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 MachineFunction *MF;
38 const MachineRegisterInfo *MRI;
40 MachineDominatorTree *DomTree;
41 VNInfo::Allocator *Alloc;
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.
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;
53 /// LiveOutMap - Map basic blocks to the value leaving the block.
54 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
56 /// LiveOut - Map each basic block where a live range is live out to the
57 /// live-out value and its defining block.
59 /// For every basic block, MBB, one of these conditions shall be true:
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
69 /// The domtree node may be null, it can be computed.
71 /// The map can be shared by multiple live ranges as long as no two are
72 /// live-out of the same block.
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.
78 // The live range set that is live-in to this block. The algorithms can
79 // handle multiple non-overlapping live ranges simultaneously.
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;
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.
91 // Live-in value filled in by updateSSA once it is known.
94 LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
95 : LR(LR), DomNode(node), Kill(kill), Value(0) {}
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;
104 /// Assuming that LI is live-in to KillMBB and killed at Kill, find the set
105 /// of defs that can reach it.
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.
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.
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);
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.
120 /// Every live-in block must be jointly dominated by the added live-out
121 /// blocks. No values are read from the live ranges.
124 /// Add liveness as specified in the LiveIn vector.
125 void updateLiveIns();
128 LiveRangeCalc() : MF(0), MRI(0), Indexes(0), DomTree(0), Alloc(0) {}
130 //===--------------------------------------------------------------------===//
131 // High-level interface.
132 //===--------------------------------------------------------------------===//
134 // Calculate live ranges from scratch.
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,
144 MachineDominatorTree*,
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.
161 /// PhysReg, when set, is used to verify live-in lists on basic blocks.
162 void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg = 0);
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);
169 /// createDeadDefs - Create a dead def in LI for every def of LI->reg.
170 void createDeadDefs(LiveInterval &LI) {
171 createDeadDefs(LI, LI.reg);
174 /// extendToUses - Extend the live range of LI to reach all uses of Reg.
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);
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);
185 //===--------------------------------------------------------------------===//
186 // Low-level interface.
187 //===--------------------------------------------------------------------===//
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
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.
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.
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);
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.
213 /// @param LR 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));
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.
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();
234 } // end namespace llvm