| //===-- 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/Analysis/AliasAnalysis.h" |
| #include "llvm/Target/TargetRegisterInfo.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/Target/TargetMachine.h" |
| #include "llvm/Target/TargetOptions.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/ADT/BitVector.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/SmallSet.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(NumAggrCommuted , "Number of instructions aggressively commuted"); |
| STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address"); |
| STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk"); |
| STATISTIC(NumReMats, "Number of instructions re-materialized"); |
| STATISTIC(NumDeletes, "Number of dead instructions deleted"); |
| |
| namespace { |
| class TwoAddressInstructionPass : public MachineFunctionPass { |
| const TargetInstrInfo *TII; |
| const TargetRegisterInfo *TRI; |
| MachineRegisterInfo *MRI; |
| LiveVariables *LV; |
| AliasAnalysis *AA; |
| |
| // DistanceMap - Keep track the distance of a MI from the start of the |
| // current basic block. |
| DenseMap<MachineInstr*, unsigned> DistanceMap; |
| |
| // SrcRegMap - A map from virtual registers to physical registers which |
| // are likely targets to be coalesced to due to copies from physical |
| // registers to virtual registers. e.g. v1024 = move r0. |
| DenseMap<unsigned, unsigned> SrcRegMap; |
| |
| // DstRegMap - A map from virtual registers to physical registers which |
| // are likely targets to be coalesced to due to copies to physical |
| // registers from virtual registers. e.g. r1 = move v1024. |
| DenseMap<unsigned, unsigned> DstRegMap; |
| |
| 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); |
| |
| bool NoUseAfterLastDef(unsigned Reg, MachineBasicBlock *MBB, unsigned Dist, |
| unsigned &LastDef); |
| |
| MachineInstr *FindLastUseInMBB(unsigned Reg, MachineBasicBlock *MBB, |
| unsigned Dist); |
| |
| bool isProfitableToCommute(unsigned regB, unsigned regC, |
| MachineInstr *MI, MachineBasicBlock *MBB, |
| unsigned Dist); |
| |
| bool CommuteInstruction(MachineBasicBlock::iterator &mi, |
| MachineFunction::iterator &mbbi, |
| unsigned RegB, unsigned RegC, unsigned Dist); |
| |
| bool isProfitableToConv3Addr(unsigned RegA); |
| |
| bool ConvertInstTo3Addr(MachineBasicBlock::iterator &mi, |
| MachineBasicBlock::iterator &nmi, |
| MachineFunction::iterator &mbbi, |
| unsigned RegB, unsigned Dist); |
| |
| typedef std::pair<std::pair<unsigned, bool>, MachineInstr*> NewKill; |
| bool canUpdateDeletedKills(SmallVector<unsigned, 4> &Kills, |
| SmallVector<NewKill, 4> &NewKills, |
| MachineBasicBlock *MBB, unsigned Dist); |
| bool DeleteUnusedInstr(MachineBasicBlock::iterator &mi, |
| MachineBasicBlock::iterator &nmi, |
| MachineFunction::iterator &mbbi, |
| unsigned regB, unsigned regBIdx, unsigned Dist); |
| |
| bool TryInstructionTransform(MachineBasicBlock::iterator &mi, |
| MachineBasicBlock::iterator &nmi, |
| MachineFunction::iterator &mbbi, |
| unsigned SrcIdx, unsigned DstIdx, |
| unsigned Dist); |
| |
| void ProcessCopy(MachineInstr *MI, MachineBasicBlock *MBB, |
| SmallPtrSet<MachineInstr*, 8> &Processed); |
| |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| TwoAddressInstructionPass() : MachineFunctionPass(&ID) {} |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesCFG(); |
| AU.addRequired<AliasAnalysis>(); |
| AU.addPreserved<LiveVariables>(); |
| AU.addPreservedID(MachineLoopInfoID); |
| AU.addPreservedID(MachineDominatorsID); |
| if (StrongPHIElim) |
| AU.addPreservedID(StrongPHIEliminationID); |
| else |
| 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, AA)) |
| 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 || KillMI == MI) |
| 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() || UseMI->isRegTiedToDefOperand(i))) |
| // 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) { |
| bool OtherUse = false; |
| for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg), |
| UE = MRI->use_end(); UI != UE; ++UI) { |
| MachineOperand &UseMO = UI.getOperand(); |
| 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(); |
| } |
| |
| /// NoUseAfterLastDef - Return true if there are no intervening uses between the |
| /// last instruction in the MBB that defines the specified register and the |
| /// two-address instruction which is being processed. It also returns the last |
| /// def location by reference |
| bool TwoAddressInstructionPass::NoUseAfterLastDef(unsigned Reg, |
| MachineBasicBlock *MBB, unsigned Dist, |
| unsigned &LastDef) { |
| LastDef = 0; |
| unsigned LastUse = Dist; |
| for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg), |
| E = MRI->reg_end(); I != E; ++I) { |
| MachineOperand &MO = I.getOperand(); |
| MachineInstr *MI = MO.getParent(); |
| if (MI->getParent() != MBB) |
| continue; |
| DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI); |
| if (DI == DistanceMap.end()) |
| continue; |
| if (MO.isUse() && DI->second < LastUse) |
| LastUse = DI->second; |
| if (MO.isDef() && DI->second > LastDef) |
| LastDef = DI->second; |
| } |
| |
| return !(LastUse > LastDef && LastUse < Dist); |
| } |
| |
| MachineInstr *TwoAddressInstructionPass::FindLastUseInMBB(unsigned Reg, |
| MachineBasicBlock *MBB, |
| unsigned Dist) { |
| unsigned LastUseDist = 0; |
| MachineInstr *LastUse = 0; |
| for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg), |
| E = MRI->reg_end(); I != E; ++I) { |
| MachineOperand &MO = I.getOperand(); |
| MachineInstr *MI = MO.getParent(); |
| if (MI->getParent() != MBB) |
| continue; |
| DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI); |
| if (DI == DistanceMap.end()) |
| continue; |
| if (DI->second >= Dist) |
| continue; |
| |
| if (MO.isUse() && DI->second > LastUseDist) { |
| LastUse = DI->first; |
| LastUseDist = DI->second; |
| } |
| } |
| return LastUse; |
| } |
| |
| /// isCopyToReg - Return true if the specified MI is a copy instruction or |
| /// a extract_subreg instruction. It also returns the source and destination |
| /// registers and whether they are physical registers by reference. |
| static bool isCopyToReg(MachineInstr &MI, const TargetInstrInfo *TII, |
| unsigned &SrcReg, unsigned &DstReg, |
| bool &IsSrcPhys, bool &IsDstPhys) { |
| SrcReg = 0; |
| DstReg = 0; |
| unsigned SrcSubIdx, DstSubIdx; |
| if (!TII->isMoveInstr(MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx)) { |
| if (MI.getOpcode() == TargetInstrInfo::EXTRACT_SUBREG) { |
| DstReg = MI.getOperand(0).getReg(); |
| SrcReg = MI.getOperand(1).getReg(); |
| } else if (MI.getOpcode() == TargetInstrInfo::INSERT_SUBREG) { |
| DstReg = MI.getOperand(0).getReg(); |
| SrcReg = MI.getOperand(2).getReg(); |
| } else if (MI.getOpcode() == TargetInstrInfo::SUBREG_TO_REG) { |
| DstReg = MI.getOperand(0).getReg(); |
| SrcReg = MI.getOperand(2).getReg(); |
| } |
| } |
| |
| if (DstReg) { |
| IsSrcPhys = TargetRegisterInfo::isPhysicalRegister(SrcReg); |
| IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg); |
| return true; |
| } |
| return false; |
| } |
| |
| /// isKilled - Test if the given register value, which is used by the given |
| /// instruction, is killed by the given instruction. This looks through |
| /// coalescable copies to see if the original value is potentially not killed. |
| /// |
| /// For example, in this code: |
| /// |
| /// %reg1034 = copy %reg1024 |
| /// %reg1035 = copy %reg1025<kill> |
| /// %reg1036 = add %reg1034<kill>, %reg1035<kill> |
| /// |
| /// %reg1034 is not considered to be killed, since it is copied from a |
| /// register which is not killed. Treating it as not killed lets the |
| /// normal heuristics commute the (two-address) add, which lets |
| /// coalescing eliminate the extra copy. |
| /// |
| static bool isKilled(MachineInstr &MI, unsigned Reg, |
| const MachineRegisterInfo *MRI, |
| const TargetInstrInfo *TII) { |
| MachineInstr *DefMI = &MI; |
| for (;;) { |
| if (!DefMI->killsRegister(Reg)) |
| return false; |
| if (TargetRegisterInfo::isPhysicalRegister(Reg)) |
| return true; |
| MachineRegisterInfo::def_iterator Begin = MRI->def_begin(Reg); |
| // If there are multiple defs, we can't do a simple analysis, so just |
| // go with what the kill flag says. |
| if (next(Begin) != MRI->def_end()) |
| return true; |
| DefMI = &*Begin; |
| bool IsSrcPhys, IsDstPhys; |
| unsigned SrcReg, DstReg; |
| // If the def is something other than a copy, then it isn't going to |
| // be coalesced, so follow the kill flag. |
| if (!isCopyToReg(*DefMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys)) |
| return true; |
| Reg = SrcReg; |
| } |
| } |
| |
| /// isTwoAddrUse - Return true if the specified MI uses the specified register |
| /// as a two-address use. If so, return the destination register by reference. |
| static bool isTwoAddrUse(MachineInstr &MI, unsigned Reg, unsigned &DstReg) { |
| const TargetInstrDesc &TID = MI.getDesc(); |
| unsigned NumOps = (MI.getOpcode() == TargetInstrInfo::INLINEASM) |
| ? MI.getNumOperands() : TID.getNumOperands(); |
| for (unsigned i = 0; i != NumOps; ++i) { |
| const MachineOperand &MO = MI.getOperand(i); |
| if (!MO.isReg() || !MO.isUse() || MO.getReg() != Reg) |
| continue; |
| unsigned ti; |
| if (MI.isRegTiedToDefOperand(i, &ti)) { |
| DstReg = MI.getOperand(ti).getReg(); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /// findOnlyInterestingUse - Given a register, if has a single in-basic block |
| /// use, return the use instruction if it's a copy or a two-address use. |
| static |
| MachineInstr *findOnlyInterestingUse(unsigned Reg, MachineBasicBlock *MBB, |
| MachineRegisterInfo *MRI, |
| const TargetInstrInfo *TII, |
| bool &IsCopy, |
| unsigned &DstReg, bool &IsDstPhys) { |
| MachineRegisterInfo::use_iterator UI = MRI->use_begin(Reg); |
| if (UI == MRI->use_end()) |
| return 0; |
| MachineInstr &UseMI = *UI; |
| if (++UI != MRI->use_end()) |
| // More than one use. |
| return 0; |
| if (UseMI.getParent() != MBB) |
| return 0; |
| unsigned SrcReg; |
| bool IsSrcPhys; |
| if (isCopyToReg(UseMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys)) { |
| IsCopy = true; |
| return &UseMI; |
| } |
| IsDstPhys = false; |
| if (isTwoAddrUse(UseMI, Reg, DstReg)) { |
| IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg); |
| return &UseMI; |
| } |
| return 0; |
| } |
| |
| /// getMappedReg - Return the physical register the specified virtual register |
| /// might be mapped to. |
| static unsigned |
| getMappedReg(unsigned Reg, DenseMap<unsigned, unsigned> &RegMap) { |
| while (TargetRegisterInfo::isVirtualRegister(Reg)) { |
| DenseMap<unsigned, unsigned>::iterator SI = RegMap.find(Reg); |
| if (SI == RegMap.end()) |
| return 0; |
| Reg = SI->second; |
| } |
| if (TargetRegisterInfo::isPhysicalRegister(Reg)) |
| return Reg; |
| return 0; |
| } |
| |
| /// regsAreCompatible - Return true if the two registers are equal or aliased. |
| /// |
| static bool |
| regsAreCompatible(unsigned RegA, unsigned RegB, const TargetRegisterInfo *TRI) { |
| if (RegA == RegB) |
| return true; |
| if (!RegA || !RegB) |
| return false; |
| return TRI->regsOverlap(RegA, RegB); |
| } |
| |
| |
| /// isProfitableToReMat - Return true if it's potentially profitable to commute |
| /// the two-address instruction that's being processed. |
| bool |
| TwoAddressInstructionPass::isProfitableToCommute(unsigned regB, unsigned regC, |
| MachineInstr *MI, MachineBasicBlock *MBB, |
| unsigned Dist) { |
| // Determine if it's profitable to commute this two address instruction. In |
| // general, we want no uses between this instruction and the definition of |
| // the two-address register. |
| // e.g. |
| // %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1 |
| // %reg1029<def> = MOV8rr %reg1028 |
| // %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead> |
| // insert => %reg1030<def> = MOV8rr %reg1028 |
| // %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead> |
| // In this case, it might not be possible to coalesce the second MOV8rr |
| // instruction if the first one is coalesced. So it would be profitable to |
| // commute it: |
| // %reg1028<def> = EXTRACT_SUBREG %reg1027<kill>, 1 |
| // %reg1029<def> = MOV8rr %reg1028 |
| // %reg1029<def> = SHR8ri %reg1029, 7, %EFLAGS<imp-def,dead> |
| // insert => %reg1030<def> = MOV8rr %reg1029 |
| // %reg1030<def> = ADD8rr %reg1029<kill>, %reg1028<kill>, %EFLAGS<imp-def,dead> |
| |
| if (!MI->killsRegister(regC)) |
| return false; |
| |
| // Ok, we have something like: |
| // %reg1030<def> = ADD8rr %reg1028<kill>, %reg1029<kill>, %EFLAGS<imp-def,dead> |
| // let's see if it's worth commuting it. |
| |
| // Look for situations like this: |
| // %reg1024<def> = MOV r1 |
| // %reg1025<def> = MOV r0 |
| // %reg1026<def> = ADD %reg1024, %reg1025 |
| // r0 = MOV %reg1026 |
| // Commute the ADD to hopefully eliminate an otherwise unavoidable copy. |
| unsigned FromRegB = getMappedReg(regB, SrcRegMap); |
| unsigned FromRegC = getMappedReg(regC, SrcRegMap); |
| unsigned ToRegB = getMappedReg(regB, DstRegMap); |
| unsigned ToRegC = getMappedReg(regC, DstRegMap); |
| if (!regsAreCompatible(FromRegB, ToRegB, TRI) && |
| (regsAreCompatible(FromRegB, ToRegC, TRI) || |
| regsAreCompatible(FromRegC, ToRegB, TRI))) |
| return true; |
| |
| // If there is a use of regC between its last def (could be livein) and this |
| // instruction, then bail. |
| unsigned LastDefC = 0; |
| if (!NoUseAfterLastDef(regC, MBB, Dist, LastDefC)) |
| return false; |
| |
| // If there is a use of regB between its last def (could be livein) and this |
| // instruction, then go ahead and make this transformation. |
| unsigned LastDefB = 0; |
| if (!NoUseAfterLastDef(regB, MBB, Dist, LastDefB)) |
| return true; |
| |
| // Since there are no intervening uses for both registers, then commute |
| // if the def of regC is closer. Its live interval is shorter. |
| return LastDefB && LastDefC && LastDefC > LastDefB; |
| } |
| |
| /// CommuteInstruction - Commute a two-address instruction and update the basic |
| /// block, distance map, and live variables if needed. Return true if it is |
| /// successful. |
| bool |
| TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi, |
| MachineFunction::iterator &mbbi, |
| unsigned RegB, unsigned RegC, unsigned Dist) { |
| MachineInstr *MI = mi; |
| DEBUG(errs() << "2addr: COMMUTING : " << *MI); |
| MachineInstr *NewMI = TII->commuteInstruction(MI); |
| |
| if (NewMI == 0) { |
| DEBUG(errs() << "2addr: COMMUTING FAILED!\n"); |
| return false; |
| } |
| |
| DEBUG(errs() << "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)); |
| } |
| |
| // Update source register map. |
| unsigned FromRegC = getMappedReg(RegC, SrcRegMap); |
| if (FromRegC) { |
| unsigned RegA = MI->getOperand(0).getReg(); |
| SrcRegMap[RegA] = FromRegC; |
| } |
| |
| return true; |
| } |
| |
| /// isProfitableToConv3Addr - Return true if it is profitable to convert the |
| /// given 2-address instruction to a 3-address one. |
| bool |
| TwoAddressInstructionPass::isProfitableToConv3Addr(unsigned RegA) { |
| // Look for situations like this: |
| // %reg1024<def> = MOV r1 |
| // %reg1025<def> = MOV r0 |
| // %reg1026<def> = ADD %reg1024, %reg1025 |
| // r2 = MOV %reg1026 |
| // Turn ADD into a 3-address instruction to avoid a copy. |
| unsigned FromRegA = getMappedReg(RegA, SrcRegMap); |
| unsigned ToRegA = getMappedReg(RegA, DstRegMap); |
| return (FromRegA && ToRegA && !regsAreCompatible(FromRegA, ToRegA, TRI)); |
| } |
| |
| /// ConvertInstTo3Addr - Convert the specified two-address instruction into a |
| /// three address one. Return true if this transformation was successful. |
| bool |
| TwoAddressInstructionPass::ConvertInstTo3Addr(MachineBasicBlock::iterator &mi, |
| MachineBasicBlock::iterator &nmi, |
| MachineFunction::iterator &mbbi, |
| unsigned RegB, unsigned Dist) { |
| MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, LV); |
| if (NewMI) { |
| DEBUG(errs() << "2addr: CONVERTING 2-ADDR: " << *mi); |
| DEBUG(errs() << "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); |
| } |
| return true; |
| } |
| |
| return false; |
| } |
| |
| /// ProcessCopy - If the specified instruction is not yet processed, process it |
| /// if it's a copy. For a copy instruction, we find the physical registers the |
| /// source and destination registers might be mapped to. These are kept in |
| /// point-to maps used to determine future optimizations. e.g. |
| /// v1024 = mov r0 |
| /// v1025 = mov r1 |
| /// v1026 = add v1024, v1025 |
| /// r1 = mov r1026 |
| /// If 'add' is a two-address instruction, v1024, v1026 are both potentially |
| /// coalesced to r0 (from the input side). v1025 is mapped to r1. v1026 is |
| /// potentially joined with r1 on the output side. It's worthwhile to commute |
| /// 'add' to eliminate a copy. |
| void TwoAddressInstructionPass::ProcessCopy(MachineInstr *MI, |
| MachineBasicBlock *MBB, |
| SmallPtrSet<MachineInstr*, 8> &Processed) { |
| if (Processed.count(MI)) |
| return; |
| |
| bool IsSrcPhys, IsDstPhys; |
| unsigned SrcReg, DstReg; |
| if (!isCopyToReg(*MI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys)) |
| return; |
| |
| if (IsDstPhys && !IsSrcPhys) |
| DstRegMap.insert(std::make_pair(SrcReg, DstReg)); |
| else if (!IsDstPhys && IsSrcPhys) { |
| bool isNew = SrcRegMap.insert(std::make_pair(DstReg, SrcReg)).second; |
| if (!isNew) |
| assert(SrcRegMap[DstReg] == SrcReg && |
| "Can't map to two src physical registers!"); |
| |
| SmallVector<unsigned, 4> VirtRegPairs; |
| bool IsCopy = false; |
| unsigned NewReg = 0; |
| while (MachineInstr *UseMI = findOnlyInterestingUse(DstReg, MBB, MRI,TII, |
| IsCopy, NewReg, IsDstPhys)) { |
| if (IsCopy) { |
| if (!Processed.insert(UseMI)) |
| break; |
| } |
| |
| DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI); |
| if (DI != DistanceMap.end()) |
| // Earlier in the same MBB.Reached via a back edge. |
| break; |
| |
| if (IsDstPhys) { |
| VirtRegPairs.push_back(NewReg); |
| break; |
| } |
| bool isNew = SrcRegMap.insert(std::make_pair(NewReg, DstReg)).second; |
| if (!isNew) |
| assert(SrcRegMap[NewReg] == DstReg && |
| "Can't map to two src physical registers!"); |
| VirtRegPairs.push_back(NewReg); |
| DstReg = NewReg; |
| } |
| |
| if (!VirtRegPairs.empty()) { |
| unsigned ToReg = VirtRegPairs.back(); |
| VirtRegPairs.pop_back(); |
| while (!VirtRegPairs.empty()) { |
| unsigned FromReg = VirtRegPairs.back(); |
| VirtRegPairs.pop_back(); |
| bool isNew = DstRegMap.insert(std::make_pair(FromReg, ToReg)).second; |
| if (!isNew) |
| assert(DstRegMap[FromReg] == ToReg && |
| "Can't map to two dst physical registers!"); |
| ToReg = FromReg; |
| } |
| } |
| } |
| |
| Processed.insert(MI); |
| } |
| |
| /// isSafeToDelete - If the specified instruction does not produce any side |
| /// effects and all of its defs are dead, then it's safe to delete. |
| static bool isSafeToDelete(MachineInstr *MI, unsigned Reg, |
| const TargetInstrInfo *TII, |
| SmallVector<unsigned, 4> &Kills) { |
| const TargetInstrDesc &TID = MI->getDesc(); |
| if (TID.mayStore() || TID.isCall()) |
| return false; |
| if (TID.isTerminator() || TID.hasUnmodeledSideEffects()) |
| return false; |
| |
| for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = MI->getOperand(i); |
| if (!MO.isReg()) |
| continue; |
| if (MO.isDef() && !MO.isDead()) |
| return false; |
| if (MO.isUse() && MO.getReg() != Reg && MO.isKill()) |
| Kills.push_back(MO.getReg()); |
| } |
| |
| return true; |
| } |
| |
| /// canUpdateDeletedKills - Check if all the registers listed in Kills are |
| /// killed by instructions in MBB preceding the current instruction at |
| /// position Dist. If so, return true and record information about the |
| /// preceding kills in NewKills. |
| bool TwoAddressInstructionPass:: |
| canUpdateDeletedKills(SmallVector<unsigned, 4> &Kills, |
| SmallVector<NewKill, 4> &NewKills, |
| MachineBasicBlock *MBB, unsigned Dist) { |
| while (!Kills.empty()) { |
| unsigned Kill = Kills.back(); |
| Kills.pop_back(); |
| if (TargetRegisterInfo::isPhysicalRegister(Kill)) |
| return false; |
| |
| MachineInstr *LastKill = FindLastUseInMBB(Kill, MBB, Dist); |
| if (!LastKill) |
| return false; |
| |
| bool isModRef = LastKill->modifiesRegister(Kill); |
| NewKills.push_back(std::make_pair(std::make_pair(Kill, isModRef), |
| LastKill)); |
| } |
| return true; |
| } |
| |
| /// DeleteUnusedInstr - If an instruction with a tied register operand can |
| /// be safely deleted, just delete it. |
| bool |
| TwoAddressInstructionPass::DeleteUnusedInstr(MachineBasicBlock::iterator &mi, |
| MachineBasicBlock::iterator &nmi, |
| MachineFunction::iterator &mbbi, |
| unsigned regB, unsigned regBIdx, |
| unsigned Dist) { |
| // Check if the instruction has no side effects and if all its defs are dead. |
| SmallVector<unsigned, 4> Kills; |
| if (!isSafeToDelete(mi, regB, TII, Kills)) |
| return false; |
| |
| // If this instruction kills some virtual registers, we need to |
| // update the kill information. If it's not possible to do so, |
| // then bail out. |
| SmallVector<NewKill, 4> NewKills; |
| if (!canUpdateDeletedKills(Kills, NewKills, &*mbbi, Dist)) |
| return false; |
| |
| if (LV) { |
| while (!NewKills.empty()) { |
| MachineInstr *NewKill = NewKills.back().second; |
| unsigned Kill = NewKills.back().first.first; |
| bool isDead = NewKills.back().first.second; |
| NewKills.pop_back(); |
| if (LV->removeVirtualRegisterKilled(Kill, mi)) { |
| if (isDead) |
| LV->addVirtualRegisterDead(Kill, NewKill); |
| else |
| LV->addVirtualRegisterKilled(Kill, NewKill); |
| } |
| } |
| |
| // If regB was marked as a kill, update its Kills list. |
| if (mi->getOperand(regBIdx).isKill()) |
| LV->removeVirtualRegisterKilled(regB, mi); |
| } |
| |
| mbbi->erase(mi); // Nuke the old inst. |
| mi = nmi; |
| return true; |
| } |
| |
| /// TryInstructionTransform - For the case where an instruction has a single |
| /// pair of tied register operands, attempt some transformations that may |
| /// either eliminate the tied operands or improve the opportunities for |
| /// coalescing away the register copy. Returns true if the tied operands |
| /// are eliminated altogether. |
| bool TwoAddressInstructionPass:: |
| TryInstructionTransform(MachineBasicBlock::iterator &mi, |
| MachineBasicBlock::iterator &nmi, |
| MachineFunction::iterator &mbbi, |
| unsigned SrcIdx, unsigned DstIdx, unsigned Dist) { |
| const TargetInstrDesc &TID = mi->getDesc(); |
| unsigned regA = mi->getOperand(DstIdx).getReg(); |
| unsigned regB = mi->getOperand(SrcIdx).getReg(); |
| |
| assert(TargetRegisterInfo::isVirtualRegister(regB) && |
| "cannot make instruction into two-address form"); |
| |
| // If regA is dead and the instruction can be deleted, just delete |
| // it so it doesn't clobber regB. |
| bool regBKilled = isKilled(*mi, regB, MRI, TII); |
| if (!regBKilled && mi->getOperand(DstIdx).isDead() && |
| DeleteUnusedInstr(mi, nmi, mbbi, regB, SrcIdx, Dist)) { |
| ++NumDeletes; |
| return true; // Done with this instruction. |
| } |
| |
| // Check if it is profitable to commute the operands. |
| unsigned SrcOp1, SrcOp2; |
| unsigned regC = 0; |
| unsigned regCIdx = ~0U; |
| bool TryCommute = false; |
| bool AggressiveCommute = false; |
| if (TID.isCommutable() && mi->getNumOperands() >= 3 && |
| TII->findCommutedOpIndices(mi, SrcOp1, SrcOp2)) { |
| if (SrcIdx == SrcOp1) |
| regCIdx = SrcOp2; |
| else if (SrcIdx == SrcOp2) |
| regCIdx = SrcOp1; |
| |
| if (regCIdx != ~0U) { |
| regC = mi->getOperand(regCIdx).getReg(); |
| if (!regBKilled && isKilled(*mi, regC, MRI, TII)) |
| // If C dies but B does not, swap the B and C operands. |
| // This makes the live ranges of A and C joinable. |
| TryCommute = true; |
| else if (isProfitableToCommute(regB, regC, mi, mbbi, Dist)) { |
| TryCommute = true; |
| AggressiveCommute = true; |
| } |
| } |
| } |
| |
| // If it's profitable to commute, try to do so. |
| if (TryCommute && CommuteInstruction(mi, mbbi, regB, regC, Dist)) { |
| ++NumCommuted; |
| if (AggressiveCommute) |
| ++NumAggrCommuted; |
| return false; |
| } |
| |
| if (TID.isConvertibleTo3Addr()) { |
| // This instruction is potentially convertible to a true |
| // three-address instruction. Check if it is profitable. |
| if (!regBKilled || isProfitableToConv3Addr(regA)) { |
| // Try to convert it. |
| if (ConvertInstTo3Addr(mi, nmi, mbbi, regB, Dist)) { |
| ++NumConvertedTo3Addr; |
| return true; // Done with this instruction. |
| } |
| } |
| } |
| return false; |
| } |
| |
| /// runOnMachineFunction - Reduce two-address instructions to two operands. |
| /// |
| bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { |
| DEBUG(errs() << "Machine Function\n"); |
| const TargetMachine &TM = MF.getTarget(); |
| MRI = &MF.getRegInfo(); |
| TII = TM.getInstrInfo(); |
| TRI = TM.getRegisterInfo(); |
| LV = getAnalysisIfAvailable<LiveVariables>(); |
| AA = &getAnalysis<AliasAnalysis>(); |
| |
| bool MadeChange = false; |
| |
| DEBUG(errs() << "********** REWRITING TWO-ADDR INSTRS **********\n"); |
| DEBUG(errs() << "********** Function: " |
| << MF.getFunction()->getName() << '\n'); |
| |
| // ReMatRegs - Keep track of the registers whose def's are remat'ed. |
| BitVector ReMatRegs; |
| ReMatRegs.resize(MRI->getLastVirtReg()+1); |
| |
| typedef DenseMap<unsigned, SmallVector<std::pair<unsigned, unsigned>, 4> > |
| TiedOperandMap; |
| TiedOperandMap TiedOperands(4); |
| |
| SmallPtrSet<MachineInstr*, 8> Processed; |
| for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end(); |
| mbbi != mbbe; ++mbbi) { |
| unsigned Dist = 0; |
| DistanceMap.clear(); |
| SrcRegMap.clear(); |
| DstRegMap.clear(); |
| Processed.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)); |
| |
| ProcessCopy(&*mi, &*mbbi, Processed); |
| |
| // First scan through all the tied register uses in this instruction |
| // and record a list of pairs of tied operands for each register. |
| unsigned NumOps = (mi->getOpcode() == TargetInstrInfo::INLINEASM) |
| ? mi->getNumOperands() : TID.getNumOperands(); |
| for (unsigned SrcIdx = 0; SrcIdx < NumOps; ++SrcIdx) { |
| unsigned DstIdx = 0; |
| if (!mi->isRegTiedToDefOperand(SrcIdx, &DstIdx)) |
| continue; |
| |
| if (FirstTied) { |
| FirstTied = false; |
| ++NumTwoAddressInstrs; |
| DEBUG(errs() << '\t' << *mi); |
| } |
| |
| assert(mi->getOperand(SrcIdx).isReg() && |
| mi->getOperand(SrcIdx).getReg() && |
| mi->getOperand(SrcIdx).isUse() && |
| "two address instruction invalid"); |
| |
| unsigned regB = mi->getOperand(SrcIdx).getReg(); |
| TiedOperandMap::iterator OI = TiedOperands.find(regB); |
| if (OI == TiedOperands.end()) { |
| SmallVector<std::pair<unsigned, unsigned>, 4> TiedPair; |
| OI = TiedOperands.insert(std::make_pair(regB, TiedPair)).first; |
| } |
| OI->second.push_back(std::make_pair(SrcIdx, DstIdx)); |
| } |
| |
| // Now iterate over the information collected above. |
| for (TiedOperandMap::iterator OI = TiedOperands.begin(), |
| OE = TiedOperands.end(); OI != OE; ++OI) { |
| SmallVector<std::pair<unsigned, unsigned>, 4> &TiedPairs = OI->second; |
| |
| // If the instruction has a single pair of tied operands, try some |
| // transformations that may either eliminate the tied operands or |
| // improve the opportunities for coalescing away the register copy. |
| if (TiedOperands.size() == 1 && TiedPairs.size() == 1) { |
| unsigned SrcIdx = TiedPairs[0].first; |
| unsigned DstIdx = TiedPairs[0].second; |
| |
| // If the registers are already equal, nothing needs to be done. |
| if (mi->getOperand(SrcIdx).getReg() == |
| mi->getOperand(DstIdx).getReg()) |
| break; // Done with this instruction. |
| |
| if (TryInstructionTransform(mi, nmi, mbbi, SrcIdx, DstIdx, Dist)) |
| break; // The tied operands have been eliminated. |
| } |
| |
| bool RemovedKillFlag = false; |
| bool AllUsesCopied = true; |
| unsigned LastCopiedReg = 0; |
| unsigned regB = OI->first; |
| for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) { |
| unsigned SrcIdx = TiedPairs[tpi].first; |
| unsigned DstIdx = TiedPairs[tpi].second; |
| unsigned regA = mi->getOperand(DstIdx).getReg(); |
| // Grab regB from the instruction because it may have changed if the |
| // instruction was commuted. |
| regB = mi->getOperand(SrcIdx).getReg(); |
| |
| if (regA == regB) { |
| // The register is tied to multiple destinations (or else we would |
| // not have continued this far), but this use of the register |
| // already matches the tied destination. Leave it. |
| AllUsesCopied = false; |
| continue; |
| } |
| LastCopiedReg = regA; |
| |
| assert(TargetRegisterInfo::isVirtualRegister(regB) && |
| "cannot make instruction into two-address form"); |
| |
| #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(i == DstIdx || |
| !mi->getOperand(i).isReg() || |
| mi->getOperand(i).getReg() != regA); |
| #endif |
| |
| // Emit a copy or rematerialize the definition. |
| const TargetRegisterClass *rc = MRI->getRegClass(regB); |
| 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, AA) && |
| isProfitableToReMat(regB, rc, mi, DefMI, mbbi, Dist)){ |
| DEBUG(errs() << "2addr: REMATTING : " << *DefMI << "\n"); |
| unsigned regASubIdx = mi->getOperand(DstIdx).getSubReg(); |
| TII->reMaterialize(*mbbi, mi, regA, regASubIdx, DefMI); |
| ReMatRegs.set(regB); |
| ++NumReMats; |
| } else { |
| bool Emitted = TII->copyRegToReg(*mbbi, mi, regA, regB, rc, rc); |
| (void)Emitted; |
| assert(Emitted && "Unable to issue a copy instruction!\n"); |
| } |
| |
| MachineBasicBlock::iterator prevMI = prior(mi); |
| // Update DistanceMap. |
| DistanceMap.insert(std::make_pair(prevMI, Dist)); |
| DistanceMap[mi] = ++Dist; |
| |
| DEBUG(errs() << "\t\tprepend:\t" << *prevMI); |
| |
| MachineOperand &MO = mi->getOperand(SrcIdx); |
| assert(MO.isReg() && MO.getReg() == regB && MO.isUse() && |
| "inconsistent operand info for 2-reg pass"); |
| if (MO.isKill()) { |
| MO.setIsKill(false); |
| RemovedKillFlag = true; |
| } |
| MO.setReg(regA); |
| } |
| |
| if (AllUsesCopied) { |
| // Replace other (un-tied) uses of regB with LastCopiedReg. |
| for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = mi->getOperand(i); |
| if (MO.isReg() && MO.getReg() == regB && MO.isUse()) { |
| if (MO.isKill()) { |
| MO.setIsKill(false); |
| RemovedKillFlag = true; |
| } |
| MO.setReg(LastCopiedReg); |
| } |
| } |
| |
| // Update live variables for regB. |
| if (RemovedKillFlag && LV && LV->getVarInfo(regB).removeKill(mi)) |
| LV->addVirtualRegisterKilled(regB, prior(mi)); |
| |
| } else if (RemovedKillFlag) { |
| // Some tied uses of regB matched their destination registers, so |
| // regB is still used in this instruction, but a kill flag was |
| // removed from a different tied use of regB, so now we need to add |
| // a kill flag to one of the remaining uses of regB. |
| for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) { |
| MachineOperand &MO = mi->getOperand(i); |
| if (MO.isReg() && MO.getReg() == regB && MO.isUse()) { |
| MO.setIsKill(true); |
| break; |
| } |
| } |
| } |
| |
| MadeChange = true; |
| |
| DEBUG(errs() << "\t\trewrite to:\t" << *mi); |
| } |
| |
| // Clear TiedOperands here instead of at the top of the loop |
| // since most instructions do not have tied operands. |
| TiedOperands.clear(); |
| 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; |
| } |