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 /// Seen - Bit vector of active entries in LiveOut, also used as a visited 38 /// set by findReachingDefs. One entry per basic block, indexed by block 39 /// number. This is kept as a separate bit vector because it can be cleared 40 /// quickly when switching live ranges. 41 BitVector Seen; 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 /// LiveOut - Map each basic block where a live range is live out to the 51 /// live-out value and its defining block. 52 /// 53 /// For every basic block, MBB, one of these conditions shall be true: 54 /// 55 /// 1. !Seen.count(MBB->getNumber()) 56 /// Blocks without a Seen bit are ignored. 57 /// 2. LiveOut[MBB].second.getNode() == MBB 58 /// The live-out value is defined in MBB. 59 /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB] 60 /// The live-out value passses through MBB. All predecessors must carry 61 /// the same value. 62 /// 63 /// The domtree node may be null, it can be computed. 64 /// 65 /// The map can be shared by multiple live ranges as long as no two are 66 /// live-out of the same block. 67 LiveOutMap LiveOut; 68 69 /// LiveInBlock - Information about a basic block where a live range is known 70 /// to be live-in, but the value has not yet been determined. 71 struct LiveInBlock { 72 // LI - The live range that is live-in to this block. The algorithms can 73 // handle multiple non-overlapping live ranges simultaneously. 74 LiveInterval *LI; 75 76 // DomNode - Dominator tree node for the block. 77 // Cleared when the final value has been determined and LI has been updated. 78 MachineDomTreeNode *DomNode; 79 80 // Position in block where the live-in range ends, or SlotIndex() if the 81 // range passes through the block. When the final value has been 82 // determined, the range from the block start to Kill will be added to LI. 83 SlotIndex Kill; 84 85 // Live-in value filled in by updateSSA once it is known. 86 VNInfo *Value; 87 88 LiveInBlock(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill) 89 : LI(li), DomNode(node), Kill(kill), Value(0) {} 90 }; 91 92 /// LiveIn - Work list of blocks where the live-in value has yet to be 93 /// determined. This list is typically computed by findReachingDefs() and 94 /// used as a work list by updateSSA(). The low-level interface may also be 95 /// used to add entries directly. 96 SmallVector<LiveInBlock, 16> LiveIn; 97 98 /// findReachingDefs - Assuming that LI is live-in to KillMBB and killed at 99 /// Kill, search for values that can reach KillMBB. All blocks that need LI 100 /// to be live-in are added to LiveIn. If a unique reaching def is found, 101 /// its value is returned, if Kill is jointly dominated by multiple values, 102 /// NULL is returned. 103 VNInfo *findReachingDefs(LiveInterval *LI, 104 MachineBasicBlock *KillMBB, 105 SlotIndex Kill, 106 SlotIndexes *Indexes, 107 MachineDominatorTree *DomTree); 108 109 /// updateSSA - Compute the values that will be live in to all requested 110 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form. 111 /// 112 /// Every live-in block must be jointly dominated by the added live-out 113 /// blocks. No values are read from the live ranges. 114 void updateSSA(SlotIndexes *Indexes, 115 MachineDominatorTree *DomTree, 116 VNInfo::Allocator *Alloc); 117 118 /// updateLiveIns - Add liveness as specified in the LiveIn vector, using VNI 119 /// as a wildcard value for LiveIn entries without a value. 120 void updateLiveIns(VNInfo *VNI, SlotIndexes*); 121 122 public: 123 //===--------------------------------------------------------------------===// 124 // High-level interface. 125 //===--------------------------------------------------------------------===// 126 // 127 // Calculate live ranges from scratch. 128 // 129 130 /// reset - Prepare caches for a new set of non-overlapping live ranges. The 131 /// caches must be reset before attempting calculations with a live range 132 /// that may overlap a previously computed live range, and before the first 133 /// live range in a function. If live ranges are not known to be 134 /// non-overlapping, call reset before each. 135 void reset(const MachineFunction *MF); 136 137 /// calculate - Calculate the live range of a virtual register from its defs 138 /// and uses. LI must be empty with no values. 139 void calculate(LiveInterval *LI, 140 MachineRegisterInfo *MRI, 141 SlotIndexes *Indexes, 142 VNInfo::Allocator *Alloc); 143 144 //===--------------------------------------------------------------------===// 145 // Mid-level interface. 146 //===--------------------------------------------------------------------===// 147 // 148 // Modify existing live ranges. 149 // 150 151 /// extend - Extend the live range of LI to reach Kill. 152 /// 153 /// The existing values in LI must be live so they jointly dominate Kill. If 154 /// Kill is not dominated by a single existing value, PHI-defs are inserted 155 /// as required to preserve SSA form. If Kill is known to be dominated by a 156 /// single existing value, Alloc may be null. 157 void extend(LiveInterval *LI, 158 SlotIndex Kill, 159 SlotIndexes *Indexes, 160 MachineDominatorTree *DomTree, 161 VNInfo::Allocator *Alloc); 162 163 /// extendToUses - Extend the live range of LI to reach all uses. 164 /// 165 /// All uses must be jointly dominated by existing liveness. PHI-defs are 166 /// inserted as needed to preserve SSA form. 167 void extendToUses(LiveInterval *LI, 168 MachineRegisterInfo *MRI, 169 SlotIndexes *Indexes, 170 MachineDominatorTree *DomTree, 171 VNInfo::Allocator *Alloc); 172 173 //===--------------------------------------------------------------------===// 174 // Low-level interface. 175 //===--------------------------------------------------------------------===// 176 // 177 // These functions can be used to compute live ranges where the live-in and 178 // live-out blocks are already known, but the SSA value in each block is 179 // unknown. 180 // 181 // After calling reset(), add known live-out values and known live-in blocks. 182 // Then call calculateValues() to compute the actual value that is 183 // live-in to each block, and add liveness to the live ranges. 184 // 185 186 /// setLiveOutValue - Indicate that VNI is live out from MBB. The 187 /// calculateValues() function will not add liveness for MBB, the caller 188 /// should take care of that. 189 /// 190 /// VNI may be null only if MBB is a live-through block also passed to 191 /// addLiveInBlock(). 192 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) { 193 Seen.set(MBB->getNumber()); 194 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0); 195 } 196 197 /// addLiveInBlock - Add a block with an unknown live-in value. This 198 /// function can only be called once per basic block. Once the live-in value 199 /// has been determined, calculateValues() will add liveness to LI. 200 /// 201 /// @param LI The live range that is live-in to the block. 202 /// @param DomNode The domtree node for the block. 203 /// @param Kill Index in block where LI is killed. If the value is 204 /// live-through, set Kill = SLotIndex() and also call 205 /// setLiveOutValue(MBB, 0). 206 void addLiveInBlock(LiveInterval *LI, 207 MachineDomTreeNode *DomNode, 208 SlotIndex Kill = SlotIndex()) { 209 LiveIn.push_back(LiveInBlock(LI, DomNode, Kill)); 210 } 211 212 /// calculateValues - Calculate the value that will be live-in to each block 213 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA 214 /// form. Add liveness to all live-in blocks up to the Kill point, or the 215 /// whole block for live-through blocks. 216 /// 217 /// Every predecessor of a live-in block must have been given a value with 218 /// setLiveOutValue, the value may be null for live-trough blocks. 219 void calculateValues(SlotIndexes *Indexes, 220 MachineDominatorTree *DomTree, 221 VNInfo::Allocator *Alloc); 222 }; 223 224 } // end namespace llvm 225 226 #endif 227
