1 //===- RegisterScavenging.h - Machine register scavenging -------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 /// \file 11 /// This file declares the machine register scavenger class. It can provide 12 /// information such as unused register at any point in a machine basic block. 13 /// It also provides a mechanism to make registers available by evicting them 14 /// to spill slots. 15 // 16 //===----------------------------------------------------------------------===// 17 18 #ifndef LLVM_CODEGEN_REGISTERSCAVENGING_H 19 #define LLVM_CODEGEN_REGISTERSCAVENGING_H 20 21 #include "llvm/ADT/BitVector.h" 22 #include "llvm/ADT/SmallVector.h" 23 #include "llvm/CodeGen/LiveRegUnits.h" 24 #include "llvm/CodeGen/MachineBasicBlock.h" 25 #include "llvm/CodeGen/MachineRegisterInfo.h" 26 #include "llvm/MC/LaneBitmask.h" 27 28 namespace llvm { 29 30 class MachineInstr; 31 class TargetInstrInfo; 32 class TargetRegisterClass; 33 class TargetRegisterInfo; 34 35 class RegScavenger { 36 const TargetRegisterInfo *TRI; 37 const TargetInstrInfo *TII; 38 MachineRegisterInfo* MRI; 39 MachineBasicBlock *MBB = nullptr; 40 MachineBasicBlock::iterator MBBI; 41 unsigned NumRegUnits = 0; 42 43 /// True if RegScavenger is currently tracking the liveness of registers. 44 bool Tracking = false; 45 46 /// Information on scavenged registers (held in a spill slot). 47 struct ScavengedInfo { 48 ScavengedInfo(int FI = -1) : FrameIndex(FI) {} 49 50 /// A spill slot used for scavenging a register post register allocation. 51 int FrameIndex; 52 53 /// If non-zero, the specific register is currently being 54 /// scavenged. That is, it is spilled to this scavenging stack slot. 55 unsigned Reg = 0; 56 57 /// The instruction that restores the scavenged register from stack. 58 const MachineInstr *Restore = nullptr; 59 }; 60 61 /// A vector of information on scavenged registers. 62 SmallVector<ScavengedInfo, 2> Scavenged; 63 64 LiveRegUnits LiveUnits; 65 66 // These BitVectors are only used internally to forward(). They are members 67 // to avoid frequent reallocations. 68 BitVector KillRegUnits, DefRegUnits; 69 BitVector TmpRegUnits; 70 71 public: 72 RegScavenger() = default; 73 74 /// Start tracking liveness from the begin of basic block \p MBB. 75 void enterBasicBlock(MachineBasicBlock &MBB); 76 77 /// Start tracking liveness from the end of basic block \p MBB. 78 /// Use backward() to move towards the beginning of the block. This is 79 /// preferred to enterBasicBlock() and forward() because it does not depend 80 /// on the presence of kill flags. 81 void enterBasicBlockEnd(MachineBasicBlock &MBB); 82 83 /// Move the internal MBB iterator and update register states. 84 void forward(); 85 86 /// Move the internal MBB iterator and update register states until 87 /// it has processed the specific iterator. 88 void forward(MachineBasicBlock::iterator I) { 89 if (!Tracking && MBB->begin() != I) forward(); 90 while (MBBI != I) forward(); 91 } 92 93 /// Invert the behavior of forward() on the current instruction (undo the 94 /// changes to the available registers made by forward()). 95 void unprocess(); 96 97 /// Unprocess instructions until you reach the provided iterator. 98 void unprocess(MachineBasicBlock::iterator I) { 99 while (MBBI != I) unprocess(); 100 } 101 102 /// Update internal register state and move MBB iterator backwards. 103 /// Contrary to unprocess() this method gives precise results even in the 104 /// absence of kill flags. 105 void backward(); 106 107 /// Call backward() as long as the internal iterator does not point to \p I. 108 void backward(MachineBasicBlock::iterator I) { 109 while (MBBI != I) 110 backward(); 111 } 112 113 /// Move the internal MBB iterator but do not update register states. 114 void skipTo(MachineBasicBlock::iterator I) { 115 if (I == MachineBasicBlock::iterator(nullptr)) 116 Tracking = false; 117 MBBI = I; 118 } 119 120 MachineBasicBlock::iterator getCurrentPosition() const { return MBBI; } 121 122 /// Return if a specific register is currently used. 123 bool isRegUsed(unsigned Reg, bool includeReserved = true) const; 124 125 /// Return all available registers in the register class in Mask. 126 BitVector getRegsAvailable(const TargetRegisterClass *RC); 127 128 /// Find an unused register of the specified register class. 129 /// Return 0 if none is found. 130 unsigned FindUnusedReg(const TargetRegisterClass *RC) const; 131 132 /// Add a scavenging frame index. 133 void addScavengingFrameIndex(int FI) { 134 Scavenged.push_back(ScavengedInfo(FI)); 135 } 136 137 /// Query whether a frame index is a scavenging frame index. 138 bool isScavengingFrameIndex(int FI) const { 139 for (SmallVectorImpl<ScavengedInfo>::const_iterator I = Scavenged.begin(), 140 IE = Scavenged.end(); I != IE; ++I) 141 if (I->FrameIndex == FI) 142 return true; 143 144 return false; 145 } 146 147 /// Get an array of scavenging frame indices. 148 void getScavengingFrameIndices(SmallVectorImpl<int> &A) const { 149 for (SmallVectorImpl<ScavengedInfo>::const_iterator I = Scavenged.begin(), 150 IE = Scavenged.end(); I != IE; ++I) 151 if (I->FrameIndex >= 0) 152 A.push_back(I->FrameIndex); 153 } 154 155 /// Make a register of the specific register class 156 /// available and do the appropriate bookkeeping. SPAdj is the stack 157 /// adjustment due to call frame, it's passed along to eliminateFrameIndex(). 158 /// Returns the scavenged register. 159 /// This is deprecated as it depends on the quality of the kill flags being 160 /// present; Use scavengeRegisterBackwards() instead! 161 unsigned scavengeRegister(const TargetRegisterClass *RC, 162 MachineBasicBlock::iterator I, int SPAdj); 163 unsigned scavengeRegister(const TargetRegisterClass *RegClass, int SPAdj) { 164 return scavengeRegister(RegClass, MBBI, SPAdj); 165 } 166 167 /// Make a register of the specific register class available from the current 168 /// position backwards to the place before \p To. If \p RestoreAfter is true 169 /// this includes the instruction following the current position. 170 /// SPAdj is the stack adjustment due to call frame, it's passed along to 171 /// eliminateFrameIndex(). 172 /// Returns the scavenged register. 173 unsigned scavengeRegisterBackwards(const TargetRegisterClass &RC, 174 MachineBasicBlock::iterator To, 175 bool RestoreAfter, int SPAdj); 176 177 /// Tell the scavenger a register is used. 178 void setRegUsed(unsigned Reg, LaneBitmask LaneMask = LaneBitmask::getAll()); 179 180 private: 181 /// Returns true if a register is reserved. It is never "unused". 182 bool isReserved(unsigned Reg) const { return MRI->isReserved(Reg); } 183 184 /// setUsed / setUnused - Mark the state of one or a number of register units. 185 /// 186 void setUsed(const BitVector &RegUnits) { 187 LiveUnits.addUnits(RegUnits); 188 } 189 void setUnused(const BitVector &RegUnits) { 190 LiveUnits.removeUnits(RegUnits); 191 } 192 193 /// Processes the current instruction and fill the KillRegUnits and 194 /// DefRegUnits bit vectors. 195 void determineKillsAndDefs(); 196 197 /// Add all Reg Units that Reg contains to BV. 198 void addRegUnits(BitVector &BV, unsigned Reg); 199 200 /// Remove all Reg Units that \p Reg contains from \p BV. 201 void removeRegUnits(BitVector &BV, unsigned Reg); 202 203 /// Return the candidate register that is unused for the longest after 204 /// StartMI. UseMI is set to the instruction where the search stopped. 205 /// 206 /// No more than InstrLimit instructions are inspected. 207 unsigned findSurvivorReg(MachineBasicBlock::iterator StartMI, 208 BitVector &Candidates, 209 unsigned InstrLimit, 210 MachineBasicBlock::iterator &UseMI); 211 212 /// Initialize RegisterScavenger. 213 void init(MachineBasicBlock &MBB); 214 215 /// Mark live-in registers of basic block as used. 216 void setLiveInsUsed(const MachineBasicBlock &MBB); 217 218 /// Spill a register after position \p After and reload it before position 219 /// \p UseMI. 220 ScavengedInfo &spill(unsigned Reg, const TargetRegisterClass &RC, int SPAdj, 221 MachineBasicBlock::iterator Before, 222 MachineBasicBlock::iterator &UseMI); 223 }; 224 225 /// Replaces all frame index virtual registers with physical registers. Uses the 226 /// register scavenger to find an appropriate register to use. 227 void scavengeFrameVirtualRegs(MachineFunction &MF, RegScavenger &RS); 228 229 } // end namespace llvm 230 231 #endif // LLVM_CODEGEN_REGISTERSCAVENGING_H 232
