| //===-- TwoAddressInstructionPass.cpp - Two-Address instruction pass ------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the TwoAddress instruction pass which is used |
| // by most register allocators. Two-Address instructions are rewritten |
| // from: |
| // |
| // A = B op C |
| // |
| // to: |
| // |
| // A = B |
| // A op= C |
| // |
| // Note that if a register allocator chooses to use this pass, that it |
| // has to be capable of handling the non-SSA nature of these rewritten |
| // virtual registers. |
| // |
| // It is also worth noting that the duplicate operand of the two |
| // address instruction is removed. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "twoaddrinstr" |
| #include "llvm/CodeGen/Passes.h" |
| #include "llvm/Function.h" |
| #include "llvm/CodeGen/LiveVariables.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/Target/TargetRegisterInfo.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/Target/TargetMachine.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/ADT/BitVector.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| using namespace llvm; |
| |
| STATISTIC(NumTwoAddressInstrs, "Number of two-address instructions"); |
| STATISTIC(NumCommuted , "Number of instructions commuted to coalesce"); |
| STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address"); |
| STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk"); |
| STATISTIC(NumReMats, "Number of instructions re-materialized"); |
| |
| namespace { |
| class VISIBILITY_HIDDEN TwoAddressInstructionPass |
| : public MachineFunctionPass { |
| const TargetInstrInfo *TII; |
| const TargetRegisterInfo *TRI; |
| MachineRegisterInfo *MRI; |
| LiveVariables *LV; |
| |
| bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI, |
| unsigned Reg, |
| MachineBasicBlock::iterator OldPos); |
| |
| bool isProfitableToReMat(unsigned Reg, const TargetRegisterClass *RC, |
| MachineInstr *MI, MachineInstr *DefMI, |
| MachineBasicBlock *MBB, unsigned Loc, |
| DenseMap<MachineInstr*, unsigned> &DistanceMap); |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| TwoAddressInstructionPass() : MachineFunctionPass(&ID) {} |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addPreserved<LiveVariables>(); |
| AU.addPreservedID(MachineLoopInfoID); |
| AU.addPreservedID(MachineDominatorsID); |
| AU.addPreservedID(PHIEliminationID); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| /// runOnMachineFunction - Pass entry point. |
| bool runOnMachineFunction(MachineFunction&); |
| }; |
| } |
| |
| char TwoAddressInstructionPass::ID = 0; |
| static RegisterPass<TwoAddressInstructionPass> |
| X("twoaddressinstruction", "Two-Address instruction pass"); |
| |
| const PassInfo *const llvm::TwoAddressInstructionPassID = &X; |
| |
| /// Sink3AddrInstruction - A two-address instruction has been converted to a |
| /// three-address instruction to avoid clobbering a register. Try to sink it |
| /// past the instruction that would kill the above mentioned register to reduce |
| /// register pressure. |
| bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB, |
| MachineInstr *MI, unsigned SavedReg, |
| MachineBasicBlock::iterator OldPos) { |
| // Check if it's safe to move this instruction. |
| bool SeenStore = true; // Be conservative. |
| if (!MI->isSafeToMove(TII, SeenStore)) |
| return false; |
| |
| unsigned DefReg = 0; |
| SmallSet<unsigned, 4> UseRegs; |
| |
| for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { |
| const MachineOperand &MO = MI->getOperand(i); |
| if (!MO.isReg()) |
| continue; |
| unsigned MOReg = MO.getReg(); |
| if (!MOReg) |
| continue; |
| if (MO.isUse() && MOReg != SavedReg) |
| UseRegs.insert(MO.getReg()); |
| if (!MO.isDef()) |
| continue; |
| if (MO.isImplicit()) |
| // Don't try to move it if it implicitly defines a register. |
| return false; |
| if (DefReg) |
| // For now, don't move any instructions that define multiple registers. |
| return false; |
| DefReg = MO.getReg(); |
| } |
| |
| // Find the instruction that kills SavedReg. |
| MachineInstr *KillMI = NULL; |
| for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(SavedReg), |
| UE = MRI->use_end(); UI != UE; ++UI) { |
| MachineOperand &UseMO = UI.getOperand(); |
| if (!UseMO.isKill()) |
| continue; |
| KillMI = UseMO.getParent(); |
| break; |
| } |
| |
| if (!KillMI || KillMI->getParent() != MBB) |
| return false; |
| |
| // If any of the definitions are used by another instruction between the |
| // position and the kill use, then it's not safe to sink it. |
| // |
| // FIXME: This can be sped up if there is an easy way to query whether an |
| // instruction is before or after another instruction. Then we can use |
| // MachineRegisterInfo def / use instead. |
| MachineOperand *KillMO = NULL; |
| MachineBasicBlock::iterator KillPos = KillMI; |
| ++KillPos; |
| |
| unsigned NumVisited = 0; |
| for (MachineBasicBlock::iterator I = next(OldPos); I != KillPos; ++I) { |
| MachineInstr *OtherMI = I; |
| if (NumVisited > 30) // FIXME: Arbitrary limit to reduce compile time cost. |
| return false; |
| ++NumVisited; |
| for (unsigned i = 0, e = OtherMI->getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = OtherMI->getOperand(i); |
| if (!MO.isReg()) |
| continue; |
| unsigned MOReg = MO.getReg(); |
| if (!MOReg) |
| continue; |
| if (DefReg == MOReg) |
| return false; |
| |
| if (MO.isKill()) { |
| if (OtherMI == KillMI && MOReg == SavedReg) |
| // Save the operand that kills the register. We want to unset the kill |
| // marker if we can sink MI past it. |
| KillMO = &MO; |
| else if (UseRegs.count(MOReg)) |
| // One of the uses is killed before the destination. |
| return false; |
| } |
| } |
| } |
| |
| // Update kill and LV information. |
| KillMO->setIsKill(false); |
| KillMO = MI->findRegisterUseOperand(SavedReg, false, TRI); |
| KillMO->setIsKill(true); |
| |
| if (LV) |
| LV->replaceKillInstruction(SavedReg, KillMI, MI); |
| |
| // Move instruction to its destination. |
| MBB->remove(MI); |
| MBB->insert(KillPos, MI); |
| |
| ++Num3AddrSunk; |
| return true; |
| } |
| |
| /// isTwoAddrUse - Return true if the specified MI is using the specified |
| /// register as a two-address operand. |
| static bool isTwoAddrUse(MachineInstr *UseMI, unsigned Reg) { |
| const TargetInstrDesc &TID = UseMI->getDesc(); |
| for (unsigned i = 0, e = TID.getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = UseMI->getOperand(i); |
| if (MO.isReg() && MO.getReg() == Reg && |
| (MO.isDef() || TID.getOperandConstraint(i, TOI::TIED_TO) != -1)) |
| // Earlier use is a two-address one. |
| return true; |
| } |
| return false; |
| } |
| |
| /// isProfitableToReMat - Return true if the heuristics determines it is likely |
| /// to be profitable to re-materialize the definition of Reg rather than copy |
| /// the register. |
| bool |
| TwoAddressInstructionPass::isProfitableToReMat(unsigned Reg, |
| const TargetRegisterClass *RC, |
| MachineInstr *MI, MachineInstr *DefMI, |
| MachineBasicBlock *MBB, unsigned Loc, |
| DenseMap<MachineInstr*, unsigned> &DistanceMap){ |
| bool OtherUse = false; |
| for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg), |
| UE = MRI->use_end(); UI != UE; ++UI) { |
| MachineOperand &UseMO = UI.getOperand(); |
| if (!UseMO.isUse()) |
| continue; |
| MachineInstr *UseMI = UseMO.getParent(); |
| MachineBasicBlock *UseMBB = UseMI->getParent(); |
| if (UseMBB == MBB) { |
| DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI); |
| if (DI != DistanceMap.end() && DI->second == Loc) |
| continue; // Current use. |
| OtherUse = true; |
| // There is at least one other use in the MBB that will clobber the |
| // register. |
| if (isTwoAddrUse(UseMI, Reg)) |
| return true; |
| } |
| } |
| |
| // If other uses in MBB are not two-address uses, then don't remat. |
| if (OtherUse) |
| return false; |
| |
| // No other uses in the same block, remat if it's defined in the same |
| // block so it does not unnecessarily extend the live range. |
| return MBB == DefMI->getParent(); |
| } |
| |
| /// runOnMachineFunction - Reduce two-address instructions to two operands. |
| /// |
| bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { |
| DOUT << "Machine Function\n"; |
| const TargetMachine &TM = MF.getTarget(); |
| MRI = &MF.getRegInfo(); |
| TII = TM.getInstrInfo(); |
| TRI = TM.getRegisterInfo(); |
| LV = getAnalysisToUpdate<LiveVariables>(); |
| |
| bool MadeChange = false; |
| |
| DOUT << "********** REWRITING TWO-ADDR INSTRS **********\n"; |
| DOUT << "********** Function: " << MF.getFunction()->getName() << '\n'; |
| |
| // ReMatRegs - Keep track of the registers whose def's are remat'ed. |
| BitVector ReMatRegs; |
| ReMatRegs.resize(MRI->getLastVirtReg()+1); |
| |
| // DistanceMap - Keep track the distance of a MI from the start of the |
| // current basic block. |
| DenseMap<MachineInstr*, unsigned> DistanceMap; |
| |
| for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end(); |
| mbbi != mbbe; ++mbbi) { |
| unsigned Dist = 0; |
| DistanceMap.clear(); |
| for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end(); |
| mi != me; ) { |
| MachineBasicBlock::iterator nmi = next(mi); |
| const TargetInstrDesc &TID = mi->getDesc(); |
| bool FirstTied = true; |
| |
| DistanceMap.insert(std::make_pair(mi, ++Dist)); |
| for (unsigned si = 1, e = TID.getNumOperands(); si < e; ++si) { |
| int ti = TID.getOperandConstraint(si, TOI::TIED_TO); |
| if (ti == -1) |
| continue; |
| |
| if (FirstTied) { |
| ++NumTwoAddressInstrs; |
| DOUT << '\t'; DEBUG(mi->print(*cerr.stream(), &TM)); |
| } |
| |
| FirstTied = false; |
| |
| assert(mi->getOperand(si).isReg() && mi->getOperand(si).getReg() && |
| mi->getOperand(si).isUse() && "two address instruction invalid"); |
| |
| // If the two operands are the same we just remove the use |
| // and mark the def as def&use, otherwise we have to insert a copy. |
| if (mi->getOperand(ti).getReg() != mi->getOperand(si).getReg()) { |
| // Rewrite: |
| // a = b op c |
| // to: |
| // a = b |
| // a = a op c |
| unsigned regA = mi->getOperand(ti).getReg(); |
| unsigned regB = mi->getOperand(si).getReg(); |
| |
| assert(TargetRegisterInfo::isVirtualRegister(regA) && |
| TargetRegisterInfo::isVirtualRegister(regB) && |
| "cannot update physical register live information"); |
| |
| #ifndef NDEBUG |
| // First, verify that we don't have a use of a in the instruction (a = |
| // b + a for example) because our transformation will not work. This |
| // should never occur because we are in SSA form. |
| for (unsigned i = 0; i != mi->getNumOperands(); ++i) |
| assert((int)i == ti || |
| !mi->getOperand(i).isReg() || |
| mi->getOperand(i).getReg() != regA); |
| #endif |
| |
| // If this instruction is not the killing user of B, see if we can |
| // rearrange the code to make it so. Making it the killing user will |
| // allow us to coalesce A and B together, eliminating the copy we are |
| // about to insert. |
| if (!mi->killsRegister(regB)) { |
| // If this instruction is commutative, check to see if C dies. If |
| // so, swap the B and C operands. This makes the live ranges of A |
| // and C joinable. |
| // FIXME: This code also works for A := B op C instructions. |
| if (TID.isCommutable() && mi->getNumOperands() >= 3) { |
| assert(mi->getOperand(3-si).isReg() && |
| "Not a proper commutative instruction!"); |
| unsigned regC = mi->getOperand(3-si).getReg(); |
| |
| if (mi->killsRegister(regC)) { |
| DOUT << "2addr: COMMUTING : " << *mi; |
| MachineInstr *NewMI = TII->commuteInstruction(mi); |
| |
| if (NewMI == 0) { |
| DOUT << "2addr: COMMUTING FAILED!\n"; |
| } else { |
| DOUT << "2addr: COMMUTED TO: " << *NewMI; |
| // If the instruction changed to commute it, update livevar. |
| if (NewMI != mi) { |
| if (LV) |
| // Update live variables |
| LV->replaceKillInstruction(regC, mi, NewMI); |
| |
| mbbi->insert(mi, NewMI); // Insert the new inst |
| mbbi->erase(mi); // Nuke the old inst. |
| mi = NewMI; |
| DistanceMap.insert(std::make_pair(NewMI, Dist)); |
| } |
| |
| ++NumCommuted; |
| regB = regC; |
| goto InstructionRearranged; |
| } |
| } |
| } |
| |
| // If this instruction is potentially convertible to a true |
| // three-address instruction, |
| if (TID.isConvertibleTo3Addr()) { |
| // FIXME: This assumes there are no more operands which are tied |
| // to another register. |
| #ifndef NDEBUG |
| for (unsigned i = si + 1, e = TID.getNumOperands(); i < e; ++i) |
| assert(TID.getOperandConstraint(i, TOI::TIED_TO) == -1); |
| #endif |
| |
| MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, LV); |
| if (NewMI) { |
| DOUT << "2addr: CONVERTING 2-ADDR: " << *mi; |
| DOUT << "2addr: TO 3-ADDR: " << *NewMI; |
| bool Sunk = false; |
| |
| if (NewMI->findRegisterUseOperand(regB, false, TRI)) |
| // FIXME: Temporary workaround. If the new instruction doesn't |
| // uses regB, convertToThreeAddress must have created more |
| // then one instruction. |
| Sunk = Sink3AddrInstruction(mbbi, NewMI, regB, mi); |
| |
| mbbi->erase(mi); // Nuke the old inst. |
| |
| if (!Sunk) { |
| DistanceMap.insert(std::make_pair(NewMI, Dist)); |
| mi = NewMI; |
| nmi = next(mi); |
| } |
| |
| ++NumConvertedTo3Addr; |
| break; // Done with this instruction. |
| } |
| } |
| } |
| |
| InstructionRearranged: |
| const TargetRegisterClass* rc = MRI->getRegClass(regA); |
| MachineInstr *DefMI = MRI->getVRegDef(regB); |
| // If it's safe and profitable, remat the definition instead of |
| // copying it. |
| if (DefMI && |
| DefMI->getDesc().isAsCheapAsAMove() && |
| DefMI->isSafeToReMat(TII, regB) && |
| isProfitableToReMat(regB, rc, mi, DefMI, mbbi, Dist,DistanceMap)){ |
| DEBUG(cerr << "2addr: REMATTING : " << *DefMI << "\n"); |
| TII->reMaterialize(*mbbi, mi, regA, DefMI); |
| ReMatRegs.set(regB); |
| ++NumReMats; |
| } else { |
| TII->copyRegToReg(*mbbi, mi, regA, regB, rc, rc); |
| } |
| |
| MachineBasicBlock::iterator prevMi = prior(mi); |
| DOUT << "\t\tprepend:\t"; DEBUG(prevMi->print(*cerr.stream(), &TM)); |
| |
| // Update live variables for regB. |
| if (LV) { |
| LiveVariables::VarInfo& varInfoB = LV->getVarInfo(regB); |
| |
| // regB is used in this BB. |
| varInfoB.UsedBlocks[mbbi->getNumber()] = true; |
| |
| if (LV->removeVirtualRegisterKilled(regB, mi)) |
| LV->addVirtualRegisterKilled(regB, prevMi); |
| |
| if (LV->removeVirtualRegisterDead(regB, mi)) |
| LV->addVirtualRegisterDead(regB, prevMi); |
| } |
| |
| // Replace all occurences of regB with regA. |
| for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) { |
| if (mi->getOperand(i).isReg() && |
| mi->getOperand(i).getReg() == regB) |
| mi->getOperand(i).setReg(regA); |
| } |
| } |
| |
| assert(mi->getOperand(ti).isDef() && mi->getOperand(si).isUse()); |
| mi->getOperand(ti).setReg(mi->getOperand(si).getReg()); |
| MadeChange = true; |
| |
| DOUT << "\t\trewrite to:\t"; DEBUG(mi->print(*cerr.stream(), &TM)); |
| } |
| |
| mi = nmi; |
| } |
| } |
| |
| // Some remat'ed instructions are dead. |
| int VReg = ReMatRegs.find_first(); |
| while (VReg != -1) { |
| if (MRI->use_empty(VReg)) { |
| MachineInstr *DefMI = MRI->getVRegDef(VReg); |
| DefMI->eraseFromParent(); |
| } |
| VReg = ReMatRegs.find_next(VReg); |
| } |
| |
| return MadeChange; |
| } |
