1 //===---- LiveRangeCalc.h - Calculate live ranges ---------------*- 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 // The LiveRangeCalc class can be used to compute live ranges from scratch. It 11 // caches information about values in the CFG to speed up repeated operations 12 // on the same live range. The cache can be shared by non-overlapping live 13 // ranges. SplitKit uses that when computing the live range of split products. 14 // 15 // A low-level interface is available to clients that know where a variable is 16 // live, but don't know which value it has as every point. LiveRangeCalc will 17 // propagate values down the dominator tree, and even insert PHI-defs where 18 // needed. SplitKit uses this faster interface when possible. 19 // 20 //===----------------------------------------------------------------------===// 21 22 #ifndef LLVM_CODEGEN_LIVERANGECALC_H 23 #define LLVM_CODEGEN_LIVERANGECALC_H 24 25 #include "llvm/ADT/BitVector.h" 26 #include "llvm/ADT/IndexedMap.h" 27 #include "llvm/CodeGen/LiveInterval.h" 28 29 namespace llvm { 30 31 /// Forward declarations for MachineDominators.h: 32 class MachineDominatorTree; 33 template <class NodeT> class DomTreeNodeBase; 34 typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode; 35 36 class LiveRangeCalc { 37 const MachineFunction *MF; 38 const MachineRegisterInfo *MRI; 39 SlotIndexes *Indexes; 40 MachineDominatorTree *DomTree; 41 VNInfo::Allocator *Alloc; 42 43 /// Seen - Bit vector of active entries in LiveOut, also used as a visited 44 /// set by findReachingDefs. One entry per basic block, indexed by block 45 /// number. This is kept as a separate bit vector because it can be cleared 46 /// quickly when switching live ranges. 47 BitVector Seen; 48 49 /// LiveOutPair - A value and the block that defined it. The domtree node is 50 /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)]. 51 typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair; 52 53 /// LiveOutMap - Map basic blocks to the value leaving the block. 54 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap; 55 56 /// LiveOut - Map each basic block where a live range is live out to the 57 /// live-out value and its defining block. 58 /// 59 /// For every basic block, MBB, one of these conditions shall be true: 60 /// 61 /// 1. !Seen.count(MBB->getNumber()) 62 /// Blocks without a Seen bit are ignored. 63 /// 2. LiveOut[MBB].second.getNode() == MBB 64 /// The live-out value is defined in MBB. 65 /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB] 66 /// The live-out value passses through MBB. All predecessors must carry 67 /// the same value. 68 /// 69 /// The domtree node may be null, it can be computed. 70 /// 71 /// The map can be shared by multiple live ranges as long as no two are 72 /// live-out of the same block. 73 LiveOutMap LiveOut; 74 75 /// LiveInBlock - Information about a basic block where a live range is known 76 /// to be live-in, but the value has not yet been determined. 77 struct LiveInBlock { 78 // The live range set that is live-in to this block. The algorithms can 79 // handle multiple non-overlapping live ranges simultaneously. 80 LiveRange &LR; 81 82 // DomNode - Dominator tree node for the block. 83 // Cleared when the final value has been determined and LI has been updated. 84 MachineDomTreeNode *DomNode; 85 86 // Position in block where the live-in range ends, or SlotIndex() if the 87 // range passes through the block. When the final value has been 88 // determined, the range from the block start to Kill will be added to LI. 89 SlotIndex Kill; 90 91 // Live-in value filled in by updateSSA once it is known. 92 VNInfo *Value; 93 94 LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill) 95 : LR(LR), DomNode(node), Kill(kill), Value(nullptr) {} 96 }; 97 98 /// LiveIn - Work list of blocks where the live-in value has yet to be 99 /// determined. This list is typically computed by findReachingDefs() and 100 /// used as a work list by updateSSA(). The low-level interface may also be 101 /// used to add entries directly. 102 SmallVector<LiveInBlock, 16> LiveIn; 103 104 /// Assuming that LI is live-in to KillMBB and killed at Kill, find the set 105 /// of defs that can reach it. 106 /// 107 /// If only one def can reach Kill, all paths from the def to kill are added 108 /// to LI, and the function returns true. 109 /// 110 /// If multiple values can reach Kill, the blocks that need LI to be live in 111 /// are added to the LiveIn array, and the function returns false. 112 /// 113 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 114 bool findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB, 115 SlotIndex Kill, unsigned PhysReg); 116 117 /// updateSSA - Compute the values that will be live in to all requested 118 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form. 119 /// 120 /// Every live-in block must be jointly dominated by the added live-out 121 /// blocks. No values are read from the live ranges. 122 void updateSSA(); 123 124 /// Add liveness as specified in the LiveIn vector. 125 void updateLiveIns(); 126 127 public: 128 LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr), 129 DomTree(nullptr), Alloc(nullptr) {} 130 131 //===--------------------------------------------------------------------===// 132 // High-level interface. 133 //===--------------------------------------------------------------------===// 134 // 135 // Calculate live ranges from scratch. 136 // 137 138 /// reset - Prepare caches for a new set of non-overlapping live ranges. The 139 /// caches must be reset before attempting calculations with a live range 140 /// that may overlap a previously computed live range, and before the first 141 /// live range in a function. If live ranges are not known to be 142 /// non-overlapping, call reset before each. 143 void reset(const MachineFunction *MF, 144 SlotIndexes*, 145 MachineDominatorTree*, 146 VNInfo::Allocator*); 147 148 //===--------------------------------------------------------------------===// 149 // Mid-level interface. 150 //===--------------------------------------------------------------------===// 151 // 152 // Modify existing live ranges. 153 // 154 155 /// extend - Extend the live range of LI to reach Kill. 156 /// 157 /// The existing values in LI must be live so they jointly dominate Kill. If 158 /// Kill is not dominated by a single existing value, PHI-defs are inserted 159 /// as required to preserve SSA form. If Kill is known to be dominated by a 160 /// single existing value, Alloc may be null. 161 /// 162 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 163 void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg = 0); 164 165 /// createDeadDefs - Create a dead def in LI for every def operand of Reg. 166 /// Each instruction defining Reg gets a new VNInfo with a corresponding 167 /// minimal live range. 168 void createDeadDefs(LiveRange &LR, unsigned Reg); 169 170 /// createDeadDefs - Create a dead def in LI for every def of LI->reg. 171 void createDeadDefs(LiveInterval &LI) { 172 createDeadDefs(LI, LI.reg); 173 } 174 175 /// extendToUses - Extend the live range of LI to reach all uses of Reg. 176 /// 177 /// All uses must be jointly dominated by existing liveness. PHI-defs are 178 /// inserted as needed to preserve SSA form. 179 void extendToUses(LiveRange &LR, unsigned Reg); 180 181 /// extendToUses - Extend the live range of LI to reach all uses of LI->reg. 182 void extendToUses(LiveInterval &LI) { 183 extendToUses(LI, LI.reg); 184 } 185 186 //===--------------------------------------------------------------------===// 187 // Low-level interface. 188 //===--------------------------------------------------------------------===// 189 // 190 // These functions can be used to compute live ranges where the live-in and 191 // live-out blocks are already known, but the SSA value in each block is 192 // unknown. 193 // 194 // After calling reset(), add known live-out values and known live-in blocks. 195 // Then call calculateValues() to compute the actual value that is 196 // live-in to each block, and add liveness to the live ranges. 197 // 198 199 /// setLiveOutValue - Indicate that VNI is live out from MBB. The 200 /// calculateValues() function will not add liveness for MBB, the caller 201 /// should take care of that. 202 /// 203 /// VNI may be null only if MBB is a live-through block also passed to 204 /// addLiveInBlock(). 205 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) { 206 Seen.set(MBB->getNumber()); 207 LiveOut[MBB] = LiveOutPair(VNI, nullptr); 208 } 209 210 /// addLiveInBlock - Add a block with an unknown live-in value. This 211 /// function can only be called once per basic block. Once the live-in value 212 /// has been determined, calculateValues() will add liveness to LI. 213 /// 214 /// @param LR The live range that is live-in to the block. 215 /// @param DomNode The domtree node for the block. 216 /// @param Kill Index in block where LI is killed. If the value is 217 /// live-through, set Kill = SLotIndex() and also call 218 /// setLiveOutValue(MBB, 0). 219 void addLiveInBlock(LiveRange &LR, 220 MachineDomTreeNode *DomNode, 221 SlotIndex Kill = SlotIndex()) { 222 LiveIn.push_back(LiveInBlock(LR, DomNode, Kill)); 223 } 224 225 /// calculateValues - Calculate the value that will be live-in to each block 226 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA 227 /// form. Add liveness to all live-in blocks up to the Kill point, or the 228 /// whole block for live-through blocks. 229 /// 230 /// Every predecessor of a live-in block must have been given a value with 231 /// setLiveOutValue, the value may be null for live-trough blocks. 232 void calculateValues(); 233 }; 234 235 } // end namespace llvm 236 237 #endif 238
