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 // LI - The live range that is live-in to this block. The algorithms can 79 // handle multiple non-overlapping live ranges simultaneously. 80 LiveInterval *LI; 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(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill) 95 : LI(li), DomNode(node), Kill(kill), Value(0) {} 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(LiveInterval *LI, 115 MachineBasicBlock *KillMBB, 116 SlotIndex Kill, 117 unsigned PhysReg); 118 119 /// updateSSA - Compute the values that will be live in to all requested 120 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form. 121 /// 122 /// Every live-in block must be jointly dominated by the added live-out 123 /// blocks. No values are read from the live ranges. 124 void updateSSA(); 125 126 /// Add liveness as specified in the LiveIn vector. 127 void updateLiveIns(); 128 129 public: 130 LiveRangeCalc() : MF(0), MRI(0), Indexes(0), DomTree(0), Alloc(0) {} 131 132 //===--------------------------------------------------------------------===// 133 // High-level interface. 134 //===--------------------------------------------------------------------===// 135 // 136 // Calculate live ranges from scratch. 137 // 138 139 /// reset - Prepare caches for a new set of non-overlapping live ranges. The 140 /// caches must be reset before attempting calculations with a live range 141 /// that may overlap a previously computed live range, and before the first 142 /// live range in a function. If live ranges are not known to be 143 /// non-overlapping, call reset before each. 144 void reset(const MachineFunction *MF, 145 SlotIndexes*, 146 MachineDominatorTree*, 147 VNInfo::Allocator*); 148 149 /// calculate - Calculate the live range of a virtual register from its defs 150 /// and uses. LI must be empty with no values. 151 void calculate(LiveInterval *LI); 152 153 //===--------------------------------------------------------------------===// 154 // Mid-level interface. 155 //===--------------------------------------------------------------------===// 156 // 157 // Modify existing live ranges. 158 // 159 160 /// extend - Extend the live range of LI to reach Kill. 161 /// 162 /// The existing values in LI must be live so they jointly dominate Kill. If 163 /// Kill is not dominated by a single existing value, PHI-defs are inserted 164 /// as required to preserve SSA form. If Kill is known to be dominated by a 165 /// single existing value, Alloc may be null. 166 /// 167 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 168 void extend(LiveInterval *LI, SlotIndex Kill, unsigned PhysReg = 0); 169 170 /// createDeadDefs - Create a dead def in LI for every def operand of Reg. 171 /// Each instruction defining Reg gets a new VNInfo with a corresponding 172 /// minimal live range. 173 void createDeadDefs(LiveInterval *LI, unsigned Reg); 174 175 /// createDeadDefs - Create a dead def in LI for every def of LI->reg. 176 void createDeadDefs(LiveInterval *LI) { 177 createDeadDefs(LI, LI->reg); 178 } 179 180 /// extendToUses - Extend the live range of LI to reach all uses of Reg. 181 /// 182 /// All uses must be jointly dominated by existing liveness. PHI-defs are 183 /// inserted as needed to preserve SSA form. 184 void extendToUses(LiveInterval *LI, unsigned Reg); 185 186 /// extendToUses - Extend the live range of LI to reach all uses of LI->reg. 187 void extendToUses(LiveInterval *LI) { 188 extendToUses(LI, LI->reg); 189 } 190 191 //===--------------------------------------------------------------------===// 192 // Low-level interface. 193 //===--------------------------------------------------------------------===// 194 // 195 // These functions can be used to compute live ranges where the live-in and 196 // live-out blocks are already known, but the SSA value in each block is 197 // unknown. 198 // 199 // After calling reset(), add known live-out values and known live-in blocks. 200 // Then call calculateValues() to compute the actual value that is 201 // live-in to each block, and add liveness to the live ranges. 202 // 203 204 /// setLiveOutValue - Indicate that VNI is live out from MBB. The 205 /// calculateValues() function will not add liveness for MBB, the caller 206 /// should take care of that. 207 /// 208 /// VNI may be null only if MBB is a live-through block also passed to 209 /// addLiveInBlock(). 210 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) { 211 Seen.set(MBB->getNumber()); 212 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0); 213 } 214 215 /// addLiveInBlock - Add a block with an unknown live-in value. This 216 /// function can only be called once per basic block. Once the live-in value 217 /// has been determined, calculateValues() will add liveness to LI. 218 /// 219 /// @param LI The live range that is live-in to the block. 220 /// @param DomNode The domtree node for the block. 221 /// @param Kill Index in block where LI is killed. If the value is 222 /// live-through, set Kill = SLotIndex() and also call 223 /// setLiveOutValue(MBB, 0). 224 void addLiveInBlock(LiveInterval *LI, 225 MachineDomTreeNode *DomNode, 226 SlotIndex Kill = SlotIndex()) { 227 LiveIn.push_back(LiveInBlock(LI, DomNode, Kill)); 228 } 229 230 /// calculateValues - Calculate the value that will be live-in to each block 231 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA 232 /// form. Add liveness to all live-in blocks up to the Kill point, or the 233 /// whole block for live-through blocks. 234 /// 235 /// Every predecessor of a live-in block must have been given a value with 236 /// setLiveOutValue, the value may be null for live-trough blocks. 237 void calculateValues(); 238 }; 239 240 } // end namespace llvm 241 242 #endif 243
