//===-- 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(); bool *PhysRegsUsed = MF.getUsedPhysregs(); // 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; } } PhysRegsUsed[PhysReg] = true; MI.getOperand(i).setReg(PhysReg); } else { PhysRegsUsed[MO.getReg()] = true; } } 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. It also tracks the instructions that defined // or used the register. typedef std::pair<unsigned, std::vector<MachineInstr*> > SSInfo; std::map<int, SSInfo> 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. It also /// returns by reference the instruction that either defines or last uses /// the register. unsigned getSpillSlotPhysReg(int Slot, MachineInstr *&SSMI) const { std::map<int, SSInfo>::const_iterator I = SpillSlotsAvailable.find(Slot); if (I != SpillSlotsAvailable.end()) { if (!I->second.second.empty()) SSMI = I->second.second.back(); return I->second.first >> 1; // Remove the CanClobber bit. } return 0; } /// addLastUse - Add the last use information of all stack slots whose /// values are available in the specific register. void addLastUse(unsigned PhysReg, MachineInstr *Use) { std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(PhysReg); while (I != PhysRegsAvailable.end() && I->first == PhysReg) { int Slot = I->second; I++; std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot); assert(II != SpillSlotsAvailable.end() && "Slot not available!"); unsigned Val = II->second.first; assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!"); // This can be true if there are multiple uses of the same register. if (II->second.second.back() != Use) II->second.second.push_back(Use); } } /// removeLastUse - Remove the last use information of all stack slots whose /// values are available in the specific register. void removeLastUse(unsigned PhysReg, MachineInstr *Use) { std::multimap<unsigned, int>::iterator I = PhysRegsAvailable.lower_bound(PhysReg); while (I != PhysRegsAvailable.end() && I->first == PhysReg) { int Slot = I->second; I++; std::map<int, SSInfo>::iterator II = SpillSlotsAvailable.find(Slot); assert(II != SpillSlotsAvailable.end() && "Slot not available!"); unsigned Val = II->second.first; assert((Val >> 1) == PhysReg && "Bidirectional map mismatch!"); if (II->second.second.back() == Use) II->second.second.pop_back(); } } /// 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)); std::vector<MachineInstr*> DefUses; DefUses.push_back(MI); SpillSlotsAvailable[Slot] = std::make_pair((Reg << 1) | (unsigned)CanClobber, DefUses); 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.first & 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].first >> 1) == PhysReg && "Bidirectional map mismatch!"); SpillSlotsAvailable[Slot].first &= ~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].first >> 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, SSInfo>::iterator It = SpillSlotsAvailable.find(Slot); if (It == SpillSlotsAvailable.end()) return; unsigned Reg = It->second.first >> 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); } // 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) { 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); } 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); 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; DEBUG(MachineBasicBlock::iterator MII = MI; DOUT << '\t' << *prior(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) { SmallSet<unsigned, 8> Rejected; return GetRegForReload(PhysReg, MI, Spills, MaybeDeadStores, Rejected); } }; } /// 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; bool *PhysRegsUsed = MBB.getParent()->getUsedPhysregs(); for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end(); MII != E; ) { MachineInstr &MI = *MII; MachineBasicBlock::iterator NextMII = MII; ++NextMII; /// 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 ((TID->Flags & M_REMATERIALIZIBLE) || TII->isLoadFromStackSlot(&MI, FrameIdx)) { bool Remove = 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())) { Remove = false; break; } } if (Remove) { VRM.RemoveFromFoldedVirtMap(&MI); ReMatedMIs.push_back(MI.removeFromParent()); MII = NextMII; continue; } } const unsigned *ImpDef = TID->ImplicitDefs; if (ImpDef) { for ( ; *ImpDef; ++ImpDef) { PhysRegsUsed[*ImpDef] = true; 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. PhysRegsUsed[MO.getReg()] = true; 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); PhysRegsUsed[Phys] = true; 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. MachineInstr *SSMI = NULL; if ((PhysReg = Spills.getSpillSlotPhysReg(StackSlot, SSMI))) { // 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); // Extend the live range of the MI that last kill the register if // necessary. bool WasKill = false; if (SSMI) { int UIdx = SSMI->findRegisterUseOperand(PhysReg, true); if (UIdx != -1) { MachineOperand &MOK = SSMI->getOperand(UIdx); WasKill = MOK.isKill(); MOK.unsetIsKill(); } } if (ti == -1) { // Unless it's the use of a two-address code, transfer the kill // of the reused register to this use. if (WasKill) MI.getOperand(i).setIsKill(); Spills.addLastUse(PhysReg, &MI); } // 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); // 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 = MBB.getParent()->getSSARegMap()->getRegClass(VirtReg); PhysRegsUsed[DesignatedReg] = true; ReusedOperands.markClobbered(DesignatedReg); MRI->copyRegToReg(MBB, &MI, DesignatedReg, PhysReg, RC); // Extend the live range of the MI that last kill the register if // necessary. bool WasKill = false; if (SSMI) { int UIdx = SSMI->findRegisterUseOperand(PhysReg, true); if (UIdx != -1) { MachineOperand &MOK = SSMI->getOperand(UIdx); WasKill = MOK.isKill(); MOK.unsetIsKill(); } } MachineInstr *CopyMI = prior(MII); if (WasKill) { // Transfer kill to the next use. int UIdx = CopyMI->findRegisterUseOperand(PhysReg); assert(UIdx != -1); MachineOperand &MOU = CopyMI->getOperand(UIdx); MOU.setIsKill(); } Spills.addLastUse(PhysReg, CopyMI); // 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 = MBB.getParent()->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); PhysRegsUsed[PhysReg] = true; 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); 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 VirtRegMap::MI2VirtMapTy::const_iterator I, End; 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! MachineInstr *SSMI = NULL; if (unsigned InReg = Spills.getSpillSlotPhysReg(SS, SSMI)) { DOUT << "Promoted Load To Copy: " << MI; MachineFunction &MF = *MBB.getParent(); 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. } else DOUT << "Removing now-noop copy: " << MI; // Either way, the live range of the last kill of InReg has been // extended. Remove its kill. bool WasKill = false; if (SSMI) { int UIdx = SSMI->findRegisterUseOperand(InReg, true); if (UIdx != -1) { MachineOperand &MOK = SSMI->getOperand(UIdx); WasKill = MOK.isKill(); MOK.unsetIsKill(); } } if (NextMII != MBB.end()) { // If NextMII uses InReg and the use is not a two address // operand, mark it killed. int UIdx = NextMII->findRegisterUseOperand(InReg); if (UIdx != -1) { MachineOperand &MOU = NextMII->getOperand(UIdx); if (WasKill) { const TargetInstrDescriptor *NTID = NextMII->getInstrDescriptor(); if (UIdx >= NTID->numOperands || NTID->getOperandConstraint(UIdx, TOI::TIED_TO) == -1) MOU.setIsKill(); } Spills.addLastUse(InReg, &(*NextMII)); } } VRM.RemoveFromFoldedVirtMap(&MI); MBB.erase(&MI); 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; 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; Spills.removeLastUse(Src, &MI); MBB.erase(&MI); 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 = MBB.getParent()->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); } } PhysRegsUsed[PhysReg] = true; 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; 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; Spills.removeLastUse(Src, &MI); MBB.erase(&MI); VRM.RemoveFromFoldedVirtMap(&MI); goto ProcessNextInst; } } } } ProcessNextInst: MII = NextMII; } } llvm::Spiller* llvm::createSpiller() { switch (SpillerOpt) { default: assert(0 && "Unreachable!"); case local: return new LocalSpiller(); case simple: return new SimpleSpiller(); } }