1 //===---- LiveRangeCalc.h - Calculate live ranges ---------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
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.
20 //===----------------------------------------------------------------------===//
22 #ifndef LLVM_LIB_CODEGEN_LIVERANGECALC_H
23 #define LLVM_LIB_CODEGEN_LIVERANGECALC_H
25 #include "llvm/ADT/BitVector.h"
26 #include "llvm/ADT/IndexedMap.h"
27 #include "llvm/CodeGen/LiveInterval.h"
31 /// Forward declarations for MachineDominators.h:
32 class MachineDominatorTree;
33 template <class NodeT> class DomTreeNodeBase;
34 typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
37 const MachineFunction *MF;
38 const MachineRegisterInfo *MRI;
40 MachineDominatorTree *DomTree;
41 VNInfo::Allocator *Alloc;
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;
47 /// LiveOutMap - Map basic blocks to the value leaving the block.
48 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
51 /// Seen - Bit vector of active entries in LiveOut, also used as a visited
52 /// set by findReachingDefs. One entry per basic block, indexed by block
53 /// number. This is kept as a separate bit vector because it can be cleared
54 /// quickly when switching live ranges.
57 /// LiveOut - Map each basic block where a live range is live out to the
58 /// live-out value and its defining block.
60 /// For every basic block, MBB, one of these conditions shall be true:
62 /// 1. !Seen.count(MBB->getNumber())
63 /// Blocks without a Seen bit are ignored.
64 /// 2. LiveOut[MBB].second.getNode() == MBB
65 /// The live-out value is defined in MBB.
66 /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
67 /// The live-out value passses through MBB. All predecessors must carry
70 /// The domtree node may be null, it can be computed.
72 /// The map can be shared by multiple live ranges as long as no two are
73 /// live-out of the same block.
76 void reset(unsigned NumBlocks) {
78 Seen.resize(NumBlocks);
79 Map.resize(NumBlocks);
82 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
83 Seen.set(MBB->getNumber());
84 Map[MBB] = LiveOutPair(VNI, nullptr);
87 LiveOutData MainLiveOutData;
89 /// LiveInBlock - Information about a basic block where a live range is known
90 /// to be live-in, but the value has not yet been determined.
92 // The live range set that is live-in to this block. The algorithms can
93 // handle multiple non-overlapping live ranges simultaneously.
96 // DomNode - Dominator tree node for the block.
97 // Cleared when the final value has been determined and LI has been updated.
98 MachineDomTreeNode *DomNode;
100 // Position in block where the live-in range ends, or SlotIndex() if the
101 // range passes through the block. When the final value has been
102 // determined, the range from the block start to Kill will be added to LI.
105 // Live-in value filled in by updateSSA once it is known.
108 LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
109 : LR(LR), DomNode(node), Kill(kill), Value(nullptr) {}
112 /// LiveIn - Work list of blocks where the live-in value has yet to be
113 /// determined. This list is typically computed by findReachingDefs() and
114 /// used as a work list by updateSSA(). The low-level interface may also be
115 /// used to add entries directly.
116 SmallVector<LiveInBlock, 16> LiveIn;
118 /// Assuming that LI is live-in to KillMBB and killed at Kill, find the set
119 /// of defs that can reach it.
121 /// If only one def can reach Kill, all paths from the def to kill are added
122 /// to LI, and the function returns true.
124 /// If multiple values can reach Kill, the blocks that need LI to be live in
125 /// are added to the LiveIn array, and the function returns false.
127 /// PhysReg, when set, is used to verify live-in lists on basic blocks.
128 bool findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
129 SlotIndex Kill, unsigned PhysReg,
130 LiveOutData &LiveOuts);
132 /// updateSSA - Compute the values that will be live in to all requested
133 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
135 /// Every live-in block must be jointly dominated by the added live-out
136 /// blocks. No values are read from the live ranges.
137 void updateSSA(LiveOutData &LiveOuts);
139 /// Transfer information from the LiveIn vector to the live ranges and update
140 /// the given @p LiveOuts.
141 void updateFromLiveIns(LiveOutData &LiveOuts);
144 LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr),
145 DomTree(nullptr), Alloc(nullptr) {}
147 //===--------------------------------------------------------------------===//
148 // High-level interface.
149 //===--------------------------------------------------------------------===//
151 // Calculate live ranges from scratch.
154 /// reset - Prepare caches for a new set of non-overlapping live ranges. The
155 /// caches must be reset before attempting calculations with a live range
156 /// that may overlap a previously computed live range, and before the first
157 /// live range in a function. If live ranges are not known to be
158 /// non-overlapping, call reset before each.
159 void reset(const MachineFunction *MF,
161 MachineDominatorTree*,
164 //===--------------------------------------------------------------------===//
165 // Mid-level interface.
166 //===--------------------------------------------------------------------===//
168 // Modify existing live ranges.
171 /// extend - Extend the live range of LI to reach Kill.
173 /// The existing values in LI must be live so they jointly dominate Kill. If
174 /// Kill is not dominated by a single existing value, PHI-defs are inserted
175 /// as required to preserve SSA form. If Kill is known to be dominated by a
176 /// single existing value, Alloc may be null.
178 /// PhysReg, when set, is used to verify live-in lists on basic blocks.
179 void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg,
180 LiveOutData &LiveOuts);
182 void extend(LiveRange &LR, SlotIndex Kill) {
183 extend(LR, Kill, 0, MainLiveOutData);
186 /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
187 /// Each instruction defining Reg gets a new VNInfo with a corresponding
188 /// minimal live range.
189 void createDeadDefs(LiveRange &LR, unsigned Reg);
191 /// Subregister aware version of createDeadDefs(LiveRange &LR, unsigned Reg).
192 /// If subregister liveness tracking is enabled new subranges are created as
193 /// necessary when subregister defs are found. As with
194 /// createDeadDefs(LiveRange &LR, unsigned Reg) new short live segments are
195 /// created for every def of LI.reg. The new segments start and end at the
196 /// defining instruction (hence the name "DeadDef").
197 void createDeadDefs(LiveInterval &LI);
199 /// extendToUses - Extend the live range of LI to reach all uses of Reg.
201 /// All uses must be jointly dominated by existing liveness. PHI-defs are
202 /// inserted as needed to preserve SSA form.
203 void extendToUses(LiveRange &LR, unsigned Reg);
205 /// Subregister aware version of extendToUses(LiveRange &LR, unsigned Reg).
206 /// If subregister liveness tracking is enabled new subranges are created
207 /// as necessary when subregister uses are found. As with
208 /// extendToUses(LiveRange &LR, unsigned Reg) the segments existing at the
209 /// defs are extend until they reach all uses. New value numbers are created
210 /// at CFG joins as necessary (SSA construction).
211 void extendToUses(LiveInterval &LI);
213 //===--------------------------------------------------------------------===//
214 // Low-level interface.
215 //===--------------------------------------------------------------------===//
217 // These functions can be used to compute live ranges where the live-in and
218 // live-out blocks are already known, but the SSA value in each block is
221 // After calling reset(), add known live-out values and known live-in blocks.
222 // Then call calculateValues() to compute the actual value that is
223 // live-in to each block, and add liveness to the live ranges.
226 /// setLiveOutValue - Indicate that VNI is live out from MBB. The
227 /// calculateValues() function will not add liveness for MBB, the caller
228 /// should take care of that.
230 /// VNI may be null only if MBB is a live-through block also passed to
231 /// addLiveInBlock().
232 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
233 MainLiveOutData.setLiveOutValue(MBB, VNI);
236 /// addLiveInBlock - Add a block with an unknown live-in value. This
237 /// function can only be called once per basic block. Once the live-in value
238 /// has been determined, calculateValues() will add liveness to LI.
240 /// @param LR The live range that is live-in to the block.
241 /// @param DomNode The domtree node for the block.
242 /// @param Kill Index in block where LI is killed. If the value is
243 /// live-through, set Kill = SLotIndex() and also call
244 /// setLiveOutValue(MBB, 0).
245 void addLiveInBlock(LiveRange &LR,
246 MachineDomTreeNode *DomNode,
247 SlotIndex Kill = SlotIndex()) {
248 LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
251 /// calculateValues - Calculate the value that will be live-in to each block
252 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
253 /// form. Add liveness to all live-in blocks up to the Kill point, or the
254 /// whole block for live-through blocks.
256 /// Every predecessor of a live-in block must have been given a value with
257 /// setLiveOutValue, the value may be null for live-trough blocks.
258 void calculateValues(LiveOutData &LiveOuts);
260 void calculateValues() {
261 calculateValues(MainLiveOutData);
265 } // end namespace llvm