From ad0a4a31f8dd16a8307060b892ac3863b9d0da2c Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Wed, 18 Jun 2008 07:49:14 +0000 Subject: [PATCH] Complete support for two-address pass rematerialization. Now *almost* always a win. llvm-svn: 52452 --- lib/CodeGen/TwoAddressInstructionPass.cpp | 177 ++++++++++++++++------ 1 file changed, 128 insertions(+), 49 deletions(-) diff --git a/lib/CodeGen/TwoAddressInstructionPass.cpp b/lib/CodeGen/TwoAddressInstructionPass.cpp index 81864b7c0e4..d680a98a7fd 100644 --- a/lib/CodeGen/TwoAddressInstructionPass.cpp +++ b/lib/CodeGen/TwoAddressInstructionPass.cpp @@ -40,6 +40,8 @@ #include "llvm/Support/CommandLine.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" @@ -49,9 +51,10 @@ 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"); static cl::opt -EnableReMat("2-addr-remat", cl::init(false), cl::Hidden, +EnableReMat("two-addr-remat", cl::init(false), cl::Hidden, cl::desc("Two-addr conversion should remat when possible.")); namespace { @@ -65,6 +68,12 @@ namespace { bool Sink3AddrInstruction(MachineBasicBlock *MBB, MachineInstr *MI, unsigned Reg, MachineBasicBlock::iterator OldPos); + + bool isSafeToReMat(unsigned DstReg, MachineInstr *MI); + bool isProfitableToReMat(unsigned Reg, const TargetRegisterClass *RC, + MachineInstr *MI, unsigned Loc, + MachineInstr *DefMI, MachineBasicBlock *MBB, + DenseMap &DistanceMap); public: static char ID; // Pass identification, replacement for typeid TwoAddressInstructionPass() : MachineFunctionPass((intptr_t)&ID) {} @@ -93,7 +102,6 @@ const PassInfo *const llvm::TwoAddressInstructionPassID = &X; /// 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) { @@ -127,7 +135,6 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB, // 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(); @@ -144,15 +151,18 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB, // 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 if before or after another instruction. Then we can use + // 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.isRegister()) @@ -165,8 +175,8 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB, if (MO.isKill()) { if (OtherMI == KillMI && MOReg == SavedReg) - // Save the operand that kills the register. We want unset the kill - // marker is we can sink MI past it. + // 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. @@ -191,6 +201,80 @@ bool TwoAddressInstructionPass::Sink3AddrInstruction(MachineBasicBlock *MBB, return true; } +/// isSafeToReMat - Return true if it's safe to rematerialize the specified +/// instruction which defined the specified register instead of copying it. +bool +TwoAddressInstructionPass::isSafeToReMat(unsigned DstReg, MachineInstr *MI) { + const TargetInstrDesc &TID = MI->getDesc(); + if (!TID.isAsCheapAsAMove()) + return false; + bool SawStore = false; + if (!MI->isSafeToMove(TII, SawStore)) + return false; + for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI->getOperand(i); + if (!MO.isRegister()) + continue; + // FIXME: For now, do not remat any instruction with register operands. + // Later on, we can loosen the restriction is the register operands have + // not been modified between the def and use. Note, this is different from + // MachineSink because the code in no longer in two-address form (at least + // partially). + if (MO.isUse()) + return false; + else if (!MO.isDead() && MO.getReg() != DstReg) + return false; + } + 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.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, unsigned Loc, + MachineInstr *DefMI, MachineBasicBlock *MBB, + DenseMap &DistanceMap) { + if (DefMI->getParent() != MBB) + return true; + // If earlier uses in MBB are not two-address uses, then don't remat. + 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(); + if (UseMI->getParent() != MBB) + continue; + DenseMap::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; + } + return !OtherUse; +} + /// runOnMachineFunction - Reduce two-address instructions to two operands. /// bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { @@ -206,16 +290,25 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { DOUT << "********** REWRITING TWO-ADDR INSTRS **********\n"; DOUT << "********** Function: " << MF.getFunction()->getName() << '\n'; - SmallPtrSet ReMattedInstrs; + // 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 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) @@ -284,6 +377,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { 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; @@ -303,21 +397,23 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { assert(TID.getOperandConstraint(i, TOI::TIED_TO) == -1); #endif - if (MachineInstr *New=TII->convertToThreeAddress(mbbi, mi, *LV)) { + MachineInstr *NewMI = TII->convertToThreeAddress(mbbi, mi, *LV); + if (NewMI) { DOUT << "2addr: CONVERTING 2-ADDR: " << *mi; - DOUT << "2addr: TO 3-ADDR: " << *New; + DOUT << "2addr: TO 3-ADDR: " << *NewMI; bool Sunk = false; - if (New->findRegisterUseOperand(regB, false, TRI)) + 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, New, regB, mi); + Sunk = Sink3AddrInstruction(mbbi, NewMI, regB, mi); mbbi->erase(mi); // Nuke the old inst. if (!Sunk) { - mi = New; + DistanceMap.insert(std::make_pair(NewMI, Dist)); + mi = NewMI; nmi = next(mi); } @@ -328,17 +424,17 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { } InstructionRearranged: - const TargetRegisterClass* rc = MF.getRegInfo().getRegClass(regA); - MachineInstr *Orig = MRI->getVRegDef(regB); - const TargetInstrDesc &OrigTID = Orig->getDesc(); - bool SawStore = false; - - if (EnableReMat && Orig && Orig->isSafeToMove(TII, SawStore) && - OrigTID.isAsCheapAsAMove() && !OrigTID.mayLoad() && - !OrigTID.isSimpleLoad()) { - DEBUG(cerr << "2addr: REMATTING : " << *Orig << "\n"); - TII->reMaterialize(*mbbi, mi, regA, Orig); - ReMattedInstrs.insert(Orig); + 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 (EnableReMat && DefMI && + isSafeToReMat(regB, DefMI) && + isProfitableToReMat(regB, rc, mi, Dist, DefMI, mbbi,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); } @@ -378,33 +474,16 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) { } if (EnableReMat) { - // Check to see if the instructions that we rematerialized are now dead. If - // they are, expunge them here. - SmallPtrSet::iterator I = ReMattedInstrs.begin(); - SmallPtrSet::iterator E = ReMattedInstrs.end(); - - for (; I != E; ++I) { - MachineInstr *MI = *I; - bool InstrDead = true; - - for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { - const MachineOperand &MO = MI->getOperand(i); - if (!MO.isRegister()) - continue; - unsigned MOReg = MO.getReg(); - - if (!MOReg || !MO.isDef() || (MO.isImplicit() && MO.isDead())) - continue; - - if (MRI->use_begin(MOReg) != MRI->use_end()) { - InstrDead = false; - break; - } + // 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(); } - - if (InstrDead) - MI->eraseFromParent(); + VReg = ReMatRegs.find_next(VReg); } + } return MadeChange;