LiveRangeCalc.h revision e25dde550baec1f79caf2fc06edd74e7ae6ffa33
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 29namespace llvm { 30 31/// Forward declarations for MachineDominators.h: 32class MachineDominatorTree; 33template <class NodeT> class DomTreeNodeBase; 34typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode; 35 36class 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(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(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 127public: 128 LiveRangeCalc() : MF(0), MRI(0), Indexes(0), DomTree(0), Alloc(0) {} 129 130 //===--------------------------------------------------------------------===// 131 // High-level interface. 132 //===--------------------------------------------------------------------===// 133 // 134 // Calculate live ranges from scratch. 135 // 136 137 /// reset - Prepare caches for a new set of non-overlapping live ranges. The 138 /// caches must be reset before attempting calculations with a live range 139 /// that may overlap a previously computed live range, and before the first 140 /// live range in a function. If live ranges are not known to be 141 /// non-overlapping, call reset before each. 142 void reset(const MachineFunction *MF, 143 SlotIndexes*, 144 MachineDominatorTree*, 145 VNInfo::Allocator*); 146 147 //===--------------------------------------------------------------------===// 148 // Mid-level interface. 149 //===--------------------------------------------------------------------===// 150 // 151 // Modify existing live ranges. 152 // 153 154 /// extend - Extend the live range of LI to reach Kill. 155 /// 156 /// The existing values in LI must be live so they jointly dominate Kill. If 157 /// Kill is not dominated by a single existing value, PHI-defs are inserted 158 /// as required to preserve SSA form. If Kill is known to be dominated by a 159 /// single existing value, Alloc may be null. 160 /// 161 /// PhysReg, when set, is used to verify live-in lists on basic blocks. 162 void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg = 0); 163 164 /// createDeadDefs - Create a dead def in LI for every def operand of Reg. 165 /// Each instruction defining Reg gets a new VNInfo with a corresponding 166 /// minimal live range. 167 void createDeadDefs(LiveRange &LR, unsigned Reg); 168 169 /// createDeadDefs - Create a dead def in LI for every def of LI->reg. 170 void createDeadDefs(LiveInterval &LI) { 171 createDeadDefs(LI, LI.reg); 172 } 173 174 /// extendToUses - Extend the live range of LI to reach all uses of Reg. 175 /// 176 /// All uses must be jointly dominated by existing liveness. PHI-defs are 177 /// inserted as needed to preserve SSA form. 178 void extendToUses(LiveRange &LR, unsigned Reg); 179 180 /// extendToUses - Extend the live range of LI to reach all uses of LI->reg. 181 void extendToUses(LiveInterval &LI) { 182 extendToUses(LI, LI.reg); 183 } 184 185 //===--------------------------------------------------------------------===// 186 // Low-level interface. 187 //===--------------------------------------------------------------------===// 188 // 189 // These functions can be used to compute live ranges where the live-in and 190 // live-out blocks are already known, but the SSA value in each block is 191 // unknown. 192 // 193 // After calling reset(), add known live-out values and known live-in blocks. 194 // Then call calculateValues() to compute the actual value that is 195 // live-in to each block, and add liveness to the live ranges. 196 // 197 198 /// setLiveOutValue - Indicate that VNI is live out from MBB. The 199 /// calculateValues() function will not add liveness for MBB, the caller 200 /// should take care of that. 201 /// 202 /// VNI may be null only if MBB is a live-through block also passed to 203 /// addLiveInBlock(). 204 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) { 205 Seen.set(MBB->getNumber()); 206 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0); 207 } 208 209 /// addLiveInBlock - Add a block with an unknown live-in value. This 210 /// function can only be called once per basic block. Once the live-in value 211 /// has been determined, calculateValues() will add liveness to LI. 212 /// 213 /// @param LI The live range that is live-in to the block. 214 /// @param DomNode The domtree node for the block. 215 /// @param Kill Index in block where LI is killed. If the value is 216 /// live-through, set Kill = SLotIndex() and also call 217 /// setLiveOutValue(MBB, 0). 218 void addLiveInBlock(LiveRange &LR, 219 MachineDomTreeNode *DomNode, 220 SlotIndex Kill = SlotIndex()) { 221 LiveIn.push_back(LiveInBlock(LR, DomNode, Kill)); 222 } 223 224 /// calculateValues - Calculate the value that will be live-in to each block 225 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA 226 /// form. Add liveness to all live-in blocks up to the Kill point, or the 227 /// whole block for live-through blocks. 228 /// 229 /// Every predecessor of a live-in block must have been given a value with 230 /// setLiveOutValue, the value may be null for live-trough blocks. 231 void calculateValues(); 232}; 233 234} // end namespace llvm 235 236#endif 237