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_LIB_CODEGEN_LIVERANGECALC_H 23 #define LLVM_LIB_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 /// LiveOutPair - A value and the block that defined it. The domtree node is 44 /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)]. 45 typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair; 46 47 /// LiveOutMap - Map basic blocks to the value leaving the block. 48 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap; 49 50 /// Bit vector of active entries in LiveOut, also used as a visited set by 51 /// findReachingDefs. One entry per basic block, indexed by block number. 52 /// This is kept as a separate bit vector because it can be cleared quickly 53 /// when switching live ranges. 54 BitVector Seen; 55 56 /// Map each basic block where a live range is live out to the live-out value 57 /// 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 Map; 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 @p LR is live-in to @p UseMBB, find the set of defs that can 105 /// reach it. 106 /// 107 /// If only one def can reach @p UseMBB, all paths from the def to @p UseMBB 108 /// are added to @p LR, and the function returns true. 109 /// 110 /// If multiple values can reach @p UseMBB, the blocks that need @p LR to be 111 /// live in 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 &UseMBB, 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 /// Transfer information from the LiveIn vector to the live ranges and update 125 /// the given @p LiveOuts. 126 void updateFromLiveIns(); 127 128 /// Extend the live range of @p LR to reach all uses of Reg. 129 /// 130 /// All uses must be jointly dominated by existing liveness. PHI-defs are 131 /// inserted as needed to preserve SSA form. 132 void extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask); 133 134 /// Reset Map and Seen fields. 135 void resetLiveOutMap(); 136 137 public: 138 LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr), 139 DomTree(nullptr), Alloc(nullptr) {} 140 141 //===--------------------------------------------------------------------===// 142 // High-level interface. 143 //===--------------------------------------------------------------------===// 144 // 145 // Calculate live ranges from scratch. 146 // 147 148 /// reset - Prepare caches for a new set of non-overlapping live ranges. The 149 /// caches must be reset before attempting calculations with a live range 150 /// that may overlap a previously computed live range, and before the first 151 /// live range in a function. If live ranges are not known to be 152 /// non-overlapping, call reset before each. 153 void reset(const MachineFunction *MF, 154 SlotIndexes*, 155 MachineDominatorTree*, 156 VNInfo::Allocator*); 157 158 //===--------------------------------------------------------------------===// 159 // Mid-level interface. 160 //===--------------------------------------------------------------------===// 161 // 162 // Modify existing live ranges. 163 // 164 165 /// Extend the live range of @p LR to reach @p Use. 166 /// 167 /// The existing values in @p LR must be live so they jointly dominate @p Use. 168 /// If @p Use is not dominated by a single existing value, PHI-defs are 169 /// inserted as required to preserve SSA form. 170 /// 171 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 172 void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg = 0); 173 174 /// createDeadDefs - Create a dead def in LI for every def operand of Reg. 175 /// Each instruction defining Reg gets a new VNInfo with a corresponding 176 /// minimal live range. 177 void createDeadDefs(LiveRange &LR, unsigned Reg); 178 179 /// Extend the live range of @p LR to reach all uses of Reg. 180 /// 181 /// All uses must be jointly dominated by existing liveness. PHI-defs are 182 /// inserted as needed to preserve SSA form. 183 void extendToUses(LiveRange &LR, unsigned PhysReg) { 184 extendToUses(LR, PhysReg, ~0u); 185 } 186 187 /// Calculates liveness for the register specified in live interval @p LI. 188 /// Creates subregister live ranges as needed if subreg liveness tracking is 189 /// enabled. 190 void calculate(LiveInterval &LI, bool TrackSubRegs); 191 192 /// For live interval \p LI with correct SubRanges construct matching 193 /// information for the main live range. Expects the main live range to not 194 /// have any segments or value numbers. 195 void constructMainRangeFromSubranges(LiveInterval &LI); 196 197 //===--------------------------------------------------------------------===// 198 // Low-level interface. 199 //===--------------------------------------------------------------------===// 200 // 201 // These functions can be used to compute live ranges where the live-in and 202 // live-out blocks are already known, but the SSA value in each block is 203 // unknown. 204 // 205 // After calling reset(), add known live-out values and known live-in blocks. 206 // Then call calculateValues() to compute the actual value that is 207 // live-in to each block, and add liveness to the live ranges. 208 // 209 210 /// setLiveOutValue - Indicate that VNI is live out from MBB. The 211 /// calculateValues() function will not add liveness for MBB, the caller 212 /// should take care of that. 213 /// 214 /// VNI may be null only if MBB is a live-through block also passed to 215 /// addLiveInBlock(). 216 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) { 217 Seen.set(MBB->getNumber()); 218 Map[MBB] = LiveOutPair(VNI, nullptr); 219 } 220 221 /// addLiveInBlock - Add a block with an unknown live-in value. This 222 /// function can only be called once per basic block. Once the live-in value 223 /// has been determined, calculateValues() will add liveness to LI. 224 /// 225 /// @param LR The live range that is live-in to the block. 226 /// @param DomNode The domtree node for the block. 227 /// @param Kill Index in block where LI is killed. If the value is 228 /// live-through, set Kill = SLotIndex() and also call 229 /// setLiveOutValue(MBB, 0). 230 void addLiveInBlock(LiveRange &LR, 231 MachineDomTreeNode *DomNode, 232 SlotIndex Kill = SlotIndex()) { 233 LiveIn.push_back(LiveInBlock(LR, DomNode, Kill)); 234 } 235 236 /// calculateValues - Calculate the value that will be live-in to each block 237 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA 238 /// form. Add liveness to all live-in blocks up to the Kill point, or the 239 /// whole block for live-through blocks. 240 /// 241 /// Every predecessor of a live-in block must have been given a value with 242 /// setLiveOutValue, the value may be null for live-trough blocks. 243 void calculateValues(); 244 }; 245 246 } // end namespace llvm 247 248 #endif 249
