReg); +public: + AvailableSpills(const MRegisterInfo *mri, const TargetInstrInfo *tii) + : MRI(mri), TII(tii) { + } + + const MRegisterInfo *getRegInfo() const { return MRI; } + + /// getSpillSlotPhysReg - If the specified stack slot is available in a + /// physical register, return that PhysReg, otherwise return 0. + unsigned getSpillSlotPhysReg(int Slot) const { + std::map<int, unsigned>::const_iterator I = SpillSlotsAvailable.find(Slot); + if (I != SpillSlotsAvailable.end()) { + return I->second >> 1; // Remove the CanClobber bit. + } + return 0; + } + + /// addAvailable - Mark that the specified stack slot is available in the + /// specified physreg. If CanClobber is true, the physreg can be modified at + /// any time without changing the semantics of the program. + void addAvailable(int Slot, MachineInstr *MI, unsigned Reg, + bool CanClobber = true) { + // If this stack slot is thought to be available in some other physreg, + // remove its record. + ModifyStackSlot(Slot); + + PhysRegsAvailable.insert(std::make_pair(Reg, Slot)); + SpillSlotsAvailable[Slot] = (Reg << 1) | (unsigned)CanClobber; + + if (Slot > VirtRegMap::MAX_STACK_SLOT) + DOUT << "Remembering RM#" << Slot-VirtRegMap::MAX_STACK_SLOT-1; + else + DOUT << "Remembering SS#" << Slot; + DOUT << " in physreg " << MRI->getName(Reg) << "\n"; + } + + /// canClobberPhysReg - Return true if the spiller is allowed to change the + /// value of the specified stackslot register if it desires. The specified + /// stack slot must be available in a physreg for this query to make sense. + bool canClobberPhysReg(int Slot) const { + assert(SpillSlotsAvailable.count(Slot) && "Slot not available!"); + return SpillSlotsAvailable.find(Slot)->second & 1; + } + + /// disallowClobberPhysReg - Unset the CanClobber bit of the specified + /// stackslot register. The register is still available but is no longer + /// allowed to be modifed. + void disallowClobberPhysReg(unsigned PhysReg); + + /// ClobberPhysReg - This is called when the specified physreg changes + /// value. We use this to invalidate any info about stuff we thing lives in + /// it and any of its aliases. + void ClobberPhysReg(unsigned PhysReg); + + /// ModifyStackSlot - This method is called when the value in a stack slot + /// changes. This removes information about which register the previous value + /// for this slot lives in (as the previous value is dead now). + void ModifyStackSlot(int Slot); +}; +} + +/// disallowClobberPhysRegOnly - Unset the CanClobber bit of the specified +/// stackslot register. The register is still available but is no longer +/// allowed to be modifed. +void AvailableSpills::disallowClobberPhysRegOnly(unsigned PhysReg) { + std::multimap<unsigned, int>::iterator I = + PhysRegsAvailable.lower_bound(PhysReg); + while (I != PhysRegsAvailable.end() && I->first == PhysReg) { + int Slot = I->second; + I++; + assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg && + "Bidirectional map mismatch!"); + SpillSlotsAvailable[Slot] &= ~1; + DOUT << "PhysReg " << MRI->getName(PhysReg) + << " copied, it is available for use but can no longer be modified\n"; + } +} + +/// disallowClobberPhysReg - Unset the CanClobber bit of the specified +/// stackslot register and its aliases. The register and its aliases may +/// still available but is no longer allowed to be modifed. +void AvailableSpills::disallowClobberPhysReg(unsigned PhysReg) { + for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) + disallowClobberPhysRegOnly(*AS); + disallowClobberPhysRegOnly(PhysReg); +} + +/// ClobberPhysRegOnly - This is called when the specified physreg changes +/// value. We use this to invalidate any info about stuff we thing lives in it. +void AvailableSpills::ClobberPhysRegOnly(unsigned PhysReg) { + std::multimap<unsigned, int>::iterator I = + PhysRegsAvailable.lower_bound(PhysReg); + while (I != PhysRegsAvailable.end() && I->first == PhysReg) { + int Slot = I->second; + PhysRegsAvailable.erase(I++); + assert((SpillSlotsAvailable[Slot] >> 1) == PhysReg && + "Bidirectional map mismatch!"); + SpillSlotsAvailable.erase(Slot); + DOUT << "PhysReg " << MRI->getName(PhysReg) + << " clobbered, invalidating "; + if (Slot > VirtRegMap::MAX_STACK_SLOT) + DOUT << "RM#" << Slot-VirtRegMap::MAX_STACK_SLOT-1 << "\n"; + else + DOUT << "SS#" << Slot << "\n"; + } +} + +/// ClobberPhysReg - This is called when the specified physreg changes +/// value. We use this to invalidate any info about stuff we thing lives in +/// it and any of its aliases. +void AvailableSpills::ClobberPhysReg(unsigned PhysReg) { + for (const unsigned *AS = MRI->getAliasSet(PhysReg); *AS; ++AS) + ClobberPhysRegOnly(*AS); + ClobberPhysRegOnly(PhysReg); +} + +/// ModifyStackSlot - This method is called when the value in a stack slot +/// changes. This removes information about which register the previous value +/// for this slot lives in (as the previous value is dead now). +void AvailableSpills::ModifyStackSlot(int Slot) { + std::map<int, unsigned>::iterator It = SpillSlotsAvailable.find(Slot); + if (It == SpillSlotsAvailable.end()) return; + unsigned Reg = It->second >> 1; + SpillSlotsAvailable.erase(It); + + // This register may hold the value of multiple stack slots, only remove this + // stack slot from the set of values the register contains. + std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(Reg); + for (; ; ++I) { + assert(I != PhysRegsAvailable.end() && I->first == Reg && + "Map inverse broken!"); + if (I->second == Slot) break; + } + PhysRegsAvailable.erase(I); +} + + + +/// InvalidateKills - MI is going to be deleted. If any of its operands are +/// marked kill, then invalidate the information. +static void InvalidateKills(MachineInstr &MI, BitVector &RegKills, + std::vector<MachineOperand*> &KillOps) { + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (!MO.isReg() || !MO.isUse() || !MO.isKill()) + continue; + unsigned Reg = MO.getReg(); + if (KillOps[Reg] == &MO) { + RegKills.reset(Reg); + KillOps[Reg] = NULL; + } + } +} + +/// UpdateKills - Track and update kill info. If a MI reads a register that is +/// marked kill, then it must be due to register reuse. Transfer the kill info +/// over. +static void UpdateKills(MachineInstr &MI, BitVector &RegKills, + std::vector<MachineOperand*> &KillOps) { + const TargetInstrDescriptor *TID = MI.getInstrDescriptor(); + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (!MO.isReg() || !MO.isUse()) + continue; + unsigned Reg = MO.getReg(); + if (Reg == 0) + continue; + + if (RegKills[Reg]) { + // That can't be right. Register is killed but not re-defined and it's + // being reused. Let's fix that. + KillOps[Reg]->unsetIsKill(); + if (i < TID->numOperands && + TID->getOperandConstraint(i, TOI::TIED_TO) == -1) + // Unless it's a two-address operand, this is the new kill. + MO.setIsKill(); + } + + if (MO.isKill()) { + RegKills.set(Reg); + KillOps[Reg] = &MO; + } + } + + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + const MachineOperand &MO = MI.getOperand(i); + if (!MO.isReg() || !MO.isDef()) + continue; + unsigned Reg = MO.getReg(); + RegKills.reset(Reg); + KillOps[Reg] = NULL; + } +} + + +// ReusedOp - For each reused operand, we keep track of a bit of information, in +// case we need to rollback upon processing a new operand. See comments below. +namespace { + struct ReusedOp { + // The MachineInstr operand that reused an available value. + unsigned Operand; + + // StackSlot - The spill slot of the value being reused. + unsigned StackSlot; + + // PhysRegReused - The physical register the value was available in. + unsigned PhysRegReused; + + // AssignedPhysReg - The physreg that was assigned for use by the reload. + unsigned AssignedPhysReg; + + // VirtReg - The virtual register itself. + unsigned VirtReg; + + ReusedOp(unsigned o, unsigned ss, unsigned prr, unsigned apr, + unsigned vreg) + : Operand(o), StackSlot(ss), PhysRegReused(prr), AssignedPhysReg(apr), + VirtReg(vreg) {} + }; + + /// ReuseInfo - This maintains a collection of ReuseOp's for each operand that + /// is reused instead of reloaded. + class VISIBILITY_HIDDEN ReuseInfo { + MachineInstr &MI; + std::vector<ReusedOp> Reuses; + BitVector PhysRegsClobbered; + public: + ReuseInfo(MachineInstr &mi, const MRegisterInfo *mri) : MI(mi) { + PhysRegsClobbered.resize(mri->getNumRegs()); + } + + bool hasReuses() const { + return !Reuses.empty(); + } + + /// addReuse - If we choose to reuse a virtual register that is already + /// available instead of reloading it, remember that we did so. + void addReuse(unsigned OpNo, unsigned StackSlot, + unsigned PhysRegReused, unsigned AssignedPhysReg, + unsigned VirtReg) { + // If the reload is to the assigned register anyway, no undo will be + // required. + if (PhysRegReused == AssignedPhysReg) return; + + // Otherwise, remember this. + Reuses.push_back(ReusedOp(OpNo, StackSlot, PhysRegReused, + AssignedPhysReg, VirtReg)); + } + + void markClobbered(unsigned PhysReg) { + PhysRegsClobbered.set(PhysReg); + } + + bool isClobbered(unsigned PhysReg) const { + return PhysRegsClobbered.test(PhysReg); + } + + /// GetRegForReload - We are about to emit a reload into PhysReg. If there + /// is some other operand that is using the specified register, either pick + /// a new register to use, or evict the previous reload and use this reg. + unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, + AvailableSpills &Spills, + std::map<int, MachineInstr*> &MaybeDeadStores, + SmallSet<unsigned, 8> &Rejected, + BitVector &RegKills, + std::vector<MachineOperand*> &KillOps) { + if (Reuses.empty()) return PhysReg; // This is most often empty. + + for (unsigned ro = 0, e = Reuses.size(); ro != e; ++ro) { + ReusedOp &Op = Reuses[ro]; + // If we find some other reuse that was supposed to use this register + // exactly for its reload, we can change this reload to use ITS reload + // register. That is, unless its reload register has already been + // considered and subsequently rejected because it has also been reused + // by another operand. + if (Op.PhysRegReused == PhysReg && + Rejected.count(Op.AssignedPhysReg) == 0) { + // Yup, use the reload register that we didn't use before. + unsigned NewReg = Op.AssignedPhysReg; + Rejected.insert(PhysReg); + return GetRegForReload(NewReg, MI, Spills, MaybeDeadStores, Rejected, + RegKills, KillOps); + } else { + // Otherwise, we might also have a problem if a previously reused + // value aliases the new register. If so, codegen the previous reload + // and use this one. + unsigned PRRU = Op.PhysRegReused; + const MRegisterInfo *MRI = Spills.getRegInfo(); + if (MRI->areAliases(PRRU, PhysReg)) { + // Okay, we found out that an alias of a reused register + // was used. This isn't good because it means we have + // to undo a previous reuse. + MachineBasicBlock *MBB = MI->getParent(); + const TargetRegisterClass *AliasRC = + MBB->getParent()->getSSARegMap()->getRegClass(Op.VirtReg); + + // Copy Op out of the vector and remove it, we're going to insert an + // explicit load for it. + ReusedOp NewOp = Op; + Reuses.erase(Reuses.begin()+ro); + + // Ok, we're going to try to reload the assigned physreg into the + // slot that we were supposed to in the first place. However, that + // register could hold a reuse. Check to see if it conflicts or + // would prefer us to use a different register. + unsigned NewPhysReg = GetRegForReload(NewOp.AssignedPhysReg, + MI, Spills, MaybeDeadStores, + Rejected, RegKills, KillOps); + + MRI->loadRegFromStackSlot(*MBB, MI, NewPhysReg, + NewOp.StackSlot, AliasRC); + Spills.ClobberPhysReg(NewPhysReg); + Spills.ClobberPhysReg(NewOp.PhysRegReused); + + // Any stores to this stack slot are not dead anymore. + MaybeDeadStores.erase(NewOp.StackSlot); + + MI->getOperand(NewOp.Operand).setReg(NewPhysReg); + + Spills.addAvailable(NewOp.StackSlot, MI, NewPhysReg); + ++NumLoads; + MachineBasicBlock::iterator MII = MI; + --MII; + UpdateKills(*MII, RegKills, KillOps); + DOUT << '\t' << *MII; + + DOUT << "Reuse undone!\n"; + --NumReused; + + // Finally, PhysReg is now available, go ahead and use it. + return PhysReg; + } + } + } + return PhysReg; + } + + /// GetRegForReload - Helper for the above GetRegForReload(). Add a + /// 'Rejected' set to remember which registers have been considered and + /// rejected for the reload. This avoids infinite looping in case like + /// this: + /// t1 := op t2, t3 + /// t2 <- assigned r0 for use by the reload but ended up reuse r1 + /// t3 <- assigned r1 for use by the reload but ended up reuse r0 + /// t1 <- desires r1 + /// sees r1 is taken by t2, tries t2's reload register r0 + /// sees r0 is taken by t3, tries t3's reload register r1 + /// sees r1 is taken by t2, tries t2's reload register r0 ... + unsigned GetRegForReload(unsigned PhysReg, MachineInstr *MI, + AvailableSpills &Spills, + std::map<int, MachineInstr*> &MaybeDeadStores, + BitVector &RegKills, + std::vector<MachineOperand*> &KillOps) { + SmallSet<unsigned, 8> Rejected; + return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected, + RegKills, KillOps); + } + }; +} + + +/// rewriteMBB - Keep track of which spills are available even after the +/// register allocator is done with them. If possible, avoid reloading vregs. +void LocalSpiller::RewriteMBB(MachineBasicBlock &MBB, VirtRegMap &VRM, + std::vector<MachineInstr*> &ReMatedMIs) { + DOUT << MBB.getBasicBlock()->getName() << ":\n"; + + // Spills - Keep track of which spilled values are available in physregs so + // that we can choose to reuse the physregs instead of emitting reloads. + AvailableSpills Spills(MRI, TII); + + // MaybeDeadStores - When we need to write a value back into a stack slot, + // keep track of the inserted store. If the stack slot value is never read + // (because the value was used from some available register, for example), and + // subsequently stored to, the original store is dead. This map keeps track + // of inserted stores that are not used. If we see a subsequent store to the + // same stack slot, the original store is deleted. + std::map<int, MachineInstr*> MaybeDeadStores; + + // Keep track of kill information. + BitVector RegKills(MRI->getNumRegs()); + std::vector<MachineOperand*> KillOps; + KillOps.resize(MRI->getNumRegs(), NULL); + + MachineFunction &MF = *MBB.getParent(); + for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end(); + MII != E; ) { + MachineInstr &MI = *MII; + MachineBasicBlock::iterator NextMII = MII; ++NextMII; + VirtRegMap::MI2VirtMapTy::const_iterator I, End; + + bool Erased = false; + bool BackTracked = false; + + /// ReusedOperands - Keep track of operand reuse in case we need to undo + /// reuse. + ReuseInfo ReusedOperands(MI, MRI); + + // Loop over all of the implicit defs, clearing them from our available + // sets. + const TargetInstrDescriptor *TID = MI.getInstrDescriptor(); + + // If this instruction is being rematerialized, just remove it! + int FrameIdx; + if (TII->isTriviallyReMaterializable(&MI) || + TII->isLoadFromStackSlot(&MI, FrameIdx)) { + Erased = true; + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (!MO.isRegister() || MO.getReg() == 0) + continue; // Ignore non-register operands. + if (MO.isDef() && !VRM.isReMaterialized(MO.getReg())) { + Erased = false; + break; + } + } + if (Erased) { + VRM.RemoveFromFoldedVirtMap(&MI); + ReMatedMIs.push_back(MI.removeFromParent()); + goto ProcessNextInst; + } + } + + if (TID->ImplicitDefs) { + const unsigned *ImpDef = TID->ImplicitDefs; + for ( ; *ImpDef; ++ImpDef) { + MF.setPhysRegUsed(*ImpDef); + ReusedOperands.markClobbered(*ImpDef); + Spills.ClobberPhysReg(*ImpDef); + } + } + + // Process all of the spilled uses and all non spilled reg references. + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (!MO.isRegister() || MO.getReg() == 0) + continue; // Ignore non-register operands. + + if (MRegisterInfo::isPhysicalRegister(MO.getReg())) { + // Ignore physregs for spilling, but remember that it is used by this + // function. + MF.setPhysRegUsed(MO.getReg()); + ReusedOperands.markClobbered(MO.getReg()); + continue; + } + + assert(MRegisterInfo::isVirtualRegister(MO.getReg()) && + "Not a virtual or a physical register?"); + + unsigned VirtReg = MO.getReg(); + if (!VRM.hasStackSlot(VirtReg)) { + // This virtual register was assigned a physreg! + unsigned Phys = VRM.getPhys(VirtReg); + MF.setPhysRegUsed(Phys); + if (MO.isDef()) + ReusedOperands.markClobbered(Phys); + MI.getOperand(i).setReg(Phys); + continue; + } + + // This virtual register is now known to be a spilled value. + if (!MO.isUse()) + continue; // Handle defs in the loop below (handle use&def here though) + + bool doReMat = VRM.isReMaterialized(VirtReg); + int StackSlot = VRM.getStackSlot(VirtReg); + unsigned PhysReg; + + // Check to see if this stack slot is available. + if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot))) { + // This spilled operand might be part of a two-address operand. If this + // is the case, then changing it will necessarily require changing the + // def part of the instruction as well. However, in some cases, we + // aren't allowed to modify the reused register. If none of these cases + // apply, reuse it. + bool CanReuse = true; + int ti = TID->getOperandConstraint(i, TOI::TIED_TO); + if (ti != -1 && + MI.getOperand(ti).isReg() && + MI.getOperand(ti).getReg() == VirtReg) { + // Okay, we have a two address operand. We can reuse this physreg as + // long as we are allowed to clobber the value and there isn't an + // earlier def that has already clobbered the physreg. + CanReuse = Spills.canClobberPhysReg(StackSlot) && + !ReusedOperands.isClobbered(PhysReg); + } + + if (CanReuse) { + // If this stack slot value is already available, reuse it! + if (StackSlot > VirtRegMap::MAX_STACK_SLOT) + DOUT << "Reusing RM#" << StackSlot-VirtRegMap::MAX_STACK_SLOT-1; + else + DOUT << "Reusing SS#" << StackSlot; + DOUT << " from physreg " + << MRI->getName(PhysReg) << " for vreg" + << VirtReg <<" instead of reloading into physreg " + << MRI->getName(VRM.getPhys(VirtReg)) << "\n"; + MI.getOperand(i).setReg(PhysReg); + + // The only technical detail we have is that we don't know that + // PhysReg won't be clobbered by a reloaded stack slot that occurs + // later in the instruction. In particular, consider 'op V1, V2'. + // If V1 is available in physreg R0, we would choose to reuse it + // here, instead of reloading it into the register the allocator + // indicated (say R1). However, V2 might have to be reloaded + // later, and it might indicate that it needs to live in R0. When + // this occurs, we need to have information available that + // indicates it is safe to use R1 for the reload instead of R0. + // + // To further complicate matters, we might conflict with an alias, + // or R0 and R1 might not be compatible with each other. In this + // case, we actually insert a reload for V1 in R1, ensuring that + // we can get at R0 or its alias. + ReusedOperands.addReuse(i, StackSlot, PhysReg, + VRM.getPhys(VirtReg), VirtReg); + if (ti != -1) + // Only mark it clobbered if this is a use&def operand. + ReusedOperands.markClobbered(PhysReg); + ++NumReused; + continue; + } + + // Otherwise we have a situation where we have a two-address instruction + // whose mod/ref operand needs to be reloaded. This reload is already + // available in some register "PhysReg", but if we used PhysReg as the + // operand to our 2-addr instruction, the instruction would modify + // PhysReg. This isn't cool if something later uses PhysReg and expects + // to get its initial value. + // + // To avoid this problem, and to avoid doing a load right after a store, + // we emit a copy from PhysReg into the designated register for this + // operand. + unsigned DesignatedReg = VRM.getPhys(VirtReg); + assert(DesignatedReg && "Must map virtreg to physreg!"); + + // Note that, if we reused a register for a previous operand, the + // register we want to reload into might not actually be + // available. If this occurs, use the register indicated by the + // reuser. + if (ReusedOperands.hasReuses()) + DesignatedReg = ReusedOperands.GetRegForReload(DesignatedReg, &MI, + Spills, MaybeDeadStores, RegKills, KillOps); + + // If the mapped designated register is actually the physreg we have + // incoming, we don't need to inserted a dead copy. + if (DesignatedReg == PhysReg) { + // If this stack slot value is already available, reuse it! + if (StackSlot > VirtRegMap::MAX_STACK_SLOT) + DOUT << "Reusing RM#" << StackSlot-VirtRegMap::MAX_STACK_SLOT-1; + else + DOUT << "Reusing SS#" << StackSlot; + DOUT << " from physreg " << MRI->getName(PhysReg) << " for vreg" + << VirtReg + << " instead of reloading into same physreg.\n"; + MI.getOperand(i).setReg(PhysReg); + ReusedOperands.markClobbered(PhysReg); + ++NumReused; + continue; + } + + const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(VirtReg); + MF.setPhysRegUsed(DesignatedReg); + ReusedOperands.markClobbered(DesignatedReg); + MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC); + + MachineInstr *CopyMI = prior(MII); + UpdateKills(*CopyMI, RegKills, KillOps); + + // This invalidates DesignatedReg. + Spills.ClobberPhysReg(DesignatedReg); + + Spills.addAvailable(StackSlot, &MI, DesignatedReg); + MI.getOperand(i).setReg(DesignatedReg); + DOUT << '\t' << *prior(MII); + ++NumReused; + continue; + } + + // Otherwise, reload it and remember that we have it. + PhysReg = VRM.getPhys(VirtReg); + assert(PhysReg && "Must map virtreg to physreg!"); + const TargetRegisterClass* RC = MF.getSSARegMap()->getRegClass(VirtReg); + + // Note that, if we reused a register for a previous operand, the + // register we want to reload into might not actually be + // available. If this occurs, use the register indicated by the + // reuser. + if (ReusedOperands.hasReuses()) + PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, + Spills, MaybeDeadStores, RegKills, KillOps); + + MF.setPhysRegUsed(PhysReg); + ReusedOperands.markClobbered(PhysReg); + if (doReMat) { + MRI->reMaterialize(MBB, &MI, PhysReg, VRM.getReMaterializedMI(VirtReg)); + ++NumReMats; + } else { + MRI->loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC); + ++NumLoads; + } + // This invalidates PhysReg. + Spills.ClobberPhysReg(PhysReg); + + // Any stores to this stack slot are not dead anymore. + if (!doReMat) + MaybeDeadStores.erase(StackSlot); + Spills.addAvailable(StackSlot, &MI, PhysReg); + // Assumes this is the last use. IsKill will be unset if reg is reused + // unless it's a two-address operand. + if (TID->getOperandConstraint(i, TOI::TIED_TO) == -1) + MI.getOperand(i).setIsKill(); + MI.getOperand(i).setReg(PhysReg); + UpdateKills(*prior(MII), RegKills, KillOps); + DOUT << '\t' << *prior(MII); + } + + DOUT << '\t' << MI; + + // If we have folded references to memory operands, make sure we clear all + // physical registers that may contain the value of the spilled virtual + // register + for (tie(I, End) = VRM.getFoldedVirts(&MI); I != End; ++I) { + DOUT << "Folded vreg: " << I->second.first << " MR: " + << I->second.second; + unsigned VirtReg = I->second.first; + VirtRegMap::ModRef MR = I->second.second; + if (!VRM.hasStackSlot(VirtReg)) { + DOUT << ": No stack slot!\n"; + continue; + } + int SS = VRM.getStackSlot(VirtReg); + DOUT << " - StackSlot: " << SS << "\n"; + + // If this folded instruction is just a use, check to see if it's a + // straight load from the virt reg slot. + if ((MR & VirtRegMap::isRef) && !(MR & VirtRegMap::isMod)) { + int FrameIdx; + if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { + if (FrameIdx == SS) { + // If this spill slot is available, turn it into a copy (or nothing) + // instead of leaving it as a load! + if (unsigned InReg = Spills.getSpillSlotPhysReg(SS)) { + DOUT << "Promoted Load To Copy: " << MI; + if (DestReg != InReg) { + MRI->copyRegToReg(MBB, &MI, DestReg, InReg, + MF.getSSARegMap()->getRegClass(VirtReg)); + // Revisit the copy so we make sure to notice the effects of the + // operation on the destreg (either needing to RA it if it's + // virtual or needing to clobber any values if it's physical). + NextMII = &MI; + --NextMII; // backtrack to the copy. + BackTracked = true; + } else + DOUT << "Removing now-noop copy: " << MI; + + VRM.RemoveFromFoldedVirtMap(&MI); + MBB.erase(&MI); + Erased = true; + goto ProcessNextInst; + } + } + } + } + + // If this reference is not a use, any previous store is now dead. + // Otherwise, the store to this stack slot is not dead anymore. + std::map<int, MachineInstr*>::iterator MDSI = MaybeDeadStores.find(SS); + if (MDSI != MaybeDeadStores.end()) { + if (MR & VirtRegMap::isRef) // Previous store is not dead. + MaybeDeadStores.erase(MDSI); + else { + // If we get here, the store is dead, nuke it now. + assert(VirtRegMap::isMod && "Can't be modref!"); + DOUT << "Removed dead store:\t" << *MDSI->second; + InvalidateKills(*MDSI->second, RegKills, KillOps); + MBB.erase(MDSI->second); + VRM.RemoveFromFoldedVirtMap(MDSI->second); + MaybeDeadStores.erase(MDSI); + ++NumDSE; + } + } + + // If the spill slot value is available, and this is a new definition of + // the value, the value is not available anymore. + if (MR & VirtRegMap::isMod) { + // Notice that the value in this stack slot has been modified. + Spills.ModifyStackSlot(SS); + + // If this is *just* a mod of the value, check to see if this is just a + // store to the spill slot (i.e. the spill got merged into the copy). If + // so, realize that the vreg is available now, and add the store to the + // MaybeDeadStore info. + int StackSlot; + if (!(MR & VirtRegMap::isRef)) { + if (unsigned SrcReg = TII->isStoreToStackSlot(&MI, StackSlot)) { + assert(MRegisterInfo::isPhysicalRegister(SrcReg) && + "Src hasn't been allocated yet?"); + // Okay, this is certainly a store of SrcReg to [StackSlot]. Mark + // this as a potentially dead store in case there is a subsequent + // store into the stack slot without a read from it. + MaybeDeadStores[StackSlot] = &MI; + + // If the stack slot value was previously available in some other + // register, change it now. Otherwise, make the register available, + // in PhysReg. + Spills.addAvailable(StackSlot, &MI, SrcReg, false/*don't clobber*/); + } + } + } + } + + // Process all of the spilled defs. + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (MO.isRegister() && MO.getReg() && MO.isDef()) { + unsigned VirtReg = MO.getReg(); + + if (!MRegisterInfo::isVirtualRegister(VirtReg)) { + // Check to see if this is a noop copy. If so, eliminate the + // instruction before considering the dest reg to be changed. + unsigned Src, Dst; + if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { + ++NumDCE; + DOUT << "Removing now-noop copy: " << MI; + MBB.erase(&MI); + Erased = true; + VRM.RemoveFromFoldedVirtMap(&MI); + Spills.disallowClobberPhysReg(VirtReg); + goto ProcessNextInst; + } + + // If it's not a no-op copy, it clobbers the value in the destreg. + Spills.ClobberPhysReg(VirtReg); + ReusedOperands.markClobbered(VirtReg); + + // Check to see if this instruction is a load from a stack slot into + // a register. If so, this provides the stack slot value in the reg. + int FrameIdx; + if (unsigned DestReg = TII->isLoadFromStackSlot(&MI, FrameIdx)) { + assert(DestReg == VirtReg && "Unknown load situation!"); + + // Otherwise, if it wasn't available, remember that it is now! + Spills.addAvailable(FrameIdx, &MI, DestReg); + goto ProcessNextInst; + } + + continue; + } + + // The only vregs left are stack slot definitions. + int StackSlot = VRM.getStackSlot(VirtReg); + const TargetRegisterClass *RC = MF.getSSARegMap()->getRegClass(VirtReg); + + // If this def is part of a two-address operand, make sure to execute + // the store from the correct physical register. + unsigned PhysReg; + int TiedOp = MI.getInstrDescriptor()->findTiedToSrcOperand(i); + if (TiedOp != -1) + PhysReg = MI.getOperand(TiedOp).getReg(); + else { + PhysReg = VRM.getPhys(VirtReg); + if (ReusedOperands.isClobbered(PhysReg)) { + // Another def has taken the assigned physreg. It must have been a + // use&def which got it due to reuse. Undo the reuse! + PhysReg = ReusedOperands.GetRegForReload(PhysReg, &MI, + Spills, MaybeDeadStores, RegKills, KillOps); + } + } + + MF.setPhysRegUsed(PhysReg); + ReusedOperands.markClobbered(PhysReg); + MRI->storeRegToStackSlot(MBB, next(MII), PhysReg, StackSlot, RC); + DOUT << "Store:\t" << *next(MII); + MI.getOperand(i).setReg(PhysReg); + + // If there is a dead store to this stack slot, nuke it now. + MachineInstr *&LastStore = MaybeDeadStores[StackSlot]; + if (LastStore) { + DOUT << "Removed dead store:\t" << *LastStore; + ++NumDSE; + InvalidateKills(*LastStore, RegKills, KillOps); + MBB.erase(LastStore); + VRM.RemoveFromFoldedVirtMap(LastStore); + } + LastStore = next(MII); + + // If the stack slot value was previously available in some other + // register, change it now. Otherwise, make the register available, + // in PhysReg. + Spills.ModifyStackSlot(StackSlot); + Spills.ClobberPhysReg(PhysReg); + Spills.addAvailable(StackSlot, LastStore, PhysReg); + ++NumStores; + + // Check to see if this is a noop copy. If so, eliminate the + // instruction before considering the dest reg to be changed. + { + unsigned Src, Dst; + if (TII->isMoveInstr(MI, Src, Dst) && Src == Dst) { + ++NumDCE; + DOUT << "Removing now-noop copy: " << MI; + MBB.erase(&MI); + Erased = true; + VRM.RemoveFromFoldedVirtMap(&MI); + UpdateKills(*LastStore, RegKills, KillOps); + goto ProcessNextInst; + } + } + } + } + ProcessNextInst: + if (!Erased && !BackTracked) + for (MachineBasicBlock::iterator II = MI; II != NextMII; ++II) + UpdateKills(*II, RegKills, KillOps); + MII = NextMII; + } +} + + +llvm::Spiller* llvm::createSpiller() { + switch (SpillerOpt) { + default: assert(0 && "Unreachable!"); + case local: + return new LocalSpiller(); + case simple: + return new SimpleSpiller(); + } +} |