//===-- PeepholeOptimizer.cpp - Peephole Optimizations --------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // Perform peephole optimizations on the machine code: // // - Optimize Extensions // // Optimization of sign / zero extension instructions. It may be extended to // handle other instructions with similar properties. // // On some targets, some instructions, e.g. X86 sign / zero extension, may // leave the source value in the lower part of the result. This optimization // will replace some uses of the pre-extension value with uses of the // sub-register of the results. // // - Optimize Comparisons // // Optimization of comparison instructions. For instance, in this code: // // sub r1, 1 // cmp r1, 0 // bz L1 // // If the "sub" instruction all ready sets (or could be modified to set) the // same flag that the "cmp" instruction sets and that "bz" uses, then we can // eliminate the "cmp" instruction. // // Another instance, in this code: // // sub r1, r3 | sub r1, imm // cmp r3, r1 or cmp r1, r3 | cmp r1, imm // bge L1 // // If the branch instruction can use flag from "sub", then we can replace // "sub" with "subs" and eliminate the "cmp" instruction. // // - Optimize Loads: // // Loads that can be folded into a later instruction. A load is foldable // if it loads to virtual registers and the virtual register defined has // a single use. // // - Optimize Copies and Bitcast (more generally, target specific copies): // // Rewrite copies and bitcasts to avoid cross register bank copies // when possible. // E.g., Consider the following example, where capital and lower // letters denote different register file: // b = copy A <-- cross-bank copy // C = copy b <-- cross-bank copy // => // b = copy A <-- cross-bank copy // C = copy A <-- same-bank copy // // E.g., for bitcast: // b = bitcast A <-- cross-bank copy // C = bitcast b <-- cross-bank copy // => // b = bitcast A <-- cross-bank copy // C = copy A <-- same-bank copy //===----------------------------------------------------------------------===// #include "llvm/CodeGen/Passes.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallSet.h" #include "llvm/ADT/Statistic.h" #include "llvm/CodeGen/MachineDominators.h" #include "llvm/CodeGen/MachineInstrBuilder.h" #include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Target/TargetSubtargetInfo.h" #include using namespace llvm; #define DEBUG_TYPE "peephole-opt" // Optimize Extensions static cl::opt Aggressive("aggressive-ext-opt", cl::Hidden, cl::desc("Aggressive extension optimization")); static cl::opt DisablePeephole("disable-peephole", cl::Hidden, cl::init(false), cl::desc("Disable the peephole optimizer")); static cl::opt DisableAdvCopyOpt("disable-adv-copy-opt", cl::Hidden, cl::init(false), cl::desc("Disable advanced copy optimization")); STATISTIC(NumReuse, "Number of extension results reused"); STATISTIC(NumCmps, "Number of compares eliminated"); STATISTIC(NumImmFold, "Number of move immediate folded"); STATISTIC(NumLoadFold, "Number of loads folded"); STATISTIC(NumSelects, "Number of selects optimized"); STATISTIC(NumUncoalescableCopies, "Number of uncoalescable copies optimized"); STATISTIC(NumRewrittenCopies, "Number of copies rewritten"); namespace { class PeepholeOptimizer : public MachineFunctionPass { const TargetInstrInfo *TII; const TargetRegisterInfo *TRI; MachineRegisterInfo *MRI; MachineDominatorTree *DT; // Machine dominator tree public: static char ID; // Pass identification PeepholeOptimizer() : MachineFunctionPass(ID) { initializePeepholeOptimizerPass(*PassRegistry::getPassRegistry()); } bool runOnMachineFunction(MachineFunction &MF) override; void getAnalysisUsage(AnalysisUsage &AU) const override { AU.setPreservesCFG(); MachineFunctionPass::getAnalysisUsage(AU); if (Aggressive) { AU.addRequired(); AU.addPreserved(); } } private: bool optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB); bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB, SmallPtrSetImpl &LocalMIs); bool optimizeSelect(MachineInstr *MI, SmallPtrSetImpl &LocalMIs); bool optimizeCondBranch(MachineInstr *MI); bool optimizeCopyOrBitcast(MachineInstr *MI); bool optimizeCoalescableCopy(MachineInstr *MI); bool optimizeUncoalescableCopy(MachineInstr *MI, SmallPtrSetImpl &LocalMIs); bool findNextSource(unsigned &Reg, unsigned &SubReg); bool isMoveImmediate(MachineInstr *MI, SmallSet &ImmDefRegs, DenseMap &ImmDefMIs); bool foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB, SmallSet &ImmDefRegs, DenseMap &ImmDefMIs); bool isLoadFoldable(MachineInstr *MI, SmallSet &FoldAsLoadDefCandidates); /// \brief Check whether \p MI is understood by the register coalescer /// but may require some rewriting. bool isCoalescableCopy(const MachineInstr &MI) { // SubregToRegs are not interesting, because they are already register // coalescer friendly. return MI.isCopy() || (!DisableAdvCopyOpt && (MI.isRegSequence() || MI.isInsertSubreg() || MI.isExtractSubreg())); } /// \brief Check whether \p MI is a copy like instruction that is /// not recognized by the register coalescer. bool isUncoalescableCopy(const MachineInstr &MI) { return MI.isBitcast() || (!DisableAdvCopyOpt && (MI.isRegSequenceLike() || MI.isInsertSubregLike() || MI.isExtractSubregLike())); } }; /// \brief Helper class to track the possible sources of a value defined by /// a (chain of) copy related instructions. /// Given a definition (instruction and definition index), this class /// follows the use-def chain to find successive suitable sources. /// The given source can be used to rewrite the definition into /// def = COPY src. /// /// For instance, let us consider the following snippet: /// v0 = /// v2 = INSERT_SUBREG v1, v0, sub0 /// def = COPY v2.sub0 /// /// Using a ValueTracker for def = COPY v2.sub0 will give the following /// suitable sources: /// v2.sub0 and v0. /// Then, def can be rewritten into def = COPY v0. class ValueTracker { private: /// The current point into the use-def chain. const MachineInstr *Def; /// The index of the definition in Def. unsigned DefIdx; /// The sub register index of the definition. unsigned DefSubReg; /// The register where the value can be found. unsigned Reg; /// Specifiy whether or not the value tracking looks through /// complex instructions. When this is false, the value tracker /// bails on everything that is not a copy or a bitcast. /// /// Note: This could have been implemented as a specialized version of /// the ValueTracker class but that would have complicated the code of /// the users of this class. bool UseAdvancedTracking; /// MachineRegisterInfo used to perform tracking. const MachineRegisterInfo &MRI; /// Optional TargetInstrInfo used to perform some complex /// tracking. const TargetInstrInfo *TII; /// \brief Dispatcher to the right underlying implementation of /// getNextSource. bool getNextSourceImpl(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Specialized version of getNextSource for Copy instructions. bool getNextSourceFromCopy(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Specialized version of getNextSource for Bitcast instructions. bool getNextSourceFromBitcast(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Specialized version of getNextSource for RegSequence /// instructions. bool getNextSourceFromRegSequence(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Specialized version of getNextSource for InsertSubreg /// instructions. bool getNextSourceFromInsertSubreg(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Specialized version of getNextSource for ExtractSubreg /// instructions. bool getNextSourceFromExtractSubreg(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Specialized version of getNextSource for SubregToReg /// instructions. bool getNextSourceFromSubregToReg(unsigned &SrcReg, unsigned &SrcSubReg); public: /// \brief Create a ValueTracker instance for the value defined by \p Reg. /// \p DefSubReg represents the sub register index the value tracker will /// track. It does not need to match the sub register index used in the /// definition of \p Reg. /// \p UseAdvancedTracking specifies whether or not the value tracker looks /// through complex instructions. By default (false), it handles only copy /// and bitcast instructions. /// If \p Reg is a physical register, a value tracker constructed with /// this constructor will not find any alternative source. /// Indeed, when \p Reg is a physical register that constructor does not /// know which definition of \p Reg it should track. /// Use the next constructor to track a physical register. ValueTracker(unsigned Reg, unsigned DefSubReg, const MachineRegisterInfo &MRI, bool UseAdvancedTracking = false, const TargetInstrInfo *TII = nullptr) : Def(nullptr), DefIdx(0), DefSubReg(DefSubReg), Reg(Reg), UseAdvancedTracking(UseAdvancedTracking), MRI(MRI), TII(TII) { if (!TargetRegisterInfo::isPhysicalRegister(Reg)) { Def = MRI.getVRegDef(Reg); DefIdx = MRI.def_begin(Reg).getOperandNo(); } } /// \brief Create a ValueTracker instance for the value defined by /// the pair \p MI, \p DefIdx. /// Unlike the other constructor, the value tracker produced by this one /// may be able to find a new source when the definition is a physical /// register. /// This could be useful to rewrite target specific instructions into /// generic copy instructions. ValueTracker(const MachineInstr &MI, unsigned DefIdx, unsigned DefSubReg, const MachineRegisterInfo &MRI, bool UseAdvancedTracking = false, const TargetInstrInfo *TII = nullptr) : Def(&MI), DefIdx(DefIdx), DefSubReg(DefSubReg), UseAdvancedTracking(UseAdvancedTracking), MRI(MRI), TII(TII) { assert(DefIdx < Def->getDesc().getNumDefs() && Def->getOperand(DefIdx).isReg() && "Invalid definition"); Reg = Def->getOperand(DefIdx).getReg(); } /// \brief Following the use-def chain, get the next available source /// for the tracked value. /// When the returned value is not nullptr, \p SrcReg gives the register /// that contain the tracked value. /// \note The sub register index returned in \p SrcSubReg must be used /// on \p SrcReg to access the actual value. /// \return Unless the returned value is nullptr (i.e., no source found), /// \p SrcReg gives the register of the next source used in the returned /// instruction and \p SrcSubReg the sub-register index to be used on that /// source to get the tracked value. When nullptr is returned, no /// alternative source has been found. const MachineInstr *getNextSource(unsigned &SrcReg, unsigned &SrcSubReg); /// \brief Get the last register where the initial value can be found. /// Initially this is the register of the definition. /// Then, after each successful call to getNextSource, this is the /// register of the last source. unsigned getReg() const { return Reg; } }; } char PeepholeOptimizer::ID = 0; char &llvm::PeepholeOptimizerID = PeepholeOptimizer::ID; INITIALIZE_PASS_BEGIN(PeepholeOptimizer, "peephole-opts", "Peephole Optimizations", false, false) INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) INITIALIZE_PASS_END(PeepholeOptimizer, "peephole-opts", "Peephole Optimizations", false, false) /// optimizeExtInstr - If instruction is a copy-like instruction, i.e. it reads /// a single register and writes a single register and it does not modify the /// source, and if the source value is preserved as a sub-register of the /// result, then replace all reachable uses of the source with the subreg of the /// result. /// /// Do not generate an EXTRACT that is used only in a debug use, as this changes /// the code. Since this code does not currently share EXTRACTs, just ignore all /// debug uses. bool PeepholeOptimizer:: optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB, SmallPtrSetImpl &LocalMIs) { unsigned SrcReg, DstReg, SubIdx; if (!TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx)) return false; if (TargetRegisterInfo::isPhysicalRegister(DstReg) || TargetRegisterInfo::isPhysicalRegister(SrcReg)) return false; if (MRI->hasOneNonDBGUse(SrcReg)) // No other uses. return false; // Ensure DstReg can get a register class that actually supports // sub-registers. Don't change the class until we commit. const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg); DstRC = TRI->getSubClassWithSubReg(DstRC, SubIdx); if (!DstRC) return false; // The ext instr may be operating on a sub-register of SrcReg as well. // PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit // register. // If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of // SrcReg:SubIdx should be replaced. bool UseSrcSubIdx = TRI->getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != nullptr; // The source has other uses. See if we can replace the other uses with use of // the result of the extension. SmallPtrSet ReachedBBs; for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg)) ReachedBBs.insert(UI.getParent()); // Uses that are in the same BB of uses of the result of the instruction. SmallVector Uses; // Uses that the result of the instruction can reach. SmallVector ExtendedUses; bool ExtendLife = true; for (MachineOperand &UseMO : MRI->use_nodbg_operands(SrcReg)) { MachineInstr *UseMI = UseMO.getParent(); if (UseMI == MI) continue; if (UseMI->isPHI()) { ExtendLife = false; continue; } // Only accept uses of SrcReg:SubIdx. if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx) continue; // It's an error to translate this: // // %reg1025 = %reg1024 // ... // %reg1026 = SUBREG_TO_REG 0, %reg1024, 4 // // into this: // // %reg1025 = %reg1024 // ... // %reg1027 = COPY %reg1025:4 // %reg1026 = SUBREG_TO_REG 0, %reg1027, 4 // // The problem here is that SUBREG_TO_REG is there to assert that an // implicit zext occurs. It doesn't insert a zext instruction. If we allow // the COPY here, it will give us the value after the , not the // original value of %reg1024 before . if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG) continue; MachineBasicBlock *UseMBB = UseMI->getParent(); if (UseMBB == MBB) { // Local uses that come after the extension. if (!LocalMIs.count(UseMI)) Uses.push_back(&UseMO); } else if (ReachedBBs.count(UseMBB)) { // Non-local uses where the result of the extension is used. Always // replace these unless it's a PHI. Uses.push_back(&UseMO); } else if (Aggressive && DT->dominates(MBB, UseMBB)) { // We may want to extend the live range of the extension result in order // to replace these uses. ExtendedUses.push_back(&UseMO); } else { // Both will be live out of the def MBB anyway. Don't extend live range of // the extension result. ExtendLife = false; break; } } if (ExtendLife && !ExtendedUses.empty()) // Extend the liveness of the extension result. Uses.append(ExtendedUses.begin(), ExtendedUses.end()); // Now replace all uses. bool Changed = false; if (!Uses.empty()) { SmallPtrSet PHIBBs; // Look for PHI uses of the extended result, we don't want to extend the // liveness of a PHI input. It breaks all kinds of assumptions down // stream. A PHI use is expected to be the kill of its source values. for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg)) if (UI.isPHI()) PHIBBs.insert(UI.getParent()); const TargetRegisterClass *RC = MRI->getRegClass(SrcReg); for (unsigned i = 0, e = Uses.size(); i != e; ++i) { MachineOperand *UseMO = Uses[i]; MachineInstr *UseMI = UseMO->getParent(); MachineBasicBlock *UseMBB = UseMI->getParent(); if (PHIBBs.count(UseMBB)) continue; // About to add uses of DstReg, clear DstReg's kill flags. if (!Changed) { MRI->clearKillFlags(DstReg); MRI->constrainRegClass(DstReg, DstRC); } unsigned NewVR = MRI->createVirtualRegister(RC); MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(), TII->get(TargetOpcode::COPY), NewVR) .addReg(DstReg, 0, SubIdx); // SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set. if (UseSrcSubIdx) { Copy->getOperand(0).setSubReg(SubIdx); Copy->getOperand(0).setIsUndef(); } UseMO->setReg(NewVR); ++NumReuse; Changed = true; } } return Changed; } /// optimizeCmpInstr - If the instruction is a compare and the previous /// instruction it's comparing against all ready sets (or could be modified to /// set) the same flag as the compare, then we can remove the comparison and use /// the flag from the previous instruction. bool PeepholeOptimizer::optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB) { // If this instruction is a comparison against zero and isn't comparing a // physical register, we can try to optimize it. unsigned SrcReg, SrcReg2; int CmpMask, CmpValue; if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue) || TargetRegisterInfo::isPhysicalRegister(SrcReg) || (SrcReg2 != 0 && TargetRegisterInfo::isPhysicalRegister(SrcReg2))) return false; // Attempt to optimize the comparison instruction. if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) { ++NumCmps; return true; } return false; } /// Optimize a select instruction. bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI, SmallPtrSetImpl &LocalMIs) { unsigned TrueOp = 0; unsigned FalseOp = 0; bool Optimizable = false; SmallVector Cond; if (TII->analyzeSelect(MI, Cond, TrueOp, FalseOp, Optimizable)) return false; if (!Optimizable) return false; if (!TII->optimizeSelect(MI, LocalMIs)) return false; MI->eraseFromParent(); ++NumSelects; return true; } /// \brief Check if a simpler conditional branch can be // generated bool PeepholeOptimizer::optimizeCondBranch(MachineInstr *MI) { return TII->optimizeCondBranch(MI); } /// \brief Check if the registers defined by the pair (RegisterClass, SubReg) /// share the same register file. static bool shareSameRegisterFile(const TargetRegisterInfo &TRI, const TargetRegisterClass *DefRC, unsigned DefSubReg, const TargetRegisterClass *SrcRC, unsigned SrcSubReg) { // Same register class. if (DefRC == SrcRC) return true; // Both operands are sub registers. Check if they share a register class. unsigned SrcIdx, DefIdx; if (SrcSubReg && DefSubReg) return TRI.getCommonSuperRegClass(SrcRC, SrcSubReg, DefRC, DefSubReg, SrcIdx, DefIdx) != nullptr; // At most one of the register is a sub register, make it Src to avoid // duplicating the test. if (!SrcSubReg) { std::swap(DefSubReg, SrcSubReg); std::swap(DefRC, SrcRC); } // One of the register is a sub register, check if we can get a superclass. if (SrcSubReg) return TRI.getMatchingSuperRegClass(SrcRC, DefRC, SrcSubReg) != nullptr; // Plain copy. return TRI.getCommonSubClass(DefRC, SrcRC) != nullptr; } /// \brief Try to find the next source that share the same register file /// for the value defined by \p Reg and \p SubReg. /// When true is returned, \p Reg and \p SubReg are updated with the /// register number and sub-register index of the new source. /// \return False if no alternative sources are available. True otherwise. bool PeepholeOptimizer::findNextSource(unsigned &Reg, unsigned &SubReg) { // Do not try to find a new source for a physical register. // So far we do not have any motivating example for doing that. // Thus, instead of maintaining untested code, we will revisit that if // that changes at some point. if (TargetRegisterInfo::isPhysicalRegister(Reg)) return false; const TargetRegisterClass *DefRC = MRI->getRegClass(Reg); unsigned DefSubReg = SubReg; unsigned Src; unsigned SrcSubReg; bool ShouldRewrite = false; // Follow the chain of copies until we reach the top of the use-def chain // or find a more suitable source. ValueTracker ValTracker(Reg, DefSubReg, *MRI, !DisableAdvCopyOpt, TII); do { unsigned CopySrcReg, CopySrcSubReg; if (!ValTracker.getNextSource(CopySrcReg, CopySrcSubReg)) break; Src = CopySrcReg; SrcSubReg = CopySrcSubReg; // Do not extend the live-ranges of physical registers as they add // constraints to the register allocator. // Moreover, if we want to extend the live-range of a physical register, // unlike SSA virtual register, we will have to check that they are not // redefine before the related use. if (TargetRegisterInfo::isPhysicalRegister(Src)) break; const TargetRegisterClass *SrcRC = MRI->getRegClass(Src); // If this source does not incur a cross register bank copy, use it. ShouldRewrite = shareSameRegisterFile(*TRI, DefRC, DefSubReg, SrcRC, SrcSubReg); } while (!ShouldRewrite); // If we did not find a more suitable source, there is nothing to optimize. if (!ShouldRewrite || Src == Reg) return false; Reg = Src; SubReg = SrcSubReg; return true; } namespace { /// \brief Helper class to rewrite the arguments of a copy-like instruction. class CopyRewriter { protected: /// The copy-like instruction. MachineInstr &CopyLike; /// The index of the source being rewritten. unsigned CurrentSrcIdx; public: CopyRewriter(MachineInstr &MI) : CopyLike(MI), CurrentSrcIdx(0) {} virtual ~CopyRewriter() {} /// \brief Get the next rewritable source (SrcReg, SrcSubReg) and /// the related value that it affects (TrackReg, TrackSubReg). /// A source is considered rewritable if its register class and the /// register class of the related TrackReg may not be register /// coalescer friendly. In other words, given a copy-like instruction /// not all the arguments may be returned at rewritable source, since /// some arguments are none to be register coalescer friendly. /// /// Each call of this method moves the current source to the next /// rewritable source. /// For instance, let CopyLike be the instruction to rewrite. /// CopyLike has one definition and one source: /// dst.dstSubIdx = CopyLike src.srcSubIdx. /// /// The first call will give the first rewritable source, i.e., /// the only source this instruction has: /// (SrcReg, SrcSubReg) = (src, srcSubIdx). /// This source defines the whole definition, i.e., /// (TrackReg, TrackSubReg) = (dst, dstSubIdx). /// /// The second and subsequent calls will return false, has there is only one /// rewritable source. /// /// \return True if a rewritable source has been found, false otherwise. /// The output arguments are valid if and only if true is returned. virtual bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg, unsigned &TrackReg, unsigned &TrackSubReg) { // If CurrentSrcIdx == 1, this means this function has already been // called once. CopyLike has one defintiion and one argument, thus, // there is nothing else to rewrite. if (!CopyLike.isCopy() || CurrentSrcIdx == 1) return false; // This is the first call to getNextRewritableSource. // Move the CurrentSrcIdx to remember that we made that call. CurrentSrcIdx = 1; // The rewritable source is the argument. const MachineOperand &MOSrc = CopyLike.getOperand(1); SrcReg = MOSrc.getReg(); SrcSubReg = MOSrc.getSubReg(); // What we track are the alternative sources of the definition. const MachineOperand &MODef = CopyLike.getOperand(0); TrackReg = MODef.getReg(); TrackSubReg = MODef.getSubReg(); return true; } /// \brief Rewrite the current source with \p NewReg and \p NewSubReg /// if possible. /// \return True if the rewritting was possible, false otherwise. virtual bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) { if (!CopyLike.isCopy() || CurrentSrcIdx != 1) return false; MachineOperand &MOSrc = CopyLike.getOperand(CurrentSrcIdx); MOSrc.setReg(NewReg); MOSrc.setSubReg(NewSubReg); return true; } }; /// \brief Specialized rewriter for INSERT_SUBREG instruction. class InsertSubregRewriter : public CopyRewriter { public: InsertSubregRewriter(MachineInstr &MI) : CopyRewriter(MI) { assert(MI.isInsertSubreg() && "Invalid instruction"); } /// \brief See CopyRewriter::getNextRewritableSource. /// Here CopyLike has the following form: /// dst = INSERT_SUBREG Src1, Src2.src2SubIdx, subIdx. /// Src1 has the same register class has dst, hence, there is /// nothing to rewrite. /// Src2.src2SubIdx, may not be register coalescer friendly. /// Therefore, the first call to this method returns: /// (SrcReg, SrcSubReg) = (Src2, src2SubIdx). /// (TrackReg, TrackSubReg) = (dst, subIdx). /// /// Subsequence calls will return false. bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg, unsigned &TrackReg, unsigned &TrackSubReg) override { // If we already get the only source we can rewrite, return false. if (CurrentSrcIdx == 2) return false; // We are looking at v2 = INSERT_SUBREG v0, v1, sub0. CurrentSrcIdx = 2; const MachineOperand &MOInsertedReg = CopyLike.getOperand(2); SrcReg = MOInsertedReg.getReg(); SrcSubReg = MOInsertedReg.getSubReg(); const MachineOperand &MODef = CopyLike.getOperand(0); // We want to track something that is compatible with the // partial definition. TrackReg = MODef.getReg(); if (MODef.getSubReg()) // Bails if we have to compose sub-register indices. return false; TrackSubReg = (unsigned)CopyLike.getOperand(3).getImm(); return true; } bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override { if (CurrentSrcIdx != 2) return false; // We are rewriting the inserted reg. MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx); MO.setReg(NewReg); MO.setSubReg(NewSubReg); return true; } }; /// \brief Specialized rewriter for EXTRACT_SUBREG instruction. class ExtractSubregRewriter : public CopyRewriter { const TargetInstrInfo &TII; public: ExtractSubregRewriter(MachineInstr &MI, const TargetInstrInfo &TII) : CopyRewriter(MI), TII(TII) { assert(MI.isExtractSubreg() && "Invalid instruction"); } /// \brief See CopyRewriter::getNextRewritableSource. /// Here CopyLike has the following form: /// dst.dstSubIdx = EXTRACT_SUBREG Src, subIdx. /// There is only one rewritable source: Src.subIdx, /// which defines dst.dstSubIdx. bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg, unsigned &TrackReg, unsigned &TrackSubReg) override { // If we already get the only source we can rewrite, return false. if (CurrentSrcIdx == 1) return false; // We are looking at v1 = EXTRACT_SUBREG v0, sub0. CurrentSrcIdx = 1; const MachineOperand &MOExtractedReg = CopyLike.getOperand(1); SrcReg = MOExtractedReg.getReg(); // If we have to compose sub-register indices, bails out. if (MOExtractedReg.getSubReg()) return false; SrcSubReg = CopyLike.getOperand(2).getImm(); // We want to track something that is compatible with the definition. const MachineOperand &MODef = CopyLike.getOperand(0); TrackReg = MODef.getReg(); TrackSubReg = MODef.getSubReg(); return true; } bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override { // The only source we can rewrite is the input register. if (CurrentSrcIdx != 1) return false; CopyLike.getOperand(CurrentSrcIdx).setReg(NewReg); // If we find a source that does not require to extract something, // rewrite the operation with a copy. if (!NewSubReg) { // Move the current index to an invalid position. // We do not want another call to this method to be able // to do any change. CurrentSrcIdx = -1; // Rewrite the operation as a COPY. // Get rid of the sub-register index. CopyLike.RemoveOperand(2); // Morph the operation into a COPY. CopyLike.setDesc(TII.get(TargetOpcode::COPY)); return true; } CopyLike.getOperand(CurrentSrcIdx + 1).setImm(NewSubReg); return true; } }; /// \brief Specialized rewriter for REG_SEQUENCE instruction. class RegSequenceRewriter : public CopyRewriter { public: RegSequenceRewriter(MachineInstr &MI) : CopyRewriter(MI) { assert(MI.isRegSequence() && "Invalid instruction"); } /// \brief See CopyRewriter::getNextRewritableSource. /// Here CopyLike has the following form: /// dst = REG_SEQUENCE Src1.src1SubIdx, subIdx1, Src2.src2SubIdx, subIdx2. /// Each call will return a different source, walking all the available /// source. /// /// The first call returns: /// (SrcReg, SrcSubReg) = (Src1, src1SubIdx). /// (TrackReg, TrackSubReg) = (dst, subIdx1). /// /// The second call returns: /// (SrcReg, SrcSubReg) = (Src2, src2SubIdx). /// (TrackReg, TrackSubReg) = (dst, subIdx2). /// /// And so on, until all the sources have been traversed, then /// it returns false. bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg, unsigned &TrackReg, unsigned &TrackSubReg) override { // We are looking at v0 = REG_SEQUENCE v1, sub1, v2, sub2, etc. // If this is the first call, move to the first argument. if (CurrentSrcIdx == 0) { CurrentSrcIdx = 1; } else { // Otherwise, move to the next argument and check that it is valid. CurrentSrcIdx += 2; if (CurrentSrcIdx >= CopyLike.getNumOperands()) return false; } const MachineOperand &MOInsertedReg = CopyLike.getOperand(CurrentSrcIdx); SrcReg = MOInsertedReg.getReg(); // If we have to compose sub-register indices, bails out. if ((SrcSubReg = MOInsertedReg.getSubReg())) return false; // We want to track something that is compatible with the related // partial definition. TrackSubReg = CopyLike.getOperand(CurrentSrcIdx + 1).getImm(); const MachineOperand &MODef = CopyLike.getOperand(0); TrackReg = MODef.getReg(); // If we have to compose sub-registers, bails. return MODef.getSubReg() == 0; } bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override { // We cannot rewrite out of bound operands. // Moreover, rewritable sources are at odd positions. if ((CurrentSrcIdx & 1) != 1 || CurrentSrcIdx > CopyLike.getNumOperands()) return false; MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx); MO.setReg(NewReg); MO.setSubReg(NewSubReg); return true; } }; } // End namespace. /// \brief Get the appropriated CopyRewriter for \p MI. /// \return A pointer to a dynamically allocated CopyRewriter or nullptr /// if no rewriter works for \p MI. static CopyRewriter *getCopyRewriter(MachineInstr &MI, const TargetInstrInfo &TII) { switch (MI.getOpcode()) { default: return nullptr; case TargetOpcode::COPY: return new CopyRewriter(MI); case TargetOpcode::INSERT_SUBREG: return new InsertSubregRewriter(MI); case TargetOpcode::EXTRACT_SUBREG: return new ExtractSubregRewriter(MI, TII); case TargetOpcode::REG_SEQUENCE: return new RegSequenceRewriter(MI); } llvm_unreachable(nullptr); } /// \brief Optimize generic copy instructions to avoid cross /// register bank copy. The optimization looks through a chain of /// copies and tries to find a source that has a compatible register /// class. /// Two register classes are considered to be compatible if they share /// the same register bank. /// New copies issued by this optimization are register allocator /// friendly. This optimization does not remove any copy as it may /// overconstraint the register allocator, but replaces some operands /// when possible. /// \pre isCoalescableCopy(*MI) is true. /// \return True, when \p MI has been rewritten. False otherwise. bool PeepholeOptimizer::optimizeCoalescableCopy(MachineInstr *MI) { assert(MI && isCoalescableCopy(*MI) && "Invalid argument"); assert(MI->getDesc().getNumDefs() == 1 && "Coalescer can understand multiple defs?!"); const MachineOperand &MODef = MI->getOperand(0); // Do not rewrite physical definitions. if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg())) return false; bool Changed = false; // Get the right rewriter for the current copy. std::unique_ptr CpyRewriter(getCopyRewriter(*MI, *TII)); // If none exists, bails out. if (!CpyRewriter) return false; // Rewrite each rewritable source. unsigned SrcReg, SrcSubReg, TrackReg, TrackSubReg; while (CpyRewriter->getNextRewritableSource(SrcReg, SrcSubReg, TrackReg, TrackSubReg)) { unsigned NewSrc = TrackReg; unsigned NewSubReg = TrackSubReg; // Try to find a more suitable source. // If we failed to do so, or get the actual source, // move to the next source. if (!findNextSource(NewSrc, NewSubReg) || SrcReg == NewSrc) continue; // Rewrite source. if (CpyRewriter->RewriteCurrentSource(NewSrc, NewSubReg)) { // We may have extended the live-range of NewSrc, account for that. MRI->clearKillFlags(NewSrc); Changed = true; } } // TODO: We could have a clean-up method to tidy the instruction. // E.g., v0 = INSERT_SUBREG v1, v1.sub0, sub0 // => v0 = COPY v1 // Currently we haven't seen motivating example for that and we // want to avoid untested code. NumRewrittenCopies += Changed; return Changed; } /// \brief Optimize copy-like instructions to create /// register coalescer friendly instruction. /// The optimization tries to kill-off the \p MI by looking /// through a chain of copies to find a source that has a compatible /// register class. /// If such a source is found, it replace \p MI by a generic COPY /// operation. /// \pre isUncoalescableCopy(*MI) is true. /// \return True, when \p MI has been optimized. In that case, \p MI has /// been removed from its parent. /// All COPY instructions created, are inserted in \p LocalMIs. bool PeepholeOptimizer::optimizeUncoalescableCopy( MachineInstr *MI, SmallPtrSetImpl &LocalMIs) { assert(MI && isUncoalescableCopy(*MI) && "Invalid argument"); // Check if we can rewrite all the values defined by this instruction. SmallVector< std::pair, 4> RewritePairs; for (const MachineOperand &MODef : MI->defs()) { if (MODef.isDead()) // We can ignore those. continue; // If a physical register is here, this is probably for a good reason. // Do not rewrite that. if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg())) return false; // If we do not know how to rewrite this definition, there is no point // in trying to kill this instruction. TargetInstrInfo::RegSubRegPair Def(MODef.getReg(), MODef.getSubReg()); TargetInstrInfo::RegSubRegPair Src = Def; if (!findNextSource(Src.Reg, Src.SubReg)) return false; RewritePairs.push_back(std::make_pair(Def, Src)); } // The change is possible for all defs, do it. for (const auto &PairDefSrc : RewritePairs) { const auto &Def = PairDefSrc.first; const auto &Src = PairDefSrc.second; // Rewrite the "copy" in a way the register coalescer understands. assert(!TargetRegisterInfo::isPhysicalRegister(Def.Reg) && "We do not rewrite physical registers"); const TargetRegisterClass *DefRC = MRI->getRegClass(Def.Reg); unsigned NewVR = MRI->createVirtualRegister(DefRC); MachineInstr *NewCopy = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(), TII->get(TargetOpcode::COPY), NewVR).addReg(Src.Reg, 0, Src.SubReg); NewCopy->getOperand(0).setSubReg(Def.SubReg); if (Def.SubReg) NewCopy->getOperand(0).setIsUndef(); LocalMIs.insert(NewCopy); MRI->replaceRegWith(Def.Reg, NewVR); MRI->clearKillFlags(NewVR); // We extended the lifetime of Src. // Clear the kill flags to account for that. MRI->clearKillFlags(Src.Reg); } // MI is now dead. MI->eraseFromParent(); ++NumUncoalescableCopies; return true; } /// isLoadFoldable - Check whether MI is a candidate for folding into a later /// instruction. We only fold loads to virtual registers and the virtual /// register defined has a single use. bool PeepholeOptimizer::isLoadFoldable( MachineInstr *MI, SmallSet &FoldAsLoadDefCandidates) { if (!MI->canFoldAsLoad() || !MI->mayLoad()) return false; const MCInstrDesc &MCID = MI->getDesc(); if (MCID.getNumDefs() != 1) return false; unsigned Reg = MI->getOperand(0).getReg(); // To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting // loads. It should be checked when processing uses of the load, since // uses can be removed during peephole. if (!MI->getOperand(0).getSubReg() && TargetRegisterInfo::isVirtualRegister(Reg) && MRI->hasOneNonDBGUse(Reg)) { FoldAsLoadDefCandidates.insert(Reg); return true; } return false; } bool PeepholeOptimizer::isMoveImmediate(MachineInstr *MI, SmallSet &ImmDefRegs, DenseMap &ImmDefMIs) { const MCInstrDesc &MCID = MI->getDesc(); if (!MI->isMoveImmediate()) return false; if (MCID.getNumDefs() != 1) return false; unsigned Reg = MI->getOperand(0).getReg(); if (TargetRegisterInfo::isVirtualRegister(Reg)) { ImmDefMIs.insert(std::make_pair(Reg, MI)); ImmDefRegs.insert(Reg); return true; } return false; } /// foldImmediate - Try folding register operands that are defined by move /// immediate instructions, i.e. a trivial constant folding optimization, if /// and only if the def and use are in the same BB. bool PeepholeOptimizer::foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB, SmallSet &ImmDefRegs, DenseMap &ImmDefMIs) { for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) { MachineOperand &MO = MI->getOperand(i); if (!MO.isReg() || MO.isDef()) continue; unsigned Reg = MO.getReg(); if (!TargetRegisterInfo::isVirtualRegister(Reg)) continue; if (ImmDefRegs.count(Reg) == 0) continue; DenseMap::iterator II = ImmDefMIs.find(Reg); assert(II != ImmDefMIs.end()); if (TII->FoldImmediate(MI, II->second, Reg, MRI)) { ++NumImmFold; return true; } } return false; } bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) { if (skipOptnoneFunction(*MF.getFunction())) return false; DEBUG(dbgs() << "********** PEEPHOLE OPTIMIZER **********\n"); DEBUG(dbgs() << "********** Function: " << MF.getName() << '\n'); if (DisablePeephole) return false; TII = MF.getSubtarget().getInstrInfo(); TRI = MF.getSubtarget().getRegisterInfo(); MRI = &MF.getRegInfo(); DT = Aggressive ? &getAnalysis() : nullptr; bool Changed = false; for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { MachineBasicBlock *MBB = &*I; bool SeenMoveImm = false; // During this forward scan, at some point it needs to answer the question // "given a pointer to an MI in the current BB, is it located before or // after the current instruction". // To perform this, the following set keeps track of the MIs already seen // during the scan, if a MI is not in the set, it is assumed to be located // after. Newly created MIs have to be inserted in the set as well. SmallPtrSet LocalMIs; SmallSet ImmDefRegs; DenseMap ImmDefMIs; SmallSet FoldAsLoadDefCandidates; for (MachineBasicBlock::iterator MII = I->begin(), MIE = I->end(); MII != MIE; ) { MachineInstr *MI = &*MII; // We may be erasing MI below, increment MII now. ++MII; LocalMIs.insert(MI); // Skip debug values. They should not affect this peephole optimization. if (MI->isDebugValue()) continue; // If there exists an instruction which belongs to the following // categories, we will discard the load candidates. if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() || MI->isKill() || MI->isInlineAsm() || MI->hasUnmodeledSideEffects()) { FoldAsLoadDefCandidates.clear(); continue; } if (MI->mayStore() || MI->isCall()) FoldAsLoadDefCandidates.clear(); if ((isUncoalescableCopy(*MI) && optimizeUncoalescableCopy(MI, LocalMIs)) || (MI->isCompare() && optimizeCmpInstr(MI, MBB)) || (MI->isSelect() && optimizeSelect(MI, LocalMIs))) { // MI is deleted. LocalMIs.erase(MI); Changed = true; continue; } if (MI->isConditionalBranch() && optimizeCondBranch(MI)) { Changed = true; continue; } if (isCoalescableCopy(*MI) && optimizeCoalescableCopy(MI)) { // MI is just rewritten. Changed = true; continue; } if (isMoveImmediate(MI, ImmDefRegs, ImmDefMIs)) { SeenMoveImm = true; } else { Changed |= optimizeExtInstr(MI, MBB, LocalMIs); // optimizeExtInstr might have created new instructions after MI // and before the already incremented MII. Adjust MII so that the // next iteration sees the new instructions. MII = MI; ++MII; if (SeenMoveImm) Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs); } // Check whether MI is a load candidate for folding into a later // instruction. If MI is not a candidate, check whether we can fold an // earlier load into MI. if (!isLoadFoldable(MI, FoldAsLoadDefCandidates) && !FoldAsLoadDefCandidates.empty()) { const MCInstrDesc &MIDesc = MI->getDesc(); for (unsigned i = MIDesc.getNumDefs(); i != MIDesc.getNumOperands(); ++i) { const MachineOperand &MOp = MI->getOperand(i); if (!MOp.isReg()) continue; unsigned FoldAsLoadDefReg = MOp.getReg(); if (FoldAsLoadDefCandidates.count(FoldAsLoadDefReg)) { // We need to fold load after optimizeCmpInstr, since // optimizeCmpInstr can enable folding by converting SUB to CMP. // Save FoldAsLoadDefReg because optimizeLoadInstr() resets it and // we need it for markUsesInDebugValueAsUndef(). unsigned FoldedReg = FoldAsLoadDefReg; MachineInstr *DefMI = nullptr; MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI, FoldAsLoadDefReg, DefMI); if (FoldMI) { // Update LocalMIs since we replaced MI with FoldMI and deleted // DefMI. DEBUG(dbgs() << "Replacing: " << *MI); DEBUG(dbgs() << " With: " << *FoldMI); LocalMIs.erase(MI); LocalMIs.erase(DefMI); LocalMIs.insert(FoldMI); MI->eraseFromParent(); DefMI->eraseFromParent(); MRI->markUsesInDebugValueAsUndef(FoldedReg); FoldAsLoadDefCandidates.erase(FoldedReg); ++NumLoadFold; // MI is replaced with FoldMI. Changed = true; break; } } } } } } return Changed; } bool ValueTracker::getNextSourceFromCopy(unsigned &SrcReg, unsigned &SrcSubReg) { assert(Def->isCopy() && "Invalid definition"); // Copy instruction are supposed to be: Def = Src. // If someone breaks this assumption, bad things will happen everywhere. assert(Def->getNumOperands() == 2 && "Invalid number of operands"); if (Def->getOperand(DefIdx).getSubReg() != DefSubReg) // If we look for a different subreg, it means we want a subreg of src. // Bails as we do not support composing subreg yet. return false; // Otherwise, we want the whole source. const MachineOperand &Src = Def->getOperand(1); SrcReg = Src.getReg(); SrcSubReg = Src.getSubReg(); return true; } bool ValueTracker::getNextSourceFromBitcast(unsigned &SrcReg, unsigned &SrcSubReg) { assert(Def->isBitcast() && "Invalid definition"); // Bail if there are effects that a plain copy will not expose. if (Def->hasUnmodeledSideEffects()) return false; // Bitcasts with more than one def are not supported. if (Def->getDesc().getNumDefs() != 1) return false; if (Def->getOperand(DefIdx).getSubReg() != DefSubReg) // If we look for a different subreg, it means we want a subreg of the src. // Bails as we do not support composing subreg yet. return false; unsigned SrcIdx = Def->getNumOperands(); for (unsigned OpIdx = DefIdx + 1, EndOpIdx = SrcIdx; OpIdx != EndOpIdx; ++OpIdx) { const MachineOperand &MO = Def->getOperand(OpIdx); if (!MO.isReg() || !MO.getReg()) continue; assert(!MO.isDef() && "We should have skipped all the definitions by now"); if (SrcIdx != EndOpIdx) // Multiple sources? return false; SrcIdx = OpIdx; } const MachineOperand &Src = Def->getOperand(SrcIdx); SrcReg = Src.getReg(); SrcSubReg = Src.getSubReg(); return true; } bool ValueTracker::getNextSourceFromRegSequence(unsigned &SrcReg, unsigned &SrcSubReg) { assert((Def->isRegSequence() || Def->isRegSequenceLike()) && "Invalid definition"); if (Def->getOperand(DefIdx).getSubReg()) // If we are composing subreg, bails out. // The case we are checking is Def. = REG_SEQUENCE. // This should almost never happen as the SSA property is tracked at // the register level (as opposed to the subreg level). // I.e., // Def.sub0 = // Def.sub1 = // is a valid SSA representation for Def.sub0 and Def.sub1, but not for // Def. Thus, it must not be generated. // However, some code could theoretically generates a single // Def.sub0 (i.e, not defining the other subregs) and we would // have this case. // If we can ascertain (or force) that this never happens, we could // turn that into an assertion. return false; if (!TII) // We could handle the REG_SEQUENCE here, but we do not want to // duplicate the code from the generic TII. return false; SmallVector RegSeqInputRegs; if (!TII->getRegSequenceInputs(*Def, DefIdx, RegSeqInputRegs)) return false; // We are looking at: // Def = REG_SEQUENCE v0, sub0, v1, sub1, ... // Check if one of the operand defines the subreg we are interested in. for (auto &RegSeqInput : RegSeqInputRegs) { if (RegSeqInput.SubIdx == DefSubReg) { if (RegSeqInput.SubReg) // Bails if we have to compose sub registers. return false; SrcReg = RegSeqInput.Reg; SrcSubReg = RegSeqInput.SubReg; return true; } } // If the subreg we are tracking is super-defined by another subreg, // we could follow this value. However, this would require to compose // the subreg and we do not do that for now. return false; } bool ValueTracker::getNextSourceFromInsertSubreg(unsigned &SrcReg, unsigned &SrcSubReg) { assert((Def->isInsertSubreg() || Def->isInsertSubregLike()) && "Invalid definition"); if (Def->getOperand(DefIdx).getSubReg()) // If we are composing subreg, bails out. // Same remark as getNextSourceFromRegSequence. // I.e., this may be turned into an assert. return false; if (!TII) // We could handle the REG_SEQUENCE here, but we do not want to // duplicate the code from the generic TII. return false; TargetInstrInfo::RegSubRegPair BaseReg; TargetInstrInfo::RegSubRegPairAndIdx InsertedReg; if (!TII->getInsertSubregInputs(*Def, DefIdx, BaseReg, InsertedReg)) return false; // We are looking at: // Def = INSERT_SUBREG v0, v1, sub1 // There are two cases: // 1. DefSubReg == sub1, get v1. // 2. DefSubReg != sub1, the value may be available through v0. // #1 Check if the inserted register matches the required sub index. if (InsertedReg.SubIdx == DefSubReg) { SrcReg = InsertedReg.Reg; SrcSubReg = InsertedReg.SubReg; return true; } // #2 Otherwise, if the sub register we are looking for is not partial // defined by the inserted element, we can look through the main // register (v0). const MachineOperand &MODef = Def->getOperand(DefIdx); // If the result register (Def) and the base register (v0) do not // have the same register class or if we have to compose // subregisters, bails out. if (MRI.getRegClass(MODef.getReg()) != MRI.getRegClass(BaseReg.Reg) || BaseReg.SubReg) return false; // Get the TRI and check if the inserted sub-register overlaps with the // sub-register we are tracking. const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo(); if (!TRI || (TRI->getSubRegIndexLaneMask(DefSubReg) & TRI->getSubRegIndexLaneMask(InsertedReg.SubIdx)) != 0) return false; // At this point, the value is available in v0 via the same subreg // we used for Def. SrcReg = BaseReg.Reg; SrcSubReg = DefSubReg; return true; } bool ValueTracker::getNextSourceFromExtractSubreg(unsigned &SrcReg, unsigned &SrcSubReg) { assert((Def->isExtractSubreg() || Def->isExtractSubregLike()) && "Invalid definition"); // We are looking at: // Def = EXTRACT_SUBREG v0, sub0 // Bails if we have to compose sub registers. // Indeed, if DefSubReg != 0, we would have to compose it with sub0. if (DefSubReg) return false; if (!TII) // We could handle the EXTRACT_SUBREG here, but we do not want to // duplicate the code from the generic TII. return false; TargetInstrInfo::RegSubRegPairAndIdx ExtractSubregInputReg; if (!TII->getExtractSubregInputs(*Def, DefIdx, ExtractSubregInputReg)) return false; // Bails if we have to compose sub registers. // Likewise, if v0.subreg != 0, we would have to compose v0.subreg with sub0. if (ExtractSubregInputReg.SubReg) return false; // Otherwise, the value is available in the v0.sub0. SrcReg = ExtractSubregInputReg.Reg; SrcSubReg = ExtractSubregInputReg.SubIdx; return true; } bool ValueTracker::getNextSourceFromSubregToReg(unsigned &SrcReg, unsigned &SrcSubReg) { assert(Def->isSubregToReg() && "Invalid definition"); // We are looking at: // Def = SUBREG_TO_REG Imm, v0, sub0 // Bails if we have to compose sub registers. // If DefSubReg != sub0, we would have to check that all the bits // we track are included in sub0 and if yes, we would have to // determine the right subreg in v0. if (DefSubReg != Def->getOperand(3).getImm()) return false; // Bails if we have to compose sub registers. // Likewise, if v0.subreg != 0, we would have to compose it with sub0. if (Def->getOperand(2).getSubReg()) return false; SrcReg = Def->getOperand(2).getReg(); SrcSubReg = Def->getOperand(3).getImm(); return true; } bool ValueTracker::getNextSourceImpl(unsigned &SrcReg, unsigned &SrcSubReg) { assert(Def && "This method needs a valid definition"); assert( (DefIdx < Def->getDesc().getNumDefs() || Def->getDesc().isVariadic()) && Def->getOperand(DefIdx).isDef() && "Invalid DefIdx"); if (Def->isCopy()) return getNextSourceFromCopy(SrcReg, SrcSubReg); if (Def->isBitcast()) return getNextSourceFromBitcast(SrcReg, SrcSubReg); // All the remaining cases involve "complex" instructions. // Bails if we did not ask for the advanced tracking. if (!UseAdvancedTracking) return false; if (Def->isRegSequence() || Def->isRegSequenceLike()) return getNextSourceFromRegSequence(SrcReg, SrcSubReg); if (Def->isInsertSubreg() || Def->isInsertSubregLike()) return getNextSourceFromInsertSubreg(SrcReg, SrcSubReg); if (Def->isExtractSubreg() || Def->isExtractSubregLike()) return getNextSourceFromExtractSubreg(SrcReg, SrcSubReg); if (Def->isSubregToReg()) return getNextSourceFromSubregToReg(SrcReg, SrcSubReg); return false; } const MachineInstr *ValueTracker::getNextSource(unsigned &SrcReg, unsigned &SrcSubReg) { // If we reach a point where we cannot move up in the use-def chain, // there is nothing we can get. if (!Def) return nullptr; const MachineInstr *PrevDef = nullptr; // Try to find the next source. if (getNextSourceImpl(SrcReg, SrcSubReg)) { // Update definition, definition index, and subregister for the // next call of getNextSource. // Update the current register. Reg = SrcReg; // Update the return value before moving up in the use-def chain. PrevDef = Def; // If we can still move up in the use-def chain, move to the next // defintion. if (!TargetRegisterInfo::isPhysicalRegister(Reg)) { Def = MRI.getVRegDef(Reg); DefIdx = MRI.def_begin(Reg).getOperandNo(); DefSubReg = SrcSubReg; return PrevDef; } } // If we end up here, this means we will not be able to find another source // for the next iteration. // Make sure any new call to getNextSource bails out early by cutting the // use-def chain. Def = nullptr; return PrevDef; }