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_CODEGEN_LIVERANGECALC_H
23 #define LLVM_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 MachineRegisterInfo *MRI;
39 MachineDominatorTree *DomTree;
40 VNInfo::Allocator *Alloc;
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.
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;
52 /// LiveOutMap - Map basic blocks to the value leaving the block.
53 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
55 /// LiveOut - Map each basic block where a live range is live out to the
56 /// live-out value and its defining block.
58 /// For every basic block, MBB, one of these conditions shall be true:
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
68 /// The domtree node may be null, it can be computed.
70 /// The map can be shared by multiple live ranges as long as no two are
71 /// live-out of the same block.
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.
77 // LI - The live range that is live-in to this block. The algorithms can
78 // handle multiple non-overlapping live ranges simultaneously.
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;
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.
90 // Live-in value filled in by updateSSA once it is known.
93 LiveInBlock(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill)
94 : LI(li), DomNode(node), Kill(kill), Value(0) {}
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;
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 VNInfo *findReachingDefs(LiveInterval *LI,
109 MachineBasicBlock *KillMBB,
112 /// updateSSA - Compute the values that will be live in to all requested
113 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
115 /// Every live-in block must be jointly dominated by the added live-out
116 /// blocks. No values are read from the live ranges.
119 /// updateLiveIns - Add liveness as specified in the LiveIn vector, using VNI
120 /// as a wildcard value for LiveIn entries without a value.
121 void updateLiveIns(VNInfo *VNI);
124 LiveRangeCalc() : MRI(0), Indexes(0), DomTree(0), Alloc(0) {}
126 //===--------------------------------------------------------------------===//
127 // High-level interface.
128 //===--------------------------------------------------------------------===//
130 // Calculate live ranges from scratch.
133 /// reset - Prepare caches for a new set of non-overlapping live ranges. The
134 /// caches must be reset before attempting calculations with a live range
135 /// that may overlap a previously computed live range, and before the first
136 /// live range in a function. If live ranges are not known to be
137 /// non-overlapping, call reset before each.
138 void reset(const MachineFunction *MF,
140 MachineDominatorTree*,
143 /// calculate - Calculate the live range of a virtual register from its defs
144 /// and uses. LI must be empty with no values.
145 void calculate(LiveInterval *LI);
147 //===--------------------------------------------------------------------===//
148 // Mid-level interface.
149 //===--------------------------------------------------------------------===//
151 // Modify existing live ranges.
154 /// extend - Extend the live range of LI to reach Kill.
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 void extend(LiveInterval *LI, SlotIndex Kill);
162 /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
163 /// Each instruction defining Reg gets a new VNInfo with a corresponding
164 /// minimal live range.
165 void createDeadDefs(LiveInterval *LI, unsigned Reg);
167 /// createDeadDefs - Create a dead def in LI for every def of LI->reg.
168 void createDeadDefs(LiveInterval *LI) {
169 createDeadDefs(LI, LI->reg);
172 /// extendToUses - Extend the live range of LI to reach all uses of Reg.
174 /// All uses must be jointly dominated by existing liveness. PHI-defs are
175 /// inserted as needed to preserve SSA form.
176 void extendToUses(LiveInterval *LI, unsigned Reg);
178 /// extendToUses - Extend the live range of LI to reach all uses of LI->reg.
179 void extendToUses(LiveInterval *LI) {
180 extendToUses(LI, LI->reg);
183 //===--------------------------------------------------------------------===//
184 // Low-level interface.
185 //===--------------------------------------------------------------------===//
187 // These functions can be used to compute live ranges where the live-in and
188 // live-out blocks are already known, but the SSA value in each block is
191 // After calling reset(), add known live-out values and known live-in blocks.
192 // Then call calculateValues() to compute the actual value that is
193 // live-in to each block, and add liveness to the live ranges.
196 /// setLiveOutValue - Indicate that VNI is live out from MBB. The
197 /// calculateValues() function will not add liveness for MBB, the caller
198 /// should take care of that.
200 /// VNI may be null only if MBB is a live-through block also passed to
201 /// addLiveInBlock().
202 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
203 Seen.set(MBB->getNumber());
204 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
207 /// addLiveInBlock - Add a block with an unknown live-in value. This
208 /// function can only be called once per basic block. Once the live-in value
209 /// has been determined, calculateValues() will add liveness to LI.
211 /// @param LI The live range that is live-in to the block.
212 /// @param DomNode The domtree node for the block.
213 /// @param Kill Index in block where LI is killed. If the value is
214 /// live-through, set Kill = SLotIndex() and also call
215 /// setLiveOutValue(MBB, 0).
216 void addLiveInBlock(LiveInterval *LI,
217 MachineDomTreeNode *DomNode,
218 SlotIndex Kill = SlotIndex()) {
219 LiveIn.push_back(LiveInBlock(LI, DomNode, Kill));
222 /// calculateValues - Calculate the value that will be live-in to each block
223 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
224 /// form. Add liveness to all live-in blocks up to the Kill point, or the
225 /// whole block for live-through blocks.
227 /// Every predecessor of a live-in block must have been given a value with
228 /// setLiveOutValue, the value may be null for live-trough blocks.
229 void calculateValues();
232 } // end namespace llvm