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 MachineRegisterInfo *MRI; 38 SlotIndexes *Indexes; 39 MachineDominatorTree *DomTree; 40 VNInfo::Allocator *Alloc; 41 42 /// Seen - Bit vector of active entries in LiveOut, also used as a visited 43 /// set by findReachingDefs. One entry per basic block, indexed by block 44 /// number. This is kept as a separate bit vector because it can be cleared 45 /// quickly when switching live ranges. 46 BitVector Seen; 47 48 /// LiveOutPair - A value and the block that defined it. The domtree node is 49 /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)]. 50 typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair; 51 52 /// LiveOutMap - Map basic blocks to the value leaving the block. 53 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap; 54 55 /// LiveOut - Map each basic block where a live range is live out to the 56 /// live-out value and its defining block. 57 /// 58 /// For every basic block, MBB, one of these conditions shall be true: 59 /// 60 /// 1. !Seen.count(MBB->getNumber()) 61 /// Blocks without a Seen bit are ignored. 62 /// 2. LiveOut[MBB].second.getNode() == MBB 63 /// The live-out value is defined in MBB. 64 /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB] 65 /// The live-out value passses through MBB. All predecessors must carry 66 /// the same value. 67 /// 68 /// The domtree node may be null, it can be computed. 69 /// 70 /// The map can be shared by multiple live ranges as long as no two are 71 /// live-out of the same block. 72 LiveOutMap LiveOut; 73 74 /// LiveInBlock - Information about a basic block where a live range is known 75 /// to be live-in, but the value has not yet been determined. 76 struct LiveInBlock { 77 // LI - The live range that is live-in to this block. The algorithms can 78 // handle multiple non-overlapping live ranges simultaneously. 79 LiveInterval *LI; 80 81 // DomNode - Dominator tree node for the block. 82 // Cleared when the final value has been determined and LI has been updated. 83 MachineDomTreeNode *DomNode; 84 85 // Position in block where the live-in range ends, or SlotIndex() if the 86 // range passes through the block. When the final value has been 87 // determined, the range from the block start to Kill will be added to LI. 88 SlotIndex Kill; 89 90 // Live-in value filled in by updateSSA once it is known. 91 VNInfo *Value; 92 LiveInBlockLiveInBlock93 LiveInBlock(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill) 94 : LI(li), DomNode(node), Kill(kill), Value(0) {} 95 }; 96 97 /// LiveIn - Work list of blocks where the live-in value has yet to be 98 /// determined. This list is typically computed by findReachingDefs() and 99 /// used as a work list by updateSSA(). The low-level interface may also be 100 /// used to add entries directly. 101 SmallVector<LiveInBlock, 16> LiveIn; 102 103 /// findReachingDefs - Assuming that LI is live-in to KillMBB and killed at 104 /// Kill, search for values that can reach KillMBB. All blocks that need LI 105 /// to be live-in are added to LiveIn. If a unique reaching def is found, 106 /// its value is returned, if Kill is jointly dominated by multiple values, 107 /// NULL is returned. 108 /// 109 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 110 VNInfo *findReachingDefs(LiveInterval *LI, 111 MachineBasicBlock *KillMBB, 112 SlotIndex Kill, 113 unsigned PhysReg); 114 115 /// updateSSA - Compute the values that will be live in to all requested 116 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form. 117 /// 118 /// Every live-in block must be jointly dominated by the added live-out 119 /// blocks. No values are read from the live ranges. 120 void updateSSA(); 121 122 /// updateLiveIns - Add liveness as specified in the LiveIn vector, using VNI 123 /// as a wildcard value for LiveIn entries without a value. 124 void updateLiveIns(VNInfo *VNI); 125 126 public: LiveRangeCalc()127 LiveRangeCalc() : MRI(0), Indexes(0), DomTree(0), Alloc(0) {} 128 129 //===--------------------------------------------------------------------===// 130 // High-level interface. 131 //===--------------------------------------------------------------------===// 132 // 133 // Calculate live ranges from scratch. 134 // 135 136 /// reset - Prepare caches for a new set of non-overlapping live ranges. The 137 /// caches must be reset before attempting calculations with a live range 138 /// that may overlap a previously computed live range, and before the first 139 /// live range in a function. If live ranges are not known to be 140 /// non-overlapping, call reset before each. 141 void reset(const MachineFunction *MF, 142 SlotIndexes*, 143 MachineDominatorTree*, 144 VNInfo::Allocator*); 145 146 /// calculate - Calculate the live range of a virtual register from its defs 147 /// and uses. LI must be empty with no values. 148 void calculate(LiveInterval *LI); 149 150 //===--------------------------------------------------------------------===// 151 // Mid-level interface. 152 //===--------------------------------------------------------------------===// 153 // 154 // Modify existing live ranges. 155 // 156 157 /// extend - Extend the live range of LI to reach Kill. 158 /// 159 /// The existing values in LI must be live so they jointly dominate Kill. If 160 /// Kill is not dominated by a single existing value, PHI-defs are inserted 161 /// as required to preserve SSA form. If Kill is known to be dominated by a 162 /// single existing value, Alloc may be null. 163 /// 164 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 165 void extend(LiveInterval *LI, SlotIndex Kill, unsigned PhysReg = 0); 166 167 /// createDeadDefs - Create a dead def in LI for every def operand of Reg. 168 /// Each instruction defining Reg gets a new VNInfo with a corresponding 169 /// minimal live range. 170 void createDeadDefs(LiveInterval *LI, unsigned Reg); 171 172 /// createDeadDefs - Create a dead def in LI for every def of LI->reg. createDeadDefs(LiveInterval * LI)173 void createDeadDefs(LiveInterval *LI) { 174 createDeadDefs(LI, LI->reg); 175 } 176 177 /// extendToUses - Extend the live range of LI to reach all uses of Reg. 178 /// 179 /// All uses must be jointly dominated by existing liveness. PHI-defs are 180 /// inserted as needed to preserve SSA form. 181 void extendToUses(LiveInterval *LI, unsigned Reg); 182 183 /// extendToUses - Extend the live range of LI to reach all uses of LI->reg. extendToUses(LiveInterval * LI)184 void extendToUses(LiveInterval *LI) { 185 extendToUses(LI, LI->reg); 186 } 187 188 //===--------------------------------------------------------------------===// 189 // Low-level interface. 190 //===--------------------------------------------------------------------===// 191 // 192 // These functions can be used to compute live ranges where the live-in and 193 // live-out blocks are already known, but the SSA value in each block is 194 // unknown. 195 // 196 // After calling reset(), add known live-out values and known live-in blocks. 197 // Then call calculateValues() to compute the actual value that is 198 // live-in to each block, and add liveness to the live ranges. 199 // 200 201 /// setLiveOutValue - Indicate that VNI is live out from MBB. The 202 /// calculateValues() function will not add liveness for MBB, the caller 203 /// should take care of that. 204 /// 205 /// VNI may be null only if MBB is a live-through block also passed to 206 /// addLiveInBlock(). setLiveOutValue(MachineBasicBlock * MBB,VNInfo * VNI)207 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) { 208 Seen.set(MBB->getNumber()); 209 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0); 210 } 211 212 /// addLiveInBlock - Add a block with an unknown live-in value. This 213 /// function can only be called once per basic block. Once the live-in value 214 /// has been determined, calculateValues() will add liveness to LI. 215 /// 216 /// @param LI The live range that is live-in to the block. 217 /// @param DomNode The domtree node for the block. 218 /// @param Kill Index in block where LI is killed. If the value is 219 /// live-through, set Kill = SLotIndex() and also call 220 /// setLiveOutValue(MBB, 0). 221 void addLiveInBlock(LiveInterval *LI, 222 MachineDomTreeNode *DomNode, 223 SlotIndex Kill = SlotIndex()) { 224 LiveIn.push_back(LiveInBlock(LI, DomNode, Kill)); 225 } 226 227 /// calculateValues - Calculate the value that will be live-in to each block 228 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA 229 /// form. Add liveness to all live-in blocks up to the Kill point, or the 230 /// whole block for live-through blocks. 231 /// 232 /// Every predecessor of a live-in block must have been given a value with 233 /// setLiveOutValue, the value may be null for live-trough blocks. 234 void calculateValues(); 235 }; 236 237 } // end namespace llvm 238 239 #endif 240