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Diffstat (limited to 'contrib/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp | 1876 |
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diff --git a/contrib/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp b/contrib/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp new file mode 100644 index 000000000000..4b72f6a84ca1 --- /dev/null +++ b/contrib/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp @@ -0,0 +1,1876 @@ +//===- 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. +// +//===----------------------------------------------------------------------===// + +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/iterator_range.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/CodeGen/LiveInterval.h" +#include "llvm/CodeGen/LiveIntervals.h" +#include "llvm/CodeGen/LiveVariables.h" +#include "llvm/CodeGen/MachineBasicBlock.h" +#include "llvm/CodeGen/MachineFunction.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineInstr.h" +#include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineOperand.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/CodeGen/SlotIndexes.h" +#include "llvm/CodeGen/TargetInstrInfo.h" +#include "llvm/CodeGen/TargetOpcodes.h" +#include "llvm/CodeGen/TargetRegisterInfo.h" +#include "llvm/CodeGen/TargetSubtargetInfo.h" +#include "llvm/MC/MCInstrDesc.h" +#include "llvm/MC/MCInstrItineraries.h" +#include "llvm/Pass.h" +#include "llvm/Support/CodeGen.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetMachine.h" +#include <cassert> +#include <iterator> +#include <utility> + +using namespace llvm; + +#define DEBUG_TYPE "twoaddressinstruction" + +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(NumReSchedUps, "Number of instructions re-scheduled up"); +STATISTIC(NumReSchedDowns, "Number of instructions re-scheduled down"); + +// Temporary flag to disable rescheduling. +static cl::opt<bool> +EnableRescheduling("twoaddr-reschedule", + cl::desc("Coalesce copies by rescheduling (default=true)"), + cl::init(true), cl::Hidden); + +// Limit the number of dataflow edges to traverse when evaluating the benefit +// of commuting operands. +static cl::opt<unsigned> MaxDataFlowEdge( + "dataflow-edge-limit", cl::Hidden, cl::init(3), + cl::desc("Maximum number of dataflow edges to traverse when evaluating " + "the benefit of commuting operands")); + +namespace { + +class TwoAddressInstructionPass : public MachineFunctionPass { + MachineFunction *MF; + const TargetInstrInfo *TII; + const TargetRegisterInfo *TRI; + const InstrItineraryData *InstrItins; + MachineRegisterInfo *MRI; + LiveVariables *LV; + LiveIntervals *LIS; + AliasAnalysis *AA; + CodeGenOpt::Level OptLevel; + + // The current basic block being processed. + MachineBasicBlock *MBB; + + // Keep track the distance of a MI from the start of the current basic block. + DenseMap<MachineInstr*, unsigned> DistanceMap; + + // Set of already processed instructions in the current block. + SmallPtrSet<MachineInstr*, 8> Processed; + + // Set of instructions converted to three-address by target and then sunk + // down current basic block. + SmallPtrSet<MachineInstr*, 8> SunkInstrs; + + // 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; + + // 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(MachineInstr *MI, unsigned Reg, + MachineBasicBlock::iterator OldPos); + + bool isRevCopyChain(unsigned FromReg, unsigned ToReg, int Maxlen); + + bool noUseAfterLastDef(unsigned Reg, unsigned Dist, unsigned &LastDef); + + bool isProfitableToCommute(unsigned regA, unsigned regB, unsigned regC, + MachineInstr *MI, unsigned Dist); + + bool commuteInstruction(MachineInstr *MI, unsigned DstIdx, + unsigned RegBIdx, unsigned RegCIdx, unsigned Dist); + + bool isProfitableToConv3Addr(unsigned RegA, unsigned RegB); + + bool convertInstTo3Addr(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned RegA, unsigned RegB, unsigned Dist); + + bool isDefTooClose(unsigned Reg, unsigned Dist, MachineInstr *MI); + + bool rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned Reg); + bool rescheduleKillAboveMI(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned Reg); + + bool tryInstructionTransform(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned SrcIdx, unsigned DstIdx, + unsigned Dist, bool shouldOnlyCommute); + + bool tryInstructionCommute(MachineInstr *MI, + unsigned DstOpIdx, + unsigned BaseOpIdx, + bool BaseOpKilled, + unsigned Dist); + void scanUses(unsigned DstReg); + + void processCopy(MachineInstr *MI); + + using TiedPairList = SmallVector<std::pair<unsigned, unsigned>, 4>; + using TiedOperandMap = SmallDenseMap<unsigned, TiedPairList>; + + bool collectTiedOperands(MachineInstr *MI, TiedOperandMap&); + void processTiedPairs(MachineInstr *MI, TiedPairList&, unsigned &Dist); + void eliminateRegSequence(MachineBasicBlock::iterator&); + +public: + static char ID; // Pass identification, replacement for typeid + + TwoAddressInstructionPass() : MachineFunctionPass(ID) { + initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry()); + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + AU.addUsedIfAvailable<AAResultsWrapperPass>(); + AU.addUsedIfAvailable<LiveVariables>(); + AU.addPreserved<LiveVariables>(); + AU.addPreserved<SlotIndexes>(); + AU.addPreserved<LiveIntervals>(); + AU.addPreservedID(MachineLoopInfoID); + AU.addPreservedID(MachineDominatorsID); + MachineFunctionPass::getAnalysisUsage(AU); + } + + /// Pass entry point. + bool runOnMachineFunction(MachineFunction&) override; +}; + +} // end anonymous namespace + +char TwoAddressInstructionPass::ID = 0; + +char &llvm::TwoAddressInstructionPassID = TwoAddressInstructionPass::ID; + +INITIALIZE_PASS_BEGIN(TwoAddressInstructionPass, DEBUG_TYPE, + "Two-Address instruction pass", false, false) +INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) +INITIALIZE_PASS_END(TwoAddressInstructionPass, DEBUG_TYPE, + "Two-Address instruction pass", false, false) + +static bool isPlainlyKilled(MachineInstr *MI, unsigned Reg, LiveIntervals *LIS); + +/// 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(MachineInstr *MI, unsigned SavedReg, + MachineBasicBlock::iterator OldPos) { + // FIXME: Shouldn't we be trying to do this before we three-addressify the + // instruction? After this transformation is done, we no longer need + // the instruction to be in three-address form. + + // Check if it's safe to move this instruction. + bool SeenStore = true; // Be conservative. + if (!MI->isSafeToMove(AA, SeenStore)) + return false; + + unsigned DefReg = 0; + SmallSet<unsigned, 4> UseRegs; + + for (const MachineOperand &MO : MI->operands()) { + 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 = nullptr; + if (LIS) { + LiveInterval &LI = LIS->getInterval(SavedReg); + assert(LI.end() != LI.begin() && + "Reg should not have empty live interval."); + + SlotIndex MBBEndIdx = LIS->getMBBEndIdx(MBB).getPrevSlot(); + LiveInterval::const_iterator I = LI.find(MBBEndIdx); + if (I != LI.end() && I->start < MBBEndIdx) + return false; + + --I; + KillMI = LIS->getInstructionFromIndex(I->end); + } + if (!KillMI) { + for (MachineOperand &UseMO : MRI->use_nodbg_operands(SavedReg)) { + if (!UseMO.isKill()) + continue; + KillMI = UseMO.getParent(); + break; + } + } + + // If we find the instruction that kills SavedReg, and it is in an + // appropriate location, we can try to sink the current instruction + // past it. + if (!KillMI || KillMI->getParent() != MBB || KillMI == MI || + MachineBasicBlock::iterator(KillMI) == OldPos || KillMI->isTerminator()) + 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 = nullptr; + MachineBasicBlock::iterator KillPos = KillMI; + ++KillPos; + + unsigned NumVisited = 0; + for (MachineInstr &OtherMI : make_range(std::next(OldPos), KillPos)) { + // Debug instructions cannot be counted against the limit. + if (OtherMI.isDebugInstr()) + continue; + 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() || (LIS && isPlainlyKilled(&OtherMI, MOReg, LIS))) { + 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; + } + } + } + assert(KillMO && "Didn't find kill"); + + if (!LIS) { + // 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); + + if (LIS) + LIS->handleMove(*MI); + + ++Num3AddrSunk; + return true; +} + +/// Return the MachineInstr* if it is the single def of the Reg in current BB. +static MachineInstr *getSingleDef(unsigned Reg, MachineBasicBlock *BB, + const MachineRegisterInfo *MRI) { + MachineInstr *Ret = nullptr; + for (MachineInstr &DefMI : MRI->def_instructions(Reg)) { + if (DefMI.getParent() != BB || DefMI.isDebugValue()) + continue; + if (!Ret) + Ret = &DefMI; + else if (Ret != &DefMI) + return nullptr; + } + return Ret; +} + +/// Check if there is a reversed copy chain from FromReg to ToReg: +/// %Tmp1 = copy %Tmp2; +/// %FromReg = copy %Tmp1; +/// %ToReg = add %FromReg ... +/// %Tmp2 = copy %ToReg; +/// MaxLen specifies the maximum length of the copy chain the func +/// can walk through. +bool TwoAddressInstructionPass::isRevCopyChain(unsigned FromReg, unsigned ToReg, + int Maxlen) { + unsigned TmpReg = FromReg; + for (int i = 0; i < Maxlen; i++) { + MachineInstr *Def = getSingleDef(TmpReg, MBB, MRI); + if (!Def || !Def->isCopy()) + return false; + + TmpReg = Def->getOperand(1).getReg(); + + if (TmpReg == ToReg) + return true; + } + return false; +} + +/// 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, unsigned Dist, + unsigned &LastDef) { + LastDef = 0; + unsigned LastUse = Dist; + for (MachineOperand &MO : MRI->reg_operands(Reg)) { + MachineInstr *MI = MO.getParent(); + if (MI->getParent() != MBB || MI->isDebugValue()) + 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); +} + +/// Return true if the specified MI is a copy instruction or an 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; + if (MI.isCopy()) { + DstReg = MI.getOperand(0).getReg(); + SrcReg = MI.getOperand(1).getReg(); + } else if (MI.isInsertSubreg() || MI.isSubregToReg()) { + DstReg = MI.getOperand(0).getReg(); + SrcReg = MI.getOperand(2).getReg(); + } else + return false; + + IsSrcPhys = TargetRegisterInfo::isPhysicalRegister(SrcReg); + IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg); + return true; +} + +/// Test if the given register value, which is used by the +/// given instruction, is killed by the given instruction. +static bool isPlainlyKilled(MachineInstr *MI, unsigned Reg, + LiveIntervals *LIS) { + if (LIS && TargetRegisterInfo::isVirtualRegister(Reg) && + !LIS->isNotInMIMap(*MI)) { + // FIXME: Sometimes tryInstructionTransform() will add instructions and + // test whether they can be folded before keeping them. In this case it + // sets a kill before recursively calling tryInstructionTransform() again. + // If there is no interval available, we assume that this instruction is + // one of those. A kill flag is manually inserted on the operand so the + // check below will handle it. + LiveInterval &LI = LIS->getInterval(Reg); + // This is to match the kill flag version where undefs don't have kill + // flags. + if (!LI.hasAtLeastOneValue()) + return false; + + SlotIndex useIdx = LIS->getInstructionIndex(*MI); + LiveInterval::const_iterator I = LI.find(useIdx); + assert(I != LI.end() && "Reg must be live-in to use."); + return !I->end.isBlock() && SlotIndex::isSameInstr(I->end, useIdx); + } + + return MI->killsRegister(Reg); +} + +/// 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 killed %reg1025 +/// %reg1036 = add killed %reg1034, killed %reg1035 +/// +/// %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. +/// +/// If allowFalsePositives is true then likely kills are treated as kills even +/// if it can't be proven that they are kills. +static bool isKilled(MachineInstr &MI, unsigned Reg, + const MachineRegisterInfo *MRI, + const TargetInstrInfo *TII, + LiveIntervals *LIS, + bool allowFalsePositives) { + MachineInstr *DefMI = &MI; + while (true) { + // All uses of physical registers are likely to be kills. + if (TargetRegisterInfo::isPhysicalRegister(Reg) && + (allowFalsePositives || MRI->hasOneUse(Reg))) + return true; + if (!isPlainlyKilled(DefMI, Reg, LIS)) + 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 (std::next(Begin) != MRI->def_end()) + return true; + DefMI = Begin->getParent(); + 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; + } +} + +/// 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) { + for (unsigned i = 0, NumOps = MI.getNumOperands(); 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; +} + +/// 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) { + if (!MRI->hasOneNonDBGUse(Reg)) + // None or more than one use. + return nullptr; + MachineInstr &UseMI = *MRI->use_instr_nodbg_begin(Reg); + if (UseMI.getParent() != MBB) + return nullptr; + 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 nullptr; +} + +/// 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; +} + +/// 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); +} + +// Returns true if Reg is equal or aliased to at least one register in Set. +static bool regOverlapsSet(const SmallVectorImpl<unsigned> &Set, unsigned Reg, + const TargetRegisterInfo *TRI) { + for (unsigned R : Set) + if (TRI->regsOverlap(R, Reg)) + return true; + + return false; +} + +/// Return true if it's potentially profitable to commute the two-address +/// instruction that's being processed. +bool +TwoAddressInstructionPass:: +isProfitableToCommute(unsigned regA, unsigned regB, unsigned regC, + MachineInstr *MI, unsigned Dist) { + if (OptLevel == CodeGenOpt::None) + return false; + + // 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 = EXTRACT_SUBREG killed %reg1027, 1 + // %reg1029 = COPY %reg1028 + // %reg1029 = SHR8ri %reg1029, 7, implicit dead %eflags + // insert => %reg1030 = COPY %reg1028 + // %reg1030 = ADD8rr killed %reg1028, killed %reg1029, implicit dead %eflags + // In this case, it might not be possible to coalesce the second COPY + // instruction if the first one is coalesced. So it would be profitable to + // commute it: + // %reg1028 = EXTRACT_SUBREG killed %reg1027, 1 + // %reg1029 = COPY %reg1028 + // %reg1029 = SHR8ri %reg1029, 7, implicit dead %eflags + // insert => %reg1030 = COPY %reg1029 + // %reg1030 = ADD8rr killed %reg1029, killed %reg1028, implicit dead %eflags + + if (!isPlainlyKilled(MI, regC, LIS)) + return false; + + // Ok, we have something like: + // %reg1030 = ADD8rr killed %reg1028, killed %reg1029, implicit dead %eflags + // let's see if it's worth commuting it. + + // Look for situations like this: + // %reg1024 = MOV r1 + // %reg1025 = MOV r0 + // %reg1026 = ADD %reg1024, %reg1025 + // r0 = MOV %reg1026 + // Commute the ADD to hopefully eliminate an otherwise unavoidable copy. + unsigned ToRegA = getMappedReg(regA, DstRegMap); + if (ToRegA) { + unsigned FromRegB = getMappedReg(regB, SrcRegMap); + unsigned FromRegC = getMappedReg(regC, SrcRegMap); + bool CompB = FromRegB && regsAreCompatible(FromRegB, ToRegA, TRI); + bool CompC = FromRegC && regsAreCompatible(FromRegC, ToRegA, TRI); + + // Compute if any of the following are true: + // -RegB is not tied to a register and RegC is compatible with RegA. + // -RegB is tied to the wrong physical register, but RegC is. + // -RegB is tied to the wrong physical register, and RegC isn't tied. + if ((!FromRegB && CompC) || (FromRegB && !CompB && (!FromRegC || CompC))) + return true; + // Don't compute if any of the following are true: + // -RegC is not tied to a register and RegB is compatible with RegA. + // -RegC is tied to the wrong physical register, but RegB is. + // -RegC is tied to the wrong physical register, and RegB isn't tied. + if ((!FromRegC && CompB) || (FromRegC && !CompC && (!FromRegB || CompB))) + return false; + } + + // 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, 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, Dist, LastDefB)) + return true; + + // Look for situation like this: + // %reg101 = MOV %reg100 + // %reg102 = ... + // %reg103 = ADD %reg102, %reg101 + // ... = %reg103 ... + // %reg100 = MOV %reg103 + // If there is a reversed copy chain from reg101 to reg103, commute the ADD + // to eliminate an otherwise unavoidable copy. + // FIXME: + // We can extend the logic further: If an pair of operands in an insn has + // been merged, the insn could be regarded as a virtual copy, and the virtual + // copy could also be used to construct a copy chain. + // To more generally minimize register copies, ideally the logic of two addr + // instruction pass should be integrated with register allocation pass where + // interference graph is available. + if (isRevCopyChain(regC, regA, MaxDataFlowEdge)) + return true; + + if (isRevCopyChain(regB, regA, MaxDataFlowEdge)) + return false; + + // 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; +} + +/// 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(MachineInstr *MI, + unsigned DstIdx, + unsigned RegBIdx, + unsigned RegCIdx, + unsigned Dist) { + unsigned RegC = MI->getOperand(RegCIdx).getReg(); + LLVM_DEBUG(dbgs() << "2addr: COMMUTING : " << *MI); + MachineInstr *NewMI = TII->commuteInstruction(*MI, false, RegBIdx, RegCIdx); + + if (NewMI == nullptr) { + LLVM_DEBUG(dbgs() << "2addr: COMMUTING FAILED!\n"); + return false; + } + + LLVM_DEBUG(dbgs() << "2addr: COMMUTED TO: " << *NewMI); + assert(NewMI == MI && + "TargetInstrInfo::commuteInstruction() should not return a new " + "instruction unless it was requested."); + + // Update source register map. + unsigned FromRegC = getMappedReg(RegC, SrcRegMap); + if (FromRegC) { + unsigned RegA = MI->getOperand(DstIdx).getReg(); + SrcRegMap[RegA] = FromRegC; + } + + return true; +} + +/// Return true if it is profitable to convert the given 2-address instruction +/// to a 3-address one. +bool +TwoAddressInstructionPass::isProfitableToConv3Addr(unsigned RegA,unsigned RegB){ + // Look for situations like this: + // %reg1024 = MOV r1 + // %reg1025 = MOV r0 + // %reg1026 = ADD %reg1024, %reg1025 + // r2 = MOV %reg1026 + // Turn ADD into a 3-address instruction to avoid a copy. + unsigned FromRegB = getMappedReg(RegB, SrcRegMap); + if (!FromRegB) + return false; + unsigned ToRegA = getMappedReg(RegA, DstRegMap); + return (ToRegA && !regsAreCompatible(FromRegB, ToRegA, TRI)); +} + +/// 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, + unsigned RegA, unsigned RegB, + unsigned Dist) { + // FIXME: Why does convertToThreeAddress() need an iterator reference? + MachineFunction::iterator MFI = MBB->getIterator(); + MachineInstr *NewMI = TII->convertToThreeAddress(MFI, *mi, LV); + assert(MBB->getIterator() == MFI && + "convertToThreeAddress changed iterator reference"); + if (!NewMI) + return false; + + LLVM_DEBUG(dbgs() << "2addr: CONVERTING 2-ADDR: " << *mi); + LLVM_DEBUG(dbgs() << "2addr: TO 3-ADDR: " << *NewMI); + bool Sunk = false; + + if (LIS) + LIS->ReplaceMachineInstrInMaps(*mi, *NewMI); + + 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(NewMI, RegB, mi); + + MBB->erase(mi); // Nuke the old inst. + + if (!Sunk) { + DistanceMap.insert(std::make_pair(NewMI, Dist)); + mi = NewMI; + nmi = std::next(mi); + } + else + SunkInstrs.insert(NewMI); + + // Update source and destination register maps. + SrcRegMap.erase(RegA); + DstRegMap.erase(RegB); + return true; +} + +/// Scan forward recursively for only uses, update maps if the use is a copy or +/// a two-address instruction. +void +TwoAddressInstructionPass::scanUses(unsigned DstReg) { + SmallVector<unsigned, 4> VirtRegPairs; + bool IsDstPhys; + bool IsCopy = false; + unsigned NewReg = 0; + unsigned Reg = DstReg; + while (MachineInstr *UseMI = findOnlyInterestingUse(Reg, MBB, MRI, TII,IsCopy, + NewReg, IsDstPhys)) { + if (IsCopy && !Processed.insert(UseMI).second) + 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, Reg)).second; + if (!isNew) + assert(SrcRegMap[NewReg] == Reg && "Can't map to two src registers!"); + VirtRegPairs.push_back(NewReg); + Reg = 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 registers!"); + ToReg = FromReg; + } + bool isNew = DstRegMap.insert(std::make_pair(DstReg, ToReg)).second; + if (!isNew) + assert(DstRegMap[DstReg] == ToReg && "Can't map to two dst registers!"); + } +} + +/// 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) { + 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!"); + + scanUses(DstReg); + } + + Processed.insert(MI); +} + +/// If there is one more local instruction that reads 'Reg' and it kills 'Reg, +/// consider moving the instruction below the kill instruction in order to +/// eliminate the need for the copy. +bool TwoAddressInstructionPass:: +rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned Reg) { + // Bail immediately if we don't have LV or LIS available. We use them to find + // kills efficiently. + if (!LV && !LIS) + return false; + + MachineInstr *MI = &*mi; + DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI); + if (DI == DistanceMap.end()) + // Must be created from unfolded load. Don't waste time trying this. + return false; + + MachineInstr *KillMI = nullptr; + if (LIS) { + LiveInterval &LI = LIS->getInterval(Reg); + assert(LI.end() != LI.begin() && + "Reg should not have empty live interval."); + + SlotIndex MBBEndIdx = LIS->getMBBEndIdx(MBB).getPrevSlot(); + LiveInterval::const_iterator I = LI.find(MBBEndIdx); + if (I != LI.end() && I->start < MBBEndIdx) + return false; + + --I; + KillMI = LIS->getInstructionFromIndex(I->end); + } else { + KillMI = LV->getVarInfo(Reg).findKill(MBB); + } + if (!KillMI || MI == KillMI || KillMI->isCopy() || KillMI->isCopyLike()) + // Don't mess with copies, they may be coalesced later. + return false; + + if (KillMI->hasUnmodeledSideEffects() || KillMI->isCall() || + KillMI->isBranch() || KillMI->isTerminator()) + // Don't move pass calls, etc. + return false; + + unsigned DstReg; + if (isTwoAddrUse(*KillMI, Reg, DstReg)) + return false; + + bool SeenStore = true; + if (!MI->isSafeToMove(AA, SeenStore)) + return false; + + if (TII->getInstrLatency(InstrItins, *MI) > 1) + // FIXME: Needs more sophisticated heuristics. + return false; + + SmallVector<unsigned, 2> Uses; + SmallVector<unsigned, 2> Kills; + SmallVector<unsigned, 2> Defs; + for (const MachineOperand &MO : MI->operands()) { + if (!MO.isReg()) + continue; + unsigned MOReg = MO.getReg(); + if (!MOReg) + continue; + if (MO.isDef()) + Defs.push_back(MOReg); + else { + Uses.push_back(MOReg); + if (MOReg != Reg && (MO.isKill() || + (LIS && isPlainlyKilled(MI, MOReg, LIS)))) + Kills.push_back(MOReg); + } + } + + // Move the copies connected to MI down as well. + MachineBasicBlock::iterator Begin = MI; + MachineBasicBlock::iterator AfterMI = std::next(Begin); + MachineBasicBlock::iterator End = AfterMI; + while (End != MBB->end()) { + End = skipDebugInstructionsForward(End, MBB->end()); + if (End->isCopy() && regOverlapsSet(Defs, End->getOperand(1).getReg(), TRI)) + Defs.push_back(End->getOperand(0).getReg()); + else + break; + ++End; + } + + // Check if the reschedule will not break dependencies. + unsigned NumVisited = 0; + MachineBasicBlock::iterator KillPos = KillMI; + ++KillPos; + for (MachineInstr &OtherMI : make_range(End, KillPos)) { + // Debug instructions cannot be counted against the limit. + if (OtherMI.isDebugInstr()) + continue; + if (NumVisited > 10) // FIXME: Arbitrary limit to reduce compile time cost. + return false; + ++NumVisited; + if (OtherMI.hasUnmodeledSideEffects() || OtherMI.isCall() || + OtherMI.isBranch() || OtherMI.isTerminator()) + // Don't move pass calls, etc. + return false; + for (const MachineOperand &MO : OtherMI.operands()) { + if (!MO.isReg()) + continue; + unsigned MOReg = MO.getReg(); + if (!MOReg) + continue; + if (MO.isDef()) { + if (regOverlapsSet(Uses, MOReg, TRI)) + // Physical register use would be clobbered. + return false; + if (!MO.isDead() && regOverlapsSet(Defs, MOReg, TRI)) + // May clobber a physical register def. + // FIXME: This may be too conservative. It's ok if the instruction + // is sunken completely below the use. + return false; + } else { + if (regOverlapsSet(Defs, MOReg, TRI)) + return false; + bool isKill = + MO.isKill() || (LIS && isPlainlyKilled(&OtherMI, MOReg, LIS)); + if (MOReg != Reg && ((isKill && regOverlapsSet(Uses, MOReg, TRI)) || + regOverlapsSet(Kills, MOReg, TRI))) + // Don't want to extend other live ranges and update kills. + return false; + if (MOReg == Reg && !isKill) + // We can't schedule across a use of the register in question. + return false; + // Ensure that if this is register in question, its the kill we expect. + assert((MOReg != Reg || &OtherMI == KillMI) && + "Found multiple kills of a register in a basic block"); + } + } + } + + // Move debug info as well. + while (Begin != MBB->begin() && std::prev(Begin)->isDebugInstr()) + --Begin; + + nmi = End; + MachineBasicBlock::iterator InsertPos = KillPos; + if (LIS) { + // We have to move the copies first so that the MBB is still well-formed + // when calling handleMove(). + for (MachineBasicBlock::iterator MBBI = AfterMI; MBBI != End;) { + auto CopyMI = MBBI++; + MBB->splice(InsertPos, MBB, CopyMI); + LIS->handleMove(*CopyMI); + InsertPos = CopyMI; + } + End = std::next(MachineBasicBlock::iterator(MI)); + } + + // Copies following MI may have been moved as well. + MBB->splice(InsertPos, MBB, Begin, End); + DistanceMap.erase(DI); + + // Update live variables + if (LIS) { + LIS->handleMove(*MI); + } else { + LV->removeVirtualRegisterKilled(Reg, *KillMI); + LV->addVirtualRegisterKilled(Reg, *MI); + } + + LLVM_DEBUG(dbgs() << "\trescheduled below kill: " << *KillMI); + return true; +} + +/// Return true if the re-scheduling will put the given instruction too close +/// to the defs of its register dependencies. +bool TwoAddressInstructionPass::isDefTooClose(unsigned Reg, unsigned Dist, + MachineInstr *MI) { + for (MachineInstr &DefMI : MRI->def_instructions(Reg)) { + if (DefMI.getParent() != MBB || DefMI.isCopy() || DefMI.isCopyLike()) + continue; + if (&DefMI == MI) + return true; // MI is defining something KillMI uses + DenseMap<MachineInstr*, unsigned>::iterator DDI = DistanceMap.find(&DefMI); + if (DDI == DistanceMap.end()) + return true; // Below MI + unsigned DefDist = DDI->second; + assert(Dist > DefDist && "Visited def already?"); + if (TII->getInstrLatency(InstrItins, DefMI) > (Dist - DefDist)) + return true; + } + return false; +} + +/// If there is one more local instruction that reads 'Reg' and it kills 'Reg, +/// consider moving the kill instruction above the current two-address +/// instruction in order to eliminate the need for the copy. +bool TwoAddressInstructionPass:: +rescheduleKillAboveMI(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned Reg) { + // Bail immediately if we don't have LV or LIS available. We use them to find + // kills efficiently. + if (!LV && !LIS) + return false; + + MachineInstr *MI = &*mi; + DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(MI); + if (DI == DistanceMap.end()) + // Must be created from unfolded load. Don't waste time trying this. + return false; + + MachineInstr *KillMI = nullptr; + if (LIS) { + LiveInterval &LI = LIS->getInterval(Reg); + assert(LI.end() != LI.begin() && + "Reg should not have empty live interval."); + + SlotIndex MBBEndIdx = LIS->getMBBEndIdx(MBB).getPrevSlot(); + LiveInterval::const_iterator I = LI.find(MBBEndIdx); + if (I != LI.end() && I->start < MBBEndIdx) + return false; + + --I; + KillMI = LIS->getInstructionFromIndex(I->end); + } else { + KillMI = LV->getVarInfo(Reg).findKill(MBB); + } + if (!KillMI || MI == KillMI || KillMI->isCopy() || KillMI->isCopyLike()) + // Don't mess with copies, they may be coalesced later. + return false; + + unsigned DstReg; + if (isTwoAddrUse(*KillMI, Reg, DstReg)) + return false; + + bool SeenStore = true; + if (!KillMI->isSafeToMove(AA, SeenStore)) + return false; + + SmallSet<unsigned, 2> Uses; + SmallSet<unsigned, 2> Kills; + SmallSet<unsigned, 2> Defs; + SmallSet<unsigned, 2> LiveDefs; + for (const MachineOperand &MO : KillMI->operands()) { + if (!MO.isReg()) + continue; + unsigned MOReg = MO.getReg(); + if (MO.isUse()) { + if (!MOReg) + continue; + if (isDefTooClose(MOReg, DI->second, MI)) + return false; + bool isKill = MO.isKill() || (LIS && isPlainlyKilled(KillMI, MOReg, LIS)); + if (MOReg == Reg && !isKill) + return false; + Uses.insert(MOReg); + if (isKill && MOReg != Reg) + Kills.insert(MOReg); + } else if (TargetRegisterInfo::isPhysicalRegister(MOReg)) { + Defs.insert(MOReg); + if (!MO.isDead()) + LiveDefs.insert(MOReg); + } + } + + // Check if the reschedule will not break depedencies. + unsigned NumVisited = 0; + for (MachineInstr &OtherMI : + make_range(mi, MachineBasicBlock::iterator(KillMI))) { + // Debug instructions cannot be counted against the limit. + if (OtherMI.isDebugInstr()) + continue; + if (NumVisited > 10) // FIXME: Arbitrary limit to reduce compile time cost. + return false; + ++NumVisited; + if (OtherMI.hasUnmodeledSideEffects() || OtherMI.isCall() || + OtherMI.isBranch() || OtherMI.isTerminator()) + // Don't move pass calls, etc. + return false; + SmallVector<unsigned, 2> OtherDefs; + for (const MachineOperand &MO : OtherMI.operands()) { + if (!MO.isReg()) + continue; + unsigned MOReg = MO.getReg(); + if (!MOReg) + continue; + if (MO.isUse()) { + if (Defs.count(MOReg)) + // Moving KillMI can clobber the physical register if the def has + // not been seen. + return false; + if (Kills.count(MOReg)) + // Don't want to extend other live ranges and update kills. + return false; + if (&OtherMI != MI && MOReg == Reg && + !(MO.isKill() || (LIS && isPlainlyKilled(&OtherMI, MOReg, LIS)))) + // We can't schedule across a use of the register in question. + return false; + } else { + OtherDefs.push_back(MOReg); + } + } + + for (unsigned i = 0, e = OtherDefs.size(); i != e; ++i) { + unsigned MOReg = OtherDefs[i]; + if (Uses.count(MOReg)) + return false; + if (TargetRegisterInfo::isPhysicalRegister(MOReg) && + LiveDefs.count(MOReg)) + return false; + // Physical register def is seen. + Defs.erase(MOReg); + } + } + + // Move the old kill above MI, don't forget to move debug info as well. + MachineBasicBlock::iterator InsertPos = mi; + while (InsertPos != MBB->begin() && std::prev(InsertPos)->isDebugInstr()) + --InsertPos; + MachineBasicBlock::iterator From = KillMI; + MachineBasicBlock::iterator To = std::next(From); + while (std::prev(From)->isDebugInstr()) + --From; + MBB->splice(InsertPos, MBB, From, To); + + nmi = std::prev(InsertPos); // Backtrack so we process the moved instr. + DistanceMap.erase(DI); + + // Update live variables + if (LIS) { + LIS->handleMove(*KillMI); + } else { + LV->removeVirtualRegisterKilled(Reg, *KillMI); + LV->addVirtualRegisterKilled(Reg, *MI); + } + + LLVM_DEBUG(dbgs() << "\trescheduled kill: " << *KillMI); + return true; +} + +/// Tries to commute the operand 'BaseOpIdx' and some other operand in the +/// given machine instruction to improve opportunities for coalescing and +/// elimination of a register to register copy. +/// +/// 'DstOpIdx' specifies the index of MI def operand. +/// 'BaseOpKilled' specifies if the register associated with 'BaseOpIdx' +/// operand is killed by the given instruction. +/// The 'Dist' arguments provides the distance of MI from the start of the +/// current basic block and it is used to determine if it is profitable +/// to commute operands in the instruction. +/// +/// Returns true if the transformation happened. Otherwise, returns false. +bool TwoAddressInstructionPass::tryInstructionCommute(MachineInstr *MI, + unsigned DstOpIdx, + unsigned BaseOpIdx, + bool BaseOpKilled, + unsigned Dist) { + if (!MI->isCommutable()) + return false; + + bool MadeChange = false; + unsigned DstOpReg = MI->getOperand(DstOpIdx).getReg(); + unsigned BaseOpReg = MI->getOperand(BaseOpIdx).getReg(); + unsigned OpsNum = MI->getDesc().getNumOperands(); + unsigned OtherOpIdx = MI->getDesc().getNumDefs(); + for (; OtherOpIdx < OpsNum; OtherOpIdx++) { + // The call of findCommutedOpIndices below only checks if BaseOpIdx + // and OtherOpIdx are commutable, it does not really search for + // other commutable operands and does not change the values of passed + // variables. + if (OtherOpIdx == BaseOpIdx || !MI->getOperand(OtherOpIdx).isReg() || + !TII->findCommutedOpIndices(*MI, BaseOpIdx, OtherOpIdx)) + continue; + + unsigned OtherOpReg = MI->getOperand(OtherOpIdx).getReg(); + bool AggressiveCommute = false; + + // If OtherOp dies but BaseOp does not, swap the OtherOp and BaseOp + // operands. This makes the live ranges of DstOp and OtherOp joinable. + bool OtherOpKilled = isKilled(*MI, OtherOpReg, MRI, TII, LIS, false); + bool DoCommute = !BaseOpKilled && OtherOpKilled; + + if (!DoCommute && + isProfitableToCommute(DstOpReg, BaseOpReg, OtherOpReg, MI, Dist)) { + DoCommute = true; + AggressiveCommute = true; + } + + // If it's profitable to commute, try to do so. + if (DoCommute && commuteInstruction(MI, DstOpIdx, BaseOpIdx, OtherOpIdx, + Dist)) { + MadeChange = true; + ++NumCommuted; + if (AggressiveCommute) { + ++NumAggrCommuted; + // There might be more than two commutable operands, update BaseOp and + // continue scanning. + BaseOpReg = OtherOpReg; + BaseOpKilled = OtherOpKilled; + continue; + } + // If this was a commute based on kill, we won't do better continuing. + return MadeChange; + } + } + return MadeChange; +} + +/// 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 no copy needs to be inserted to untie mi's operands +/// (either because they were untied, or because mi was rescheduled, and will +/// be visited again later). If the shouldOnlyCommute flag is true, only +/// instruction commutation is attempted. +bool TwoAddressInstructionPass:: +tryInstructionTransform(MachineBasicBlock::iterator &mi, + MachineBasicBlock::iterator &nmi, + unsigned SrcIdx, unsigned DstIdx, + unsigned Dist, bool shouldOnlyCommute) { + if (OptLevel == CodeGenOpt::None) + return false; + + MachineInstr &MI = *mi; + unsigned regA = MI.getOperand(DstIdx).getReg(); + unsigned regB = MI.getOperand(SrcIdx).getReg(); + + assert(TargetRegisterInfo::isVirtualRegister(regB) && + "cannot make instruction into two-address form"); + bool regBKilled = isKilled(MI, regB, MRI, TII, LIS, true); + + if (TargetRegisterInfo::isVirtualRegister(regA)) + scanUses(regA); + + bool Commuted = tryInstructionCommute(&MI, DstIdx, SrcIdx, regBKilled, Dist); + + // If the instruction is convertible to 3 Addr, instead + // of returning try 3 Addr transformation aggresively and + // use this variable to check later. Because it might be better. + // For example, we can just use `leal (%rsi,%rdi), %eax` and `ret` + // instead of the following code. + // addl %esi, %edi + // movl %edi, %eax + // ret + if (Commuted && !MI.isConvertibleTo3Addr()) + return false; + + if (shouldOnlyCommute) + return false; + + // If there is one more use of regB later in the same MBB, consider + // re-schedule this MI below it. + if (!Commuted && EnableRescheduling && rescheduleMIBelowKill(mi, nmi, regB)) { + ++NumReSchedDowns; + return true; + } + + // If we commuted, regB may have changed so we should re-sample it to avoid + // confusing the three address conversion below. + if (Commuted) { + regB = MI.getOperand(SrcIdx).getReg(); + regBKilled = isKilled(MI, regB, MRI, TII, LIS, true); + } + + if (MI.isConvertibleTo3Addr()) { + // This instruction is potentially convertible to a true + // three-address instruction. Check if it is profitable. + if (!regBKilled || isProfitableToConv3Addr(regA, regB)) { + // Try to convert it. + if (convertInstTo3Addr(mi, nmi, regA, regB, Dist)) { + ++NumConvertedTo3Addr; + return true; // Done with this instruction. + } + } + } + + // Return if it is commuted but 3 addr conversion is failed. + if (Commuted) + return false; + + // If there is one more use of regB later in the same MBB, consider + // re-schedule it before this MI if it's legal. + if (EnableRescheduling && rescheduleKillAboveMI(mi, nmi, regB)) { + ++NumReSchedUps; + return true; + } + + // If this is an instruction with a load folded into it, try unfolding + // the load, e.g. avoid this: + // movq %rdx, %rcx + // addq (%rax), %rcx + // in favor of this: + // movq (%rax), %rcx + // addq %rdx, %rcx + // because it's preferable to schedule a load than a register copy. + if (MI.mayLoad() && !regBKilled) { + // Determine if a load can be unfolded. + unsigned LoadRegIndex; + unsigned NewOpc = + TII->getOpcodeAfterMemoryUnfold(MI.getOpcode(), + /*UnfoldLoad=*/true, + /*UnfoldStore=*/false, + &LoadRegIndex); + if (NewOpc != 0) { + const MCInstrDesc &UnfoldMCID = TII->get(NewOpc); + if (UnfoldMCID.getNumDefs() == 1) { + // Unfold the load. + LLVM_DEBUG(dbgs() << "2addr: UNFOLDING: " << MI); + const TargetRegisterClass *RC = + TRI->getAllocatableClass( + TII->getRegClass(UnfoldMCID, LoadRegIndex, TRI, *MF)); + unsigned Reg = MRI->createVirtualRegister(RC); + SmallVector<MachineInstr *, 2> NewMIs; + if (!TII->unfoldMemoryOperand(*MF, MI, Reg, + /*UnfoldLoad=*/true, + /*UnfoldStore=*/false, NewMIs)) { + LLVM_DEBUG(dbgs() << "2addr: ABANDONING UNFOLD\n"); + return false; + } + assert(NewMIs.size() == 2 && + "Unfolded a load into multiple instructions!"); + // The load was previously folded, so this is the only use. + NewMIs[1]->addRegisterKilled(Reg, TRI); + + // Tentatively insert the instructions into the block so that they + // look "normal" to the transformation logic. + MBB->insert(mi, NewMIs[0]); + MBB->insert(mi, NewMIs[1]); + + LLVM_DEBUG(dbgs() << "2addr: NEW LOAD: " << *NewMIs[0] + << "2addr: NEW INST: " << *NewMIs[1]); + + // Transform the instruction, now that it no longer has a load. + unsigned NewDstIdx = NewMIs[1]->findRegisterDefOperandIdx(regA); + unsigned NewSrcIdx = NewMIs[1]->findRegisterUseOperandIdx(regB); + MachineBasicBlock::iterator NewMI = NewMIs[1]; + bool TransformResult = + tryInstructionTransform(NewMI, mi, NewSrcIdx, NewDstIdx, Dist, true); + (void)TransformResult; + assert(!TransformResult && + "tryInstructionTransform() should return false."); + if (NewMIs[1]->getOperand(NewSrcIdx).isKill()) { + // Success, or at least we made an improvement. Keep the unfolded + // instructions and discard the original. + if (LV) { + for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) { + MachineOperand &MO = MI.getOperand(i); + if (MO.isReg() && + TargetRegisterInfo::isVirtualRegister(MO.getReg())) { + if (MO.isUse()) { + if (MO.isKill()) { + if (NewMIs[0]->killsRegister(MO.getReg())) + LV->replaceKillInstruction(MO.getReg(), MI, *NewMIs[0]); + else { + assert(NewMIs[1]->killsRegister(MO.getReg()) && + "Kill missing after load unfold!"); + LV->replaceKillInstruction(MO.getReg(), MI, *NewMIs[1]); + } + } + } else if (LV->removeVirtualRegisterDead(MO.getReg(), MI)) { + if (NewMIs[1]->registerDefIsDead(MO.getReg())) + LV->addVirtualRegisterDead(MO.getReg(), *NewMIs[1]); + else { + assert(NewMIs[0]->registerDefIsDead(MO.getReg()) && + "Dead flag missing after load unfold!"); + LV->addVirtualRegisterDead(MO.getReg(), *NewMIs[0]); + } + } + } + } + LV->addVirtualRegisterKilled(Reg, *NewMIs[1]); + } + + SmallVector<unsigned, 4> OrigRegs; + if (LIS) { + for (const MachineOperand &MO : MI.operands()) { + if (MO.isReg()) + OrigRegs.push_back(MO.getReg()); + } + } + + MI.eraseFromParent(); + + // Update LiveIntervals. + if (LIS) { + MachineBasicBlock::iterator Begin(NewMIs[0]); + MachineBasicBlock::iterator End(NewMIs[1]); + LIS->repairIntervalsInRange(MBB, Begin, End, OrigRegs); + } + + mi = NewMIs[1]; + } else { + // Transforming didn't eliminate the tie and didn't lead to an + // improvement. Clean up the unfolded instructions and keep the + // original. + LLVM_DEBUG(dbgs() << "2addr: ABANDONING UNFOLD\n"); + NewMIs[0]->eraseFromParent(); + NewMIs[1]->eraseFromParent(); + } + } + } + } + + return false; +} + +// Collect tied operands of MI that need to be handled. +// Rewrite trivial cases immediately. +// Return true if any tied operands where found, including the trivial ones. +bool TwoAddressInstructionPass:: +collectTiedOperands(MachineInstr *MI, TiedOperandMap &TiedOperands) { + const MCInstrDesc &MCID = MI->getDesc(); + bool AnyOps = false; + unsigned NumOps = MI->getNumOperands(); + + for (unsigned SrcIdx = 0; SrcIdx < NumOps; ++SrcIdx) { + unsigned DstIdx = 0; + if (!MI->isRegTiedToDefOperand(SrcIdx, &DstIdx)) + continue; + AnyOps = true; + MachineOperand &SrcMO = MI->getOperand(SrcIdx); + MachineOperand &DstMO = MI->getOperand(DstIdx); + unsigned SrcReg = SrcMO.getReg(); + unsigned DstReg = DstMO.getReg(); + // Tied constraint already satisfied? + if (SrcReg == DstReg) + continue; + + assert(SrcReg && SrcMO.isUse() && "two address instruction invalid"); + + // Deal with undef uses immediately - simply rewrite the src operand. + if (SrcMO.isUndef() && !DstMO.getSubReg()) { + // Constrain the DstReg register class if required. + if (TargetRegisterInfo::isVirtualRegister(DstReg)) + if (const TargetRegisterClass *RC = TII->getRegClass(MCID, SrcIdx, + TRI, *MF)) + MRI->constrainRegClass(DstReg, RC); + SrcMO.setReg(DstReg); + SrcMO.setSubReg(0); + LLVM_DEBUG(dbgs() << "\t\trewrite undef:\t" << *MI); + continue; + } + TiedOperands[SrcReg].push_back(std::make_pair(SrcIdx, DstIdx)); + } + return AnyOps; +} + +// Process a list of tied MI operands that all use the same source register. +// The tied pairs are of the form (SrcIdx, DstIdx). +void +TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, + TiedPairList &TiedPairs, + unsigned &Dist) { + bool IsEarlyClobber = false; + for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) { + const MachineOperand &DstMO = MI->getOperand(TiedPairs[tpi].second); + IsEarlyClobber |= DstMO.isEarlyClobber(); + } + + bool RemovedKillFlag = false; + bool AllUsesCopied = true; + unsigned LastCopiedReg = 0; + SlotIndex LastCopyIdx; + unsigned RegB = 0; + unsigned SubRegB = 0; + for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) { + unsigned SrcIdx = TiedPairs[tpi].first; + unsigned DstIdx = TiedPairs[tpi].second; + + const MachineOperand &DstMO = MI->getOperand(DstIdx); + unsigned RegA = DstMO.getReg(); + + // Grab RegB from the instruction because it may have changed if the + // instruction was commuted. + RegB = MI->getOperand(SrcIdx).getReg(); + SubRegB = MI->getOperand(SrcIdx).getSubReg(); + + 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. + MachineInstrBuilder MIB = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(), + TII->get(TargetOpcode::COPY), RegA); + // If this operand is folding a truncation, the truncation now moves to the + // copy so that the register classes remain valid for the operands. + MIB.addReg(RegB, 0, SubRegB); + const TargetRegisterClass *RC = MRI->getRegClass(RegB); + if (SubRegB) { + if (TargetRegisterInfo::isVirtualRegister(RegA)) { + assert(TRI->getMatchingSuperRegClass(RC, MRI->getRegClass(RegA), + SubRegB) && + "tied subregister must be a truncation"); + // The superreg class will not be used to constrain the subreg class. + RC = nullptr; + } + else { + assert(TRI->getMatchingSuperReg(RegA, SubRegB, MRI->getRegClass(RegB)) + && "tied subregister must be a truncation"); + } + } + + // Update DistanceMap. + MachineBasicBlock::iterator PrevMI = MI; + --PrevMI; + DistanceMap.insert(std::make_pair(&*PrevMI, Dist)); + DistanceMap[MI] = ++Dist; + + if (LIS) { + LastCopyIdx = LIS->InsertMachineInstrInMaps(*PrevMI).getRegSlot(); + + if (TargetRegisterInfo::isVirtualRegister(RegA)) { + LiveInterval &LI = LIS->getInterval(RegA); + VNInfo *VNI = LI.getNextValue(LastCopyIdx, LIS->getVNInfoAllocator()); + SlotIndex endIdx = + LIS->getInstructionIndex(*MI).getRegSlot(IsEarlyClobber); + LI.addSegment(LiveInterval::Segment(LastCopyIdx, endIdx, VNI)); + } + } + + LLVM_DEBUG(dbgs() << "\t\tprepend:\t" << *MIB); + + 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; + } + + // Make sure regA is a legal regclass for the SrcIdx operand. + if (TargetRegisterInfo::isVirtualRegister(RegA) && + TargetRegisterInfo::isVirtualRegister(RegB)) + MRI->constrainRegClass(RegA, RC); + MO.setReg(RegA); + // The getMatchingSuper asserts guarantee that the register class projected + // by SubRegB is compatible with RegA with no subregister. So regardless of + // whether the dest oper writes a subreg, the source oper should not. + MO.setSubReg(0); + + // Propagate SrcRegMap. + SrcRegMap[RegA] = RegB; + } + + if (AllUsesCopied) { + bool ReplacedAllUntiedUses = true; + if (!IsEarlyClobber) { + // Replace other (un-tied) uses of regB with LastCopiedReg. + for (MachineOperand &MO : MI->operands()) { + if (MO.isReg() && MO.getReg() == RegB && MO.isUse()) { + if (MO.getSubReg() == SubRegB) { + if (MO.isKill()) { + MO.setIsKill(false); + RemovedKillFlag = true; + } + MO.setReg(LastCopiedReg); + MO.setSubReg(0); + } else { + ReplacedAllUntiedUses = false; + } + } + } + } + + // Update live variables for regB. + if (RemovedKillFlag && ReplacedAllUntiedUses && + LV && LV->getVarInfo(RegB).removeKill(*MI)) { + MachineBasicBlock::iterator PrevMI = MI; + --PrevMI; + LV->addVirtualRegisterKilled(RegB, *PrevMI); + } + + // Update LiveIntervals. + if (LIS) { + LiveInterval &LI = LIS->getInterval(RegB); + SlotIndex MIIdx = LIS->getInstructionIndex(*MI); + LiveInterval::const_iterator I = LI.find(MIIdx); + assert(I != LI.end() && "RegB must be live-in to use."); + + SlotIndex UseIdx = MIIdx.getRegSlot(IsEarlyClobber); + if (I->end == UseIdx) + LI.removeSegment(LastCopyIdx, UseIdx); + } + } 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 (MachineOperand &MO : MI->operands()) { + if (MO.isReg() && MO.getReg() == RegB && MO.isUse()) { + MO.setIsKill(true); + break; + } + } + } +} + +/// Reduce two-address instructions to two operands. +bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) { + MF = &Func; + const TargetMachine &TM = MF->getTarget(); + MRI = &MF->getRegInfo(); + TII = MF->getSubtarget().getInstrInfo(); + TRI = MF->getSubtarget().getRegisterInfo(); + InstrItins = MF->getSubtarget().getInstrItineraryData(); + LV = getAnalysisIfAvailable<LiveVariables>(); + LIS = getAnalysisIfAvailable<LiveIntervals>(); + if (auto *AAPass = getAnalysisIfAvailable<AAResultsWrapperPass>()) + AA = &AAPass->getAAResults(); + else + AA = nullptr; + OptLevel = TM.getOptLevel(); + // Disable optimizations if requested. We cannot skip the whole pass as some + // fixups are necessary for correctness. + if (skipFunction(Func.getFunction())) + OptLevel = CodeGenOpt::None; + + bool MadeChange = false; + + LLVM_DEBUG(dbgs() << "********** REWRITING TWO-ADDR INSTRS **********\n"); + LLVM_DEBUG(dbgs() << "********** Function: " << MF->getName() << '\n'); + + // This pass takes the function out of SSA form. + MRI->leaveSSA(); + + TiedOperandMap TiedOperands; + for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end(); + MBBI != MBBE; ++MBBI) { + MBB = &*MBBI; + unsigned Dist = 0; + DistanceMap.clear(); + SrcRegMap.clear(); + DstRegMap.clear(); + Processed.clear(); + SunkInstrs.clear(); + for (MachineBasicBlock::iterator mi = MBB->begin(), me = MBB->end(); + mi != me; ) { + MachineBasicBlock::iterator nmi = std::next(mi); + // Don't revisit an instruction previously converted by target. It may + // contain undef register operands (%noreg), which are not handled. + if (mi->isDebugInstr() || SunkInstrs.count(&*mi)) { + mi = nmi; + continue; + } + + // Expand REG_SEQUENCE instructions. This will position mi at the first + // expanded instruction. + if (mi->isRegSequence()) + eliminateRegSequence(mi); + + DistanceMap.insert(std::make_pair(&*mi, ++Dist)); + + processCopy(&*mi); + + // First scan through all the tied register uses in this instruction + // and record a list of pairs of tied operands for each register. + if (!collectTiedOperands(&*mi, TiedOperands)) { + mi = nmi; + continue; + } + + ++NumTwoAddressInstrs; + MadeChange = true; + LLVM_DEBUG(dbgs() << '\t' << *mi); + + // 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) { + SmallVectorImpl<std::pair<unsigned, unsigned>> &TiedPairs + = TiedOperands.begin()->second; + if (TiedPairs.size() == 1) { + unsigned SrcIdx = TiedPairs[0].first; + unsigned DstIdx = TiedPairs[0].second; + unsigned SrcReg = mi->getOperand(SrcIdx).getReg(); + unsigned DstReg = mi->getOperand(DstIdx).getReg(); + if (SrcReg != DstReg && + tryInstructionTransform(mi, nmi, SrcIdx, DstIdx, Dist, false)) { + // The tied operands have been eliminated or shifted further down + // the block to ease elimination. Continue processing with 'nmi'. + TiedOperands.clear(); + mi = nmi; + continue; + } + } + } + + // Now iterate over the information collected above. + for (auto &TO : TiedOperands) { + processTiedPairs(&*mi, TO.second, Dist); + LLVM_DEBUG(dbgs() << "\t\trewrite to:\t" << *mi); + } + + // Rewrite INSERT_SUBREG as COPY now that we no longer need SSA form. + if (mi->isInsertSubreg()) { + // From %reg = INSERT_SUBREG %reg, %subreg, subidx + // To %reg:subidx = COPY %subreg + unsigned SubIdx = mi->getOperand(3).getImm(); + mi->RemoveOperand(3); + assert(mi->getOperand(0).getSubReg() == 0 && "Unexpected subreg idx"); + mi->getOperand(0).setSubReg(SubIdx); + mi->getOperand(0).setIsUndef(mi->getOperand(1).isUndef()); + mi->RemoveOperand(1); + mi->setDesc(TII->get(TargetOpcode::COPY)); + LLVM_DEBUG(dbgs() << "\t\tconvert 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; + } + } + + if (LIS) + MF->verify(this, "After two-address instruction pass"); + + return MadeChange; +} + +/// Eliminate a REG_SEQUENCE instruction as part of the de-ssa process. +/// +/// The instruction is turned into a sequence of sub-register copies: +/// +/// %dst = REG_SEQUENCE %v1, ssub0, %v2, ssub1 +/// +/// Becomes: +/// +/// undef %dst:ssub0 = COPY %v1 +/// %dst:ssub1 = COPY %v2 +void TwoAddressInstructionPass:: +eliminateRegSequence(MachineBasicBlock::iterator &MBBI) { + MachineInstr &MI = *MBBI; + unsigned DstReg = MI.getOperand(0).getReg(); + if (MI.getOperand(0).getSubReg() || + TargetRegisterInfo::isPhysicalRegister(DstReg) || + !(MI.getNumOperands() & 1)) { + LLVM_DEBUG(dbgs() << "Illegal REG_SEQUENCE instruction:" << MI); + llvm_unreachable(nullptr); + } + + SmallVector<unsigned, 4> OrigRegs; + if (LIS) { + OrigRegs.push_back(MI.getOperand(0).getReg()); + for (unsigned i = 1, e = MI.getNumOperands(); i < e; i += 2) + OrigRegs.push_back(MI.getOperand(i).getReg()); + } + + bool DefEmitted = false; + for (unsigned i = 1, e = MI.getNumOperands(); i < e; i += 2) { + MachineOperand &UseMO = MI.getOperand(i); + unsigned SrcReg = UseMO.getReg(); + unsigned SubIdx = MI.getOperand(i+1).getImm(); + // Nothing needs to be inserted for undef operands. + if (UseMO.isUndef()) + continue; + + // Defer any kill flag to the last operand using SrcReg. Otherwise, we + // might insert a COPY that uses SrcReg after is was killed. + bool isKill = UseMO.isKill(); + if (isKill) + for (unsigned j = i + 2; j < e; j += 2) + if (MI.getOperand(j).getReg() == SrcReg) { + MI.getOperand(j).setIsKill(); + UseMO.setIsKill(false); + isKill = false; + break; + } + + // Insert the sub-register copy. + MachineInstr *CopyMI = BuildMI(*MI.getParent(), MI, MI.getDebugLoc(), + TII->get(TargetOpcode::COPY)) + .addReg(DstReg, RegState::Define, SubIdx) + .add(UseMO); + + // The first def needs an undef flag because there is no live register + // before it. + if (!DefEmitted) { + CopyMI->getOperand(0).setIsUndef(true); + // Return an iterator pointing to the first inserted instr. + MBBI = CopyMI; + } + DefEmitted = true; + + // Update LiveVariables' kill info. + if (LV && isKill && !TargetRegisterInfo::isPhysicalRegister(SrcReg)) + LV->replaceKillInstruction(SrcReg, MI, *CopyMI); + + LLVM_DEBUG(dbgs() << "Inserted: " << *CopyMI); + } + + MachineBasicBlock::iterator EndMBBI = + std::next(MachineBasicBlock::iterator(MI)); + + if (!DefEmitted) { + LLVM_DEBUG(dbgs() << "Turned: " << MI << " into an IMPLICIT_DEF"); + MI.setDesc(TII->get(TargetOpcode::IMPLICIT_DEF)); + for (int j = MI.getNumOperands() - 1, ee = 0; j > ee; --j) + MI.RemoveOperand(j); + } else { + LLVM_DEBUG(dbgs() << "Eliminated: " << MI); + MI.eraseFromParent(); + } + + // Udpate LiveIntervals. + if (LIS) + LIS->repairIntervalsInRange(MBB, MBBI, EndMBBI, OrigRegs); +} |